从热力学第一、第二定律的角度出发,结合水平管外降膜蒸发的特点,推导出了降膜蒸发过程单位熵产数Ns的公式,并在所建立的管外液膜厚度模型的基础上进行了求解。结果表明：沸腾蒸发时的单位熵产数Ns要小于表面蒸发时的值;采用强化表面可以有效地降低单位熵产数Ns;单位熵产数Ns随液膜雷诺数Re的变化比较小。通过分析,降膜蒸发的单位熵产分析法对于最大限度地减少不可逆损失、提高能量利用率等方面具有指导意义。
Unit entropy generation number Ns for process of falling film evaporation was deducted in this study on the basis of the first and second laws of thermodynamics,coupled with the characteristics of the falling film evaporation.Based on the presented model of liquid membrane thickness on the tubes,the unit entropy generation number was solved.The results showed that the unit entropy generation number Ns of boiling evaporation is smaller than that of surface evaporation.Moreover,we noted that the unit entropy generation number decreased significantly when the surface was enhanced and the variation of the unit entropy generation number with the liquid membrane Reynolds number Re was negligible.The unit entropy generation analysis method for the falling film evaporation is useful in the aspects of reducing the irreversible loss maximally and increasing the energy utilization.
参考文献
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