综合考虑制冷剂的环保性、安全性、热工性能以及市场可获得性等，R32是R22有前景的替代工质之一。随着通道尺寸的减小，微细通道内工质的流动沸腾换热规律已明显不同于常规通道。因此，研究R32在微细通道内的流动沸腾特性，具有重要的理论意义和实用价值。本文主要工作如下：实验方面：研究了R32在内径2 mm的微细光管和内径1.7 mm的多孔微肋扁管内的流动沸腾特性。实验条件为质量流速100~400 kg/(m2•s)、热流密度10~40 kW/m2、饱和温度10~20oC、干度0.05~0.98。结果表明两种实验段内的流动沸腾特性类似：换热系数随质量流速、热流密度及饱和温度的增加而增大；临界干度随质量流速、热流密度及饱和温度的增加而变小；两相摩擦压降随质量流速、热流密度和干度的增加以及饱和温度的减小而增大；但多孔微肋扁管内流动沸腾换热系数和压降均高于微细光管，分别平均高出41%和48%。关联式方面：引入体现管径对流动沸腾影响的限制数Co，针对临界干度前后，分别在Chen换热模型和Cheng换热模型的基础上拟合了新的换热系数关联式；在Lockhart-Martinelli压降模型的基础上拟合了新的压降关联式。新换热系数关联式对93%的已有实验数据和89.5%的本文实验数据预测偏差在±20%之内，新压降关联式对85%的已有实验数据和本文所有的实验数据预测偏差在±20%之内。数值模拟方面：采用Mixture多相流模型和Hertz–Knudsen相变模型，对R32在内径2 mm水平微细光管内的流动沸腾进行了三维稳态数值模拟。结果表明：质量流速的增加消弱了重力对两相分布的影响；热流密度的增加强化了壁面附近的核态沸腾。数值模拟所得换热系数和压降与实验结果的平均偏差分别为11.3%和–1.1%。

Considering the balance of environmental characteristics, safety, theoretic cycle performance and market availability, R32 would be one of the promising refrigerants alternatived to replace R22. With decreasing of channel dimension, the flow boiling heat transfer characteristics of R32 in micro-channels would be significantly different from the conventional channels. As a result, the research on R32 flow boiling characteristics in micro-channels would have the important theoretical significance and practical value. The main work of this paper is as follows:Experiment: R32 flow boiling characteristics in a smooth micro-tube with inner diameter of 2 mm and a multiport extruded tube with micro-fin and inner diameter of 1.7 mm were investigated. The experimental conditions were 100~400 kg/(m2•s) mass flux, 10~40 kW/m2 heat flux, 10~20oC saturation temperature, 0.05~0.98 quality. Results showed that the flow boiling characteristics in smooth the two micro-channels were similar: Heat transfer coefficient increases with increasing mass flux, heat flux and saturation temperature.The critical steam quality decreases with increasing mass flux, heat flux and saturation temperature. The pressure drop increases with increasing mass flux, heat flux, quality but decreases with increasing saturation temperature. The heat transfer coefficient and pressure drop in multiport extrude with micro-fin are 40.51% and 48.3% larger than in smooth micro-tube respectively on average.Correlation: Confinement number Co, which reflects the effect of channel dimension on flow boiling, was introduced into the heat transfer coefficient and pressure drop correlation. The new heat transfer coefficient correlations for smooth micro-tube before and after critical quality were developed. The new pressure drop correlation was developed based on Lockhart-Martinelli pressure drop correlation. The new heat transfer coefficient could correlate 93% the existing experimental data and 89.5% the present experimental data were within ±20% errors. The new pressure drop could correlate 85% the existing experimental data and all the present experimental data were within ±20% errors.Simulation: A three-dimensional steady simulation, using Mixture multiphase flow model and Hertz–Knudsen phase change model by FLUENT, was conducted to investigate the flow boiling heat transfer of R32 in a 2 mm smooth micro-tube. The results showed that the effect of gravity on two phase distribution weakens with increasing mass flux, and the nucleate boiling near the wall strengthens with increasing heat flux. The average deviations of heat transfer coefficient and pressure drop between numerical and experimental results are 11.3% and –1.1%, respectively.