Numerical investigation of flow instability and heat transfer characteristics inside pulsating heat pipes with different numbers of turns

Abstract

Pulsating heat pipes (PHPs) are multiphase devices with relatively well known properties. Like other heat pipes, PHPs provide high heat transfer rates over long distances due to the fluid phase changes that take place within them. Several studies focused on improving our understanding of the processes driving PHPs, but limited advances have been made to date. For instance, no comprehensive theory about the processes driving PHPs has been developed. This severely restricts PHP use because of uncertainties in predictions of the behaviors of new PHP designs, particularly for sub-optimal conditions such as non-vertical orientations. Computational fluid dynamics can be used to inspect PHPs non-intrusively, but have only been used for a few PHPs with simple geometries. Here, Volume Of Fluid and Lee phase-change models of PHPs with seven, 16, and 23 turns were compared with experimental data and a semi-empirical correlation and used to analyze flow instability and heat transfer. The flow structure, velocity, and temperature profiles at predefined locations and periods were assessed to describe the PHP operating ranges. Cross-correlations of the internal velocity and pressure signals helped explain the effects of the number of turns on PHP thermo-hydrodynamics. These techniques and additional experimental and numerical analyses can improve our understanding of PHPs.