超临界压力下低温甲烷传热特性数值研究

对16 mm内径的光滑圆管内超临界压力下低温甲烷的流动与传热进行数值研究,系统地模拟热流密度为100～400 kW/m2工况下不同流动方向的传热,分析传热强化和恶化过程中流体温度、速度和物性分布。结果表明:热流密度越大,传热强化发生的越早、峰值越高、恶化越迅速,而在较低热流密度下则不发生传热强化和恶化行为;水平流动中管顶、底的换热系数在强化段存在差异,而竖直向上流动中换热系数的分布具有对称性;边界层内的大质量热容和密度差产生的浮升力是传热强化的主要原因,边界层内的低质量热容和轴向上的热加速效应是传热恶化的主要原因。
The fluid and heat transfer characteristics of cryogenic methane were studied in a horizontal pipe of 16mm inner diameter under the supercritical pressure. The heat transfer processes were simulated in the range from 100 to 400 kW/m2 heat fluxes in different flow directions. The velocity, temperature and thermo-physical properties of cryogenic methane were analyzed. The results show that the bigger the heat flux is, the earlier the heat transfer enhancement behavior happens; and the faster the heat transfer deterioration changes,the bigger the peak and the valley values are. There are different heat transfer coefficients between the top and bottom of the horizontal tube, while the heat transfer coefficients are symmetrically distributed in the vertical tube. The buoyancy induced by density differences enhances the heat transfer when a big specific heat exits in the layer; while the thermal acceleration effects induced by the density difference deteriorated the heat transfer when the specific heat recovers the normal value in the thermal layer