Thermal performance evaluation of a water-filled axially grooved copper flat heat pipe for electronics cooling

This study deals with the experimentation and modeling of a flat axially grooved heat pipe (FAGHP) which is water-filled with an automatized apparatus to ensure an adequate charge. The main feature of this work is the use of chemical oxidation that enhances capillary pumping. The tests are performed over a wide range of heat input powers (10–60 W) and three heat sink temperatures (10 °C, 20 °C, and 40 °C) with the FAGHP being oriented horizontally. Results reveal that when compared to a copper plate, the FAGHP is more efficient in reducing temperature gradients. Moreover, the capillary limit ranges between 30 and 40 W. The results indicate also that effective thermal conductivity, which depends on the heat input power and the heat sink temperature, can reach 2.4 times that of copper under the optimum operating conditions. Original correlations for evaporation and condensation phenomena are proposed based on a dimensionless analysis and the experimental results are correlated within ± 10%. A mathematical model based on the mass, momentum, and energy balance equations is developed, and it takes into account the fill charge. The model, which is validated by the experimental tests, can determine the variations of the liquid and vapor velocities and pressures, and predict the wall temperature distribution along the FAGHP as well as the drying and flooding lengths. A parametric analysis is carried out to highlight the effects of the geometrical characteristics of the grooves, and the evaporator and condenser lengths on the hydrodynamic and thermal parameters. Augmenting the groove dimensions as well as the evaporator and condenser lengths results in lowering the capillary driving pressure, thus reducing the FAGHP thermal performance. Shallow and large grooves, as well as large evaporator and condenser sections, decrease the wall temperature.