CFD analysis on flow and heat transfer mechanism of a microchannel Ω-shape heat pipe under zero gravity condition

摘要

This paper utilizes the CFD approaches to investigate the unsteady flow, heat and mass transfer mechanisms in an axial microchannel Ω-shape aluminum-ammonia grooved heat pipe (GHP) under zero gravity condition. The established numerical model considers the spurious velocity due to discretizing the gradient term of phase volume fraction adjacent to the phase interface. The dynamic contact angle, which is a function of the local velocity, is also modeled based on the Hoffman function via user-defined function (UDF). The Lee model is used to calculate the mass transfer rate between the phases in the evaporator as well as condenser section, while the empirical coefficients in the model are calibrated by comparing the calculated temperature distributions with the experimental data by ourselves. The whole mathematical framework is also evaluated by the experiment. Different heat flux and filling ratios are modeled to probe the heat transfer mechanisms in the GHP. The results capture the pressure profiles along the axial direction and the pressure difference across the phase interface in the cross-section perpendicular to the axis, which is balanced by the surface tension with the different contact angles along the axis. It is found that the Ω-shape GHP is capable of transporting heat over relatively large distances with a minuscule temperature difference. The results give rich insights into the flow, heat and mass transfer mechanism of the studied heat pipe.