Open Access

ARTICLE

Effect of Vapor Pressure Difference on the Operating Characteristics of Pulsating Heat Pipe Using Non-Azeotropic Water/HFE-7100 Mixture

Zeyuan Zhao¹, Dong Zhang^1,2,3,*, Haixia Li¹, Qingdong Deng², Yong Ding³, Zehao Li¹, Zhoujian An^1,3
1 School of Energy and Power Engineering, Lanzhou University of Technology, Lanzhou, China
2 Anhui East China Optoelectronic Technology Research Institute Co., Ltd., Wuhu, China
3 School of Aeronautical and Astronautical Engineering, Guizhou Institute of Technology, Guiyang, China
* Corresponding Author: Dong Zhang. Email:

Energy Engineering https://doi.org/10.32604/ee.2026.078035

Received 22 December 2025; Accepted 19 February 2026; Published online 29 July 2026

Abstract

Pulsating heat pipes (PHPs), as highly efficient heat transfer devices, have been widely employed in thermal management systems in recent years. However, their unique structural characteristics often lead to stagnation, intermittent oscillation, and dry-out, particularly at low inclination angles. In this study, a three-dimensional closed-loop PHP charged with a non-azeotropic mixture of water and HFE-7100 was designed with the aim of broadening the operational range of PHPs. Comparative experiments were conducted between the non-azeotropic mixture PHP and single-fluid PHP charged with either water or HFE-7100 under identical operating conditions, in order to evaluate the enhancement of heat transfer performance. The enhancement mechanism of the non-azeotropic working fluid was analyzed in detail from the perspective of its thermophysical properties. The experimental results demonstrate that, under low inclination angles, the water charged PHP is more susceptible to dry-out. The thermal resistance of the HFE-7100 PHP is consistently higher than that of the mixture PHP. The non-azeotropic mixture effectively extends the stable operating range of the PHP. However, due to the significant difference in the saturated vapor pressures of the two working fluids, the water-charged PHP exhibits superior heat transfer performance at 50% filling ratio under inclination angles of 70° and 90°. Therefore, this study comprehensively analyzes the operating characteristics of the HFE-7100/water mixture PHP based on thermophysical properties in conjunction with temperature and pressure data. Finally, recommendations are provided for the selection of non-azeotropic immiscible working fluids.

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Keywords

Non-azeotropic working fluids; three-dimensional structure; heat transfer limit; saturated vapor pressure; thermal performance; pulsating heat pipe

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