不同强化换热管内流动沸腾换热特性对比

采用实验方法对比制冷剂R410A在6根强化换热管和1根光滑管内的流动沸腾换热特性. 实验测试段饱和温度为6 ℃，进出口干度分别为0.2和0.9，质量流速变化范围为80～350 kg/（m²s）.实验结果表明：三维强化管相对光滑管流动沸腾换热系数的强化倍率可达1.14～1.53，因为强化表面上的凹痕阵列能够增强两相间湍动、提高汽化核心数目并打断液膜边界层制造分离流和二次流从而强化换热. 三维强化管中，管1EHT在低质量流速范围内具有较好的换热性能，而管2EHT在相对较高的质量流速时强化性能更优；齿形参数不同的3根内螺纹管间的换热系数差距较大，其中当内螺纹管螺旋角足够大时齿高与液膜厚度之比相近的内螺纹管具有较好的换热性能.

Comparison of flow boiling heat transfer characteristics inside different enhanced heat transfer tubes

Flow boiling heat transfer characteristics of refrigerant R410A in six disparate horizontal enhanced tubes and a plain circular tube were investigated experimentally. The experiment results were collected at a saturation temperature of 6℃, a mass velocity range of 80~350 kg/(m²s,) inlet vapor quality of 0.2 and outlet vapor quality of 0.9. Results indicate that the 3D tubes can augment heat transfer of evaporation substantially, and the enhanced ratio relative to the plain tube is in the range of 1.14 to 1.53. The dimple arrays on the surface of 3D tubes can augment interfacial turbulence, increase nucleation sites, irrupt boundary layer development and produce separation flow as well as secondary flow to intensify the heat transfer. There are apparent differences among the heat transfer coefficient of three micro-fin tubes, which can be attributed to different geometries of fins. In addition, the micro-fin tube whose ratio of the fin height with the liquid film thickness is close to unity has the best heat transfer performance, when they have an large enough helical angle.