Study On The Performance Of Organic Rankine Cycle Containing New Working Fluid

With the development of China’s economy, energy consumption is increasing and the dependence on foreign oil keeps growing. Energy shortage has become a big problem. However, a large amount of heat with low temperature, such as geothermal, industrial waste heat, solar energy and et al, have not been fully utilized. Organic Rankine Cycle (ORC) is an effective way to utilize low temperature heat. Currently, the study on ORC is focused on the subcritical Organic Rankine Cycle with pure hydrofluorocarbon working fluid. Its efficiency is low due to the low high temperature.Compared to subcritical ORC, supercritical ORC works at the higher temperature and the variable temperature during heating process matches very well with the heat source temperature profile, thus it has a higher effeciency. On the other hand, the problem of global warming has received worldwide attention and the study of low GWP working fluid in ORC has attracted more and more attention. R1234yf and R1234ze (ODP=0 and GWP<1) have been considered as potential working fluid with excellent environmental performance. Non-azeotropic mixtures containing low GWP working fluid also can match the heat source temperature profile well due to the temperature glide in the evaporation process. Therefore, the following are theoretical studied in this thesis.The performances of the basic supercritical ORC were theoretical analyzed for 8 organic working fluids. The results showed that R152a and R134a as working fluids for supercritical ORC had higher unit net power output and cycle efficiency, as well as smaller volumetric flow rate. The regenerative cycle could further improve the cycle efficiency.The performances, exergy efficiency and exergy loss of reheat supercritical ORC were analyzed for R134a, R227ea, RC318, low GWP fluids R1234yf and R1234ze. Compared with R134a, R1234yf and R1234ze had the similar performances. Both of them were suitable for replacing R134a as working fluids in supercritical ORC.Performance comparison between subcritical ORC with R142b, R236ea, R245fa, R600a and supercritical ORC with R1234yf, R1234ze, R134a, R227ea were performed at the same working conditions. The results indicated that the performance of supercritical ORC was mainly batter than that of subcritical ORC, such as unit net power output, volumetric flow rate, exergy efficiency, thermal efficiency of the system and exergy efficiency of the system. For fixed heat source, with the decrease of pinch point temperature difference of heater, the net power output, thermal efficiency and exergy efficiency increase. Considering the performances and environmental properties of working fluids, R1234yf and R1234ze, were recommended as the working fluids of supercritical ORC to recovery waste heat.R32 was selected to mix with R1234yf and R1234ze with mass ratio of 1:1, respectively. The performances were analyzed for subcritical ORC with these two non-azeotropic mixtures. The results showed that non-azeotropic mixtures could significantly improve the thermal efficiency and exergy efficiency, and reduce exergy loss and the expander inlet flow.