A comparative study of the behavior of working fluids and their properties on the performance of pulsating heat pipes (PHP)

Pulsating heat pipe (PHP) is an increasingly promising technology in the application of many industrial fields, but a comprehensive understanding of its thermo-hydrodynamic mechanism is still far from enough. This study investigated the oscillation characteristics and the heat transfer performance of a closed-loop PHP (inner diameter = 2 mm) charged with deionized water, methanol, ethanol and acetone, so as to single out the thermo-physical properties that mostly affect the PHP's performance under diverse situations like different heat inputs (HI = 5-100 W) or/and different filling ratios (FR = 20-95%). It was found that at relatively low HI, the heat transfer depended highly on whether the oscillation started up or whether the flow was fast if started, and had a close relationship with dynamic viscosity. With the increase in HI, the effect of dynamic viscosity on heat transfer dwindled and that of working fluids' energy carrying ability characterized by liquid specific heat and latent heat of vaporization (LHV), especially the latter (LHV), enhanced gradually. Higher LHV was favorable for the heat transfer at higher HI. At low filling ratio, the working fluids with lower boiling point, and lower LHV were easier to dry out. There exists a heat transfer limit, which is almost independent of the type of the working fluids, but largely depends on the PHP itself (the material and the structure) and the cooling condition. Given certain PHP, it may because, after certain heating power, the equivalent thermal resistance inside the tube wall became negligible compared to the outside thermal resistance of air convection. (C) 2014 Elsevier Masson SAS. All rights reserved.