This research aims to study the effect of pipe flattening on heat transfer characteristics and internal phenomena of a sintered wick heat pipe by using the three-dimensional finite element method (3D FEM). The 3D simulation program had been established to study the effect of pipe flattening. The calculation domains were separated into three important regions, i.e., vapor core, wick, and wall. The Cartesian coordinates and the three-dimensional tetrahedral elements are applied in this model. The original diameter of the heat pipe is 6 mm. Water was used as a working fluid. The vapor flow is assumed to be laminar and incompressible. The composite wick which made from sintered copper and grooved copper pipe was used. The thickness of wick and wall were 0.70 and 0.30 mm. The wall temperature distribution is recorded when the heat pipe reached steady state operation and the overall thermal resistance is determined to validate with that obtained from the 3D simulation. It was found that the predicted wall temperature and thermal resistance agreed well with the experimental data with the standard deviations of ±5.95% and ±32.85%, respectively. These pressure drops agreed well with Dacry-Weisbach equation and Engineering Sciences Data Unit (ESDU) 79012 with the standard deviation of ±13.84% and ±26.02%, respectively. Furthermore, the overall thermal resistances of the tubular heat pipes (original diameter of 6 mm), which are flattened into the final thickness of 4.0 mm and 3.0 mm, decreased from 0.91 °C/W to 0.83 °C/W, respectively, due to an increase of the contact surface for the heat transfer. However, the overall thermal resistance of a flattened heat pipe with the final thickness of 2.5 mm increased to 0.88 °C/W, In addition, the critical value of the final thickness of heat pipe was about 45% from original diameter.
Keywords: Flattened Heat Pipe, Three-Dimensional Finite Element Model, Temperature Distribution, Thermal Resistance
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