Simulation of Flow Inside Heat Pipe: Sensitivity Study, Conditions and Configuration

Heat pipes are widely used as a heat transporting device in a variety of applications. From space satellites, large industrial appliances to a heat sink for cooling electronic components and packages. Heat pipes are extremely efficient because of their high effective thermal conductivity, compactness, low cost and reliability. Therefore, the designers of heat sinks are often required to optimize the performance of the heat pipe itself in order to improve the overall thermal management system of any particular equipment. However, the detailed internal modeling of a heat pipe presents a challenging problem for an engineer. It is a multi physics problem including two phase flow within porous media and with conjugate heat transfer adding the solicited high capillary and surface tension effect. In this present study, detailed modeling of the heat pipe considering the mentioned effects is pursued. A basic review of the governing equations describing the complete heat pipe operation is given. The commercially available simulation tool Fluent 6.3 is used to describe and solve these equations in a coupled conjugate heat transfer set up. The geometry of heat pipe is divided in two different regions which solve simultaneously. The first region is core region where only vapor flow is assumed. The second region consists of wall and wick structure through which the mass transfer due to wettability and heat dissipates through conduction. Water was used as flowing fluids through wick porous structure. Previous experimental as well as numerical models regarding the heat pipes have been studied and used for the verification of the present model along with a standard grid convergence study. The effects of different heat pipe length, heat fluxes, wall thickness, wall material and porosity are investigated. The pressure drop and wall temperature increase with the value of heat flux. Similarly, porosity and wall material affect the wall temperature distribution. The effect of wall thickness and heat pipe length was not significant. In addition, a theoretical model is developed for the pressure drop across the heat pipe in vapor region and the respective output was used for the simulation. Finally, the temperature distribution in wall and wick is shown and discussed.