Performance of flat-plate, flexible polymeric pulsating heat pipes at different bending angles

The heat transfer performance of a flat-plate, flexible polypropylene pulsating heat pipe (PHP) is evaluated experimentally when the device is bent at different angles, and for different layouts of the evaporator and the condenser. Flexible pulsating heat pipes are a passive thermal management technology with important prospective applications in foldable portable electronics, deployable systems (such as cube satellites), soft robotics, and many others. While a number flexible PHPs have been developed in the recent past, to date, there is insufficient information about the influence of the bending angle (conformation) and of the reciprocal positions of the heat sink and source (configuration) on their thermal performance. Several polypropylene PHP prototypes (250 mm ×100 mm ×1.5 mm) with a channel width of 5 mm and different loop geometries were fabricated using selective transmission laser welding technology. Ethanol and FC-72 were used as heat transfer fluids at a filling ratio of 50%. The PHP performance was evaluated through the equivalent thermal resistance of the device, calculated from the surface temperatures of both the evaporator and the condenser during an ascending/descending stepped heat input ramp applied to the evaporator. The experimental results show that conformation arrangements have no significant effect on the thermal performance, however it may affect the PHP start-up.