Experimental Study And Modeling Of CO₂ Cooler With Parallel Flow

The carbon dioxide automotive air conditioning system (CO₂-AACS) is an energy-saving and environment-friendly air conditioning system. It uses CO₂ as work medium in refrigeration. This dissertation focuses on researching the flow and heat transfer characteristics of CO₂, aiming to determine methods for increasing heat transfer efficiency in the gas cooler of micro-channel with parallel flow (GCMCPF). We expect the findings of this research to contribute to the industrial production of this equipment. Toward these ends, the following measures were taken:First, an algorithm was developed based on the analysis of the GCMCPF structure in homogeneous flow of work medium and mean temperature difference. Using GCMCPF technical data, numerical analysis of both the circle and rectangle micro-channels of the GCMCPF was performed. The CO₂-AACS has to work under high pressure; thus, we developed a structure formation method called pierce and flanging, which can help improve strength in the welding region for construction of collecting tubes that can withstand high pressure in work conductions. This structure lays the foundation for studying CO₂ flow and heat transfer.Second, we studied the principle of refrigeration of CO₂ circulation in trans-critical flow. Considering the characteristics in trans-critical flow, we designed and constructed an experimental platform for a carbon dioxide air conditioner in trans-critical (CO₂-ACTC) flow. This platform uses a CO₂ compressor (CO₂-C) and the GCMCPF as the main components. Experiments were conducted simulating the work conditions of a car. Results show that the platform can work well, and satisfies the requirements of research on the characteristics of a parallel flow cooler that uses CO₂ as work medium.We designed the experimental scheme taking into consideration the main factors influencing flow and heat exchange of CO₂ and the performance of the experimental platform. Performance analysis of flow and heat transfer in the circle and rectangle micro-channels of the GCMCPF was conducted. The results serve as guidelines for further research on intensified heat transfer of the GCMCPF.To solve the problems of fluency and unbalanced heat transfer generated by the single-channel model of the GCMCPF, two multi-channel models of the rectangle and circle micro-channels were designed and constructed in the experiment. Experimental results show that multi-channel GCMCPF can considerably increase the heat transfer efficiency of the GCMCPF and enhance its applicability in engineering.In this dissertation, the GCMCPF was constructed using the pierce and flanging method, and an algorithm was established and applied to the experimental conditions of the GCMCPF. The experimental platform of the CO₂-ACTC using CO₂-C and GCMCPF as the main components was designed and constructed. The influence of different working conditions on flow and heat exchange of CO₂ in the GCMCPF was analyzed based on experiments on the GCMCPF. The work in this dissertation can provide theoretical and experimental support in GCMCPF applications, as well as facilitate research on the characteristics of relevant systems that use CO₂ as work medium.