Experimental investigation of the characteristics of thermosyphon with flat evaporator and micro-pillar arrays

Abstract

This study experimentally investigated the cascaded start-up performance of thermosyphon with a flat evaporating surface combined with different sizes of micro-pillars. The thermosyphon was composed of a condenser section and an evaporator section. Different sizes of micro-pillar were processed on the surface of the evaporator bottom plate to enhance the heat transfer. A smooth flat surface was used as the standard reference for comparison with the micro-pillar surfaces. Deionized water was used as the working fluid to cool the condenser section of the thermosyphon. The operating pressure of thermosyphon was measured using a pressure sensor. Additionally, the evaporator section wall temperature and the temperature and flow rate of the cooling water were measured at nine different heat fluxes. The start-up performances of the thermosyphon with a smooth evaporator bottom plate (THSE) and thermosyphon with a micro-pillar in the evaporator bottom plate (THMPE) were compared. The THSE had a longer start-up time and a higher start-up temperature than the THMPE. When the heat flux was 68.6 W/cm2, the start-up time of the THMPE with a micro-pillar width of 0.2 mm and a height of 0.8 mm was reduced by 57.1% compared to THSE, and the start-up temperature was reduced by 28%. Thermosyphons with different micro-pillar widths showed various start-up performances for different heat fluxes. For a narrow micro-pillar width, THMPEs with larger micro-pillar heights had a lower start-up temperature and a shorter start-up time. As the micro-pillar width increased, the micro-pillar height had a different and more complex effect on the start-up performance of the thermosyphon. When the micro-pillar heights were 0.2 mm and 0.4 mm, the thermosyphon with wider micro-pillars had a longer start-up time with a lower heat flux but a shorter start-up time with a higher heat flux. When the micro-pillar heights were 0.6 mm and 0.8 mm, varying the micro-pillar width had a smaller influence on the start-up performance of the thermosyphon, but was dependent on the heat flux.