The Pulsating Heat Pipe (PHP) is a promising device in the family of heat pipes. With no need for a wick, they exhibit a high heat transfer to weight ratio. Moreover, the wickless design removes limits commonly associated with conventional heat pipes, increasing the maximum power transfer per single heat pipe. These peculiarities make it an ideal candidate for many high power applications. Nonetheless, there exists only partial knowledge on the driving mechanism, which limits the prediction accuracy of current design methods. Most Pulsating Heat Pipe studies rely on experiments to test configurations, while simulations usually depend on semi-empirical correlations or adaptations of reduced theoretical models. Experiments provide detailed data for a particular geometry in fixed laboratory conditions, but offer limited flexibility to test alternative configurations. Semi-empirical models use previous experimental data to create non-dimensional formulations. Though approaching an increased set of conditions, correlations apply with reasonable accuracy only to a small range, outside of which the prediction ability progressively falls. High order numerical analysis such as CFD modeling could potentially provide full visualization, but due to the complex flow behavior previous studies have used this method only in simple configurations with a small number of turns. The present research will expand the potential of this modeling technique by presenting the CFD analysis of a complex Pulsating Heat Pipe configuration. The importance of this study lies in the fact that this configuration, with a number of turns greater than a critical parameter, shows reduced sensitivity to gravity and is therefore particularly important for applications where installation constraints make the heat pipe orientation sub-optimal. Using commercial CFD software the research simulates a two-dimensional Pulsating Heat Pipe with sixteen turns. The heat pipe, with a 2 mm internal diameter, is filled with water at 50%. To visualize the oscillation pattern of liquid and vapor slugs and plugs inside the Pulsating Heat Pipe, the model performs a transient analysis on the device. A VOF solver for multiphase analysis, coupled with the Lee model for evaporation and condensation mass transfer, calculates the interactions between the liquid and the gas phase inside the tube. The study follows the geometric and operational conditions from previous experiments. The analysis simulates a Pulsating Heat Pipe operating in a vertical orientation with the condenser section placed in the upper sector. During the initial stabilization phase, the system flow distribution fluctuates between different flow modes as the fluid structure forms. After stabilizing, the heat transfer results agree well with the experimental values. Moreover, the increased resolution allows full visualization of the internal operation, retrieving additional information on the temperature and ratio of liquid and gas phases along the heat pipe.


Numerical Analysis of the Phase-Change Heat Transfer Inside a Pulsating Heat Pipe With Overcritical Number of Turns

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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