Effect of Low-Frequency Oscillations on the Performance of Closed-Loop Pulsating Heat Pipe*

The pulsating heat pipe (PHP) is a simple heat exchange device, which differs from conventional heat pipes in terms of construction and flow behavior and it has no wick structures inside. The present study focuses on experimentally investigating and exploring the effects of low-frequency oscillations on the thermal performance of the pulsating heat pipe. To understand the thermal performance of the closed loop PHP, a copper capillary tube of seven turns with an internal diameter of 2mm and an external diameter of 3mm with evaporator and condenser sections of length 80 mm each, adiabatic section of length 126mm has been designed. Hot and cold fluids are circulated by using temperature baths in evaporator and condenser sections separately, by varying evaporator (45ºC-60ºC) and condenser temperatures (10ºC-20ºC). The CLPHP performance has been studied for the filling ratio of 50% (n-pentane as working fluid) in bottom mode heating mode subjected to transverse oscillations by mounting it on a linear motor and operating at a frequency range of 0-3Hz at an amplitude of 1mm and 3mm respectively. The results show thermal resistance increases with the increase in the evaporator temperature. Thermal resistance shows a decreasing trend expectably with an increase in heat input. The external forcing triggers the oscillations of the slug-plug flow. But there is no substantial change in the heat input, however, heat input increases with the amplitude of forcing and thus reduces the thermal resistance.