针对CO2水平微细管内流动沸腾换热流态及流态转变特性进行实验研究。实验工况：热流密度（5-35 k W/m^2）、质量流率（50-600 kg/（m^2·s））、饱和温度（-40-0℃）、管径（0.5-1.5 mm）。实验表明：CO2在微细管内实际流态分别是泡状流、弹状流、间歇流、层流、波状流、混状流、环状流和雾状流;干涸过程中的流态主要为环状流-雾状流、波状流-雾状流的过程及不稳定的环状流;通过理论计算获得CO2微细管内流动沸腾换热流态图,流态图显示热流密度对高干度区域流态转变有显著影响,质量流率大小直接决定了换热过程所经历的流态;不同饱和温度工质热物性不同改变了流型;理论分析所采用的流态形式与实际CO2在微细管内所具有的流态类型基本一致。
Experimentally studied were the flow boiling and heat exchange flow pattern as well as its transition characteristics of CO2 in a horizontal micro tube and given as follows were the test conditions： heat flux density,5 to 35 kW · m^-2 ,mass flow rate,50 to 600 kg · m^-2 · s^-1 ,saturated temperature, -40 to 0 ℃ ,tube diameter,0.5 to 1.5 mm. It has been found that the actual flow patterns of CO2 in a micro channel are as follows respectively： bubble flow, slug flow, intermittent flow, laminar flow, wavy flow, mixed flow, annular flow and mist flow. The flow patterns in the drying-up process are mainly as follows： annular flow to mist flow and wavy flow to mist flow transition process and unsteady annular flow. A flow boiling heat exchange flow pattern diagram of CO2 in a micro channel was obtained through a theoretical calculation. The flow pattern diagram shows that the heat flux density will have a noted influence on the flow pattern transition in the high dryness zones and the magnitude of the mass flow rate will directly determine the flow patterns appearing in the heat exchange process. At various saturated temperatures, the working medium will have different thermo-physical properties and change its flow pattern transition characteristics. The flow patterns adopted in the theoretical analysis were basically in agreement with actual ones of CO2 in the micro channel.
Journal of Engineering for Thermal Energy and Power