An experiment and three-dimensional numerical simulation of pulsating heat pipes

An experimental and analytical study of pulsating heat pipe (PHP) has been carried out in order to develop a more reliable numerical simulation model. The test PHP was made of transparent Pyrex tubes with the inner diameter of 1.85mm and a total of sixteen tubes formed eight turns of PHP. Both heating and cooling were provided by water jackets in which inlet and outlet temperatures were precisely measured for estimating heat transfer rate. The working fluid was R123. Visualization using a high-speed camera showed various flow patterns as well as the fluid motions. The wall temperature measured at various locations revealed its relation to the fluid motion and the direction of circulation. The circulation motion was dominant in most tests. The heat transfer rate was measured and the difference for filling ratio of 50 and 60% was little. A three-dimensional computational fluid dynamics modeling has been developed for pulsating heat pipe using ANSYS Fluent. The VOF model with variable density and vapor pressure relation successfully simulated the circulating motions of PHP. The predicted wall temperatures showed the same indication of mode of flow motion and the flow direction as observed in the experiment. The predicted heat transfer rates agreed well with the experimental data within 5%. The success of the simulation of the experiment implies that the realizable k-epsilon turbulence model is appropriate to PHP simulation and the use of variable density for liquid and vapor and the vapor pressure equation is crucial. (C) 2020 Elsevier Ltd. All rights reserved.