Numerical Simulation For Performance Of Evaporator Of CO₂ Heat Pump

With the development of Chinese economy, the proportion of building energy consumption accounting for social energy consumption is increasing rapidly, and up to 27.45% now. Meanwhile, the percentage of heating and cooling energy consumption accounting for building energy consumption reach 65%. So building energy conservation is urgent to be solved for the whole country. As a novel technology of building energy conservation, the heat pump can recover the low-grade heat sources such as the heat of air to meet the demand of energy consumption for heating in the building, and effectively reduce the traditional energy sources (such as coal, oil and so on) consumption.Presently, the research on the performance of the various components of heat pump system have been problems needed to be solved urgently for the purpose of using natural refrigerant CO2 instead of the traditional refrigerant R22 to protect environment. In this dissertation, the fin-and-tube evaporator which has been used extensively in heat pump system is investigated with the method of numerical simulation. The steady-state distributed parameter mathematical model is established, and the corresponding simulation program is built with Matlab software to shorten the development cycle of the fin-and-tube evaporator and reduce its cost. For these purposes, the following theoretical works have been made in this dissertation:(1) The steady-state distributed parameter mathematical model of the fin-and-tube evaporator was established. In the model, a simulation module which could judge different operating condition of the fin-and-tube evaporator, including dry condition, partially wet condition, and fully wet condition was developed;(2) The model algorithms which were developed by the principle of top-down and stepwise refinement were constituted of the top-level algorithm which is the backbone of the model algorithms (i.e. the overall iterative algorithm of the model) and the basic algorithm which could realized concreted computing of the top-level algorithm (i.e. the algorithm of the unit control volume and the evaporator module). Meanwhile, the simulation program was developed by Matlab based on the model and its algorithm.(3) The steady-state distributed parameter mathematical model of the fin-and-tube evaporator was validated with the experimental data in the published literature. The relative error between simulated result and experimental result is less than 8%. The maximum and minimum error is 7.9% and 2.6%, respectively. The simulation model is proved to be correct;(4) The research on the accuracy of the simulation model was conducted by introducing the air-side sensible heat transfer and mass transfer correlation under partially wet and fully wet condition to the heat transfer calculations, and calculating method of the fin efficiency using one-dimensional analytical solution. The results indicate that the maximum and minimum error of simulation model is 3.3% and 0.1%, respectively;(5) By using the fin-and-tube heat exchanger simulation model, several parameters affected on the performance of CO2 fin-and-tube evaporator were investigated. Meanwhile, the performance of natural refrigerant CO2 was studied and compared with that of traditional refrigerant R22 in the same condition;...