Research On Simulation Modeling And Performance Optimization Of VM Cycle Heat Pump System

As a heat-driven heat pump,Vuilleumier(VM)cycle heat pump can recover waste heat for heating and cooling,which is of great significance in improving the utilization rate of primary energy and protecting the ecology.Compared with the ideal VM cycle,the regenerative loss and other irreversible losses in the actual working process greatly reduce the thermal efficiency of the heat pump.Therefore,by establishing the theoretical model and simulation model of the VM cycle heat pump,this paper studies and optimizes the internal losses and the influence of structural parameters of the system.The VM cycle heat pump is composed of three working chambers,two regenerators,three heat exchangers and a driving mechanism that pushes the piston.By analyzing its thermal process,a theoretical adiabatic model of the working chamber,regenerator and heat exchanger is established.Taking the low temperature side parameters as the characteristic size,the dimensionless simplification of the model is carried out.A total of 11 influencing parameters,including two dimensionless heat transfer temperatures,three dimensionless stroke volumes,four dimensionless dead volumes,thermal cavity advance angle,and working fluid specific heat capacity ratio,are obtained.According to the parameters of the prototype,the theoretical performance calculation and analysis are carried out.The results show that there is exergy loss in the theoretical model,and it is mainly located in the low temperature chamber and the room temperature chamber.Except that the theoretical heating capacity has a maximum value with the increase of the volume phase angle,the other performance indicators of the system change monotonously with the increase of 11 input parameters.To study the various irreversible losses of the actual heat pump,a simulation model of the heat pump is established based on the theoretical model and the separation calculation method.The model was verified by using the literature parameters,and the calculation error was less than 5%.The calculation results of the prototype data show that the heat recovery loss and the flow resistance loss account for the largest proportion,and the hot side loss is greater than the cold side loss.The exergy loss in the actual cycle is also much larger than the exergy loss in the theoretical model.In order to improve the performance of the prototype,the effect of the structural parameters on the performance of the VM cycle heat pump was studied by simulation.Better heat pump performance can be achieved when the volume phase angle is 90°.The increase in the diameter of the heat connecting rod has little effect on the heating capacity but will reduce the heat pump COP.For the diameter of the cold connecting rod,the length and cross-sectional area of the cold and hot regenerator,and the tube length of the three heat exchangers,there are most optimal solutions to maximize the COP or heating capacity.Finally,the NSGA-II algorithm is used to perform multi-objective optimization with heating power and COP as the objective function.The Pareto optimal solution set is obtained,and the TOPSIS optimization method is used to make plan decision.The results show that compared with the simulation benchmark value,when the COP is basically unchanged,the heating capacity can be increased by 55.8%,and when the heating capacity is basically the same,the COP can be increased by 6.5%.