水平管内自然对流对热进口段空气强制对流传热的影响

Free Convection Effects on Forced Convective Heat Transfer in the Thermal Entrance Region of Horizontal Pipe for Airflow

本文研究了水平管内空气层流强制对流传热时，自然对流对热进口段传热和流动的影响。数值计算结果显示：速度和温度分布因自然对流影响变形为非对称，速度最大值和温度最小值向管下部偏移。对流传热系数在圆周上的最小和最大值分别出现在管顶部和底部，二者之差最大可达5倍，其平均努塞尔特数明显高于无自然对流影响的强制对流。

Free convection effects on laminar forced convective heat transfer have been investigated for airflow in the thermal entrance region of a horizontal pipe. The numerical results show that the velocity and temperature profiles are distorted and become asymmetric because of the effect of secondary flow due to free convection, and both maximum velocity and minimum temperature displace towards the bottom pipe wall. The local heat transfer coefficient takes the minimum and maximum at the top and bottom pipe wall, respectively, the difference between the minimum and maximum can reach about 5 times. The circumferential average Nusselt number is higher than that of forced convection without free convection effects and exhibits a peak at the location where the secondary now is most intense.