Effect of inner diameter and working fluids on the geyser boiling phenomenon in two-phase closed thermosyphon

This study aims to elucidate the mechanism of the Geyser boiling phenomenon (GBP) in a two-phase closed thermosyphon (TPCT). While TPCTs offer high heat transfer performance and simple structure, unstable flows like GBP can undermine their stability. Few studies have addressed the combined effects of working fluid and TPCT diameter on GBP. Experiments were conducted using deionized (DI) water, ethanol, and acetone, with different inner diameters ( D i ) of 10 mm, 15 mm, and 20 mm. Quantitative and qualitative analyses were performed to investigate GBP onset and flow characteristics. High-speed visualization and load cell measurements were used to assess bubble arrival location, liquid layer thickness, bubble acceleration, and bubble survival. The working fluid properties and TPCT diameter were found to influence GBP occurrence strongly. Even without GBP, frequent liquid movement to the condenser produced notable impact forces. This study offers fundamental data for establishing GBP control strategies and supports the development of stable TPCT design guidelines.