Thermodynamic Study And Optimization Of Combined Cooling,Heating And Power System Based On Combination Of CO₂ Brayton Cycle And Lorentz Cycle

The combined cooling,heating and power cycle(CCHP)is a relatively efficient energy utilization cycle.Researching the combined cooling,heating and power cycle is extremely important for energy conservation and efficient use of energy.In the paper,based on the combined cycle with ejector,an improved combined cold,heat and power cycle is proposed.Theoretical calculations and simulations of the two cycles are performed.The main difference between the improved cycle and the one with ejector is that the ejector is replaced by an expander and a small compressor,and the internal heat exchanger is added at the inlet of the high-pressure compressor,and the temperature of the inlet working medium of the high-pressure compressor is increased by the internal heat of the cycle itself.Thermodynamic models of two cycle and thermo-economic models were established in Matlab,and the corresponding thermodynamic research on the two-cycle was carried out,and the influence of key operating parameters on system thermodynamic performance parameters and device cost was analyzed.The results show that,compared with the combined cycle with ejector,the device cost of the improved combined cycle is increased by 4.618%,but the thermoelectric efficiency,COP and exergic efficiency are increased by 6.947%,6.269%and 1.235%,respectively.The results of exergy analysis show that the exergy loss of the system is mainly concentrated in gas heater,heater and gas cooler.Then,multi-objective optimization of two cycles is operated basing on the genetic algorithm.The highest cyclic exergy efficiency,the lowest device cost,the highest thermal efficiency and the lowest device cost,the highest cyclic thermoelectric efficiency and the highest cyclic exergy efficiency were selected as two objective function combinations.Based on TOPSIS principle,the final optimization results of two cycles in different combinations of objective functions are determined from the pareto optimal frontier.Finally,the effects of turbine inlet and outlet pressure,turbine inlet temperature,evaporation temperature and compressor inlet pressure on cyclic thermodynamic performance parameters are studied.It is found that the optimal inlet and outlet pressure of the turbine exists in both cycles,which makes the COP of the cycle maximum.The thermal performance parameters of both cycles increase as the inlet temperature of the turbine increases.Evaporation temperature has no effect on the thermoelectric efficiency and COP of the cycle with ejector,but the increase of evaporation temperature increases the COP and exergy efficiency of the improved cycle and decrease the thermoelectric efficiency.The inlet pressure of the compressor increases the COP and exergy efficiency of the two cycles,increase the thermoelectric efficiency of the improved cycle,and decrease the thermoelectric efficiency of the injector cycle.The cost of both cycles almost always increases with the increase of these operating parameters.