Thermal spreading characteristics of novel radial pulsating heat pipes with diverging nonuniform channels

The heat-spreading performance of a pulsating heat pipe (PHP) can be enhanced by increasing the driving force using a novel channel structure. The objective of this study is to investigate the thermal characteristics of novel radial PHPs with diverging channels under horizontal operation. The heat spreading characteristics of radial PHPs with diverging uniform channels (PHP1) and nonuniform channels (PHP2) were measured and analyzed under various working fluids, filling ratios, and heat inputs. HFE-7100, HFE-7200, and ethanol were used as the working fluids. Furthermore, the flow patterns and pressure variations in the PHPs within a short time frame were analyzed. Based on the measured data for both PHPs, the optimum filling ratio for each working fluid was determined to achieve the maximum performance. In addition, the maximum thermal performances of PHP1 and PHP2 were evaluated, aiming to achieve the lowest thermal resistance and maximum heat flux. Overall, the thermal resistance and heat flux of PHP2 were 5.9–11.7% lower and 20–37.5% higher than those of PHP1, respectively.