超临界CO_2水平直管内冷却换热的数值模拟
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摘要
为了提高CO_2热泵的传热性能,基于Fluent的数值模拟方法研究了超临界CO_2在水平圆直管内的换热特性。采用标准k-ε湍流模型对超临界CO_2流体在内径为4 mm、长度为2 000 mm的水平圆管内的冷却换热进行了数值模拟,主要探究了超临界CO_2流体在管内冷却条件下的温度场分布以及传热系数的变化规律,并研究了CO_2质量流量及进口温度对管内传热性能的影响。模拟结果表明:超临界CO_2的传热系数随质量流量的增加而变大,质量流量增加100 kg/(m~2·s~2),平均传热系数增加约为12%;随着制冷剂进口温度的增加,管内平均传热系数变小,但局部传热系数的最大值并不会发生改变,只会使其出现的节点延后。研究结果可为水平直管在CO_2热泵中的应用提供理论与数据支持。
In order to enhance the heat transfer performance of CO_2 heat pump, the heat transfer performance of supercritical carbon dioxide in horizontal straight tube is conducted based on Fluent numerical simulation method. Cooling heat transfer of supercritical CO_2 in a horizontal tube with diameter of 4 mm and length of 2 000 mm is numerically investigated with k-ε turbulence model. The temperature field and heat transfer coefficient of supercritical carbon dioxide fluid under in-tube cooling conditions are mainly investigated. The effects of mass flow rate and inlet temperature on heat transfer performance in horizontal straight tubes are studied. The simulation results show that the heat transfer coefficient of supercritical carbon dioxide increases with the increase of mass flow, the mass flow increases by 100 kg/(m~2·s~2), and the average heat transfer coefficient increases by about 12%. With the increase of supercritical carbon dioxide inlet temperature, the average heat transfer coefficient becomes small, but the maximum value of the local heat transfer coefficient doesn't change, only delaying the appearance of the maximum value of the local heat transfer coefficient. The research result may provide important theory and data support for the application of the horizontal straight tube in CO_2 heat pump.
In order to enhance the heat transfer performance of CO_2 heat pump, the heat transfer performance of supercritical carbon dioxide in horizontal straight tube is conducted based on Fluent numerical simulation method. Cooling heat transfer of supercritical CO_2 in a horizontal tube with diameter of 4 mm and length of 2 000 mm is numerically investigated with k-ε turbulence model. The temperature field and heat transfer coefficient of supercritical carbon dioxide fluid under in-tube cooling conditions are mainly investigated. The effects of mass flow rate and inlet temperature on heat transfer performance in horizontal straight tubes are studied. The simulation results show that the heat transfer coefficient of supercritical carbon dioxide increases with the increase of mass flow, the mass flow increases by 100 kg/(m~2·s~2), and the average heat transfer coefficient increases by about 12%. With the increase of supercritical carbon dioxide inlet temperature, the average heat transfer coefficient becomes small, but the maximum value of the local heat transfer coefficient doesn't change, only delaying the appearance of the maximum value of the local heat transfer coefficient. The research result may provide important theory and data support for the application of the horizontal straight tube in CO_2 heat pump.
引文
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[16] 杨传勇,徐进良,王晓东,等.管道倾斜角度对超临界CO2管内换热特性的影响[J].原子能科学技术,2013,47(9):1522-1528.YANG Chuanyong,XU Jinliang,WANG Xiaodong,et al.Effect of tube inclination angel on heat transfer characteristics of supercritical CO2 in tube[J].Atomic Energy Science and Technology,2013,47(9):1522-1528.
[17] 马建宗,阴继翔,吴广剑.矩形偏心翅片椭圆管流动与换热的数值研究[J].热力发电,2014,43(8):89-93.MA Jianzong,YIN Jixiang,WU Guangjian.Numerical study on heat and mass transfer of rectangular eccentric corrugated fin-and-oval tube heat exchangers[J].Thermal Power Generation,2014,43(8):89-93.
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[2] SARKAR J,BHATTACHARYYA S,GOPAL M R.Optimization of atranscritical CO2 heat pump cycle for simultaneous cooling and heating applications[J].International Journal of Refrigeration,2004,27(8):830-838.
[3] YOKOYAMA R,WAKUI T,KAMAKARI J,et al.Performance analysis of a CO2 heat pump water heating system under a daily change in a standardized demand[J].Energy,2010,35(2):718-728.
[4] YAMAGUCHI S,KATO D,SAITO K,et al.Development and validation of static simulation model for CO2 heat pump[J].International Journal of Heat and Mass Transfer,2011,54(9):1896-1906.
[5] 刘业凤,朱洪亮,张峰,等.CO2热泵热水器充注量确定及系统实验研究[J].上海理工大学学报,2015,37(1):49-56.LIU Yefeng,ZHU Hongliang,ZHANG Feng,et al.Determining the refrigerant charging amount and experimental study on CO2 heat pump water heater[J].Journal of University of Shanghai for Science and Technology,2015,37 (1):49-56.
[6] 崔海亭,刘东岳,赵华丽,等.CO2热泵热水器多毛细管组合节流特性的研究[J].流体机械,2017,45(3):65-68.CUI Haiting,LIU Dongyue,ZHAO Huali,et al.Study on throttling characteristic of multiple capillary combination used in CO2 heat pump water heater[J].Fluid Machinery,2017,45(3):65-68.
[7] 张姣阳,曹绛敏,韩筱.矩形翅片椭圆管和圆管换热器的数值仿真[J].上海电力学院学报,2015,31(4):327-332.ZHANG Jiaoyang,CAO Jiangmin,HAN Xiao.Numerical simulation of rectangular finned elliptical tube and circular tube heat exchanger[J].Journal of Shanghai University of Electric Power,2015,31(4):327-332.
[8] 赵兰萍,宋亚军,杨志刚.矩形翅片椭圆换热管束性能[J].同济大学学报(自然科学版),2016,44(7):1096-1100.ZHAO Lanping,SONG Yajun,YANG Zhigang.Performance of rectangular finned elliptical tube heat exchanger[J].Journal of Tongji University(Natural Science),2016,44(7):1096-1100.
[9] 刘生晖,黄彦平,刘光旭,等.管内超临界二氧化碳强迫对流传热浮升力效应数值研究[J].核动力工程,2016,37(6):18-22.LIU Shenghui,HUANG Yanping,LIU Guangxu,et al.Numerical investigation of buoyancy effect in forced convective heat transfer to supercritical carbon dioxide flowing in a tube[J].Nuclear Power Engineering,2016,37(6):18-22.
[10] 徐峰,郭烈锦.超临界压力下水在螺旋管内的混合对流换热[J].西安交通大学学报,2005,39(9):978-981.XU Feng,GUO Liejin.Mixed convective flow and heat transfer of water in a helicoidal pipe under supercritical pressure[J].Journal of Xi’an Jiaotong University,2005,39(9):978-981.
[11] 赖澳澳.CO2气体冷却器管内传热特性数值模拟[J].机电工程技术,2009,38(6):92-94.LAI Aoao.Numerical simulation about the heat transfer characteristics of the carbon dioxide gas cooler[J].Mechanical & Electrical Engineering Technology,2009,38(6):92-94.
[12] ZHANG Xinrong,YAMAGUCHI H.Forced convection heat transfer of supercritical CO2 in a horizontal circular tube[J].Journal of Supercritical Fluids,2007,41:412-420.
[13] 杨传勇,徐进良,王晓东,等.超临界二氧化碳水平管内层流混合对流换热数值模拟[J].低温工程,2012(4):24-29.YANG Chuanyong,XU Jinliang,WANG Xiaodong,et al.Numerical simulation of laminar mixed convection heat transfer of supercritical carbon dioxide in horizontal tube[J].Cryogenics,2012(4):24-29.
[14] 张宇,姜培学,石润富,等.竖直圆管中超临界压力CO2在低Re数下对流换热研究[J].工程热物理学报,2008,29(1):118-120.ZHANG Yu,JIANG Peixue,SHI Runfu,et al.Convection heat transfer of CO2 at supercritical pressures in a vertical tube at low reynolds numbers[J].Journal of Engineering Thermophysics,2008,29(1):118-120.
[15] 刘占斌,费继友,杨一凡,等.管径对超临界CO2管内流动换热的影响研究[J].工程热物理学报,2016,37(2):357-360.LIU Zhanbin,FEI Jiyou,YANG Yifan,et al.Numerical study on the effect of diameter on supercritical CO2 heat transfer and flow in horizontal tubes[J].Journal of Engineering Thermophysics,2016,37(2):357-360.
[16] 杨传勇,徐进良,王晓东,等.管道倾斜角度对超临界CO2管内换热特性的影响[J].原子能科学技术,2013,47(9):1522-1528.YANG Chuanyong,XU Jinliang,WANG Xiaodong,et al.Effect of tube inclination angel on heat transfer characteristics of supercritical CO2 in tube[J].Atomic Energy Science and Technology,2013,47(9):1522-1528.
[17] 马建宗,阴继翔,吴广剑.矩形偏心翅片椭圆管流动与换热的数值研究[J].热力发电,2014,43(8):89-93.MA Jianzong,YIN Jixiang,WU Guangjian.Numerical study on heat and mass transfer of rectangular eccentric corrugated fin-and-oval tube heat exchangers[J].Thermal Power Generation,2014,43(8):89-93.
[18] 杨世铭,陶文铨.传热学[M].北京:高等教育出版社,2006.
[19] NIST REFPROP V9.0.NIST Standard Reference Database 23[S].
[20] 白万金,徐肖肖,吴杨杨.低质量流速下超临界CO2在管内冷却换热特性[J].化工学报,2016,67(4):1244-1250.BAI Wanjin,XU Xiaoxiao,WU Yangyang.Heat transfer characteristics of supercritical CO2 at low mass flux in tube[J].CIESC Journal,2016,67(4):1244-1250.