采用SST k-ω湍流模型对冷却条件下超临界压力CO2（S-CO2）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-CO2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。
Abstract
The SST k-ω turbulence model was used to numerically simulate the heat transfer characteristics of supercritical pressure CO2 （S-CO2） 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 32.33% and 33.12% 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-CO2 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.
关键词
太阳能热发电 /
超临界压力CO2 /
数值模拟 /
布雷顿循环 /
传热强化 /
渐扩管
Key words
solar thermal power generation /
supercritical pressure CO2 /
numerical simulation /
Brayton cycle /
heat transfer enhancement /
diverging tube
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基金
国家自然科学基金（51675254; 51966009）; “科技助力经济 2020”重点专项（SQ2020YFF0420989）; 甘肃省科技计划（20YF8GA057）
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