太阳能热发电中超临界压力CO_(2)在渐扩变截面圆管内冷却传热强化机理

COOLING HEAT TRANSFER ENHANCEMENT MECHANISM OF SUPERCRITICAL PRESSURE CO_(2)IN DIVERGING VARIABLE CROSS-SECTION CIRCULAR TUBE IN SOLAR THERMAL POWER GENERATION

采用SST k-ω湍流模型对冷却条件下超临界压力CO_(2)(S-CO_(2))在等截面圆管、水平渐扩管以及不同倾斜角的渐扩管内的传热特性进行数值模拟。模拟结果表明,在相同换热面积下,相比较于等截面圆管,水平渐扩管的总传热系数提高了32.33%,30°倾斜渐扩管提高了33.12%;水平渐扩管的压降降低了53.87%,30°渐扩管降低了9.86%。采用综合性能评价准则PEC,得到水平渐扩管的综合性能最优。基于S-CO_(2)在拟临界温度Tpc处发生“类相变”的假设,获得了类液膜厚度沿管长方向的分布规律,在同一截面处,30°渐扩管的类液膜厚度最小,等截面圆管的类液膜厚度最大,从超临界态类两相的角度解释了强化传热。

The SST k-ωturbulence model was used to numerically simulate the heat transfer characteristics of supercritical pressure CO_(2)(S-CO_(2))in constant-section circular tube,horizontal diverging tube and diverging tubes with different inclination angles under cooling conditions.The computational results indicate that compared with that of the uniform cross-section tube,the total heat transfer coefficient of the horizontal diverging tube and the 30°inclined diverging tube are increased by 32.3%and 33.1%respectively under same heat transfer area,and the pressure drop are decreased by 53.87%and 9.86%,respectively.Using comprehensive Performance Evaluation Criteria PEC,it is found that the comprehensive performance of the horizontal diverging tube is the best.Based on the assumption that S-CO_(2)has"phase-transition-like"at pseudo-critical temperature Tpc,the distribution of the liquid-like film along the length of the tube is obtained,and it is found that at the same section,the thickness of the liquid-like film of the 30°diverging tube is the smallest,the liquid-like film thickness of the constant-section circular tube is the biggest.The mechanism of heat transfer enhancement is explained from the point of view of supercritical two-phase-like.