Effect of tube diameter on boiling heat transfer of R-134a in horizontal small-diameter tubes
Effect of tube diameter on boiling heat transfer of R-134a in horizontal small-diameter tubes
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DOI：
10.1016/j.ijheatmasstransfer.2005.03.035
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发表时间：
2005-11
影响因子：
5.2
通讯作者：
S. Saitoh;H. Daiguji;E. Hihara
中科院分区：
文献类型：
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作者：
S. Saitoh;H. Daiguji;E. Hihara
对R-134 a制冷剂在内径为0.51、1.12和3.1mm的水平小管径管内的沸腾换热进行了实验研究。在热流密度为5 ~ 39 kW/m ~ 2、质量流量为150 ~ 450 kg/m ~ 2s、蒸发温度为278.15 ~ 288.15K、入口干度为0 ~ 0.2的工况下，测量了局部换热系数和压降。利用高速摄像机，通过蒸发器入口处的观察窗，观察了流态。结果表明，随着管径的减小，局部换热系数在干度较低时开始减小。虽然质量流量对局部换热系数的影响随着管径的减小而减小，但在所有三种管中，热通量的影响都很强。内径为3.1 mm的管的压降测量值与Lockhart-Martinelli关联式预测值吻合较好，但当内径为0.51 mm时，压降测量值与均相压降模型预测值吻合较好。随着管径的减小，管内流动趋于均匀。随着内管直径的减小，强制对流蒸发对沸腾换热的贡献逐渐减小。
The boiling heat transfer of refrigerant R-134a flow in horizontal small-diameter tubes with inner diameter of 0.51, 1.12, and 3.1mm was experimentally investigated. Local heat transfer coefficient and pressure drop were measured for a heat flux ranging from 5 to 39kW/m2, mass flux from 150 to 450kg/m2s, evaporating temperature from 278.15 to 288.15K, and inlet vapor quality from 0 to 0.2. Flow patterns were observed by using a high-speed video camera through a sight glass at the entrance of an evaporator. Results showed that with decreasing tube diameter, the local heat transfer coefficient starts decreasing at lower vapor quality. Although the effect of mass flux on the local heat transfer coefficient decreased with decreasing tube diameter, the effect of heat flux was strong in all three tubes. The measured pressure drop for the 3.1-mm-ID tube agreed well with that predicted by the Lockhart–Martinelli correlation, but when the inner tube diameter was 0.51mm, the measured pressure drop agreed well with that predicted by the homogenous pressure drop model. With decreasing tube diameter, the flow inside a tube approached homogeneous flow. The contribution of forced convective evaporation to the boiling heat transfer decreases with decreasing the inner tube diameter.