Heat Transfer Enhancement Using Micro Porous Structured Surfaces

Abstract

The parabolic trough solar collector as a popular technique is widely used in solar concentrating technologies (SCTs). The solar absorber tube is the key position of the trough solar thermal power system. The internal modification of the absorber tube is one of the most interesting techniques for increasing the collector’s performance. At present, most of the methods to enhance heat transfer efficiency focus on designing alternative parabolic trough collectors (PTC) absorbers and improving the internal structure of absorption tubes. Due to the limitation of temperature range, most absorption tubes use oil as heat absorbing liquid, and very few heat absorbing tubes directly use water as working fluid. This is because water is limited by critical heat flux in high temperature environment, resulting in low heat transfer performance. In this work, we designed a new porous absorber tube with the function of allowing liquid resupply and vapor overflow from different paths, which can effectively improve the critical heat flux of the absorber tube when using distilled water as working fluid. In order to obtain better heat transfer performance of the absorber and verify the feasibility of vapor–liquid separation mechanism, a simplified model of the absorber was carried out in pool boiling. In this work, we fabricated an arterial porous structure with the function of regulating vapor–liquid flow path based on vacuum sintering technique, and the effect of different heating methods on boiling heat transfer performance are analyzed. The maximum heat flux of 450 W/cm2 was achieved without any dry-out at the superheat of 42 °C, and the unique evaporation/boiling curve was obtained.