Thermal performance of a novel flat thermosyphon for avionics thermal management

Abstract

In this study, a novel flat thermosyphon was conceived to operate as a thermally active chassis wall of avionics enclosures. The flat thermosyphon, specifically designed to operate in vertical orientation, has the dimensions: 320 × 193 × 24 mm and consists of nine 316L stainless steel plates stacked and diffusion bonded. The flat thermosyphon was fabricated and tested under five different heating conditions, allowing for the study of the influence of the heater size and position on its thermal performance. Heat was added to the evaporator by aluminum heater blocks (50 × 50 mm) within which internal cartridge resistances are lodged, and it was extracted from the condenser by natural convection. Four filling ratios were tested (7.5%, 15%, 30% and 50%). The empty thermosyphon, in which only conduction heat transfer takes place, was also tested for comparison purposes. The input power varied from 15 W to 60 W. In total, the novel device was tested under fifteen different configurations. Test results are presented in terms of the temperature evolution with time, the thermal resistance (one-dimensional and spreading) and the temperature uniformity on the condenser surface. The filling ratio severely influenced the thermal performance of the device. The thermal resistance varied from 0.047 to 0.327 °C/W for tests with the optimum filling ratio of 7.5%. The increase in input power improved the thermal performance of the flat thermosyphon, whereas the decrease in heater size negatively affected it. The thermal resistance results showed that the spreading is the dominant and that this dominance increases with the decrease in heater size. In addition, the thermal resistance of the novel flat thermosyphon was proved competitive when compared to other flat heat pipes studied in the literature.