槽式太阳能集热器内耦合换热特性研究

NUMERICAL STUDY ON COUPLED HEAT-TRANSFER PROCESS IN A PARABOLIC SOLAR COLLECTOR

对槽式太阳能集热器内的耦合换热过程建立了统一求解模型,推导了无量纲控制方程,并进行了耦合求解。结果表明:随Ra增加,管内自然对流形成的涡逐渐向右侧管壁方向移动,等温线中心向下偏移;环形空间内自然对流形成的涡向顶部移动,等温线向下偏转;随管径比增加,管内的混合对流换热系数增加,管外环形空间的换热系数减小。内管内外表面的温度梯度及局部换热系数均随着角度的增加而增加。在θ=π/4和θ=π/2的截面内,环形空间中间区域内温度沿半径方向不降反升,出现偏转;而在θ=3π/4和θ=π的截面内,圆管内部中间区域内的温度沿着径向不升反降,也出现偏转。

A numerical model of the coupled heat-transfer process in a solar collector tube was developed and the unified dimensionless governing equations were derived. The results show that with the increase of Ra, the nature convection vortex moves to the tube surface and the center of the isothermal moves to lower side for the inner tube; for the circular space, the nature convection vortex moves to the top side and the isothermal curves to the lower side. With the increase in tube diameter ratio, the Nu increases in the inner tube and decreases in the circular space. The temperature gradient and local Nu on the inner tube surfaces increase along the θ direction. Due to the effects of nature convection, along the radius direction, the temperatures in the circular space in the central region of θ=π/4 and θ=π/2 sections increase instead of decreasing and the temperatures in the inner tube in the central region of θ=3π/4 and θ=π sections decrease instead of increasing.