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

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