Numerical study on the flow and thermal characteristics of a two-phase closed thermosyphon filled with low surface tension working fluid under various wettability

Abstract

Although two-phase closed thermosyphons (TPCTs) with low surface tension fluids are increasingly being applied in various fields, existing studies mainly focus on TPCTs with water as the working fluid under different wettability, and there is a lack of research on the condensation dynamics of low surface tension fluids in TPCTs under varying wettability. This paper addresses this gap by presenting a novel CFD model that integrates a dynamic condensation mass transfer time relaxation parameter into the Lee model and couples it with the contact angle model. The results indicate that the numerical model is more accurate in simulating the formation of a liquid film when the liquid phase is set for the primary phase and the density model of the vapor phase is used as an incompressible ideal gas. When low surface tension working fluids, such as methanol and ethanol, are used in TPCTs, the size of bubbles and boiling intensity in the evaporator are lower compared to when water is used as the working fluid. Surface tension and gravity induce the formation of a fluctuating condensate film on the condenser of a methanol-TPCT. The liquid film in the condenser of the ethanol-TPCT is approximately 1.5 times thicker than that of the methanol-TPCT. As the contact angle increases, the thickness of the liquid film on the wall decreases, leading to the phenomenon of temperature rise on the upper wall of the evaporator. These advancements provide a design tool for next-generation TPCTs in applications like data center cooling and hyperloop systems.