超临界CO2在水平螺旋凹槽管中传热和压降特性的数值研究
摘要：采用RNG K-ε模型对超临界CO2在水平螺旋凹槽管和光管管内的冷却换热特性进行了数值模拟，并对速度场、温度场及涡量进行了对比分析，证明了螺旋凹槽管比光管具有更好的换热性能。探究了在不同入口雷诺数、入口压力及有无浮升力条件下，螺旋凹槽管整体换热性能的变化。结果显示：螺旋凹槽管的换热系数随着入口雷诺数的增大而增大，而在不同入口压力下，换热系数与比热容的变化趋势一致；在不同入口压力和入口雷诺数条件下，螺旋凹槽管的换热系数都在拟临界温度附近达到最大值；有浮升力可以增强换热强度，且主要表现在拟临界温度附近，随着雷诺数增大，重力引起的浮升力效应更明显；压降随着入口压力和入口雷诺数的增大而增大，随温度单调降低，随着超临界CO2温度的升高，低温状态下压降急剧降低，在拟临界温度后开始缓慢变化。
关键词：超临界CO2螺旋凹槽管换热系数压降拟临界温度雷诺数压力浮升力
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[2] YOON S H,KIM J H,HWANG Y W,et al.Heat transfer and pressure drop characteristics during the in-tube cooling process of carbon dioxide in the supercritical region[J].International journal of refrigeration,2003,26(8):857- 864.
[3] 饶政华，廖胜明.超临界二氧化碳管内湍流流动和传热的数值模拟[J].流体机械，2005(1):71- 75.
[4] 诸凯，侯晓飞，秦娜，等.超临界二氧化碳水平管内传热的数值模拟及与实验对比[J].热科学与技术，2008,7(1):17- 22.
[5] 单金玲.超临界CO2管内冷却换热的理论模拟与实验研究[D].北京：华北电力大学，2014:1- 51.
[6] ZHU Y,HUANG Y,LIN S,et al.Study of convection heat transfer of CO2 at supercritical pressures during cooling in fluted tube-in-tube heat exchangers[J].International journal of refrigeration,2019,104:161- 170.
[7] BOVARD S,ABDI M,NIKOU M,et al.Numerical investigation of heat transfer in supercritical CO2 and water turbulent flow in circular tubes[J].Journal of supercritical fluids,2017,119:88- 103.
[8] 徐肖肖，吴杨杨，刘朝，等.水平螺旋管内超临界CO2冷却换热的数值模拟[J].物理学报，2015,64(5):250- 256.
[9] LI Y,SUN F,XIE G,et al.Numerical investigation on flow and thermal performance of supercritical CO2 in horizontal cylindrically concaved tubes[J].Applied thermal engineering,2019,153:655- 668.
[10] TANG G L,SHI H,WU Y X,et al.A variable turbulent Prandtl number model for simulating supercritical pressure CO2 heat transfer[J].International journal of heat and mass transfer,2016,102:1082- 1092.
[11] SON C H,PARK S J.An experimental study on heat transfer and pressure drop characteristics of carbon dioxide during gas cooling process in a horizontal tube[J].International journal of refrigeration,2006,29(4):539- 546.
[12] 崔海亭，刘思文，王少政.超临界CO2水平直管内冷却换热的数值模拟[J].河北科技大学学报，2019(3):252- 258.
[13] YANG M.Numerical study of the heat transfer to carbon dioxide in horizontal helically coiled tubes under supercritical pressure[J].Applied thermal engineering,2016,109:685- 696.
[14] DANG C,HIHARA E.In-tube cooling heat transfer of supercritical carbon dioxide.Part 1.Experimental measurement[J].International journal of refrigeration,2004,27(7):736- 747.
Numerical study on heat transfer and pressure drop characteristics of supercritical CO2in horizontal spirally concaved tubes
Abstract: The RNG K-ε model is used to simulate the cooling heat transfer characteristics of supercritical CO2 in horizontal spirally concaved tubes and smooth tubes, the velocity field, temperature field and vorticity are compared and analysed, and it is proved that the spirally concaved tube has better heat transfer performance than smooth tube. The change of overall heat transfer performance of spirally concaved tubes is investigated under different inlet Reynolds numbers, inlet pressures, and whether there is buoyancy or not. The results show that the heat transfer coefficient of spirally concaved tubes increases with the increase of the inlet Reynolds number, and the changing trend of the heat transfer coefficient and the specific heat capacity is consistent at different inlet pressures. The heat transfer coefficient of spirally concaved tubes reaches the maximum near the quasi-critical temperature under the conditions of different inlet pressures and inlet Reynolds numbers. The heat transfer intensity can be enhanced with buoyancy, which is mainly manifested near the quasi-critical temperature, and the buoyancy effect caused by gravity becomes more obvious with the increase of Reynolds number. The pressure drop increases with the increase of inlet pressure and Reynolds number, and decreases monotonously with the increase of temperature. With the increase of supercritical CO2 temperature, the pressure drop decreases sharply at low temperature, and begins to change slowly after the quasi-critical temperature.
Keywords: supercritical CO2; spirally concaved tube; heat transfer coefficient; pressure drop; quasi-critical temperature; Reynolds number; pressure; buoyancy;
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