硝基熔盐纳米流体在扭曲扁管内流动与换热特性

Nitrate molten salt-based nanofluid flow and heat transfer characteristics in twisted tube

熔盐作为传热储热介质在太阳能光热发电系统中广泛应用,研究发现通过在熔盐中添加纳米粒子可以改善熔盐的热物性。本工作采用数值模拟方法,对熔盐纳米流体在不同结构扭曲扁管内的流动和换热特性进行了研究。研究结果表明,熔盐纳米流体在扭曲扁管内的对流换热系数和压降随着长短轴比的增加而增加,随着导程的增加而减小。在Re=10000~35000时,扭曲扁管内熔盐纳米流体的对流换热系数相比于圆管最高提升了34.6%,压降最大升高了141.3%,并拟合得到了扭曲扁管内熔盐纳米流体的努塞尔数Nu和阻力系数f的经验关联式。通过综合性能和场协同分析发现,在Re=30000时,长短轴比a/b=2,导程S=300 mm时,强化传热因子PEC最大为1.16,扭曲扁管长轴顶端的协同角最小。

In concentrating solar power plant,molten salt is widely used for heat transfer and energy storage medium.It is found that the thermophysical properties of molten salt can be improved by adding nanoparticles to molten salt.In this paper,numerical simulation was used to analyze the flow and heat transfer characteristics of molten salt nanofluids in twisted tubes with different structures.The results show that the convective heat transfer coefficient and pressure drop of molten salt nanofluids in twisted tubes increase with the increase in the ratio of the long axis to short axis,and decrease with the increasing of the pitch.When Re=10000-35000,the convective heat transfer coefficient of molten salt nanofluids in twisted tubes is 34.6%higher than that in smooth tube,and the maximum pressure drop is 141.3%.The empirical correlations of the nusselt number and resistance coefficient of molten salt nanofluids in twisted tubes are fitted.Through the comprehensive performance and field synergy analysis,it is found that when Re=30000,the ratio of the long and short axis a/b=2,and the pitch S=300 mm.The maximum enhanced heat transfer factor is 1.16,and the synergy angle at the top of the long axis of the twisted tube is the smallest.