Influence of process variables on the hydrodynamics and performance of a single loop pulsating heat pipe

An experimental investigation on the performance of closed loop pulsating heat pipe (CLPHP) is reported in this article. The chosen single loop geometry can be considered as the basic building block of a multi turn CLPHP. The loop with 4 mm internal diameter is made of quartz glass tube to facilitate the visualization of the circulation process through the entire loop including evaporator and condenser. Temperatures measured at different locations of the loop on its wall also help to understand the complex hydrodynamics. The observation reveals different operating ranges like no flow, oscillating flow and through flow depending on the loop orientation, filling ratio and input power. There also exists an optimum filling ratio (within 50-40%) and an optimum inclination angle (within 50-70°) where the thermal resistance of the loop is the minimum. From the visualization a possible explanation for the best loop performance at a typical angle of inclination has been provided. Cease of circulation at an inclination angle close to 0° has also been visualized. Finally, a flow regime map for single loop CLPHP is presented.