CO2 Evaporation Process Modeling: Fundamentals and Engineering Applications

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This paper presents critical analysis of process modeling and mechanisms of CO2 evaporation inside macro- and micro-channels. First, some existing experimental results of CO2 evaporation heat transfer in macro-channels and micro-channels are compared and discussed. Then, the comprehensive two-phase flow pattern map of Cheng et al. for CO2 evaporation inside channels is presented. The flow pattern map has widely been used to predict flow patterns of CO2 evaporation processes and favorably agrees with observed CO2 two phase flow patterns in various channels. Next, the Cheng et al. generalized CO2 evaporation heat transfer model based on flow patterns is compared to the experimental data. It has been proved that the heat transfer model favorably agrees with the experimental data by many researchers over the past decade. Simulation results of evaporation heat transfer in both macro- and micro-channels using the model are also presented. Furthermore, evaporation heat transfer mechanisms are analyzed from the flow regime variations and unstable evaporation heat transfer characteristics in both macro- and micro-channels. Finally, applications of the Cheng et al. CO2 evaporation heat transfer model in evaporator design for various thermal systems are reviewed. Future research needs are identified according to this comprehensive analysis and review.