CO2跨临界循环吸热过程换热性能理论分析

通过对两相流型和干涸现象进行分析，发现CO2在吸热沸腾过程中，环状流是主要的流型，液滴夹带和沉降是支持环状流最可能的机理。与其他制冷剂相比，CO2出现环状流以及发生干涸时的干度值要低得多。并且干涸前和干涸后的传热特点，以及关联式形式存在很大差别，应该区分对待。因此，研究能淮确描述CO2流动沸腾换热关联式，为CO2跨临界制冷循环蒸发器的优化设计提供理论依据，是非常必要的。

Theoretical analysis of heat transfer performance for heat absorbing process in trans-critical carbon dioxide cycle

Based on an analysis of the two-phase flow pattern and the dry-out phenomenon, it was clear that annular flow was the predominant flow pattern, and liquid entrainment and deposition were the most important mechanism to sustain the annular flow during the heat absorbing boiling process of CO_2. The mass quality of onset of annular flow and dry-out was much earlier than that of the other conventional refrigerants. The heat transfer characteristics and correlations of pre-dryout and post-dryout were quite different and thus should be dealt with differently. It is indispensable to investigate the correlations which can describe the boiling heat transfer of carbon dioxide accurately so as to provide theoretical basis for the optimization design of evaporator in trans-critical carbon dioxide cycle.