关键词: 槽式太阳能集热管, 相变微胶囊悬浮液, 强化换热, 热应力, 数值模拟

Abstract: 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.

Key words: trough solar collector, microencapsulated phase change material slurry, heat transfer enhancement, thermal stress, numerical simulation