Experimental study of heat transfer characteristics of supercritical CO2 fluid in collectors of solar Rankine cycle system

Heat transfer characteristics of supercritical CO2 (S-CO2) fluid in collectors of a solar Rankine cycle system is experimentally investigated at different flow conditions. In the experiments, temperature, pressure and mass flow rate are measured, and local and average heat transfer coefficients are investigated. Study shows that the thermophysical properties of CO2 near the critical point have significant effects on the S-CO2 local heat transfer behaviors. The heat transfer of S-CO2 is also dependent on the mass flow rate, input heat flux and pressure at inlet of test section.

Research highlights
► We carried out an experimental investigation of the heat transfer characteristics of S-CO2 in a heating tube in order to obtain the optimized high efficiency operation condition of the solar collector in a proposed S-CO2-based SRCS.
► It is found that the heat transfer of S-CO2 can be enhanced greatly by slightly increasing the mass flow rate.
► Reducing the input heat flux and the inlet pressure can also improve the heat transfer of S-CO2.
► The present investigations suggest that it is better to set the operating conditions of the proposed SRCS at high mass flow rate and the inlet near-critical pressure in order to obtain high heat transfer of S-CO2 in the collector.