Investigation on start-up and thermal performance of the single-loop pulsating heat pipe with variable diameter

Abstract

The start-up performance and heat transfer performance of three-dimensional single-loop pulsating heat pipes (PHP) with three diameter ratios are numerically probed in present work. The various heating power (20W-50W) and inclination angle (0°-90°) are employed in present numerical simulation. The results show that the start-up and heat transfer performance of the uniform PHP are significantly affected by inclination angle. When PHP is placed vertically, two start-up processes are observed for the PHP with three diameter ratios and the heating power of 20W. The start-up of PHP with variable diameter has a sharp decline in temperature, while the temperature variation of uniform PHP in start-up is continuous and stable. By comparing three PHPs with different diameters, it can be found that the variable diameter structure can increase additional pressure difference to reduce the sensitivity of PHP to gravity, and even the start-up phenomenon can be observed with horizontal arrangement. In addition, under the condition of the heating power of 20W, the PHP with diameter ratio of 4:2 has the greatest thermal resistance, while the PHP with diameter ratio of 4:3 has the least thermal resistance, among which the thermal resistance of PHP with diameter ratio of 4:3 reduces by 3.37% under the inclination angle of 10°. Besides, the larger the diameter ratio is, the easier the PHP is to dry-out due to less liquid mass and greater flow resistance with the same filling ratio.