Study on heat transfer mechanisms of a pulsating heat pipe

Abstract

Recent advances in the performance of semiconductor devices have led to a significant rise in the chip power intensity as well as in the generated heat flux as a waste byproduct. This has adversely increased the temperature of hot spots on an electronic chip, which limits further performance enhancements and reduces the overall lifespan of the chip. Thus, the demand for effective cooling devices is on the rise. Micro pulsating heat pipes (MPHPs) are one of the promising candidates for the thermal management of very thin electronic devices owing to the high thermal performance and simple design without a wick.

In the present study, the heat transfer mechanism of a PHP was investigated numerically, and experimentally. First, heat transfer enhancement in oscillating flow, which is closely related to sensible heat transfer in a PHP, was studied using numerical method. The numerical results show that the oscillating flow augments sensible heat transfer significantly. Nevertheless, it is still hard to explain the high thermal performance of a PHP. To verify this finding, the contributions of the sensible/latent heat transfer in a PHP were clarified experimentally. A five-turn closed loop MPHP was fabricated. Using infrared (IR) thermometry, the temperature and heat flux distributions at the fluid-wall interface were measured over the entire MPHP for the first time. High-speed flow visualization, which was synchronized to heat transfer measurements, was utilized to identify the local flow patterns corresponding to the local temperature and heat flux. A quantitative analysis of these data clarified the contributions of sensible/latent heat transfer to overall heat transfer. The results showed that latent heat transfer not only induces the oscillating flow but also contributes significantly to overall heat transfer, whereas sensible heat transfer is a byproduct of the oscillating flow. Latent heat transfer is shown to be the dominant heat transfer mechanism in a PHP.