Experimental investigation on heat transfer and flow patterns of pulsating heat pipe assisted by ultrasonic cavitation

As an active enhanced method, ultrasonic cavitation could evidently improve the heat transfer efficiency of the Pulsating Heat Pipe (PHP). In this work, the influences of ultrasonic and nanofluid on the heat transfer performance of PHP were conducted and analyzed. First, the full visualization experiment was conducted with a high-speed camera to obtain the more detailed flow patterns of PHP. Then, the relative position and instantaneous velocity of vapor bubble was captured to describe the change of flow pattern and the movement of working fluid. Finally, the effects of SiO2-H2O nanofluid with different concentrations (0.5 wt%, 1.0 wt%, 1.5 wt% and 2 wt%) with or without ultrasonic were experimentally investigated. The results reveal that the instantaneous velocity and driving force of working fluid are increased with the power of ultrasonic, and the startup time of PHP can be shortened simultaneously. Moreover, the microjet produced by the collapse of cavitation bubble and cavitation oscillation could promote the dispersion of nanoparticles. Thus, the heat transfer performance of high concentration nanofluid PHP is improved. The work would provide useful inspiration for further development and application of PHP with ultrasonic. (c) 2021 Elsevier Ltd. All rights reserved.