Computational fluid dynamics model for a variable conductance thermosyphon

Abstract

A variable conductance thermosyphon is a unique type of heat pipe that responds passively to changes in thermal environment because of the presence of non-condensable gas (NCG). In this study, we develop a computational fluid dynamics (CFD) model to predict the behavior of a cylindrical-shaped variable conductance thermosyphon in the vertical orientation for a range of evaporator-side operating temperatures between 66.70 °C and 87.32 °C. Experiments are performed on a variable conductance thermosyphon that is made of a 262 mm long stainless steel tube with an outer diameter of 9.5 mm and a wall thickness of 0.92 mm. The working fluid is methanol and the NCG is argon. The model is able to predict the fluid flow and heat transfer in the fluid domain and the conjugate heat transfer to the solid wall domain. Experimental thermocouple data for both forced convection and natural convection test cases show temperature remaining almost uniform in the adiabatic section and dropping rapidly across the vapor/NCG interface between the vapor and NCG. This behavior of wall temperature change was also captured accurately by the CFD model, evidenced by MAEs of 3.09% and 3.52% for forced and natural convection test cases, respectively.