周向非均匀热流边界条件下混合熔融盐在太阳能高温吸热管内的强化换热研究

Enhanced Heat Transfer Characteristics of Molten Salt in Solar Thermal Absorber Tubes With Circumferentially Non-uniform Heat Flux Boundary Condition

周向非均匀高密度热流引发的过热问题一直影响着太阳能热发电站中高温吸热器的运行安全,混合熔融盐作为高温传热工质的引入使得这一问题更加严峻。该文建立了混合熔融盐在太阳能高温吸热管内对流换热与强化换热数值计算模型,研究了周向非均匀热流边界条件下混合熔融盐在光滑管与强化换热管内的换热性能。结果显示:内插螺旋纽带强化换热方式对周向非均匀热流边界条件下吸热管的管壁温度和管内流体温度分布均匀性有明显改善。间隙率C与扭曲率y的减小都有助于强化换热效果的增加,特别是C=0,即内插纽带完全接触管壁时,强化传热效果最为显著,但与此同时小的间隙率与扭曲率也造成阻力系数的增大。

The overheating issue which is caused by circumferentially non-uniform heat flux has affected safe operations of the receiver in solar thermal power plant. Molten salt as a kind of working fluid makes this problem become more serious. This paper presented numerical studies of the enhanced turbulent heat transfer of molten salt in solar thermal absorber tubes. The results show that the insert twisted tape can significantly improve the uniformity of temperature distribution of tube wall and molten salt. The decrease of clearance rate C and twisted rate C can enhance the heat transfer effectively. Especially when clearance rate C=0, heat transfer enhancement effect with tight-fit twisted tape is the most significant. But at the same time, the decrease of clearance rate and twisted rate also lead to the increase of the friction factor.