Abstract

Oxy-combustion power plants, where high-purity oxygen instead of air is used for the combustion of fossil fuels, could become more common in the future because they are well-suited for carbon capture and storage (CCS). The supply method of high-purity oxygen is critical for the profitability of those power plants because it is highly energy-intensive and requires expensive equipment. Currently, the most mature method, is cryogenic air separation, but an efficient alternative is membranes that separate oxygen by electronic and ionic conduction, The integration of these membranes in the Graz Cycle, a promising oxy-combustion power cycle, has already led to a remarkable improvement in efficiency. Therefore, it is studied if membranes can also improve the NET power cycle, another interesting oxy-combustion power cycle with supercritical as working fluid, although its high efficiency is based on the utilization of heat from the cryogenic air separation. For this, thermodynamic simulations of the integration of two different membrane technologies were performed using the cloud based process simulation platform IPSE GO.

Case 1 has a 3-end membrane, on whose permeate side pure oxygen is under vacuum pressure while hot pressurized air is fed to the other side. In Case 2, cycle flue gas with low oxygen content is fed to the permeate side of a 4-end membrane. Both membrane cycles use a cascade of compressors, turbines and heat exchangers to achieve optimum efficiency. In this study the membrane area, the temperature differences of the heat exchangers in the oxygen production cycle as well as the membrane operating conditions were varied in search for an optimum. The net cycle efficiency of the optimized Case 1 is still only 50.73%, which is remarkably lower than the 52.72% of the base case with cryogenic air separation. But the efficiency of the optimized Case 2 is with 52.66% almost as high as that in the base case, which can make membranes an interesting alternative to cryogenic air separation.

To explore the potential of oxy-fuel technology, a detailed thermodynamic analysis is performed for four different oxy-fuel combustion cycles: the SCOC-CC, Matiant cycle, S-Graz cycle, and Allam cycle. Based on the literature data, these thermal cycles are modeled and simulated at full load using commercial software Aspen Plus with the same input and boundary conditions. The results show that the Allam cycle and S-Graz reach the highest net energy efficiency with 56.04% and 53.19%, respectively. The Matiant cycle and SCOC-CC have lower efficiencies at 50.02% and 45.23%, respectively. The exergy efficiency is also higher for the Allam cycle (52.87%) and the S-Graz cycle (50.18%). Moreover, the CCS efficiency penalty is comparatively higher for S-Graz, SCOC-CC, and Matiant, with 3.88%, 1.78%, and 1.70%, respectively. This is primarily because of the lower condenser pressure than the Allam cycle, which has a penalty of 0.42%. The ASU efficiency penalty is consistent at 10.31% for all cycles due to the same delivery pressure, flow rate, and oxygen purity. However, in the Allam cycle, it is marginally higher by 0.71 ppt due to an extra oxygen compressor. The results also indicate that the turbine main parameters, such as inlet temperature, inlet pressure, outlet pressure, and condenser pressure, strongly influence the system overall performance. The Allam cycle generally stands out for its high thermal efficiency and simple configuration.

This work focuses on the definition of the operating envelope and the boundary conditions for the start-up of the transcritical CO₂ blended power plant developed in the framework of the DESOLINATION project. The goal of the project is to build and operate a 1.8 MW_el demonstrational concentrated solar power plant, which is currently in the design phase. The demonstrator aims to test a series of innovative systems in a 2000h campaign to prove the system's reliability and efficiency in real operational conditions. The novel technology is mainly represented by CO₂/SO₂ (82% -18% mole) mixture working fluid, implementation of concentrated solar power as a stream of hot molten salt, and unconventional high-pressure mixture condenser for heat rejection. Due to the complex nature of the project, a continuous interaction between component manufacturers and the partners in charge of plant simulation has been established. This paper aims first to present the consolidated plant configuration including the most recent specification of the different components, such as performance maps for pump and turbine and off-design performance of heat exchangers. Then, the operative envelope is derived varying both ambient temperature and mass flow rate of hot molten salt. The system’s inventory is fixed, and an air-cooled condenser unit with an embedded subcooler is implemented. Limit conditions in the operability of the plant at both extreme temperatures and low thermal input were identified and solved by varying air cooled condenser fan speed. Finally, equilibrium pressure in case of plant shutdown (Settling Out Pressure) is calculated in case of both hot and cold conditions highlighting the expected conditions at the beginning of the start-up process. The results provide the expected amount of fluid to be removed from the system to meet the specifications of condenser and turbine manufacturers.

In this paper, an off-design analysis of a lab-scale cycle sCO2 Thermally Integrated - Pumped Thermal Energy Storage (TI-PTES), based on Brayton type cycle, is presented.

Off-design conditions arise due to load-schedule following, or due to variations in storage tank temperatures (e.g. for incomplete charging/discharging of the TES) or due to the temperature of the external heat source integrated in the cycle or the ambient temperature. The goal of this off-design analysis is to identify the potential operating envelope for the off-design temperatures in the cycle. To that end, the off-design envelope for the off-design of ambient temperature and the integrated heat source is evaluated. The off-design envelope is mapped for the rotational speed of the hot machines in the charging and discharging cycles of the TI-PTES. Based on the off-design envelope, mitigation strategies have been proposed with the target to bring the storage temperatures to design point. Inventory control for the heat transfer fluid of TES has been proposed for all the temperature related off-design conditions, as it is a less complex strategy than controlling the mass flow rate of the CO2 loop. The operational range of hot turbomachines, storage temperatures, pressure ratios, powers and performance of the cycles have been evaluated for the selected off-design cases.

Energy storage is crucial for reducing the imbalances between energy demand and generation and thus an important asset to increase the share of renewable energy. This work proposes an efficient, zero-pollution, self-contained integrated energy system for energy conversion and storage. The integrated energy system comprises a supercritical CO₂ gas turbine, an electrolyzer, and a methanol synthesis unit. With this system, excess renewable electrical energy is stored by producing hydrogen in the electrolyzer and converting it into methanol in the methanol synthesis unit. The renewable methanol is used as a fuel in a supercritical CO₂ gas turbine system with direct combustion, to generate electrical energy and heat on demand. This paper investigates the supercritical CO₂ gas turbine systems with the aim of achieving high thermal efficiency. The thermal characteristics of the supercritical CO₂ gas turbine cycle are assessed and the influence of different design and operating parameters is determined.

To assess the thermal characteristics of supercritical CO₂ gas turbines a thermodynamic model is developed in MATLAB. To calculate the properties of CO₂ and CO₂/H₂O mixture CoolProp is used. In an environment of recirculating CO₂, the methanol is oxidized using the stored oxygen from the electrolysis. High pressure and high temperature gases (CO₂/H₂O mixture) expand in the gas turbine, generating mechanical energy. Later, the combustion products, H₂O and CO₂ are separated from the recirculating CO₂ at the cold side of the regenerator and stored to be reused for fuel production. The influence of various operating conditions, such as (i) compressor outlet pressure, (ii) gas turbine inlet temperature, (iii) compressor isentropic efficiency, (iv) gas turbine isentropic efficiency, (v) regenerator temperature difference, and (vi) pressure drop in heat exchangers, is determined.

The results of the investigation show that high thermal efficiency of the supercritical CO₂ gas turbine (above 60 %) can be achieved. Hereby, the low compression work needed to compress the fluid near the critical point to the desired pressure is essential to achieve this high efficiency. The supercritical CO₂ gas turbine is a crucial component of the integrated energy system for energy conversion and storage, which generates electricity with high efficiency and zero pollutants. The mass and energy flow balances of the supercritical CO₂ gas turbine and the renewable fuel generation lead to a self-contained closed energy system with high round-trip efficiency.

This study deals with the off-design operation and controller tuning of a 5 MWth, air-cooled recuperated supercritical carbon dioxide (sCO₂) Brayton Cycle. Previous studies indicated that implemented PID controllers require gain scheduling for efficient operation under fluctuating air temperatures or load levels. However, regarding sCO₂ cycles, limited literature explicitly covers controller tuning, with a majority relying on manual methods. Therefore, this study presents and implements a gain scheduling approach for the air-cooled heat sink of the cycle in a systematic and automized manner, includes the following steps: Calculation of the steady-state boundary conditions, determination of transfer functions from step tests, controller tuning using Matlab and Internal Model Control and, finally, controller testing.

It was found that the Internal Model Control approach, with a closed loop time constant equal to 1/10 of the open loop one, yields a stable and efficient controller performance for all boundary conditions, except cases with a low air mass flow rate. Consequently, it is recommended to avoid such extreme part-load conditions, e.g. by cooler modularization. Finally, important considerations for the following tuning of the inventory control are presented, highlighting the interaction of component design and controllability.

The Oxford Laser Heating Facility (OLAHF) has been upgraded with a supercritical carbon dioxide (sCO2) flow circulating loop, capable of providing component level flow rates to test pieces at temperatures and pressures up to 100 C and 100 bar. Near to the critical point, the large variations in sCO2 thermophysical properties can lead to adverse cooling and heat transfer effects. There are currently gaps in the understanding of the effects of larger thermal gradients (i.e. heat fluxes) on the heat transfer performance of sCO2 systems. An initial experimental campaign was performed on an additively manufactured stainless steel test piece containing an array of 11, 1.5 mm square internal channels using the high power laser modules located at OLAHF. Heat fluxes ranging from 116 to 1000 kW/m2 to the upper surface of the horizontally-oriented test piece. Data were obtained for fluid inlet temperatures between 18 and 28C and mass fluxes of 1500 and 3000 kg/m2s at a constant inlet pressure of 80 bar (inlet Reynolds numbers from 3 x 10^4 to 8 x 10^4). Resulting heat transfer coefficients were determined using a combination of ray tracing and finite element (FE) analyses of the test piece at each experimental condition. Average heat transfer coefficients were shown to exhibit a significant dependence on applied heat flux for both mass flux conditions and all inlet temperatures. The heat transfer coefficients were compared to empirical correlations with varied levels of agreement. The data was additionally examined for the potential existence of buoyancy and flow acceleration effects.

Minichannel printed circuit heat exchangers (PCHEs) are commonly utilized in supercritical CO₂ (sCO₂) power cycles. In this study, an experimental single plate PCHE with various header configurations is investigated in terms of flow maldistribution using computational fluid dynamics (CFD) techniques. A series of header optimization simulations with different mass flow rates, inlet/outlet configurations, and header sizes are performed and analyzed. The numerical model of this PCHE is set up and solved with ANSYS-CFX. The variation in thermophysical properties of sCO₂ was incorporated into the numerical model via real gas property data. Additionally, the computed results for temperature distribution i.e., maximum hotspot temperatures and pressure drop were validated with experimental data, showing a good agreement with a maximum discrepancy of 8.6%. The results from this study indicated that optimizing inlet and outlet positions reduced the maldistribution factor (MDF) by 34% at 40 g/sec and 29% at 90 g/sec, as compared to the baseline configuration of the PCHE. Increasing the header area ratio further reduced the MDF by 51% at 40 g/sec and 48% at 90 g/sec, resulting in uniform temperature distribution and effective mitigation of local hotspots. Furthermore, the suggested header configuration also minimized hot and cold stream mixing inside the collector header which can significantly reduce thermal stresses, extending the life span of PCHEs.

The promise of high thermal efficiencies and low initial capital cost make supercritical carbon dioxide (sCO₂) power cycles an attractive technology for concentrated solar power (CSP) applications. As CSP plants are usually located in arid or semi-arid regions, cooling options that minimize water consumption are preferred. Natural draft direct dry cooling systems (NDDDCSs) offer an alternative to traditional dry cooling technologies such as air-cooled condensers (ACCs) or indirect natural draft dry cooling systems. NDDDCSs combine the benefits of low auxiliary power consumption with direct heat rejection, while minimising operational costs and noise.

This study investigates the performance of a NDDDCS when utilised as cooling technology for a precooler and intercooler (combined in one tower) of a partial cooling with reheat (PCRH) sCO₂ cycle for a conceptual 50 MWe CSP plant. Initial work involves the development of a zero-dimensional (0D) lumped parameter sizing model to assess overall system performance and aid in selecting the best-performing geometry between the evaluated cases. Thereafter, a higher fidelity simulation model is developed in Flownex SE software, which employs a thermofluid network approach to solve the governing mass-, momentum-, and energy balance equations for the air- and sCO₂ streams. Empirical heat transfer and pressure drop correlations are also integrated for both air- and sCO₂-sides to capture component characteristics. After verification with the 0D model, the thermofluid network model (TNM) is extended to include discretised finned-tube heat exchangers and a one-dimensional (1D) discretised air-side tower to simulate the natural draft. This model is valuable for providing detailed insights into potential maldistribution effects, particularly under off-design conditions, and is used to evaluate the performance of the cooling system under varying ambient temperature and part-load conditions.

The best-performing system was selected based on minimising both lost work (sCO₂-side pressure drop) and estimated total heat exchanger and tower material costs. The selected configuration features an inlet diameter of 55.79 m, inlet height of 11.14 m, tower height of 55.79 m and outlet diameter of 27.89 m, designed to meet combined heat rejection requirements for the precooler (PC) and intercooler (IC) at design point. At design conditions, the system’s air mass flow rate and total heat rejection rate are 3702 kg/s and 85.03 MW, respectively.

Simulation of the cooling system using the discretised network model shows reductions of 4.7% and 0.8% in overall heat rejection and air mass flow rate at the design point, compared to the lumped model. While significant variations in fluid properties, pressure drops and heat transfer coefficients are observed on the discretised sCO₂-side, the resulting air-side effects dominate differences from the lumped model results.

Further simulations investigate the effects of off-design ambient temperature and crosswind variations. Significant differences in sCO₂-side temperatures and heat transfer coefficients arise from ambient temperature changes. Flow and pressure drop characteristics during partial bypass operation (to avoid overcooling impact on the cycle) of heat exchangers are also illustrated. Simulations highlight the differing impacts of crosswinds on heat rejection, sCO₂ outlet temperature and pressure drop for the PC and IC.

Fluids display sharp, non-linear variations of thermodynamic properties when they are heated at a supercritical pressure. As such, near-pseudo-critical heat transfer is often characterized by large variations in density, leading to sharp near-wall accelerations or strong stratifications when buoyancy becomes dominant. We study the modulation of heat transfer and turbulence by non-negligible buoyancy in such property-variant flows, for the development of near-pseudo-critical heat exchangers for supercritical energy conversion systems. In particular, a liquid-like, horizontal base flow of carbon dioxide at 88.5 bar and 32.6 ◦C is considered, which is subjected to a vertical heat flux of up to 12.0 kW/m2 at Reynolds numbers of up to ReDh ≤ 10.000. Here, optical- and surface temperature measurements are used concurrently to evaluate the flow. Integrated visualizations of the flow field show the onset of strong stratifications with limited heating rates in the near-pseudo-critical region. During unstable stratification, the channel flow is dominated by the upward motion of thermal plumes. When the stratification is stable, any vertical motion and turbulence present in an equivalent neutrally buoyant flow is suppressed. As a result, wall heat is removed more effectively in the unstably stratified configuration than in a forced convective flow, whereas the opposite is true for a stably stratified flow. The difference in the perceived heat transfer between the considered configurations increases as buoyancy becomes more dominant.

Heat exchangers are major components that significantly influence the performance and size of industrial processes. Supercritical CO2 (sCO2) is a highly promising working fluid for various applications due to its potential to reduce equipment size, lower environmental impact, and enhance performance. The properties of CO2 near the critical point exhibit significant variations, making it particularly favorable for heat transfer. As part of the Horizon 2020 DESOLINATION (DEmonstration of concentrated SOLar power coupled wIth advaNced desAlinaTion system in the gulf regION) project, a printed circuit heat exchanger (PCHE) for an sCO2 power cycle was designed, manufactured, and tested. Computational fluid dynamics (CFD) simulations using the SST k-ω turbulence model and real-gas equation of state were used to analyze the heat transfer performance and friction losses of the PCHE in detail. By combining experimental measurements with numerical simulations, this study provides a comprehensive evaluation of the thermo-hydraulic performance of sCO2 near the pseudo-critical region under various operating conditions (73.78 < p < 92.32 bar, 307.02 < T_b < 334.74 K, 1823 < 𝐺 < 4064 kg/m²s). A new friction factor correlation, derived from experimental data, is proposed to enhance the accuracy of friction loss predictions for sCO2 flows in microchannels, with errors within ±10%. The findings highlight the superior heat transfer performance of PCHEs while addressing the challenges associated with their performance prediction due to steep fluid property gradients in the supercritical region.

Highly valuable attributes such as high efficiency and competitive capital costs are the underlying factors for the prominence of carbon dioxide (CO2) cycles not only in theoretical fields but also in commercial applications. As a result, we are witnessing an increasing number of research projects and support for activities related to these cycles. Recently, there has been a new initiative to develop an even more promising working fluid by mixing CO2 with certain dopants. One of them seems to be the CO2-SO2 mixture. Given the promising potential of this specific mixture, which seems to be exceptionally well-suited for application in transcritical cycles, this paper provides an overview of the early results of the transient analysis of transcritical Rankine cycle using this mixture in waste heat recovery applications (WHR).

The primary focus of this paper is to utilize the CO2-SO2 mixture in a 70-30 ratio for the double recuperated recompression Rankine cycle. In doing so, this study not only examines the unique characteristics of this mixture but also explores its potential applications for WHR under fluctuating operational conditions. The paper describes the modeling methodology implemented in Aspen Plus software and illustrates the key plant components transient operating conditions. By conducting the analysis of this working fluid, the paper aims to evaluate its effectiveness in harnessing waste heat, thereby contributing to the advancement of more sustainable and efficient energy solutions.

Decarbonization of power generation, transportation, and energy-intensive industries (i.e., steel and iron, cement, aluminum, glass, food and beverage, paper, etc.) is necessary to reduce CO₂ emissions considering the continually growing world population and related increasing energy consumption. CO₂ emissions from energy-intensive industries can be reduced through several different approaches (i.e., direct - alternative fuel or energy source and Carbon capture systems; indirect - utilization of waste heat for the plant’s own consumption), where waste heat recovery represents a low-cost, zero-emissions power generation option with near-term deployment opportunities. In this paper, the steelmaking process is investigated as a potential source of waste heat to reduce the plant’s own consumption. The steelmaking process has three sources of waste heat in three different steps where the waste heat can be utilized. The exhaust gas stream is only approximately 10 % of the available waste heat. However, the temperatures are between 473 and 1573 K based on the process step and type of furnace (i.e., Blast furnace, Basic oxygen furnace, Electric arc furnace). Due to the large temperature range, potential retrofitting, and limited footprint, a sCO₂ waste heat recovery system can be an ideal candidate for utilizing waste heat streams in the steelmaking processes. The paper is focused on the optimization of potential waste heat recovery systems based on sCO₂ power cycle for a steel plant with several electric arc furnaces (EAF). Several different sCO₂ cycle layouts (i.e., Simple, Recuperated, Intercooling, Re-compression, Reheating, Split expansion cycle) have been investigated to meet the requirements. Results show higher performance of the sCO₂ cycle and potential retrofitting into the current steel plants. The sCO₂ power cycles can reach cycle efficiencies above 40 % and provide approximately 800 kWel from the waste heat stream. Part of the work is cost analysis which provided additional parameter/decision value for cycle layout selection.

In the face of mounting global interest in reducing
greenhouse gas emissions and achieving carbon neutrality, there
is an urgent need to develop and implement diverse measures. In
particular, it is imperative to explore the potential of utilising
waste heat from industrial processes and power generation, as
this has the potential to significantly enhance energy efficiency
and reduce greenhouse gas emissions while also capturing
otherwise wasted energy.
Concurrently, supercritical CO2 power generation is
regarded as a prospective technology for fossil, nuclear, solar,
thermal energy storage and waste heat recovery applications,
attributable to its elevated thermodynamic efficiency,
miniaturised plant configuration, and environmental stability.
sCO2 power cycles function above the critical point of CO2
(31.1°C, 7.38 MPa) and deliver higher energy density and heat
transfer performance in comparison to conventional power
cycles. It is particularly effective for power generation systems
using medium-temperature waste heat and has the advantage of
being applicable to various industrial environments. KEPCO
(Korea Electric Power Corporation) has been promoting research
and development of sCO2 power cycles as a promising future
technology since 2014. Following a series of feasibility studies,
KEPCO aimed to construct an MW-scale sCO2 power
generation system that recovers waste heat at low temperatures
and has the capacity to reduce risks in the early stages of
development. Additionally, the system was designed to achieve
a high probability of demonstration success and initial
marketability. In 2016, with the support of KEPCO, we initiated
a strategic project to achieve a net output of 2MW by recovering
waste heat from engines. A suitable onshore power generation
engine to output MW-scale sCO2 power output was selected as
well as a partial heating sCO2 cycle to recover waste heat from
the engine exhaust. A design feasibility study was also
conducted. This paper provides an overview of the development
of KEPCO's 2MW sCO2 power generation system designed to
recover waste heat. This paper also describes the cycle analysis
results and the specifications and fabrication of major equipment
(turbine, compressor, heat exchanger, etc.).

Compressors operating with carbon dioxide near the critical point experience complex aerothermodynamic phenomena, where deviations from perfect-gas similarity and two-phase flow effects dominate. Existing models inadequately capture the impact of intake thermodynamic conditions on the choked flow rate, leaving a gap in predictive capabilities for these machines. This work addresses this gap by deriving a correlation to predict the choked flow rate as a function of two generalized parameters: the cavitation/condensation parameter and the isentropic pressure-volume coefficient, which describe two-phase and non-ideal effects.

A database of 100 speedlines, generated through CFD simulations with varying thermodynamic conditions and fixed peripheral Mach number, was used to train a symbolic regression algorithm based on gene expression programming. This method was chosen to derive an explicit, easy-to-use analytical expression without assuming a priori functional forms.

Results showed that the choked flow rate could vary from 90% to 155% of the nominal value depending on thermodynamic conditions, highlighting the dominant role of the two parameters. The derived correlation demonstrated trends consistent with CFD predictions, with an accuracy of ±3 percentage points for most cases. However, an a-posteriori validation against varying peripheral Mach numbers and an alternative impeller geometry revealed significant discrepancies, underscoring the interplay between thermodynamic conditions, geometry, and aerodynamics. This analysis showed that the peripheral Mach number and the geometric features influence choking behavior unpredictably, limiting the correlation's general applicability.

While the proposed correlation is not adequate for quantitative scaling across designs, it provides preliminary insights into qualitative trends. For accurate predictions, high-fidelity CFD remains necessary, highlighting the inherent challenges of universal scaling for near-critical operations in sCO₂ compressors.

sCO2 energy conversion cycles technology development is reaching the MW-scale cycle demonstration phase. At the moment of this abstract writing, the STEP plant is going through the different phases of commissioning and has already produced electrical power. Other demonstration projects are reaching the end of the design phase and forecast a commissioning start in 2026. Nuovo Pignone Baker Hughes is part of the Desolination project consortium. Desolination project aims to decarbonise the desalination process in arid regions by demonstrating in a real environment the efficient coupling of a concentrating solar power plant to a direct osmosis desalination system. The sCO2 cycle involved in this process is a Rankine evolving a blended CO2 mixture optimized to enable condensation in hot ambient temperature areas.

Nuovo Pignone contributes to the Desolination project developing the pump and the expander of the sCO2 cycle. Expander development has reached the completion of the detailed design phase and the procurement of long lead material has started. This paper will provide a comprehensive overview of the expander development process, from conceptual design through to detailed design, displaying the key technology challenges peculiar of sCO2 expanders and illustrating the engineering methodologies applied to optimize the expander design.

This paper is dedicated to the performance map computation of centrifugal compressors operated with carbon dioxide at supercritical states (sCO$_2$) and inlet conditions in the vicinity of the critical point. Three-dimensional computational fluid dynamics (3D-CFD) simulations are utilised. First, different approaches to model two-phase flows are reviewed. Second, the impact of two-phase flow on the speed of sound and the choking limit is further investigated. The flow through Laval nozzles is analysed to simplify the problem to its fundamental aspects. The 3D-CFD calculations match well with the ones conducted with simple one-dimensional CFD programs and the theory of equilibrium phase change. Third, the throttle curve of an industrial-scale centrifugal compressor is computed and compared to the one for air. Total inlet conditions are supercritical in the so-called liquid-like region. A considerable shift of the choking line towards lower flow coefficients is found. The reason for this shift is a drop in the speed of sound when bubbles are formed in the liquid, and a two-phase flow is established while the flow is accelerated around the compressor’s leading edge. Finally, a log(p)-h diagram is provided, enabling a quick assessment of the risk of two-phase flow in centrifugal compressors.

Ensuring a CO₂-neutral supply of process heat is critical for advancing the energy transition in industrial sectors. One promising approach is the integration of high-temperature heat pumps, powered by renewable electricity, to generate process steam, which is widely used in the chemical industry at pressures up to 110 bar. An ultra-high temperature heat pump concept with supercritical CO₂ as the working medium, designed for the supply of a generic chemical plant, was developed as part of the project CO2NEICHEM.

This study evaluates this high-temperature heat pump using a transcritical reverse Brayton cycle with an internal heat exchanger and an expansion turbine. The process involves compressing water to operating pressure, followed by preheating, evaporation and superheating using the transcritical reverse Brayton cycle for heat supply. Various circuit designs and key sensitivities are analyzed to optimize performance. Additionally, it is explored how the efficiency of the heat pump varies with process steam pressure and superheating temperature.

Furthermore, part load operation is considered by varying the heat source flow. In all configurations, the study investigates thermodynamic modeling details of the cycle and its heat exchangers and turbomachinery and the resulting performance. Moreover, first drafts of the turbomachinery design are presented for a selected application case.

Carbon dioxide (CO₂) is a commercially viable working fluid for transcritical high-temperature heat pumps (HTHPs), but its low critical temperature (31°C) limits efficiency with cold sources above 40°C. Using a CO₂-based mixture with a higher critical temperature dopant can mitigate this issue by reducing temperature differences at the evaporator and enhancing heat transfer. This study focuses on fluorobenzene (C₆H₅F) as a dopant due to its high critical temperature, low cost, negligible global warming potential, and regulatory compliance in Europe.

To address the lack of vapor-liquid equilibrium (VLE) data for CO₂-fluorobenzene mixtures, an experimental campaign is conducted at the University of Brescia to measure bubble points using an isochoric apparatus. The data are used to select the most suitable equation of state for cycle calculations.

The heat pump’s analysis – both at design and off-design- is evaluated in a case study of integration with an Air Separation Unit (ASU). Waste heat from the ASU’s main air compressor is exploited through an intermediate closed-loop water cooling circuit operating at around 90°C. The heat pump upgrades this thermal energy to supply a local district heating network with a design supply temperature of 110°C. At this design point, the system achieves a coefficient of performance (COP) of 7.7, decreasing to 6.2 for higher off-design supply temperatures (e.g., 127°C).

Climate change necessitates innovative solutions for producing clean energy and decreasing atmospheric CO­₂ levels. Using CO­₂ as a working fluid in geothermal applications is a smart strategy to achieve this goal, as it has the potential to outperform conventional water-driven geothermal systems in terms of power produced, and for some cases, simultaneously increase the amount of CO­₂ that can be geologically sequestered. Power plant technology plays an important role in maximizing the value of geothermal resources. This is achieved through versatile power plant components that, barring large differences in CO­₂ purity, can operate across various geothermal systems. This research compares the use of similar power plant components and technologies across various types of CO₂-based geothermal energy systems: hydrothermal systems with CO₂ as a secondary working fluid, Advanced Geothermal Systems (AGS), Enhanced Geothermal Systems (EGS), and CO­₂-Plume Geothermal (CPG) systems. After providing ranges in possible operating conditions of these systems, the study employs TANGO (Techno-economic Analysis of Geo-energy Operations) to calculate the extracted energy and the Levelized Cost of Electricity (LCOE) for an example AGS, EGS, and CPG project, each with 10 MWe installed capacity. The findings indicate that CO­₂ is an effective geothermal working fluid and that most CO­₂ equipment can be used across the different geothermal systems. Given the extensive drilling required for AGS, LCOEs of CPG and EGS were found to be more competitive at current well construction costs.

This paper describes the development of a supercritical carbon dioxide test facility to mimic the primary heat exchanger inlet operation conditions of a recompression sCO₂ Brayton cycle. The experimental facility is used to test and evaluate the heat transfer performance of a particle-to-sCO₂ heat exchanger for concentrated solar power applications. The sCO₂ flow loop is comprised of five main components: a positive displacement gear pump, piston accumulator, sCO₂ preheater, experimental test section, and sCO₂ post cooler. The test facility is instrumented with measurement devices to quantify the heat and mass flows within the system. The loop operates at isobaric conditions up to 20 MPa and is split into a hot and cold side. On the cold side, the sCO₂ is cooled below room temperature by the post cooler, increasing the density of the sCO₂ high enough such that it can be circulated using the gear pump. The 10.8 kW preheater delivers sCO₂ to the test section at temperatures up to 600°C at flow rates up to 0.013 kg s^-1. Within the test section the sCO₂ is further heated by inert CARBO HSP 40/70 particles. The development of the novel particle-to-sCO₂ heat exchanger is also reported in this work. The heat exchanger was tested at dilute and dense flow conditions in the particle domain. The heat transfer performance and particle-to-sCO2 recovery effectiveness are characterized and compared to model predictions. By validating the model with the collected experimental data, it can be used to guide the design of future larger scale particle-to-sCO₂ heat exchangers.

Supercritical carbon dioxide (sCO₂) has shown a high potential in power generation cycles to increase the thermal efficiency and decrease the physical footprint. Supercritical CO₂ power cycles operate at relatively high temperatures compared to steam and air, necessitating the development of new sealing materials. In this paper, the design challenges, development and preliminary test results of a 500^oC, 200 bar sCO₂ dry gas seals test rig are presented. The main rig components are pressure control devices (liquid pump and expansion valves), heat exchangers (liquid condenser, gas heaters, and air cooler), and measuring instruments. Various design challenges are identified due to the thermo-physical properties as well as the operating conditions of the sCO₂ test rig such as the ice formation during start-up, heat loss to the ambient air, and material compatibility with the various test rig components. A thermodynamic design model has been developed to size the test rig components and estimate the gas conditions across the rig. The model includes tube and valve sizing, heat exchanger design, and thermal insulation models. The initial phase of the test campaign was conducted at Cranfield University (CU) to verify the ability of the test rig in delivering sCO₂ at the required conditions and to validate the developed numerical models. The results showed the validity of the proposed setup to supply sCO₂ steadily at 500^oC and 200 bar at a flow rate of 15 kg/h. The heat exchanger model, applied to a finned tube bundle air cooler, showed close estimations to the test results with a maximum deviation in the heat capacity of 2.3%. The thermal insulation model including the heating tape showed reasonable predictions to the temperature rise across the heating sections with a maximum deviation from the experimental measurements of 10^oC when the temperature rise was around 240^oC. The suitability of using rock wool insulation and stainless steel 316 tubes with dry CO₂ at 500^oC was verified.

The project „Purification and purity control of CO₂ gas in power cycles” (acronym CiCiMe) has been solved since the year 2019 and is going to be finished in 2025. Within the project the information concerning possible impurities in CO₂ and sCO₂ power systems were summarized. On the basis of the information the purification and purity control system for sCO₂ power system was proposed. The methods of impurities separation were tested and verified. The CO₂ purification unit for sCO₂ experimental loop was designed and is under construction. Last but not least the autoclave for material testing in sCO₂ was constructed and several tests were performed in the autoclave. Last test was carried out at the temperature of 300 °C and total pressure 25 MPa. After some improvements the device is planned to be able to long-term operate at the temperature 700 °C. The main results of the “CiCiMe” project will be introduced at the conference.

High-temperature heat pumps are gaining increasing interest as a means for electrifying process heat. While a number of systems for steam production has been reported, there are only a few publications on heating air e.g. for drying processes. Due to its high temperature glide in trans-critical cycles, as well as its beneficial physical and environmental parameters, CO₂ is an interesting candidate working fluid for such applications. We have developed a relatively simple cycle that allows the heating of air or other sensible media with few components, where the most complex one (besides the compressor) is a three-stream heat exchanger for simultaneously heating the air as well as allowing internal heat exchange. Simulations show that ambient air can be heated up to 200 °C with a COP of 2.61 and evaporating temperatures of 10°C, allowing for economic provision of process heat, for example for milk powder drying.

Thermal-power cycles operating with supercritical carbon dioxide (sCO2) could have a significant role in future power generation systems. This includes applications like nuclear power, concentrated-solar power, fossil fuel, and waste-heat recovery. However, there remain challenges which needs to be resolved that relate to the design and operation of the turbomachinery components and heat exchangers, material selection considering the high operating temperatures and pressures, in addition to characterizing the behavior of supercritical CO2. This working fluid may be incompatible with thermohydraulic components of device, such as the heat exchangers, where issues around material strength and corrosion may be significant. Therefore, innovative solutions are required.

Brazing process as a coating on a base material offer such a solution. The aim of our contribution was to verify the functionality of the coatings, which were applied to base materials by using of the brazing process. The coatings were on base of aluminum oxide and BNi-5. Two types of steel were used as the base material - 316Ti and 253 MA. These specimens were then exposed to 1000 hours of loop operation at a maximum operating temperature of 550°C and a maximum operating pressure of 25 MPa, with a constant flow rate of sCO2 medium of 0.1 kg.s^-1.

The EU funded Horizon Europe SCO2OP-TES project aims to develop a Thermally Integrated Pumped Thermal Energy Storage (TI-PTES) system based on sCO2 components and test it in an operative environment valorising the waste heat coming from a combined cycle power plant.

The test-rig, hosted in the joint laboratory by University of Genova and Tirreno Power, will consist of two purposely designed charging (Heat Pump) and discharging (Recuperated Power Cycle) cycles integrating different sCO2 enabling components and having as common component an innovative Solid Media Thermocline TES inter-exchanging heat with the sCO2 cycles via a Molten Salt loop to facilitate its controllability. In specific relation to the different enabling components (Heat exchangers and machines), the project aims to validate he reliability and the technical performance of all key components present in both the cycles. Ultimately, the overarching goal of the project is to serve as a stepping-stone towards the evaluation of the viability of sCO2 based TI-PTES and also of high temperature heat pumps based on sCO2 components . Besides the specific validation objectives, and related component development and verification, the project aims to investigate the techno-economic performance of the proposed sCO2 TI-PTES also looking at alternative layouts and operating temperature/pressure levels (also in terms of waste heat sources to be valorised) as well as the electric market strategicity.

Supercritical carbon dioxide (sCO₂) has emerged as a transformative fluid in energy systems, offering promising improvements in efficiency, performance, size of the equipment, and environmental impact. Recent developments in sCO₂ applications highlight its potential in various energy sectors, including power generation, waste heat recovery, and concentrated solar power. The key advantages of sCO₂ systems include higher thermal efficiency, reduced footprint, and lower operational costs compared to traditional steam cycles. Innovations in sCO₂ cycle designs, such as the Allam Cycle and various recompression cycles, have demonstrated significant improvements in efficiency and environmental impact. Recent developments include novel sCO₂ cycle configurations such as the recompression, partial cooling, and dual-fluid cycles, which optimize efficiency and operational flexibility. Additionally, cutting-edge control technologies and integration techniques are addressing previously challenging operational issues. Advances in materials science and component technologies, including high-temperature alloys and compact heat exchangers, have further enhanced the viability of sCO₂ systems. This study reviews the latest progress in sCO₂ key technological breakthroughs and their implications for the future of energy production, evaluates their integration into existing and new energy systems, and explores ongoing research aimed at addressing technical challenges and optimizing performance. The continued evolution of sCO₂ applications holds the potential to significantly influence the future landscape of energy systems, contributing to more sustainable and efficient energy solutions.

A new and innovative method for visualizing the sub-processes of various thermodynamic cycles used by heat-to-power and power-to-heat processes in heat pumps, cooling systems, and various heat engines will be introduced. Specific attention has been paid to carbon dioxide (CO₂) as a working fluid, whose thermodynamic properties are particularly relevant in modern thermal systems, being able to utilize heat sources around ambient temperature. Due to the unique characteristics of CO₂, an accurate and detailed understanding of the processes is of paramount importance, especially in cycles that start from saturated states and end in saturated final states, such as liquid-liquid, liquid-critical, liquid-gas, gas-liquid, gas-critical, and gas-gas transitions.

In our research, we have focused on the detailed analysis of isothermal (constant temperature), isobaric (constant pressure), and isenthalpic (constant enthalpy) processes. The visualization method we have developed allows a transparent representation of these processes, thus facilitating the understanding of the thermal cycle context.

In particular, our visualization technique is helpful in clearly labeling isobaric, isentropic, and real adiabatic (non-isentropic) expansion processes that occur during CO₂-cycles. These processes are critical in CO₂-based systems because real expansion processes often deviate from ideal conditions, especially in the high pressure and temperature ranges typical of transcritical CO₂-cycles.

Our method also has significant educational benefits by allowing the audience to better understand the complex structure and operating principles of CO₂-cycles. 3D diagrams allow for a clearer understanding of the relationship between the different state changes and a deeper understanding of how CO₂-based power-generating, cooling and heat pump systems work. Furthermore, the method provides the opportunity to explore in more detail the specific characteristics of CO₂ cycles and analyze the differences and similarities between them in more depth, thus facilitating more effective learning and a better understanding of practical applications.

Overall, our work demonstrates how this visualization method can make CO₂-based thermodynamic processes more transparent and understandable and how it can contribute to a better understanding and appreciation of thermal cycles in both practical and educational applications.

Given the increasing demand for eco-friendly refrigeration technologies, the use of natural refrigerants in thermal management systems for High Energy Physics (HEP) detectors is becoming more and more significant. While the application of boiling CO2 for cooling purposes is well-established at CERN, particularly in scenarios requiring low temperatures, this study explores the heat transfer potential of carbon dioxide under supercritical conditions. In this context, fluids above their critical point exhibit key properties such as high thermal capacity and low density and viscosity. Additionally, due to their inherently single-phase-like behaviour, supercritical fluids may facilitate simpler fluid management in complex, multi-branched circuits. These characteristics, coupled with a critical temperature of 31 °C, position supercritical carbon dioxide (sCO2) as an ideal candidate for thermal management systems where electronics are operated above 32 °C. Nevertheless, several aspects of this topic remain unresolved in existing literature. Specifically, the variability in the effects of certain parameters on the heat transfer coefficient creates challenges in establishing reliable correlations, highlighting the need for further precise experimental data.

This study presents the development and implementation of a specialized test rig to evaluate the thermodynamic performance and efficiency of sCO₂-based systems. The rig is designed to measure the heat transfer coefficient and pressure drop in a single small pipe under various operating conditions. It operates at pressures up to 120 bar, with mass fluxes ranging from 500 kg/m²s to 1200 kg/m²s, and uses pipes with inner diameters from 1 to 3 mm. By providing different heat fluxes and controlling inlet temperatures between 20 to 40 °C, the rig ensures a thorough analysis of system behaviour, offering valuable insights for the optimization of sCO₂-based thermal management systems.

The rig is now under commissioning phase. Due to unexpected delays, sCO2 data could not be included in this article. However, the first operation commissioning step, showing the ability of the system to stably and precisely regulate the working pressure at a desired level, is shown at the end of the manuscript.

CO₂ is commercially available in various purity grades, typically containing impurities such as air components: nitrogen, oxygen, and water. This study investigates the impact of impurities on the performance of a supercritical CO₂ (sCO₂) system operating in a sequential heating architecture under both supercritical and transcritical regimes. A multi-fluid mixture model was used to model the thermophysical properties of the investigated mixtures. The parametric analysis indicates that impurities strongly alter the thermodynamic properties of CO₂, such as specific heat, viscosity, and density, and significantly impact cycle performance. By analyzing twenty CO₂-based mixtures with varying purity levels and chemical compositions, the study reveals that impurities particularly affect the density of CO₂, leading to performance degradation. The results show that system performance is highly sensitive to CO₂ purity levels. Mixtures over 99.8% purity exhibited minimal performance losses, with net power reductions limited to 2%. Mixtures with 99% purity experienced losses ranging from 5% to 11%, while mixtures with 96% purity suffered reductions of up to 30%. These findings highlight the importance of analyzing impurity levels and compositions in CO₂ supply for sCO₂ systems, as they significantly influence efficiency and operational feasibility. The results also highlight the need for impurity analyses tailored to specific system architectures and operating regimes

This paper proposes a new formulation of the momentum balance equation for real gases applied in the thermofluid network modelling methodology, and then systematically compares it with the conventional incompressible flow and ideal gas approaches. The case studies address a range of phenomena including isentropic flow through diffusors and nozzles, and flows with and without work, losses and heat transfer. The results confirm that near the critical point the real fluid behaviour is more like that of an incompressible liquid, than that of a gas. Therefore, the ideal gas model provides very inaccurate results in this area. At some distance away from the critical point, the results from the ideal gas model compares well with that of the real gas model and both models satisfy the entropy balance equation. Here, the incompressible model does not compare well with the real gas model and shows notable imbalances in the entropy balance equation. The proposed real gas methodology properly treats all cases with or without work input or output, with or without losses, with or without heat transfer, as well as any combination of these, while fully satisfying entropy balance requirement. This means that it can be applied with confidence in all the regimes of interest in sCO2 power cycles.

-

The Dutch maritime sector aims to develop a maritime nuclear reactor within 10 years to support its decarbonization efforts. Naval vessels are a key area of interest, but their significant power fluctuations challenge conventional nuclear reactors, which are designed for stable operation. This study assesses the technical feasibility of nuclear propulsion for naval vessels by investigating a Very High Temperature Reactor combined with a supercritical carbon dioxide recompression cycle using a dynamic modeling approach. Simulation results show that shaft speed remains stable, the reactor operates within a safe temperature region, and turbomachinery stays within design limits. However, temperature and pressure variations in the heat exchangers raise material integrity concerns, potentially requiring a redesign of the cycle configuration. Nevertheless, the results strongly suggest that a nuclear power plant can achieve gas turbine level power ramps. Therefore, further research should not be limited by the assumption that nuclear power is only suitable for baseload operation.

ARC-100 plant control during load following has been investigated using coupled SAS4A/SASSYS-1 and PDC codes. ARC-100 is a 286 MW_th/100 MW_e sodium-cooled fast reactor featuring sCO₂ cycle for energy conversion. A linear reduction in grid demand from 100% to 0% at 5%/min rate was simulated and the required plant control action was calculated to match that grid demand. The paper presents the results of the ARC-100 plant load following with inventory control on the sCO₂ cycle and several reactor control options.

The UK Industrial Fusion Solutions Ltd is paving pathway for a commercial magnetically confined fusion power plant, namely Spherical Tokamak for Energy Production (STEP), with the ambition of building a STEP Prototypic Powerplant (SPP) by 2040. The fusion power cycle design poses the following key challenges: 1) high power cycle conversion efficiency to overcome large plant parasitic loads, 2) integration of different heat sources at multiple temperature levels from the tokamak in-vessel components, including low temperature heat sources, 3) high power cycle operational flexibility, and 4) high reliability and plant life for intermittent pulse mode of operation of SPP during the initial phases. Closed-loop CO2 power cycle show promises in realising high efficiency (>550 °C), efficient integration of low-grade heat by capitalizing the enthalpy gap due to real gas effect of CO2, and high power density CO2 turbine & compact heat exchangers signifying the potential of realising operational flexibility. This paper compares the thermodynamic performance of three novel CO2 cycle configurations, namely 1) transcritical CO2 cycle variant; 2) supercritical CO2 cycle variant; and 3) transcritical CO2 blend based power cycle variant (using SO2 as the dopant), to efficiently integrate four different heat sources at different temperature levels from the fusion machine, demonstrating the feasibility of using such a power cycle design for SPP.

This research addresses the challenges of clean energy production for industrial applications and highlights the role of nuclear power in achieving economic, safety and environmental sustainability goals. A thermodynamic analysis of a high-temperature nuclear reactor integrating Brayton cycle and reboiler was carried out. System performance was evaluated by varying turbine inlet temperature and compressor pressure ratio. The results show that higher reboiler inlet temperature significantly improves the power cycle efficiency up to the optimal threshold of 740°C, beyond which the efficiency improvements diminish. However, increasing turbine efficiency can significantly increase thermal efficiency, raising it from around 25% to 45%. The effect of compressor efficiency is less pronounced, with thermal efficiency increasing from 21% to 25%. The net power output increases with the turbine inlet temperature and compressor pressure ratio, with the peak temperature of 725°C and pressure ratio of 4.0, with the maximum power output of approximately 3.35MW. These insights are critical to optimize the design and operation of nuclear-driven thermal power systems to maximize efficiency and net power output.

Next generation solar tower plants aims at increasing the maximum achievable temperature thanks to the adoption of advanced heat transfer medium and sCO₂ cycles. In this context, the Horizon Europe Powder2Power project aims at demonstrating at MW-scale the adoption of fluidized particles as heat transfer medium in CSP plants. This work focuses on the numerical model for the sizing and simulation of the sCO₂-particle multistage heat exchanger to be used for the overall plant analysis. The developed model adopts reliable heat transfer correlations available in the literature to size the heat exchanger based on the target thermal duty and pressure losses. A sensitivity analysis is presented to study the effect of the main design parameters on the component size and efficiency. The model is then used in a case study for the complete techno-economic optimization of fluidized particle based CSP plants. Results show that the temperature differences at the cold- and hot-end of the heat exchanger greatly influences the minimum number of stages and that an increase in the number of stages leads to a reduction in the total heat transfer surface. The economic optimization highlights that the fluidized bed heat exchanger represents a marginal share of the plant overall cost and thus that there is no convenience to adopt a component with a little number of stages and penalize the efficiency and that the stage number in real plants would be likely more constrained by other technical aspects related to components manufacturing.

While all commercial concentrating solar power (CSP) plants with central receivers are equipped with the steam Rankine power cycle, supercritical CO₂ (sCO₂) cycles are seen as a promising advancement. They offer higher efficiencies and more compact turbomachinery at high temperatures compared to the steam Rankine cycle, however, sCO₂ cycles face challenges related to high pressures and temperatures, which increase material demands and the mass and cost of heat exchangers. As the need for flexible electricity generation grows, the thermal inertia of the power block, linked to its metal mass, becomes increasingly important. This study examines and compares the component sizes, material usage, and economic and flexibility impacts of sCO₂, CO₂ mixtures, and steam Rankine cycles for commercial-scale CSP applications. All cycles are designed with the same thermal energy input, keeping the solar field and thermal storage constant. Heat exchanger designs, including primary heaters, recuperators, and air-cooled units, follow the ASME Code and are modeled using Aspen Exchanger Design & Rating. Since no commercial sCO₂ turbines exist at this scale, turbine design parameters are estimated using a developed simplified approach. Results are compared with existing studies to assess component-level and system-level implications in terms of cost, performance, and flexibility.

Shaft-end sealing for sCO2 turbomachinery is more challenging than typical applications in centrifugal compressors for Oil & Gas. Due to strong influence of specific heat capacity near the critical point and low dynamic viscosity of sCO2 on machine efficiency and cycle performance, the lowest leakage rates are crucial for the technical feasibility of many applications. These requirements mandate the use of contactless sliding face seals (Dry Gas Seals – DGS). One of the most demanding applications is within radial expanders for power cycles, where process gas temperatures and pressures exceed 500 °C and 80 bar, with tangential speeds of rotating ring higher than 180 m/s. Current designs use a thermal management zone to limit the temperature on DGS (especially for secondary sealing elements of polymers or elastomers) to 200 °C. Such thermal zones utilize hot and cold flows to create an optimal thermal gradient on the shaft while not resulting in excessive thermal stress. A high-temperature resistant DGS with low leakage rates as a replacement for the thermal management zone would increase machine thermal efficiency, simplify the gas inlet and outlet flows, reduce the axial length required for shaft-end sealing (making possible the addition of new machine stages or shortening machine shaft) and reduce thermal stresses on machine shaft.

This paper presents the preliminary results of the development of a prototype DGS for turbomachinery in sCO2 applications with leakage rates no higher than 1,5 Nl/min for each bar sealing pressure operating with sealing gas at 510 °C and 89 bar and rotating ring tangential speed of 192 m/s. The machine shaft diameter is 110 mm.

The first project stage comprises the development of one DGS component: a high-temperature resistant balance sealing element, which seals the radial gap between stationary ring and balancing sleeve. Subjected to a dynamic reciprocating motion it is one of the most critical components in any DGS. The prototypes were tested with air/helium at room temperature and with CO2 at material design temperature (600 °C). The second project stage consists of upgrading two DGS (one tandem and one single with identical core parts) to a high-temperature resistant design. This was done by replacing usual temperature limited components by their respective high-temperature versions and doing the required design adaptations each at a time. After every upgrade each DGS was statically and dynamically tested to the operating conditions with air/helium mixture supplied at room temperature (the highest recorded temperature inside DGS was about 220 °C). Tests allowed the evaluation of equipment performance by means of leakage rates and leakage stability after changing operating conditions (speed and pressure). Visual inspection of internal parts after each test were performed. The test bench for CO2 supplied at 510 °C is still being commissioned to the time of this publication.

It was verified during the dynamic tests with air/helium supplied at room temperature that the leakage rates remained stable and around 1 to 1,3 Nl/min/bar for operating conditions. Design is still to be validated with dynamic tests with CO2 supplied at design temperature.

Supercritical carbon dioxide (sCO₂) Brayton power cycles offer higher efficiency and more compact component sizes than traditional Rankine power cycles. These attributes make sCO₂ technology particularly appealing for future concentrated solar power (CSP) applications, as the increased cycle efficiency could lead to smaller CSP components, such as the mirror field. One of the major factors affecting the efficiency of these cycles is the design of the turbomachinery. It has been shown that marginal increases in the efficiencies of the compressors and turbines can significantly reduce the size of the costly recuperators, thereby lowering cycle costs and further enhancing overall cycle efficiency.

The focus of this work is on the preliminary design of high-pressure compressors (HPC), low-pressure compressors (LPC) and recompression compressors (RCC) for a 50 MWe partial cooling sCO₂ Brayton power cycle. For the current work the scope is limited to the design of centrifugal compressors. The design calculations utilise an in‑house developed real‑gas mean-line analysis approach along with aerodynamic and parasitic loss models accounting for phenomena such as incidence and disk friction losses. Initially the study sets out to design the compressors using typical values for flow coefficients, work coefficients, rotor tip diameter ratios and meridional velocity ratios. Once the reference compressors have been designed, a sensitivity study is conducted to assess the impact of various design parameters on compressor geometries and thermodynamic performance. The sensitivity study includes sets of design variables selected to comprehensively cover the design space using Latin-Hypercube sampling. For each of the generated samples, the mean-line analysis code, developed in the Engineering Equation Solver (EES) software, is utilised to calculate compressor geometries and thermodynamic performance of the machines. The impact of the various design variables are therefore determined, and finally a compressor train is designed for the partial cooling power cycle.

The design of the compressor train for the 50 MWe power cycle is completed using flow coefficients between 0.1-0.55, work coefficients between 0.26-0.9, meridional velocity ratios between 0.23-0.99 and rotor tip diameter ratios between 0.6-0.75. This resulted in a five compressor system with a single HPC and RCC together with three LPCs in parallel, all with a design rotational speed of 20000 rpm. For the LPC reference case, the requirement for three machines in parallel is dictated by the low pressure-ratio combined with the high volume flow rate. The sensitivity analysis yielded compressor design configurations with isentropic efficiencies ranging from 75% to 90% and rotor tip diameters between 210 mm and 250 mm, demonstrating the potential for high efficiency and compact designs in sCO₂ Brayton power cycles.

As a consequence of global warming caused by greenhouse gases, there has been an increase in interest in improving energy efficiency and developing carbon-free energy sources. In particular, there is a considerable amount of unused waste heat and unused energy globally. It is anticipated that greenhouse gas emissions could be significantly reduced if energy conversion technologies capable of utilising this waste heat were developed. Among the aforementioned waste heat-based energy conversion technologies, supercritical CO₂ power generation is attracting considerable attention.

Carbon dioxide is attracting attention as an environmentally friendly working fluid due to its non-flammable, non-toxic, high thermal stability and economic characteristics. The supercritical CO2 power generation system utilises a compact configuration, low pressure ratio, small turbine size and the ability to be applied to various heat sources by exploiting the unique physical properties of CO2. This system has significant potential as a next-generation energy conversion technology, as it is capable of efficiently converting power from a range of energy sources, including solar, geothermal, waste heat and nuclear. In particular, the utilisation of waste heat is beneficial for improving energy efficiency and reducing greenhouse gases. Consequently, KEPCO has focused on the development of waste heat utilisation technology due to the abundance of potential resources. The supercritical CO2 power generation system is comprised of two principal components: compressors and turbines. In particular, compressors are known to be challenging to operate due to the rapid alteration of numerous physical properties in the vicinity of the critical point. In order to enhance the likelihood of success of the demonstration at the nascent stage of the development of the supercritical CO2 power generation system utilising waste heat, and to expedite its commercialisation, KEPCO facilitated the advancement of the system through the utilisation of units that were nearing commercialisation. At that time, the inlet conditions of the compressor were selected to be extremely low in order to minimise the inlet temperature, thereby increasing the efficiency and output of the system, while the integrated gear-type compressor was selected to reduce the system cost. This paper presents the initial attempts and results related to the design, fabrication and testing of the compressor and turbine during the development of a 2 MW supercritical CO2 power generation system using waste heat, which has been under development by KEPCO since 2016. The paper also discusses the challenges encountered during this process.

Supercritical Carbon Dioxide (sCO₂) turbines, modeled on traditional axial-flow steam turbine design practices, often rely on empirical loss models developed by experimental campaigns on steam and gas turbines blades with aspect ratio greater than one. This study evaluates the applicability of these models for designing sCO₂ turbines featuring low aspect ratio blades (under 1). A low fidelity modeling tool (zTurbo), originally formulated based on Craig and Cox (CC) and Traupel (TR) loss correlations, was extended by integrating loss models proposed by Kacker Okappu (KO) and Aungier (AG). zTurbo was applied for Mean Line Design (MLD) of a five-stage axial-flow low aspect ratio sCO₂ turbine (236.5 bar, 893.2 K inlet; 81 bar outlet). The four MLDs conceived using CC, KO, TR, AG loss models achieved flowpath total-to-total efficiency of 87.5%, 87.5%, 90.8%, and 91.9%. A detailed comparative analysis of four MLDs led to selection of AG loss model coupled with TR tip loss correlation to effectively capture all the losses within sCO₂ turbine flowpath. zTurbo was linked with the Non-linear optimization algorithm to generate optimized AG based MLD flowpath exhibiting a total-to-total efficiency of 92.2 %. The optimized AG based MLD was then modeled to form full 3D flowpath, and high fidelity numerical simulations were performed to evaluate the turbine performance and losses encountered along the flowpath. Both modeling approaches showed strong agreement for estimating turbine flowpath total-to-total aerodynamic efficiency, differing by less than 0.1%. A detailed loss analysis comparison between two modeling techniques showed AG loss correlation reliability for estimating profile losses; however it overestimated the secondary losses, highlighting the need for detailed investigation into secondary flow development in sCO₂ turbines featuring low aspect ratio blades.

The Brayton Loop facility at Sandia National Laboratories (SNL) has been instrumental in identifying technology gaps and developing solutions critical for the commercialization of supercritical carbon dioxide (sCO2) power cycles. The benefits afforded by these new conversion technologies are required to fully leverage the potential from the next generation of nuclear reactors: increased efficiency, smaller footprint, and the ability to use dry cooling. While the recompression closed-loop Brayton Cycle (RCBC) test loop test program has been successful, its full potential has been stymied by the poor reliability of the turbine-alternator-compressor (TAC) bearings. While many of the early events were due to poor controllability issues, resulting from the first-generation power electronics, it demonstrated their lack of robustness necessary for these high-power density machines.

Despite contactless operation at speed, foil air bearings are in contact with the shaft at all speeds that are below that required for lift-off; around 8,000 RPM. Therefore, surface to surface contact occurs during start and shutdown, leading to wear. These unpreventable events contribute to loss of low friction surface treatment and are life limiting. While fully developed foil bearings are commercially applied to air cycle machines and small gas turbines (microturbines), rotors of low mass, this failure mechanism is amplified for large commercial sCO2 systems with heavy rotors and larger loads, rendering them unsuitable for future commercial small modular reactors (SMRs). It was therefore decided to identify and test more robust bearing solutions that would not only improve run time accumulation and facilitate performance and cycle configuration testing, but also demonstrate solutions which are scalable and better suited for large commercial systems.

As part of the TAC improvement program, and after the control system upgrade, the bearings were identified as the main technology to increase TAC reliability and efficiency. TACs currently employ aerodynamic foil type bearings. This report considers the retrofit design, acceptance testing, and the initial testing of a TAC retrofitted with externally pressurized porous (EPP) gas bearings. Both radial and axial constraint are required to support the rotor and react the axial thrust load. This was accomplished by replacing the compressor journal and thrust bearings with a single EPP bearing assembly, and a simple replacement of the journal on the turbine side.

Long duration energy storage systems with 8-12 hours of capacity are one of the best options to reduce the increasing curtailment of renewable energy, being able to provide intra-day storage. Among those systems, Carnot batteries operating with CO₂ can be a promising solution due to the relatively high round trip efficiencies (up to 60%), being site-independent, including the possibility to store and sell both cold and hot thermal power in addition to electricity. In this work, the detailed sizing of the main components of a CO₂ Carnot battery is proposed: in particular, an interesting and promising feature of the system is represented by in the adoption of the same heat exchangers during the charging and the discharging phase, while the cold and hot storage systems are inspired by the commercial solution proposed by Echogen Power Systems. Specifically, the hot storage consists of two heat transfer fluid loops: a pressurized water loop and a diathermic oil loop, requiring two different insulated tanks, whereas the cold storage is based on an ice slurry tank. A routine in MATLAB has been developed to properly design the system and optimize its main variables to maximize the round-trip efficiency and minimize the storage costs, but also including the calculation of the levelized cost of storage. The battery is simulated with a cold storage at 0°C and hot storage between 71.6°C and 293.7°C, with the cycle maximum pressure of 250 bar and a round-trip efficiency of 54.6%. The specific capital cost of the system is 2033 €/kW_el,ch, with the largest share being the storage systems. The levelized cost of storage is estimated around 0.1 and 0.3 €/kWh, depending on the electricity selling price, and a relatively large internal temperature difference in the hot storage (20°C) is suggested for these systems.

The European Commission promotes technologies that support economic growth decoupled from the use of fossil fuels and promote carbon emissions mitigation. Its objectives for 2050 include the achievement of greenhouse gas neutrality, energy transition towards renewable and sustainable sources (e.g. solar, wind, hydro, etc.) and replacement of fossil fuels and feedstocks. These ambitious goals should be achieved by promoting research and technological development in clean energy, industrial efficiency and innovative technologies. One promising technology addressing these challenges is a large-scale CO₂-based electrothermal energy and geological storage system. When excess renewable energy is available, the system acts as a heat pump, storing electrical energy in the form of heat at two temperature levels and as mechanical energy in CO₂ injected in geological formations. The trigeneration system allows flexible coverage of electricity, heating or cooling demand, compensating for the temporary mismatch between renewable energy supply and demand. The use of CO₂ as a working fluid makes the system potentially integrable in carbon capture, utilisation and storage (CCUS) processes. The pressure (30-200 bar) and low-temperature conditions of transcritical CO₂ cycles are compatible with the transport of captured CO₂ under supercritical conditions. This work analyses different integration options for transporting and conditioning CO₂ captured in stationary sources to conditions suitable for injection in geological formations. Options for transport as liquid CO₂ in storage tanks and supercritical CO₂ by pipeline are considered. Different scenarios where the CEEGS system could complement the process are studied, and the cycle behaviour and impact are evaluated. CEEGS system is positioned as suitable technology in the process of using and conditioning the captured CO₂ to transport as well as geological injection conditions. The energy storage concept of CEEGS can present strong synergies with the implementation process of carbon capture plants, allowing the captured CO₂ to be conditioned through a cycle of energy storage and power production from renewable sources with roundtrip efficiencies higher than 50%, and the flexible coverage of electrical or thermal demands (heating and cooling). Renewable energy could be used for the energy needs of the entire process of conditioning and transporting the captured CO₂.

The management of electrical energy represents a significant challenge that must be overcome, given that electricity must be consumed immediately upon production. In this regard, an innovative energy storage solution is proposed, employing a heat pump with a supercritical Brayton cycle using pure CO₂ and CO₂–based mixtures to enhance the system's performance. This analysis encompasses a techno-economic, energetic, entropic and exergetic study, with consideration given to the levelized cost of storage (LCOS).

This study is concerned with the effect of binary mixtures based on pure CO₂ on the round-trip efficiency and the levelized cost of storage (LCOS), taking into account the irreversibilities associated with each component of the cycle. The methodology employed in the calculation of the plant performance entails the optimisation of the parameters of work of the components within the cycle under study. The simulations presented here are based on a code developed in MatLab. It employs a Python wrapper that enables access to a database of the working fluid's thermodynamic properties in REFPROP.

Based on exergetic and entropy analysis of the cycle studied, a comparison between pure supercritical carbon dioxide and sCO₂ mixtures is carried out. The initial results indicate that the blends result in a lower LCOS compared to the standard fluid in the cycle studied.

The management of electrical energy represents a significant challenge that must be overcome, given that electricity must be consumed immediately upon production. In this regard, an innovative energy storage solution is proposed, employing a heat pump with a supercritical Brayton cycle using pure CO₂ and CO₂–based mixtures to enhance the system's performance. This analysis encompasses a techno-economic, energetic, entropic and exergetic study, with consideration given to the levelized cost of storage (LCOS).

This study is concerned with the effect of binary mixtures based on pure CO₂ on the round-trip efficiency and the levelized cost of storage (LCOS), taking into account the irreversibilities associated with each component of the cycle. The methodology employed in the calculation of the plant performance entails the optimisation of the parameters of work of the components within the cycle under study. The simulations presented here are based on a code developed in MatLab. It employs a Python wrapper that enables access to a database of the working fluid's thermodynamic properties in REFPROP.

Based on exergetic and entropy analysis of the cycle studied, a comparison between pure supercritical carbon dioxide and sCO₂ mixtures is carried out. The initial results indicate that the blends result in a lower LCOS compared to the standard fluid in the cycle studied.

High heat fluxes from nuclear fusion pose a challenge for heat exchange. Supercritical CO₂ and micro-channel heat exchangers offer a way to solve this challenge, however heat transfer correlations for supercritical fluids do not necessarily carry over to higher heat fluxes. This experimental study investigates a promising geometry of S-Shaped fin micro-channel heat exchangers at heat fluxes up to 1 MW/m². Experiments were conducted at the Oxford Laser Heating Facility at conditions representative of the heat fluxes seen on the first wall of a fusion reactor across a range of flow rates and sCO₂ temperatures. Experimental results were calculated using a combination of finite element modelling and a thermal resistance network model. Internal heat transfer coefficients calculated using these methods matched both experimental temperatures and correlations developed for similar geometries. Heat transfer coefficients were consistently seen to be above 5 kW/m²K, with little dependence on applied heat flux. They were, however, strongly dependent on inlet sCO₂ temperature. Separately, computational fluid dynamics simulations (CFD) were performed at the same conditions from the experimental study. Although agreement between the experimental results and CFD was poor, overall results were improved when scaling the CFD-generated heat transfer coefficient profiles in the finite element models. At these elevated heat fluxes, heat transfer coefficients were largely in agreement with correlations in the literature. This enables these designs to be effectively deployed in the blanket of a fusion reactor.

Supercritical CO₂ (sCO₂), employed as a working fluid in sCO₂ power cycle, offers enhanced thermal efficiency and compact system design due to its favorable thermophysical properties. The intersection of thermophysical properties of sCO₂ with the two-phase-like regime indicates the presence of pseudo-boiling phenomenon (PBP). The thicker vapor-like layer formed during PBP reduces convective heat transfer efficiency, leading to the onset of heat transfer deterioration (HTD). Notably, this HTD is closely linked to PBP, significantly impacting the overall performance of the system. In this study, an investigation was conducted to explore the magnitude of HTD by considering the characteristics of the vapor-like layer in a heated tube. A diverse range of mass and heat fluxes and pressures (mass fluxes(200kg/(m²s) 800kg/(m²s)), heat fluxes(25kW/m² 100kW/m²), and pressures(7.5MPa 30MPa)) have been simulated in both vertical and horizontal tubes with 4 mm inner diameter. Computational fluid dynamic simulations were conducted using the Eulerian method with turbulence model that was validated against experimental data. The results show that magnitude of HTD beyond 10MPa can be ignored in cases where the Richardson number is less than 0.01. In other words, the study provides a roadmap for identifying critical threshold of the magnitude of HTD in tube heat exchangers and thermal systems.

Despite the increasing interest in supercritical carbon dioxide (sCO2) cycles in place of Rankine cycles for power generation, there is limited information available on the design and off-design performance of mechanical air-cooled heat rejection systems for sCO2 power cycles. In this work, the conceptual design and thermofluid system modelling of an air-cooled heat exchanger (ACHE) system for a 50 MWe sCO2 CSP plant is presented. The design includes the selection of major components for the ACHE system including the piping, fan, and finned-tube bundle, as well as the development of an in-house thermofluid model of the system using Python. A model of the system was also developed using the commercial code Flownex to simulate off-design conditions. To limit auxiliary power consumption, sCO2 ACHEs require deep finned-tube bundles with forced-draft fans that operate at a relatively high static pressure rise, and a relatively low volume flow rate. The results show that flow bypass combined with fan on-off control is an effective method to maintain a bulk outlet sCO2 temperature. However, to prevent local over-cooling to temperatures below the critical point, fan speed control is required. Additionally, employing fan speed control significantly lowers auxiliary power consumption relative to bypass control.

Sustainability in power production requires the proper utilization of all – or most – sources. Despite the growth in solar and wind power, the majority of electricity is still generated from heat by various heat-to-power methods. Often, heat is produced explicitly for power generation, but numerous existing heat sources (including some renewable ones) could also be used for this purpose. Among these sources, the majority of them have low heat flow rate (max. a few tens of kWth, where th denotes thermal power), which would limit the production of more than a few kWel (el indicates electric power), even with advanced heat-to-power methods. In such cases, minimizing the device cost and the power losses could be more important than maximizing the cycle efficiency or the net power. A novel approach is presented here to introduce a simple but still efficient cycle. The new cycle – existing only on a conceptual level – is a trilateral trans-critical cycle. With fewer components, the expected costs and theoretical self-consumption are low. These properties make the cycle feasible to economically utilize heat sources with very low heat flow rates for power production. The conception of the cycle will be presented in detail by using carbon dioxide as working fluid.

In the last years the importance of natural gas in the global energy mix has increasedlargely, due to its role in the energy transition toward a decarbonization. While in 2000 natural gas contributed to the overall primary energy supply with slightly more than 20%, its share has increased up to 24.7% in 2020, corresponding to 137.6 EJ. The higher natural gas consumption has led to a large increase of interregional trades (940∙10⁹ m³ in 2020, with an annual growth rate of 4% over the last decade). Among natural gas transportation technologies, Liquefied Natural Gas (LNG) plays a dominant role, and it recently surpassing pipelines as main transportation technology. In fact, in 2020 LNG contributed to about 52% of the overall natural gas trades, growing from a share of 41% in 2010. In this context, an efficient operation of LNG terminals becomes a key aspect both for environmental as well as economic reasons. Especially the recovery of the cold energy available at receiving terminals during the LNG regasification process assumes a fundamental importance. As of today, at the regasification terminals a significant amount of cold energy (LNG is typically stored at about -160 °C and ambient pressure) is often wasted.

This paper explores the integration of the LNG regasification process with one or more topping cycles, in which the working fluid directly exploits the available LNG cold energy through its condensation process. Two different categories of topping cycles have been considered, depending on the heating source of the working fluid: a) a low-temperature one using seawater as a heat source and b) a high-temperature one using exhausts from a gas turbine as a heat source. The topping gas turbine has been assumed to be fed with a portion of the natural gas from the regasification process. The choice of working fluid is critical, as its condensation temperature is far below ambient temperature. This study evaluates two working fluids: CO₂ and an organic fluid (R125) have been selected as working fluids in this study, and their performance has been compared. CO₂ is analyzed in both subcritical and supercritical conditions, depending on the operating temperature range of the topping cycle The performance of the overall system has been calculated as a function of the pressure of both the regasification process and the natural gas distribution grid. Additionally, a gas turbine has been also introduced in the LNG regasification line in order to exploit the difference between regasification pressure and distribution pressure.

A medium-size regasification terminal (50 kg/s) has been chosen as reference, leading to a topping cycle power output ranging between 3 and 35 MW depending on the heat source and on the working fluid. The topping gas turbine is a medium- to large-scale gas turbine with a power output of approximately 70-80 MW.

Dedicated models have been developed using the Aspen Plus commercial software to simulate the regasification process the integrated topping cycles, and their mutual energy integrations.

The development of hydrogen turbines combine cycle is crucial for advancing the hydrogen economy. However, the performance of the combined cycle is significantly influenced by the selection of an optimal bottoming cycle. Among various options, the supercritical carbon dioxide (sCO₂) cycle has emerged as a promising candidate due to its superior thermal efficiency compared to traditional steam cycles. This study investigates the performance of hydrogen gas turbines integrated with an sCO₂ bottoming cycle. The Kawasaki M1A-17 turbine was selected as the gas turbine and the turbine model was corroborated by comparing the results with the KAWASAKI catalogue. The partial heating cycle layout of the sCO₂ us selected as the bottoming cycle, since the partial heating cycle has been shown to outperform other configuration in terms of waste heat recovery. The analysis employed energy and exergy perspective to provide a comprehensive assessment of each configuration. The exergy analysis revealed the optimum turbine inlet temperature is 400°C for the inlet pressure of 210 bar. At 400°C and a compressor inlet temperature of 35°C, the sCO₂ cycle produces net power of 834.31 kW. At these conditions, the H₂ turbine only efficiency is 28.8% while the combine cycle offers an efficiency of 40.9%. The sCO₂ cycle performance improves considerably at cooler temperatures. For a compressor inlet temperature of 15°C, the sCO₂ can produce net power of 931 kW and the 1.5%-pt improvement in the combined cycle efficiency can be observed.

Compared to conventional technology, power cycles that use supercritical carbon dioxide (sCO2) as working fluid promise more effective energy conversion, very low dimension, and high flexibility, especially at high temperatures. These abilities are very suitable for use with advanced small modular reactors (SMRs). The concept of an SMR based on a fluoride salt (FLiBe) coolant and a sCO2-based conversion cycle, called ‘Energy Well’, is being developed by Centrum výzkumu Řež (CVR).

During the research and development of the Energy Well nuclear reactor and long-term activities of CVR in the field of sCO2 technologies, a loop-type experimental facility working with FLiBe was developed, assembled, and operated. The facility was coupled with another unique infrastructure, the sCO2 loop, to support the development of a potential interface between the FLiBe coolant and an innovative conversion cycle fluid (sCO2). This facility intends to test the key components and operational procedures important in the application of similar technologies on a larger scale. The key components of the FLiBe loop are the main circulation pump, the heat exchanger (FLiBe/sCO2) and the electrical heater, which represents the core of a molten salt reactor. All components were developed and assembled by CVR. Some aspects of the design of these components were validated using CFD tools.

A description of the first operational experience and experimental data are provided in this paper. The resulting outlet temperatures, heat flux and FLiBe mass flow rate were compared with experimental measurements and the overall heat transfer coefficient was estimated.

As part of the experimental campaign, the circulation pump for FLiBe was first tested separately. After this successful test, the experimental FLiBe circuit was connected to the existing sCO2 loop, which is operated by CVR, via the heat exchanger.

During the experimental campaign, data were obtained from the operations of both coupled devices, including from the commissioning procedure of the FLiBe circuit and the controlling of the two devices simultaneously. Experimental data were processed and evaluated. Unfortunately, large uncertainties were found in the FLiBe temperature measurements and, consequently, the resulting mass flow rates.

The European Commission aims at achieving a net-zero greenhouse gas emissions economy until 2050. For this reason, renewable electricity generation is expected to increase up to 69% by 2030. However, the intermittent nature of solar and wind power generation requires sustainable storage systems, in order to compensate for the mismatch between energy supply and demand. Large-scale thermal energy storage in combination with supercritical carbon dioxide (sCO₂) power cycles is a promising solution to address this issue.

The EU-project CEEGS (Novel CO₂-based Electrothermal Energy and Geological Storage System) aims to develop a highly efficient, cost-effective and scalable energy storage technology. When excess renewable electricity is available, a compressor drives a heat pump cycle to increase temperature and pressure. The hot CO₂ heats a hot water storage and cools down before entering an expansion turbine. The low-temperature CO₂ cools a cold-water storage tank before entering the compressor. In the discharge cycle, CO₂ is pumped from the geological reservoir into the surface components and gets heated by the stored thermal energy through a heat exchanger, before entering the turbine to generate electricity. The low-pressure CO₂ is liquified by entering a condenser, which is cooled by the cold-water reservoir, and pumped back into the subsurface reservoir through an injection well to extract heat from the subsurface.

In order to demonstrate the transcritical cycle of the CEEGS concept and to validate the surface components, a 20 kW demonstrator was designed, built and operated at the Helmholtz-Zentrum Dresden-Rossendorf. In the present contribution, the design of the facility and the operation of the discharge cycle at CO₂ temperature and pressure of up to 250 °C and 235 bar will be presented and discussed. The safety and measurement concept of the facility is presented. The design of the main components, such as the high-temperature heat exchanger (HXW), the low-temperature heat exchanger (HXI) and the CO₂-pump, as well as the cycle behavior are presented. The experimental results show a lower Reynolds number at higher cycle pressures, due to the more closed valve position. Particular attention is paid to the performance of the high-temperature heat exchanger in terms of overall heat transfer coefficient. Convective heat transfer on the CO₂ side plays a dominant role in the thermal resistance of the heat exchanger. The thermal efficiency of the cycle during discharge is strongly influenced by the maximum cycle pressure. In fact, at higher pressures, higher cycle efficiency is achieved due to greater expansion work.

The experimental results will be used by the project partners to validate the numerical models. Future experimental campaigns will investigate the dynamic operation of the facility.