Performance Optimization And Experimental Investigation Of Dual-loop Organic Rankine Cycle System Using Mixture Working Fluids

The rapid development of global economy has led to the increasingly serious energy shortage.The development of renewable energy and waste heat recovery technology becomes more and more important.In our country,there are a lot of waste heat resources in various industries,especially low-grade low-temperature heat energy.It has become a research focus to recover this kind of heat energy reasonably and efficiently.The organic Rankine cycle?ORC?technology has been proved to be an effective method for the low-medium temperature waste heat recovery and improving energy utilization.In this paper,the numerical models of the Supercritical-Subcritical organic Rankine cycle?SSORC?and the series dual-pressure evaporation organic Rankine cycle?STORC?are established,and the parametric analysis and systematic optimization are been investigated.Meanwhile,a 10 kW organic Rankine cycle power generation system experiment is carried out.The main conclusions are as follows:?1?The influences of five operating parameters on the thermal and economic performance are examined.A single-objective optimization for maximizing net work output,maximizing exergy efficiency and minimizing heat transfer requirement(UA_sys)is examined and compared,and the dual-objective optimization for maximizing exergy efficiency and minimizing UA_sys simultaneously is addressed.Research demonstrates that the net output power increases first and then decreases as supercritical stage temperature and pressure.UA_sys decreases first and then increases with the supercritical stage temperature.Lower pressure and temperature of supercritical cycle and higher condensation temperature could benefit improving the system economic performance.The Pareto-optimal solutions for exergy efficiency and UA_sys are 61.25%and 20.08 kW/K based on NSGA-II algorithm.?2?The influences of six key operating parameters on STORC thermal-economic performance are analyzed and compared.The thermal-economic optimization for exergy efficiency and Levelized energy cost?LEC?is carried out.The results show that the optimal mixture proportion for R245fa/pentane is 0.77/0.23.The thermal-environmental optimization for exergy efficiency,LEC and Equivalent carbon dioxide emission?ECE?are developed.The Pareto optimal solutions for exergy efficiency,LEC and ECE are 61.37%,0.2086$/kWh,and 9.43 kgCO₂eq/kWh.Higher low-pressure evaporation temperature,lower condensation temperature and superheating degree are conducive to improving the system comprehensive performance.?3?A 10 kW organic Rankine cycle power generation system testing platform is established,and the experimental analysis and comparison for common organic Rankine cycle?BORC?and regenerative organic Rankine cycle?RORC?are investigated.Experimental results show that the heat source temperature utilization rate for BORC is 25%higher than that for RORC.The maximum generation efficiency of BORC and RORC is 3.4%and 2.5%respectively,while the thermal efficiency of BORC is higher than RORC when the input heat is less than 65 kW,indicating adding regenerator may not lead to the better power generation efficiency or thermodynamic performance.The pump exergy loss is lowest while that of evaporator accounts for the largest proportion under the fixed input heat,so the selection and construction design of evaporator component could be targetedly improve for better system performance.