壁面下方圆管加热熔盐自然对流换热的数值研究

Numerical study on natural convection heat transfer of molten salt aroundcirculartubeunder upper-wall

以熔融盐硝酸锂为工作介质,对壁面下方布置的水平圆管自然对流换热进行了数值模拟,研究了圆管周围热羽流态的变化,以及上壁面和圆管间距(h/d)对圆管壁面自然对流换热特性的影响。结果发现:h/d=1时,随着Ra增大,上壁面和圆管间流动滞止区逐渐压缩,热羽逐渐从圆管左右上方移向正上方,圆管顶部换热主要方式从导热变为自然对流;圆管壁面自然对流换热性能随着上壁面远离逐渐增强并趋于稳定,临界间距随着Ra增大而减小;对于Ra≥10 000的自然对流,当h/d≥3以后,上壁面对圆管换热几乎没有影响。

Using the molten salt lithium nitrate as the working fluid,the natural convection heat transfer of a horizontal circular tube under the wall is numerically simulated.The change of upper wall on the buoyant plume generated above the heated tube,and the influence of the spacing between the tube and upper wall(h/d)on the natural convection heat transfer characteristics around the heated tube were investigated.The results show that when h/d=1,with Ra increases,the stagnant region between the upper wall and heat tube is gradually compressed,the rising thermal plume of heated tube shifts from the upper right and upper left to the top,the main mode of heat transfer at the top part of tube is transferred from conduction to natural convection.The natural convection heat transfer characteristics of the heated tube gradually increase and then tend to be stable with the increase of h/d,and the critical spacing is decreasing with the increase of Ra.For the natural convection of Ra≥10000,the upper wall has almost no effect on the heat transfer of heated tube when h/d≥3.