脉动气流对沸腾表面水分蒸发影响的数值模拟
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摘要
【目的】考察脉动气流掠过沸腾水面时,流动参数对水分蒸发效果的影响,探究脉动气流强化蒸发过程的机理。【方法】建立二维物理与数学模型,采用商用软件ANSYS FLUENT 14.5进行数值模拟,研究正弦脉动气流掠过沸腾水面时水分的蒸发情况,分析一定蒸发时间内脉动气流的振幅、频率、气流速度以及温度对水分蒸发的影响。【结果】相比于匀速气流,气流脉动时沸腾表面水分的相对蒸发量提高了约50%;脉动气流的相对振幅从0增加至1.0时,沸腾表面水分的相对蒸发量提高了约1.8倍;脉动气流的频率从0 Hz增加至110 Hz时,沸腾表面水分的相对蒸发量呈现出先增加后减小的变化;气流速度从4 m/s增加至10 m/s时,沸腾表面水分的相对蒸发量提高了约15.3倍;脉动气流的温度对沸腾表面水分蒸发的影响不明显;气流脉动时,水分蒸发速率呈周期性变化。【结论】脉动气流周期性地对水面水蒸气浓度边界层进行扰动,强化了水面的对流传质,从而促进了水分蒸发。
【Objective】To study the effects of different flow parameters on the water evaporation and investigate the mechanism of pulsating airflow's intensified evaporation when the pulsating airflow sweeping through the boiling water surface. 【Method】A two-dimensional physical and mathematical model is established. Additionally, commercial software ANSYS FLUENT 14.5 is adopted for numerical simulation, to study the evaporation of water when the sinusoidal pulsating airflow was sweeping through the boiling water surface. The impacts of the amplitude, frequency, airflow velocity and temperature of the pulsating airflowat certain evaporation time on evaporation of water were investigated.【Result】Compared with uniform airflow, the relative evaporation of water on boiling surface increased by about 50% when airflow is pulsating. When the relative amplitude of pulsating airflow increased from 0 to 1.0, the relative evaporation of water on boiling surface increased by about 1.8 times. When the frequency of pulsating airflow increased from 0 Hz to 110 Hz, the relative evaporation of water on boiling surface increased first and then decreased. When airflow velocity increased from 4 m/s to 10 m/s, the relative evaporation of water on boiling surface increased by 15.3 times. The effect of the temperature of pulsating airflow on evaporation of water on boiling surface is not obvious. When the airflow is pulsating, the water evaporation rate fluctuates periodically. 【 Conclusion 】Pulsating airflow perturbed the boundary layer of surface vapor concentration periodically and intensified the convective mass transfer of surface, thus facilitating water evaporation.
【Objective】To study the effects of different flow parameters on the water evaporation and investigate the mechanism of pulsating airflow's intensified evaporation when the pulsating airflow sweeping through the boiling water surface. 【Method】A two-dimensional physical and mathematical model is established. Additionally, commercial software ANSYS FLUENT 14.5 is adopted for numerical simulation, to study the evaporation of water when the sinusoidal pulsating airflow was sweeping through the boiling water surface. The impacts of the amplitude, frequency, airflow velocity and temperature of the pulsating airflowat certain evaporation time on evaporation of water were investigated.【Result】Compared with uniform airflow, the relative evaporation of water on boiling surface increased by about 50% when airflow is pulsating. When the relative amplitude of pulsating airflow increased from 0 to 1.0, the relative evaporation of water on boiling surface increased by about 1.8 times. When the frequency of pulsating airflow increased from 0 Hz to 110 Hz, the relative evaporation of water on boiling surface increased first and then decreased. When airflow velocity increased from 4 m/s to 10 m/s, the relative evaporation of water on boiling surface increased by 15.3 times. The effect of the temperature of pulsating airflow on evaporation of water on boiling surface is not obvious. When the airflow is pulsating, the water evaporation rate fluctuates periodically. 【 Conclusion 】Pulsating airflow perturbed the boundary layer of surface vapor concentration periodically and intensified the convective mass transfer of surface, thus facilitating water evaporation.
引文
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[3]贺小华.薄膜蒸发器蒸发过程数值模拟及其CAD系统开发[D].南京:南京工业大学,2005.
[4]马空军,黄玉代,蔺何,等.声场强化溶液蒸发的效果及机理[J].声学技术,2008,27(3):375-380.
[5]尹婷,吴高杨,聂万胜.压力振荡环境下液滴蒸发动态响应特性研究[J].火箭推进,2015,41(4):19-28.
[6]李倩.旋转超空泡蒸发器叶片参数优化的数值模拟研究[D].哈尔滨:哈尔滨工业大学,2015.
[7]李国能,项忠晓,郑友取,等.层流中脉动气流横掠平板强化传热[J].化工学报,2012,63(6):1717-1722.
[8]冯自平,郭烈锦,陈学俊.卧式螺旋管压力降脉动瞬态及时均传热特性研究[J].核科学与工程,1998,18(1):1-7.
[9]韩占忠,王敬,兰小平.FLUENT:流体工程仿真计算实例与应用[M].2版.北京:北京理工大学出版社,2010:20-22.
[10]闫晓惠,陈新,李华煜.基于标准和Realizable k~ε湍流模型的阶梯式溢洪道流的数值模拟[J].水利科技与经济,2015,21(10):29-31.
[11]段磊.通气空泡多相流流动特性研究[D].北京:北京理工大学,2014.
[12]潘瑜芬.被动蒸发冷却风洞温度场模拟与实验研究[D].广州:华南理工大学,2005.
[13]陶文铨.数值传热学[M].2版.西安:西安交通大学出版社,1988:347-353.
[14]翟明,董芃,王希影,等.圆管湍流脉动流动与换热的数值模拟[J].中国电机工程学报,2009,29(20):85-91.
[15]蒋翔,朱冬生,吴治将,等.立式蒸发式冷凝器传热传质的CFD模拟[J].高校化学工程学报,2009,23(4):566-571.
[16]杨卫卫,何雅玲,陶文铨,等.凹槽通道中脉动流动强化传质的数值研究[J].西安交通大学学报,2004,38(11):1119-1122.
[17]FRAENKEL S L,NOGUEIRA J A H,CARVALHO JR J A,et al.Heat transfer coefficients for drying in pulsating flows[J].International Communications in Heat and Mass Transfer,1998,25(4):471-480.
[18]HOMMEMA S E,TEMPLE K A,JONES J D,et al.Heat transfer in condensing,pulsating flows[J].International Journal of Heat and Mass Transfer,2002,45(1):57-65.
[19]孙腾.海水淡化浓盐水制盐过程的模拟和优化设计[D].青岛:中国海洋大学,2015.
[20]高习群.气液界面传质机理与强化[D].天津:天津大学,2008.