周向非均匀加热水平圆管内超临界正癸烷换热特性

doi:10.11949/0438-1157.20200377

摘要/Abstract

摘要：

针对超燃冲压发动机再生冷却热防护问题，开展了顶部加热和底部加热水平圆管内超临界压力正癸烷换热的模拟研究。探究了两种加热模式下的换热特征和换热差别，阐述了通道外表面热通量、质量流速、运行压力及通道热导率对换热的影响机制。实现了周向平均换热的预测。结果表明：两种加热模式下的浮升力作用不同，通道内壁面周向呈现了不同的管壁温度和热通量分布情况。顶部加热时随周向角增大传热恶化逐渐减弱，底部加热时二次流更强，周向始终存在传热恶化问题。高温流体拟膜态热阻是传热恶化的原因。采用高热导率通道、增加运行压力、降低热质比可以缩小周向壁温和热通量差别。提出的关联式能合理预测周向平均换热情况，满足热防护设计的工程应用。

关键词: 超临界流体, 正癸烷, 传热, 浮升力, 二次流, 预测

Abstract:

Aiming at the problem of heat protection for scramjet regenerative cooling, a simulation study on the heat transfer of supercritical pressure n-decane in a horizontal tube with top heating and bottom heating was carried out. The heat transfer characteristics and differences under these two heating conditions have been analyzed. The influence mechanisms of outer-wall heat flux, mass flux, operating pressure and tube thermal conductivity on heat transfer were investigated. The prediction of average heat transfer in the circumferential direction was obtained. The results show that the different inner-wall temperature and heat flux distributions under the two heating conditions have been observed because of the different buoyancy effects. The heat transfer deterioration is gradually weakened with the increase of circumferential angle when the top is heated. The secondary flow is more significant under the bottom heating condition, the heat transfer deterioration always occurs in the circumferential direction. The pseudo-film thermal resistance of high-temperature fluid is the cause of this heat transfer deterioration. Using the high thermal conductivity channel, increasing the operating pressure, and decreasing the heat-to-mass ratio can reduce the differences of inner-wall temperature and heat flux in the circumferential direction. The proposed correlation can reasonably predict the average heat transfer in the circumferential direction, and meet the engineering application of thermal protection design.

Key words: supercritical fluid, n-decane, heat transfer, buoyancy, secondary flow, prediction

中图分类号:

王彦红, 陆英楠, 李素芬, 东明. 周向非均匀加热水平圆管内超临界正癸烷换热特性[J]. 化工学报, 2021, 72(3): 1342-1353.

WANG Yanhong, LU Yingnan, LI Sufen, DONG Ming. Heat transfer characteristics of supercritical n-decane in horizontal circular tubes with circumferentially non-uniform heating[J]. CIESC Journal, 2021, 72(3): 1342-1353.

图/表 19

图1 水平管示意图

Fig.1 Schematic diagram of the horizontal tube

图2 超临界条件下正癸烷热物性随温度的变化情况

Fig.2 Thermo-physical properties variations with temperature of n-decane at supercritical conditions

表1 网格无关性分析

Table 1 Grid-independence analysis

网格方案个数	T_out/K		u_out/(m·s^-1)
网格方案个数	TH	BH	TH	BH
2012×800	788.46	788.44	13.94	13.93
2800×800	791.38	791.37	14.92	14.92
3586×800	791.54	791.55	15.18	15.19
2800×400	787.27	787.25	13.06	13.05
2800×1200	791.46	791.46	15.02	15.02

图3 管截面网格

Fig.3 Mesh configuration in the cross section

图4 数值模型验证

Fig.4 Validation of numerical model

图5 内壁温度、内壁热通量和传热系数的轴向分布情况

Fig.5 Axial distributions of inner-wall temperature, inner-wall heat flux and heat transfer coefficient

图6 管截面温度分布情况

Fig.6 Temperature distributions at tube cross sections

图7 P2截面密度和轴向流速

Fig.7 Density and axial velocity at P2 cross section

图8 管截面二次流速度

Fig.8 Secondary flow velocity at tube cross sections

图9 Grashof数和Reynolds数的轴向分布情况

Fig.9 Axial distributions of Grashof number and Reynolds number

图10 热通量对Twi,0、ΔTwi、qi,0和Δqi轴向分布的影响

Fig.10 Effect of heat flux on axial distributionsof Twi,0, ΔTwi, qi,0 and Δqi

图11 质量流速对Twi,0、ΔTwi、qi,0和Δqi轴向分布的影响

Fig.11 Effect of mass flux on axial distributionsof Twi,0, ΔTwi, qi,0 and Δqi

图12 压力对Twi,0、ΔTwi、qi,0和Δqi轴向分布的影响

Fig.12 Effect of pressure on axialdistributionsof Twi,0, ΔTwi, qi,0 and Δqi

图13 不同工况下传热系数的轴向分布情况

Fig.13 Heat transfer coefficient axial distributions under different conditions

图14 不同工况下Se的轴向分布情况

Fig.14 Axial distributions of Se under different conditions

图15 管热导率对Twi,0、ΔTwi、qi,0和Δqi轴向分布的影响

Fig.15 Effect of tube thermal conductivity on axialdistributionsof Twi,0, ΔTwi, qi,0 and Δqi

图16 不同管热导率下传热系数的轴向分布情况

Fig.16 Axial distributions of heat transfer coefficient under different tube thermal conductivity conditions

图17 不同管热导率下Se的轴向分布情况

Fig.17 Axial distributions of Se under different tube thermal conductivity conditions

图18 平均Nusselt数拟合公式值与数值结果的比较

Fig.18 Comparison of the average Nusselt number from fitted correlation with the numerical data

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