Thermal performance of a two-phase loop thermosyphon with an additively manufactured evaporator

Abstract

• Thermal performance and instabilities were studied for a loop thermosyphon. • The loop was examined at different powers and charges of water and ethanol. • An additively manufactured evaporator was compared to a machined counterpart. • A model was developed to explain the relation between flow rate and instabilities. • 3D-printed surface demonstrated better stability, but with higher thermal resistance. This work investigates the effects of an additively manufactured (AM) evaporator on two-phase loop thermosyphon performance. The thermosyphon employs a radially finned, air-cooled condenser connected to an aluminum side-heated evaporator by nylon tubing. Two evaporator surfaces were examined: one with smooth conventionally machined aluminum channels and the other with channels additively manufactured by selective laser melting (SLM). The loop thermal performance and the operational instabilities were characterized for different working fluid charge volumes using water and ethanol. The instabilities were quantified using the maximum fluctuation amplitude of the evaporator wall temperature. Results show that increasing the input power decreases the total resistance and lessens the corresponding instabilities. Low fluid charges result in better thermal performance and lower evaporator temperature instabilities, but they reduce the loop’s maximum heat transport capacity. The peak in condenser resistance was found to serve as a good indicator for the end of geysering. Finally, the AM evaporator resulted in slightly higher thermal resistances compared with the conventionally machined version; however, it decreased temperature fluctuations at the heat source.