Effects of the evaporator and condenser length on the performance of pulsating heat pipes

A two-dimensional single loop closed-loop pulsating heat pipe (CLPHP) is investigated by CFD in present work. The volume of fluid (VOF) method is used to investigate the start-up characteristic and thermal performance of CLPHP with different ratios of the evaporator length to that of the condenser. Considering the action of wall adhesion and the effect of surface tension, the continuum surface force (CSF) model is adopted. The investigation is carried out by changing input power (from 10 W to 40 W) and filling ratio (from 30% to 60%). The numerical results are compared with available experimental results at the same condition. It's found that the start-up time and the thermal resistance of CLPHP reduces with the increase of input power. At the same filling ratio and input power condition, reducing the length of condenser within a suitable range would accelerate the start-up process and decrease the thermal resistance while the dry-out occurred easily at low filling ratio. Two types of start-up, sudden temperature increasing starts at lower input power and the smooth temperature increasing starts at higher input power are observed. The bubbles creation and growth motions are observed inside the CLPHP with vapor plugs oscillation and circulation motions. (C) 2015 Elsevier Ltd. All rights reserved.