Experimental investigation of heat transfer and pressure drop in tubes to cool CO2 near the critical point

In the frame of EU-project sCO2-flex the design of a 25 MWe supercritical CO2 (sCO2) Brayton cycle will be developed. The system will be optimized to meet flexibility requirements, while reducing environmental impact and focusing on cost efficiency. In the context of a sCO2 Brayton cycle, the gas cooler is a key component to achieve a high overall efficiency. Close to the critical point, due to varying properties, heat transfer and pressure drop of carbon dioxide (CO2) are difficult to predict. By performing experiments with the “SCARLETT” facility of the University of Stuttgart, expertise will be gained using CO2 as working fluid in the pseudocritical region. The results of the fundamental experiments will be used for validation and improvement of correlations to develop heat exchangers working with high efficiency. The heat transfer and pressure drop of carbon dioxide near the critical point cooled in a 2 mm diameter was investigated. The outer wall surface temperature is determined by soldering calibrated T-type thermocouples into the copper tube wall. Thermocouples are evenly distributed along the 1.2 m cooled length. The effects of the CO2 mass flux of 400-1400 kg/m²s, inlet pressures of 7.7-8.5 MPa, bulk fluid temperatures of 10-85 °C and the flow orientation (upward, downward and horizontal) on the heat transfer and pressure drop were examined.
Conference Proceedings of the European sCO2 Conference3rd European Conference on Supercritical CO2 (sCO2) Power Systems 2019: 19th-20th September 2019, p. 255