基于扁管的蒸发式冷凝器管外传热传质特性研究
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摘要
强化蒸发式冷凝器管外传热传质可有效降低系统能耗,利用Fluent软件,结合自编译程序及组分输运模型对扁管蒸发式冷凝器管外传热传质过程建模,选取了等周长圆管模型进行比较,研究了二者传热传质性能的差异。通过研究管外液膜厚度及速度,以及管外温度分布和含湿量的变化规律,对比了扁管和圆管的平均表面传热系数,结果表明扁管的平均表面传热系数于圆管提升了9.04%。模拟了风速从1.5 m·s~(-1)变化至3 m·s~(-1)以及喷淋密度从0.15 kg·m~(-1)·s~(-1)增加至0.3 kg·m~(-1)·s~(-1)时对扁管式蒸发式冷凝器换热的影响,得到随着风速及喷淋密度的增加其平均表面传热系数分别增加了5.68%和30.26%。对扁管式蒸发式冷凝器管外的传热传质特性的研究为其应用提供了理论指导。
Enhancement of the heat and mass transfer outside the tube of evaporative condensers can effectively reduce the energy consumption in a refrigeration system. The improving characteristics of heat and mass transfer outside a flat tube for evaporative condensers were investigated. Numerical simulation of the heat and mass transfer on the flat tube was carried out in Fluent using user define functions and component transport models. The heat transfer performance of a circular tube with the same perimeter was compared with that of the flat tube. The thickness and velocity of the liquid film outside the tube, the temperature distribution and the variation of moisture content outside the tube are studied, and the average heat transfer coefficients of the flat tube and the circular tube are compared. The results show that the average heat transfer coefficient of the flat tube is 9.04% higher than that of the circular tube. In addition, the influence of wind speed and spray density on the heat transfer of flat tube evaporative condenser is calculated. The wind speed varies from 1.5 m·s-1 to 3 m·s-1 and the spray density varies from 0.15 kg·m-1·s-1 to 0.3 kg·m-1·s-1. The results show that the average heat transfer coefficient increases by5.68% and 30.26% respectively. Investigating the heat and mass transfer characteristics outside a flat tube for evaporative condensers provides theoretical guidance for the application of the flat tube in evaporative condensers.
Enhancement of the heat and mass transfer outside the tube of evaporative condensers can effectively reduce the energy consumption in a refrigeration system. The improving characteristics of heat and mass transfer outside a flat tube for evaporative condensers were investigated. Numerical simulation of the heat and mass transfer on the flat tube was carried out in Fluent using user define functions and component transport models. The heat transfer performance of a circular tube with the same perimeter was compared with that of the flat tube. The thickness and velocity of the liquid film outside the tube, the temperature distribution and the variation of moisture content outside the tube are studied, and the average heat transfer coefficients of the flat tube and the circular tube are compared. The results show that the average heat transfer coefficient of the flat tube is 9.04% higher than that of the circular tube. In addition, the influence of wind speed and spray density on the heat transfer of flat tube evaporative condenser is calculated. The wind speed varies from 1.5 m·s-1 to 3 m·s-1 and the spray density varies from 0.15 kg·m-1·s-1 to 0.3 kg·m-1·s-1. The results show that the average heat transfer coefficient increases by5.68% and 30.26% respectively. Investigating the heat and mass transfer characteristics outside a flat tube for evaporative condensers provides theoretical guidance for the application of the flat tube in evaporative condensers.
引文
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[11] Tsay Y L, Lin T F. Evaporation of a heated falling liquid film into a laminar gas stream[J]. Experimental Thermal and Fluid Science,1995, 11(7):61-71.
[12]罗林聪.水平异形管降膜蒸发流动与传热强化机理及实验研究[D].济南:山东大学, 2014.Luo L C. Analysis of flow and heat transfer enhancement and experimental research on falling film evaporation on horizontal shaped tubes[D]. Jinan:Shandong University, 2014.
[13] Fiorentino M, Starace G. A numerical model to investigate evaporative condensers behaviour at tube scale[C]//ASME 2014-12th Biennial Conference on Engineering Systems and Analysis.American Society of Mechanical Engineering, 2014.
[14]程嫚.水平管外水风传热传质数值模拟[D].武汉:华中科技大学, 2014.Cheng M. Numerical simulation of heat and mass transfer of water and air outside the horizontal tube[D]. Wuhan:Huazhong University of Science and Technology, 2014.
[15] Parker R O, Treybal R E. The heat mass transfer characteristics of evaporative coolers[J]. AIChE Chemical Engineering Progress Symposium Series, 1962, 57(32):138-149.
[2]朱东生,孙荷静,蒋翔.蒸发式冷凝器的研究现状及其应用[J].流体机械, 2008, 36(8):28-34.Zhu D S, Sun H J, Jiang X. Research progress and application of evaporative condenser[J]. Fluid Machinery, 2008, 36(8):28-34.
[3] Fiorentino M, Starace G. Numerical investigations on two-phase flow modes in evaporative condensers[J]. Applied Thermal Engineering, 2016, 94:777-785.
[4] Dreyer A A, Erens P J. Heat and mass transfer coefficient and pressure drop correlations for a crossflow evaporative cooler[C]//Proceeding of the International Heat Transfer Conference.Jerusalem, 1990.
[5] Mizushina T, Ito R, Miyashita H. Experimental study of an evaporative cooler[J]. International Chemical Engineering, 1967, 7(4):727-732.
[6] Jahangeer K A, Tay A A O, Islam M R. Numerical investigation of transfer coefficients of an evaporatively-cooled condenser[J].Applied Thermal Engineering, 2011:1655-1663.
[7] Islam M R, Jahangeer K A, Chua K J. Experimental and numerical study of an evaporatively-cooled condenser of airconditioning systems[J]. Energy, 2015,(87):390-399.
[8] Acunha J I C, Schneider P S. Numerical simulation of air-water flows in an evaporative condenser[J]. Thermal Engineering, 2009,8(1):24-30.
[9]朱冬生,张景卫,吴治将,等.板式蒸发式冷凝器两相降膜流动CFD模拟及传热研究[J].华南理工大学学报(自然科学版),2008, 36(7):6-10.Zhu D S, Zhang J W, Wu Z J, et al. CFD simulation and investigation into heat transfer for falling film with two-phase flow in plate-type evaporative condenser[J]. Journal of South China University of Technology(Natural Science Edition), 2008, 36(7):6-10.
[10]王定标,万方方,周俊杰.蒸发式冷凝器异型扁管性能分析及数值模拟[J].郑州大学学报(工学版), 2010, 31(2):64-67.Wang D B, Wan F F, Zhou J J. Performance analysis and numerical simulation of evaporative condenser with specialshaped flat tube[J]. Journal of Zhengzhou University(Engineering Science), 2010, 31(2):64-67.
[11] Tsay Y L, Lin T F. Evaporation of a heated falling liquid film into a laminar gas stream[J]. Experimental Thermal and Fluid Science,1995, 11(7):61-71.
[12]罗林聪.水平异形管降膜蒸发流动与传热强化机理及实验研究[D].济南:山东大学, 2014.Luo L C. Analysis of flow and heat transfer enhancement and experimental research on falling film evaporation on horizontal shaped tubes[D]. Jinan:Shandong University, 2014.
[13] Fiorentino M, Starace G. A numerical model to investigate evaporative condensers behaviour at tube scale[C]//ASME 2014-12th Biennial Conference on Engineering Systems and Analysis.American Society of Mechanical Engineering, 2014.
[14]程嫚.水平管外水风传热传质数值模拟[D].武汉:华中科技大学, 2014.Cheng M. Numerical simulation of heat and mass transfer of water and air outside the horizontal tube[D]. Wuhan:Huazhong University of Science and Technology, 2014.
[15] Parker R O, Treybal R E. The heat mass transfer characteristics of evaporative coolers[J]. AIChE Chemical Engineering Progress Symposium Series, 1962, 57(32):138-149.