超临界CO2水平直管内冷却换热的数值模拟

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摘要：为了提高CO2热泵的传热性能，基于Fluent的数值模拟方法研究了超临界CO2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CO2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CO2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CO2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CO2的传热系数随质量流量的增加而变大，质量流量增加100 kg/（m2·s2），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CO2热泵中的应用提供理论与数据支持。

关键词：工程热力学;数值模拟;Fluent;超临界CO2;水平直管;换热特性

中图分类号：TB657.5;TK12文献标志码：A

CUI Haiting，LIU Siwen，WANG Shaozheng.Numerical simulation of convection heat transfer of supercritical carbon dioxide in horizontal straight tube[J].Journal of Hebei University of Science and Technology，2019，40（3）：252-258.Numerical simulation of convection heat transfer of supercritical

carbon dioxide in horizontal straight tube

CUI Haiting， LIU Siwen， WANG Shaozheng

（School of Mechanical Engineering，Hebei University of Science and Technology，Shijiazhuang， Hebei 050018，China）

Abstract：In order to enhance the heat transfer performance of CO2 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 CO2 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/（m2·s2）， 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 CO2 heat pump.

Keywords：engineering thermodynamic;numerical simulation; Fluent; supercritical carbon dioxide; horizontal straight tube; heat transfer performance

二氧化碳工质作为制冷剂的跨临界热泵机组，因其对臭氧层无破坏（ODP=0）、温室效应潜能极小（GWP=1）;系统稳定性高、安全性好;结构紧凑、占用空间小;具有较高的制热能效比而引起广泛的关注与研究[1-6]。近年来，由于热泵热水器高效、节能和环保的特点，二氧化碳作为制冷剂再次引起了行业的重视，并且在中国发展迅速，具有良好的经济效益和社会效益，而对于怎样增强跨临界CO2热泵系统的换热性能便成为了研究的重點。目前的研究多集中于改变换热管的结构以增强超临界CO2在管内的换热，其中研究较多的便是简单易用的直管，且多基于实验探究管内的传热特性，而由于实验的实际条件局限，很多时候并不能得到理想的结果，因此，一些研究者运用数值模拟的方法来探究CO2在管内的传热特性[7-11]。