Lee model based numerical scheme for steady vapor chamber simulations

Abstract

Vapor chamber is a phase-change based heat spreader widely used in thermal management. Steady numerical simulation is a useful practice for vapor chamber design and optimization. In numerical simulations, assuming incompressible flow and isothermal vapor core is common to alleviate the stability issues raised at liquid-vapor interfaces because the mass/energy transfers at such interfaces are sensitive to the fluctuations of pressure, temperature, and density. It is also typical to preset a single kind of phase change behavior at a liquid-vapor interface (either condensation or evaporation). However, these assumptions could no longer be appropriate when input heat flux is high, the ratio of heating area to evaporator area is small, and/or pillars are presented. This paper presents a novel numerical scheme for vapor chamber simulations by accounting for both the flow compressibility and the temperature variations within the vapor core while applying mass/energy source terms to liquid-vapor interfaces based on the Lee model through the ghost fluid method. No preset of the phase change behavior at liquid-vapor interfaces is needed as well. The results show that, under the input heat flux from 5.6 to 38.9 W/cm2, the average temperature errors between the experiments and the simulations range from 3.0% to 5.0% for the heating area, 5.5% to 8.0% for the evaporator, and 1.4% to 3.0% for the condenser. Although these temperature errors are not exceptional, this proposed scheme is numerically stable by exhibiting good grid independence and being able to converge in 128 iterations over four million elements. Furthermore, attributed to fewer assumptions needed, this proposed scheme can simulate flow characteristics that well agree with the sense of phase change behaviors and is also applicable to other two-phase based heat spreaders (such as heat pipes) at various conditions in structure, dimension, heat input, and convergence criteria.