Experimental study on the pressure drop characteristics of a supercritical CO₂/R134a mixture in a rectangular microchannel

The proper addition of additives to pure CO2 can improve the performance of CO2 as a working fluid. By working fluid, we mean a fluid used for the CO2-based transcritical power cycle characterized by the addition of R134a to CO2. Hence, an experimental investigation of the pressure drop characteristics of a supercritical CO2/R134a mixture in a rectangular microchannel was conducted. For this purpose, an accurate and stable CO2/R134a mixture thermal-hydraulic experimental system was designed and built. The experimental results show that the pressure drop of the CO2/R134a mixture is lower than that of pure CO2 under the same conditions. The proportion of friction resistance to the total pressure drop decreases with an increase in R134a composition. Finally, a frictional resistance correlation that fully considers the effects of CO2/R134a mixture components and thermophysical property variations is proposed, which can guide the design of mixture heat transfer devices.