球窝/球凸结构下的U型通道蒸汽冷却性能
Heat Transfer Performance in Steam-Cooled U-Shaped Channel with Concave/Convex Structure

采用标准k-ω湍流模型研究了球窝/球凸结构下U型通道内蒸汽的传热与阻力特性,计算、分析了雷诺数为1×104～5×104、来流温比为0.79～0.93、出口压力为0.5～3 MPa时通道内的流动与传热性能,获得了拟合的传热关联式,对比了蒸汽与空气冷却特性的差异。研究结果表明:雷诺数增加在提升总体传热效果的同时能够有效降低流动阻力系数;来流温比增大对强化传热的作用并不明显,但可以有效降低流动阻力损失;提高出口压力可以有效增强传热效果,但大大增加了流动阻力;出口压力为1.5～2 MPa、来流温比为0.84～0.88时蒸汽冷却参数能够获得较为理想的综合换热效果;与空气相比,蒸汽的热物性更容易受到温度和压力的影响,导致传热增强系数的变化较大,此时雷诺数的变化对传热增强系数的贡献并不显著;拟合的传热关联式可以准确预测通道内蒸汽冷却换热系数。
Heat transfer performance and flow resistance characteristics of a steam？？cooled U-shaped channel with concave/convex structure were numerically investigated by standard k-ω turbulent model. The heat transfer correlations were evaluated and analyzed for Reynolds number from 10 000 to 50 000, inlet temperature ratio from 0？？79 to 0.93, and outlet pressure from 0.5 to 3 MPa. The different cooling performances of steam and air were discussed. It reveals that the overall heat transfer performance rises while the friction factor falls with the increasing Reynolds number; the increasing inlet temperature ratio effectively enables to reduce the flow resistance and enhance heat transfer performance obviously; the heightening outlet pressure is beneficial to heat transfer enhancement, but it also leads to greatly increased flow resistance. Thus, a combination of moderate steam pressure from 1.5 MPa to 2 MPa, and medium inlet temperature ratio from 0.84 to 0.88 is suggested to achieve an ideal heat transfer performance. The thermophysical properties of steam are more prone to be affected by temperature and pressure compared with those of air. As a result, the heat transfer performance evaluation criterion for steam varies obviously while the Reynolds number exerts slight influence