Effect of inclination angles on heat transfer characteristics of a closed loop pulsating heat pipe (CLPHP)

At present Closed Loop Pulsating Heat Pipe (CLPHP) is a novel cooling strategy for successful thermal management though it is a complex heat transfer device having a strong thermo-hydrodynamic coupling to govern the thermal performance. This research is to study the effect of inclination angle and working fluid on the heat transfer characteristics and performance of CLPHP. The performance characterization has been done using two different working fluids of water and ethanol with inclination angle of 0 degrees (vertical), 30 degrees, 45 degrees, 60 degrees, 75 degrees and 90 degrees (horizontal). The experiment is conducted on a CLPHP made of 148 cm long copper capillary tube of 3.0 mm outer diameter and 2.0 mm inner diameter creating a total of 13 turns. The total length of evaporator section is 39.5 cm and condenser section is 31.5 cm; while the rest is assumed to be adiabatic. The evaporator section is heated by electrical heat input, while the condenser section is cooled by atmospheric air flow. Since a PHP is recognized as a two phase heat transfer device, for comparative studies it is operated as a double-phase system by filling it 70% with the working fluid. The comparative study results in a better understanding of the underlying physics of the PHP operation. The experimental results indicate a strong influence of gravity and thermo physical properties of the working fluid on the performance of the CLPHP. The results demonstrate the effect of the input heat flux, inclination angle and physiochemical properties of the working fluid on the thermal performance of the device. (C) 2012 The authors, Published by Elsevier Ltd.