Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.
A series of experiments was performed to investigate the effect of a dual-diameter channel on the flow and heat transfer characteristics of single-turn pulsating heat pipes (PHPs). Various types of PHPs were made of glass capillary tubes with various inner diameters, and experiments to evaluate thermal performance of the PHPs were performed with varying input power and inclination angle. Quantitative data obtained by highspeed photography that asymmetric PHPs with a dual-diameter channel promote circulating flow over a wider range of experimental conditions compared to symmetric PHPs with a uniform diameter channel. Circulating flow promoted by a dualdiameter channel helps to enhance the thermal performance of the PHP and reduces thermal resistance by up to 45%. A simplified model was developed to predict thermal characteristics of asymmetric PHPs with circulating flow, and the predicted data matched well with experimental data to within the error of 15%. Experimental and calculated data show that there exists an optimum range of diameter deviation where the thermal performance enhancement is maximized. The optimal range of dimensionless diameter deviation is found to be between 0.25 and 0.4, and this study provides design guidelines to improve thermal performance of the PHP.