The present investigation reports a theoretical and experimental study of a wire screen heat pipe, the evaporator section of which is subjected to forced convective heating and the condenser section to natural convective cooling in air. The theoretical study deals with the development of an analytical model based on thermal resistance network approach. The model computes thermal resistances at the external surface of the evaporator and condenser as well as inside the heat pipe. A test rig has been developed to evaluate the thermal performance of the heat pipe. The effects of operating parameters (i.e., tilt angle of the heat pipe and heating fluid inlet temperature at the evaporator) have been experimentally studied. Experimental results have been used to compare the analytical model. The heat transfer coefficients predicted by the model at the external surface of the evaporator and condenser are reasonably in agreement with experimental results.
With the incremental heat dissipation requirements of the CPU and intricate electronic circuits requiring flexible piping for the extraction of large amount of heat, a loop heat pipe [LHP] is studied and empirically designed. An experimental study of a LHP has been conducted under the natural convection conditions taking into consideration the variable heat inputs and the quantities of working fluid. The LHP made of copper tubing with horizontal evaporator having a brass mesh wick have been studied and presented for various heat inputs 25 W, 50 W, 75 W, 100 W, 125 W and 150 W. The heat was transferred to the evaporator by constructing a parallel flow heat exchanger. The study was conducted at a vertical orientation using distilled water as the working fluid. Exhaustive attempt has been done in analyzing the effect of various quantities of working fluid (120 gm, 125 gm, 130 gm, 135 gm and 140 gm) on heat transfer parameters. The results includes an achievement of an averaged value of LHP efficiency of 94%, irrespective of the power input in the range of 25 W to 150 W, when working fluid is filled at 40% (130 gm) of evaporator volume. Another credited feature is the attainment of a constant value of LHP efficiency within the range of 75 W to 150 W irrespective of the change in the mass of working fluid.
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