为了探究超临界二氧化碳（SCO2）对流换热的影响因素，在考虑了管道倾角和钢管壁厚引起热流密度不均的情况下，针对SCO2在上、下半周不同热流密度条件、管道放置倾角、质量流量以及压力值时的换热情况进行了研究。模拟计算中金属管外径16 mm、内径12 mm、长度1 500 mm；外壁面热流密度为425.6 kW/m2；管内出口压力工况参数分别为7.6，8.5和9.5 MPa；质量流量分别为101.788，76.341和50.894 kg/s；管道倾角分别为0°（水平），30°，45°，60°和90°（垂直）。结果表明：在均匀加热条件下，由于钢管导热的影响使钢管内壁上半周的热流密度低于下半周；随着倾角的增大，二次流动能降低，上半周的热流密度逐渐接近下半周，同时，下半周的换热系数减小，上半周的换热系数增大。在非均匀加热条件下，沿着流动方向，初始阶段上半周的换热系数高于下半周的换热系数，随着流体温度增加，这种现象会发生逆转。因为当质量流量和压力增加时，上、下半周的换热系数均会增加，并且可以降低管道内壁面峰值温度。而不同加热方式下，上、下半周的温差与二次流动能有关。

In order to investigate the influence factors of convective heat transfer of supercritical carbon dioxide(SCO2),the heat transfer of SCO2 under different heat flux densities,pipe placement angles, mass flow rates and pressure values in the upper and lower half cycles was studied, considering the uneven heat flux density caused by the pipe angles and the thickness of the steel pipe wall.The simulated metal pipe has outer diameter of 16 mm,inner diameter of 12 mm and length of 1 500 mm.The heat flux density on the outer wall is 425.6 kW/m2.〖JP〗The outlet pressure parameters in the pipe are 7.6 MPa,8.5 MPa and 9.5 MPa respectively; the mass flow rates are 101.788 kg/s,76.341 kg/s and 50.894 kg/s respectively; the pipe inclination angles are 0° (horizontal),30°,45°,60° and 90° (vertical)respectively. The results show that under the uniform heating condition,the heat flux density in the upper half cycle of the steel pipe inner wall is lower than that in the lower half cycle due to the heat conduction of the steel pipe; with the increase of inclination angle,the secondary flow kinetic energy decreases,the heat flux density in the upper half cycle gradually approaches that in the lower half cycle,at the same time the heat transfer coefficient in the lower half cycle decreases and that in the upper half cycle increases. Under the nonuniform heating condition,along the flow direction,the heat transfer coefficient in the upper half cycle is higher than that in the lower half cycle at the beginning,and as the fluid temperature increases,this phenomenon will reverse.When the mass flow and the pressure increase,the heat transfer coefficients both increase in the upper and lower half cycles of the pipe,and the peak temperature of the pipe inner wall can be reduced.The temperature difference between the upper and lower half cycles is related to the secondary flow kinetic energy under different heating methods.

TM623

国家自然科学基金（51976127）