| Organic Rankine cycle system(ORC)based on the traditional Rankine cycle.It uses organic medium with lower boiling point to replace water vapor as power source to drive generatORC to generate electricity and drive machines to do work,so as to realize energy transformation.It has a wide application prospect in industrial waste heat,solar energy,geothermal energy,biomass energy and other fields.Due to its simple structure,no fuel,no greenhouse gas emissions,suitable working pressure and other advantages,the system is considered by scholars as one of the most effective and environmentally friendly methods to recover low-temperature waste heat.Based on the background of recovering industrial waste heat at low temperature(100?~200 ?),through studying the thermodynamic process and performance of ORC,an experimental platform of ORC power generation system is built.Through simulation and experiment,the performance of ORC system is optimized,and the following main research results are obtained:(1)By analyzing the thermodynamic process of ORC system,a simpler and more convenient thermodynamic model is proposed and its accuracy is verified.By simplifying the model,the formulas for calculating the optimal evaporation temperature corresponding to the maximum net output power and the maximum thermal efficiency are derived,and compared with the theoretical solution,the errORC are acceptable.The calculation shows that the optimum evaporation temperature corresponding to the maximum net output work of each working medium is closely related to the heat source temperature,which is about 65% of the heat source temperature,and the optimum evaporation temperature corresponding to the maximum thermal efficiency of each working medium is related to the physical properties of the working medium itself,which is about 95% of the critical temperature of the working medium:(2)The improved ant colony algorithm is applied to single-objective andmulti-objective optimization of ORC system.Based on the improved ant colony algorithm,its reliability is verified: its optimization time,efficiency and stability are superior to other optimization algorithms in the literature.Based on the improved ant colony algorithm,the performance of ORC system is studied,and the changing rules of ORC system performance under different working conditions and different working fluids are investigated.The results show that:(1)In different heat source temperature ranges,the corresponding working fluids of ORC system are different;(2)When the critical temperature of working fluids is less than 15 C,the corresponding maximum net output work is optimal.The maximum net output power decreases with the increase of critical temperature,and the optimal evaporation temperature is about 65% of the heat source temperature.(3)The thermal efficiency of refrigerant increases with the increase of evaporation temperature,but the increasing trend slows down gradually,and finally approaches the maximum value.(4)Based on the improved ant colony algorithm multi-objective optimization and TOPSIS selection method,taking net output power and thermal efficiency as objective functions,the Pareto optimal frontier and TOPSIS optimal points are obtained.The operating points of each working fluid under TOPSIS optimal points are different,but they are all close to the maximum output power of the system.(3)The performance and thermal economy of ORC system with different mixtures of R-245fa/R-141 b are studied and analyzed.The results show that when the mass fraction of R-245fa/R-141 b is 0.5/0.5 to 0.9/0.1,the overall thermal performance of ORC system with mixtures of R-245fa/R-141 b is better than that of pure R-245 fa and R-141b;when the mixtures of R-245fa/R-141 b are 0.8/0.2,the net output power of the system is the highest.The temperature slip of mixed refrigerant will reduce the average heat transfer temperature difference of heat exchanger,increase the heat transfer area and equipment investment.Compared with pure refrigerant,the thermal economic performance of mixed refrigerant is worse than that of pure refrigerant.(4)The influence of pure and mixed refrigerants on the performance of ORC system was studied on the experimental platform of ORC low temperature waste heat power generation system.The results show that the range of thermal efficiencycalculated and measured by ORC system is 7.1%~11.8% and 2.8%~5.3%,respectively;the range of power generated by ORC system calculated and measured is 705.2~2038.7W and 70.83~354.6W,respectively.Under the condition of0.8R-245fa/0.2R-141 b,the thermal efficiency of mixed refrigerants increased by0.47% and 2.98% respectively for two pure refrigerants R-245 fa and R-141 b.The net output power of mixed refrigerants 0.8R-245fa/0.2R-141 b increased by 6% and18.6% respectively for two pure refrigerants R-245 fa and R-141 b. |
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