The Performance Simulation And Optimization Of Portable Air Conditioners With Carbon Dioxide As Refrigerant

With the objective of optimizing the coefficient of performance (COP) of trans-critical refrigeration systems, both the characteristic and thermodynamics property of several kinds of trans-critical circle mode was investigated theoretically. Fur-thermore, a simulation model was developed for micro-channel gas coolers in trans-critical carbon dioxide refrigeration systems. Following are the main points of this thesis.1. To identify the main factors that affect CO2 system performance, the second law of thermodynamic analysis on the entire CO2 refrigeration cycle is conducted so that the ef-fectiveness of the components of the system can be deduced and ranked, allowing future efforts to focus on improving the components that have the highest potential for advance-ment. The analysis reveals that the compressor and the gas cooler exhibit the largest non-idealities within the system, and hence, efforts should be focused on improving these components.2. Some models were developed for several kinds of trans-critical carbon dioxide re-frigeration circles. Relationship between COP and high-side pressure etc were presented. Results indicated that two stage compression with intermediate inadequacy cooling is the best.3. A model was developed for micro-channel gas cooler s in trans-critical carbon diox-ide refrigeration systems. Fluid flow and heat transfer processes in both refrigerant and air sides were analyzed with t he latest physical properties database and t he corresponding correlations. The model was validated by the comparison between simulation results and experimental data under various conditions. Furthermore, the influences of major parame-ters on gas cooler performance were analyzed and discussed. The results indicated that the exit enthalpy of gas cooler could be reduced by increasing refrigerant pressure, increasing pass number or decreasing port diameter, but with the side effects of greater input power or pressure drop. So the above parameters should be considered comprehensively in the optimal design of gas cooler. The model developed in this paper could be used for the op-timal design of gas coolers.The study in this paper provides theoretical foundation to investigation of carbon diox-ide portable air conditioners (PACs).