This paper presents the experimental tests on HFC-134a condensation inside a commercial brazed plate heat exchanger: the effects of refrigerant mass flux, saturation temperature and vapour super-heating are investigated. The experimental results are reported in terms of refrigerant side heat transfer coefficients and frictional pressure drop. At low refrigerant mass flux (< 20 kg/m{sup}2s) the heat transfer coefficients for saturated vapour are not dependent on mass flux and are well predicted by the Nusselt (1916) analysis for vertical surface: the condensation process is gravity controlled. For higher refrigerant mass flux (> 20 kg/m{sup}2s) the heat transfer coefficients depend on mass flux and are well predicted by the Akers et al. (1959) equation: forced convection condensation occurs. In the forced convection condensation region the heat transfer coefficients show a 30% increase for a doubling of the refrigerant mass flux. The condensation heat transfer coefficients of super-heated vapour are 8 - 10% higher than those of saturated vapour. The heat transfer coefficients show weak sensitivity to saturation temperature. The frictional pressure drop shows a linear dependence on the kinetic energy per unit volume of the refrigerant flow and therefore a quadratic dependence on the refrigerant mass flux.
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机译:本文介绍了商业钎焊板换热器内的HFC-134A冷凝的实验试验:研究了制冷剂质量通量,饱和温度和蒸汽超加热的影响。在制冷剂侧传热系数和摩擦压降方面报道了实验结果。在低制冷剂质量通量(<20kg / m {sup} 2s)处,饱和蒸汽的传热系数不依赖于质量磁通,并且通过NUSEREL(1916)进行垂直表面的良好预测:冷凝过程是重力控制。对于较高的制冷剂质量磁通(> 20kg / m {sup} 2s),传热系数取决于质量磁通,并通过Akers等人预测。 (1959)方程式:发生强制对流冷凝。在强制对流冷凝区域中,传热系数显示制冷剂质量通量的加倍增加30%。超加热蒸汽的冷凝传热系数比饱和蒸气高8-10%。传热系数显示对饱和温度的敏感性较弱。摩擦压降显示了对制冷剂流量的每单位体积的动能的线性依赖性,因此对制冷剂质量通量的二次依赖性。
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