In recent years, NASA space exploration has achieved new feats due to advancement in aerodynamics, propulsion, and other related technologies. Future missions, including but not limited to manned mission to Mars, deep space exploratory missions, and orbit transfer vehicles, require advanced thermal management system. Current state-of-the-art for spacecrafts is a mechanically pumped single phase cooling loop that are not enough to meet thermal-related challenges for future space missions. Loop heat pipes (LHP) are the solution for the required thermal management system that is compact, light-weight, reliable, precise, and energy efficient. These are two-phase systems that employ capillary forces instead of pumps to circulate the coolant. In these devices, the coolant evaporates and condenses in the evaporator and condenser, respectively. The condensed coolant liquid is driven toward the evaporator by capillary action in a wick structure located inside the evaporator. A mechanical pump is added to the liquid line of the loop to reach the distributed heat loads while controlling the temperature to produce an isothermal surface. In this work, flow patterns and heat transfer in the LHP evaporator wick is studied for various flow rates of the working fluid, wick thermal conductivity, porosity and permeability of wick, heat flux, and gravity condition. A CFD model has been developed to predict the performance of LHP due to the change in these parameters. The Volume of Fluid (VOF) model in ANSYS Fluent was modified using a User Defined Function (UDF) to calculate mass transfer between the liquid and vapor phases at the interface. The Lee phase change model was used to calculate the mass flux due to evaporation and condensation.
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