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.