Nihon Kikai Gakkai ronbunshu (Feb 2021)
Correlation of average liquid film thickness formed during liquid column oscillation in a channel
Abstract
Liquid film thickness is an important parameter for predicting phase change heat transfer in pulsating heat pipes (PHPs). This study experimentally evaluated the liquid film thickness formed during the oscillation of the liquid column within PHPs. The liquid column was oscillated sinusoidally under various oscillating conditions to simulate the flow phenomena. The average thickness of the liquid film formed during the oscillations was determined by comparing the oscillation amplitudes of the tip of the liquid column with and without the liquid film. It was confirmed that the average thickness of the liquid film varied with the capillary number for each working liquid (water, ethanol, and FC-40). The characteristic velocity of the capillary number was the time-average velocity of the tip of the liquid column, which was derived by assuming that the tip of the liquid column oscillated sinusoidally. Additionally, the average liquid film thicknesses during the liquid column oscillations were evaluated according to the correlations for various flow conditions proposed in previous studies. In this evaluation, the velocity and acceleration values obtained by assuming that the tip of the liquid column oscillated sinusoidally were determined based on the experimental results. This evaluation demonstrated the acceleration effect, thereby indicating that the acceleration made the liquid film thinner when the capillary number was higher than the threshold of the capillary number for each working liquid. Finally, empirical correlations with and without the acceleration effect were proposed for the average liquid film thickness of oscillating flows in terms of capillary and Laplace numbers. It was demonstrated that the proposed correlations could predict the average liquid film thickness within the range of approximately ±15 % accuracy.
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