Abstract:

An entropy mathematical model is proposed for the evaporator in boiling two-phase flow region.The evaporator is a water-refrigerant type with refrigerant HFC22 flowing inside and water flowing outside the horizontal tube.The entropy resulted from losses due to heat transfer and pressure drop is represented in terms of entropy generation number, Ns.The two-phase separated flow model is adopted for this thermodynamic analysis.The developed model requires the use of empirical correlations for the evaluation of convective heat transfer, pressure drop and void fraction.Comparisons with the analytical and existing experimental data are presented in order to verify and validate the model.The effects of heat transfer and pressure drop of water side and refrigerant side on entropy generation are evaluated.Results from the mathematic model show that the system entropy is mostly caused by two-phase pressure drop.The entropy generation number decreases rapidly to a certain value with increasing water flow rate and increases with increasing refrigerant flow rate in an exponential form.In addition, the entropy generation number increases with the water inlet temperature and tube length.

Key words: FONT-SIZE: 9pt, mso-ascii-font-family: Times New Roman, mso-bidi-font-family: Times New Roman, mso-font-kerning: 1.0pt, mso-ansi-language: EN-US, mso-fareast-language: ZH-CN, mso-bidi-language: AR-SA">FONT-SIZE: 10.5pt, mso-ascii-font-family: Times New Roman, mso-bidi-font-family: Times New Roman, mso-font-kerning: 1.0pt, mso-ansi-language: EN-US, mso-fareast-language: ZH-CN, mso-bidi-language: AR-SA">蒸发器；两相流；熵产数；沸腾

摘要：

以管内侧制冷剂，管外侧水的蒸发换热器为研究对象，基于热力学第一、第二定律建立了蒸发器沸腾两相流段的熵产计算模型，用量纲1熵产数N_s表示管内外流体因温差传热和压降损失引起的不可逆损失。分析水侧、制冷剂侧质量流量，水侧入口温度和管长尺寸对系统熵产数的影响。结果表明：系统熵产主要由制冷剂侧两相压降引起；系统熵产数随水侧质量流率的增大迅速降低并趋于稳定，随制冷剂侧质量流率的增大呈指数增长，随水侧进口温度和管长尺寸的增大而增加。

关键词: FONT-SIZE: 9pt, mso-ascii-font-family: Times New Roman, mso-bidi-font-family: Times New Roman, mso-font-kerning: 1.0pt, mso-ansi-language: EN-US, mso-fareast-language: ZH-CN, mso-bidi-language: AR-SA">FONT-SIZE: 10.5pt, mso-ascii-font-family: Times New Roman, mso-bidi-font-family: Times New Roman, mso-font-kerning: 1.0pt, mso-ansi-language: EN-US, mso-fareast-language: ZH-CN, mso-bidi-language: AR-SA">蒸发器；两相流；熵产数；沸腾