An experimental study on the recuperative low temperature solar Rankine cycle using R245fa

An experimental study is conducted to investigate the performance of a low-temperature solar recuperative Rankine cycle system using working fluid R245fa. The experimental setup consisted of typical Rankine cycle components, such as throttling valves, working fluid pumps, air cooled condensers, and a flat plate collector for gathering solar energy. Prior to boiler, the working fluid is typically preheated; this process is simulated in the experiment using an electric tracing ribbon. Experiments conducted during typical winter weather conditions in Tianjin, China. Results showed that for conditions of constant working fluid flow rates, the introduction of a recuperator did not improve the thermal efficiency of the experimental system obviously, which remained constant at about 3.67%. Furthermore, preheating caused the collector inlet temperature to increase, which led to lower collector efficiencies and ultimately, lower overall system efficiencies. Results also showed that both thermal and collector efficiencies could be improved significantly by adjusting the working fluid flow rate to an appropriate level based on the solar heat flux. Significant improvements in thermal efficiency can also be achieved with an improved expander.