Simulation And Experimental Research On CO₂ Transcritical Water-water Heat Pump

For the deterioration of ozone depletion and greenhouse effect, natural working fluid CO₂ is attracting much more attention. The study in this thesis is to develop a high accuracy simulator of CO₂ trans-critical water-water heat pump for prediction of further development in cycle performance and optimization of system design.Based on the specific experiment rig of CO₂ trans-critical water-water heat pump, models of all components are built up. The model of compressor is obtained by means of efficiency analysis. By employing heat transfer correlations that are selected and modified in advance, heat exchangers are simulated in steady state with the method of lumped parameters. Through simulation of the cycle with throttling valve under various external parameters, it is found that the average deviation in coefficient of performance for heating is 16.9%, which indicates that the simulation results accord with the experimental data.By thermodynamic analysis of a rotary expander, models of leakage, friction and heat losses are set up respectively. According to energy and mass conservation principles, differential equations of two working chambers are established. With the help of EULER numerical method, equations are solved discretely, which brings out the leakage rates through all leaking passages at different rotation angles and the corresponding thermal parameters inside chambers. Furthermore, the influences of all inlet parameters of expander, evaporator pressure and nominal load on expander efficiency are analyzed by simulation. Then the simulation results of the whole cycle with expander under various external parameters are compared with corresponding experimental data, and the average deviation in coefficient of performance for heating approaches tol7.8%, which accounts for veracity and accuracy of the simulation.By calculation based on the verified simulator, it is proposed that there are several methods for optimizing the system. Finally, in this thesis some advices are put forward for further improvement.