Heat transfer performance of pulsating heat pipe with zeotropic immiscible binary mixtures

Abstract

Working fluid is an important influencing factor for the heat transfer performance of a pulsating heat pipe (PHP). In this study, zeotropic immiscible working fluid was proposed based on the difficult start and easy dry-out with large heat flux of PHP. Deionized water mixed with HFE-7100 was used as the working fluid. The volume mixing ratios used were 4:1, 2:1, 1:1, 1:2, and 1:4, and the heating power ranged from 20 W to 250 W with inclination angles of 30°, 45°, 60°, 75°, and 90°. The filling ratio was 50%. Result shows that at a high heating power (210 W, 250 W), the PHP with mixtures could quickly start and achieve a stable one-way pulsation cycle with low thermal resistance. Meanwhile, the dry-out phenomenon of the working fluid with high boiling point had been inhibited because of the working fluid with low boiling point and high saturation vapor pressure, thereby raising the heat transfer limit of the PHP. During operation, the two working fluids were pulped and stirred to form an emulsion, which promoted the heat transfer between them. When the mixing ratio was 1:1, the two working fluids could be uniformly mixed, the contact surface between them was large, and the heat transfer property performed well. The lowest thermal resistance achieved with mixing ratio of 1:2 was 0.1634 °C/W due to some of the HFE-7100 would exist in gaseous form when the heating power was high (250 W, with an inclination angle of 90°).