Experimental study on flow condensation heat transfer of R134a in serrated mini channel
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摘要:
采用空气射流冲击通道壁面的冷却方式，研究了制冷剂R134a在3种规格锯齿翅片微小通道内的冷凝传热特性，通道当量直径分别为1.13、1.18 mm和1.44 mm。工况范围为：干度0～1，质量流率：56～430 kg/（m2·s）， 饱和温度：50～70 ℃，热流密度：8.4～44.2 kW/m2。实验获得了通道内局部冷凝传热系数，分析了锯齿翅片几何结构、干度、质量流率、饱和温度以及热流密度对冷凝传热的影响。结果表明：干度和质量流率的增加导致流体湍流度上升、冷凝液膜厚度减小，冷凝传热增强。饱和温度提高伴随着制冷剂液相导热系数、液汽密度比和黏度比降低，增加液膜热阻的同时减小了汽液界面的剪切力，减弱了冷凝传热。提高热流密度可引起传热系数的提高，但随着干度降低，液膜厚度增加，热流密度的作用逐渐减小并趋于消失。对于翅片高度相同的锯齿通道，减小翅片截距可以增大冷凝传热系数。对比截距相同的锯齿通道，翅片高度变化对冷凝传热系数的影响不明显。基于实验数据，提出了适用于不同锯齿翅片微小通道的冷凝传热系数的计算关联式。
Abstract:The flow condensation heat transfer characteristics of refrigerant R134a in three types of serrated mini channels were studied using air jet impingement cooling method on the channel wall. The equivalent diameters of the channels were 1.13, 1.18 mm, and 1.44 mm, respectively. The experimental conditions included: vapor quality from 0 to 1, mass flux from 56 to 430 kg/(m2·s), heat flux in ranges of 8.4—44.2 kW/m2, and the saturation temperature of refrigerant between 50 ℃ and 70 ℃. The local condensation heat transfer coefficient of the channel was obtained, and the effects of serrated fin geometry, vapor quality, saturation pressure, mass flux and heat flux on the condensation heat transfer were analyzed. The results indicated that the increase in vapor quality and mass flux led to an increase in fluid turbulence, a decrease in condensate film thickness, and enhanced condensation heat transfer. The increase in saturation temperature was accompanied by a decrease in the liquid phase thermal conductivity, liquid vapor density ratio, and viscosity ratio of the refrigerant. This increased the thermal resistance of the liquid film while reducing the shear force at the gas-liquid interface, thereby weakening the condensation heat transfer. The higher heat flux indicated the greater heat transfer coefficient. However, as the vapor quality decreased and the liquid film thickness increased, the effect of heat flux gradually decreased and tended to disappear. For serrated mini channels with the same fin height, reducing the fin spacing can increase the condensation heat transfer coefficient. For serrated channels with the same fin spacing, the effect of fin height variation on condensation heat transfer coefficient was not significant. Based on experimental data, a correlation was proposed to calculate the condensation heat transfer coefficient of different serrated mini channels.
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Key words:
- offset strip fin /
- mini channel /
- jet impingement /
- condensation heat transfer /
- two-phase flow
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图 3 射流装置传热系数的标定实验结果
Figure 3. Calibration experimental results of heat transfer coefficient of jet device
图 6 质量流率对冷凝传热系数的影响
Figure 6. Effect of mass flux on condensation heat transfer coefficient
图 7 饱和温度对冷凝传热系数的影响
Figure 7. Effect of saturation temperature on condensation heat transfer coefficient
图 8 热流密度对冷凝传热系数的影响
Figure 8. Effect of heat flux on condensation heat transfer coefficient
图 9 不同锯齿通道的冷凝传热系数比较
Figure 9. Comparison of condensation heat transfer coefficients of different serrated channel
图 10 新经验公式预测值与实验数据的比较
Figure 10. Comparison of experimental data and new correlation predicted value
表 1 锯齿翅片几何尺寸
Table 1. Structure size of serrated fins
mm 编号 h s L t d JC1614 1.6 1.4 3 0.15 1.44 JC1610 1.6 1.0 3 0.15 1.18 JC1014 1.0 1.4 3 0.15 1.13 
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表 2 流动冷凝实验工况范围
Table 2. Range of working conditions for flow condensation experiment
序号 G/（kg/（m2·s）） tsat/℃ qk/（kW/m2） JC1614 56～270 50, 60, 70 9.7～28.6 JC1610 110～323 50, 60, 70 8.4～28.9 JC1014 213～430 50, 60, 70 12.1～44.2
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表 3 参数的不确定度
Table 3. Uncertainties of parameters in present study
参数 不确定度 温度/℃ ±0.2 绝对压力/kPa ±4.8 质量流量（空气）/（kg/h） ±2.5 质量流量（制冷剂）/（kg/h） ±0.125 冷凝热流密度/% ±1.93～2.88 冷凝传热系数/% ±3.18～10.94 干度/% ±2.06～2.99
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