Study on the thermal performance of pulsating heat pipe with dual-diameter channels

Abstract

This study was performed to address the effect of dual-diameter channels on operational characteristics of the pulsating heat pipe (PHP) and to determine the optimum range of the difference in channel diameters for which thermal performance enhancement is maximized. To quantitatively observe and understand the characteristics of the PHP, a series of experiments was conducted with varying input power and inclination angle using thermometry and high-speed photography. It was confirmed that unbalanced forces caused by dual-diameter channels help to enhance a flow of the working fluid in the PHP, and it is advantageous for the PHP functionality as the PHP thermal resistance was reduced. The difference between the two tube diameters is small, it makes little difference to operational characteristics of a PHP. On the other hand, too large a diameter difference could lead to an adverse effect on the performance due to large imbalance in driving forces and flow resistances. Therefore, there exists a proper difference in the channel diameters for which thermal performance enhancement of the PHP is guaranteed. In chapter 2, to fundamentally understand the effect of dual-diameter tube on the characteristics of the PHP, experiments were performed using a single-turn PHP which has simplest design. Based on the experi-mental observations, a theoretical model was developed to predict the flow and thermal characteristics of PHPs with a circulating and to suggest guidelines for the design of PHPs with a dual-diameter tube. The model predicts the experimental data well within the error of 15%, and the optimal dimensionless diameter difference was suggested to be $0.15<ΔD/D_{avg}<0.35$. In chapter 3, dual-diameter channels were applied to the flat plate PHP (FP-PHP) applicable to cooling for very thin electronic devices. In the optimal range of the dimensionless diameter difference, the dual-diameter channels not only improve thermal performance of the FP-PHP at vertical positio...