中文摘要：

本文对超临界压力二氧化碳在内径为1mm的竖直细圆管中的对流换热进行了实验研究。分析了流体的热流密度、进口温度、质量流量以及流动方向对超临界压力二氧化碳对流换热的影响。实验研究发现，热流密度、进口温度、质量流量以及浮升力对细圆管内对流换热的影响很大，对流换热系数在准临界温度附近存在峰值。在加热的前半段向上流动的对流换热强于向下流动，在加热的后半段则相反。随着热流密度与质量流量比值的不断增加，向上流动与向下流动对流换热强弱转换的交点不断向流体进口方向推移，并且向上流动的壁面温度出现峰值，发生换热恶化，而向下流动则没有出现换热恶化。

英文摘要：

Convection heat transfer of CO2 at supercritical pressures in vertical small tubes with diameter of 1 mm was investigated experimentally. The tests investigated the effects of inlet temperature, mass flow rate, heat flux, buoyancy and flow direction on the convection heat transfer. The experimental data indicates that the inlet temperature, mass flow rate and buoyancy significantly affected the convection heat transfer of supercritical pressure CO2 in the vertical small tubes. With the increase of the ratios of the heat flux to the mass flow rate, the heat transfer deterioration occurred for upward flow, but not for downward flow.