Thermal performance of various adiabatic section lengths of closed-loop pulsating heat pipe designed for energy recovery applications

This experimental study aims to emphasize on thermal performance and temperature variation of the closed-loop pulsating heat pipe (CLPHP) affected by various adiabatic section lengths. A capillary copper tube has been bent to have 10 and 20 meandering turns to form the CLPHPs with 1.78 mm internal diameter. The evaporator section length was 150 mm, which was the same as of the condenser section length. The adiabatic section length was varied from 75 to 150, 300, and 450 mm. Ethanol, R123, and water was selected to be working fluid with the volumetric filling ratio of 50%. Hot water was pumped through the heating jacket for supplying the heat input to the evaporator section. Heat flux selected as the thermal performance in this study was measured by means of the calorific method across the cooling jacket enveloping the condenser section. It could be concluded that effect of the adiabatic section length has two different trends that are: (i) When the adiabatic section length increases, the heat flux continuously increases until the evaporator section length exceeds a certain value, the heat flux then decreases. And (ii) when the adiabatic section length increases, the heat flux continuously increases. The different effects between both trends are depended on the working fluid’s flow velocity, surface tension, density, and viscosity.