槽式太阳能集热管内相变微胶囊悬浮液的热力性能分析

针对传统使用水基和油基的太阳能集热器换热效果低和管壁热应力大的问题，以相变微胶囊悬浮液为工作流体，对抛物型槽式太阳能集热器进行了三维建模。采用蒙特卡罗射线追踪法结合有限容积法和有限元法的方法求解了太阳能集热管的光?热?力耦合问题，采用欧拉?欧拉多相流模型研究了相变微胶囊悬浮液在集热管内的流动换热特性。结果表明，相变微胶囊悬浮液强化了集热管内的对流换热，不仅降低了集热管的沿程壁温，且减少了集热管的周向温差，均化了集热管温度分布。集热管周向等效热应力呈花瓣型分布，对应的5个高温度梯度的位置附近(圆周角θ=5°, 90°, 175°, 225°和315°)出现等效应力局部峰值。吸热管内壁面θ=90°处轴向热应力为压应力，作用于整个管程，而径向热应力和切向热应力为拉应力，主要作用在进出口端。相变微胶囊悬浮液浓度越高，强化换热效果越好，集热管热应力越小，但产生的压降也随之增大。

Thermal mechanical characteristics analysis of trough solar collector with microencapsulated phase change suspensions

In view of the low heat transfer effect and high thermal stress of tube wall of traditional water-based and oil-based solar collectors, three-dimensional modeling of parabolic trough solar collectors was carried out with phase change microcapsule suspension as the working fluid. The optic-thermal- mechanical coupling problem of solar thermal tube was solved by combining the Monte Carlo ray-trace method, the finite volume method and the finite element method. The heat transfer and thermal stress of microcapsule phase change material slurries in a collector tube were numerically studied by using Eulerian?Eulerian multiphase flow model. The results showed that the microencapsulated phase change material slurries enhanced the convection heat transfer in the collector tube, reduced not only the temperature along the flow path of the collector tube, but also the circumferential temperature difference and homogenized the temperature distribution of the collector tube. The circumferential effective thermal stress on the collector wall was the petal shaped distribution, and the five regions (circumference angle θ=5°, 90°, 175°, 225° and 315°) with higher temperature gradient corresponded to the local maximum of the effective stress. The axial thermal stress at θ=90° on the wall surface behaved as compressive stress along the absorber tube, while the radial thermal stresses and tangential thermal stresses mainly behaved as tensile stress at the tube inlet and outlet ends. The more the mass fraction of the microencapsulated phase change material slurries was, the better the enhanced heat transfer effect was, and the smaller the thermal stress on collector was, but the resulting pressure drop also increased.