The closed loop pulsating heat pipe (CLPHP) is a passive two-phase heat transfer device, patented by Akachi (1990). Due to its excellent features, PHP has been considered as one of the promising technologies for electronic cooling, heat exchanger, etc. This paper presents an experimental study shows the effect of inclination angle on the thermal performance of CLPHP, which consist of 10 turns of copper tubes having inner and outer diameter 2 mm and 3.6 mm respectively. The equal lengths of evaporator, condenser and adiabatic sections are 50 mm each. Different working fluids are used as R-134a, Methanol and Water. For all experimentations, an optimum filling ratio was maintained 50% by volume. The thermal performance have been investigated with different inclination angles (viz. 0°, 20°, 40°, 60° and 90°) at various heat input from 5 to 50W in the steps of 5W. The thermal resistance (which is inversely proportional to thermal performance) of CLPHP at various heat input are plotted for different working fluids. The result shows that, the thermal resistance decreases as heat input increases. But at low heat input i.e. upto 25W, the thermal resistance decreases rapidly and the PHP performance is more sensitive to the inclination angle whereas high heat input i.e. above 25W, the thermal resistance decreases smoothly and less independent to the inclination angle. In all inclination angles, vertical bottom heat position (at 90°) of CLPHP gives best thermal performance due to presence of gravity force. At all inclination angles, the working fluid R-134a show best thermal performance followed by methanol and water.

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