NUMERICAL MODEL DEVELOPMENT FOR THE TRANSIENT HEAT AND MASS TRANSFER PERFORMANCE OF A WATER-COPPER WICKED HEAT PIPE

The application of heat pipes in space nuclear reactors, radiators, and thermal management has gained an enormous amount of attention nowadays. A 3D transient model is needed to study the flow and heat transfer characteristics when considering the complex processes and conditions such as the start-up process, power variation process, non-uniform heating condition, microgravity condition, and so on. In this study, a 3D CFD model for water-copper wicked heat pipe was developed to predict the transient characteristic of heat pipes. A novel source terms method was used through user-defined functions (UDFs) to calculate the evaporation and condensation rates on the water-vapor interface. The laminar flow hypothesis was applied to the flow region. The compressibility of liquid and vapor was considered and the ideal gas equation was adopted for the vapor flow. The Darcy flow characteristic of liquid wick flow was considered in the porous wick region. The simulated outer wall temperature, velocity, pressure, and temperature variation of the wick and vapor during the startup process were obtained and compared with the experimental data. Good prediction results were obtained under the same conditions. The heat flux on the condenser wall will increase quickly due to the quick response-ability of heat pipes. The max vapor velocity shows a minor decrease trend due to the vapor pressure recovery. The distribution of vapor temperature has a significant non-uniformity due to the compression work at the initial time. The beginning of the condensation point will migrate to the condenser section in the start-up process. This study can provide both knowledge and tool for the design of space thermal radiators.