Experimental investigation of the influence of the geyser boiling phenomenon on the thermal performance of a two-phase closed thermosyphon

Heat pipes' thermal performance can be greatly affected by the occurrence of geyser boiling, a phase-changing phenomenon. Thus, it is important to investigate the effect of such a phenomenon on the thermal characteristics of the heat pipe. In the current work, extensive experimental investigations have been carried out to consider the influence of geyser boiling on the thermal performance of a two-phase closed thermosyphon (TPCT), in terms of temperature distribution and thermal resistance. This study has been conducted for different water fill ratios as a working fluid (25%, 65%, 100%) and at various orientations (90, 60, 30, 10°) with a wide range of heat loads (20–400 W). The study reveals that the temperature distributes uniformly on the thermosyphon wall after the geyser effect occurrence. In addition, after the geyser boiling, a considerable decrease in the evaporator wall temperature is obtained; especially at a fill ratio of 100% and tilt angles of 90 and 30°, regardless of the increase in the heat loads. Consequently, for example, at the vertical orientation and a heat load of 20 W, the thermal resistance of the TPCT for the fill ratio of 100% decreases from about 200% higher than that for a fill ratio of 25% to become the lowest thermal resistance at a heat input of 50 W. Also, the results show that the heat transfer limit of the thermosyphon heat pipe can be noticeably increased after the occurrence of the geyser boiling. This study highlights the effects of the geyser boiling on the thermal performance of heat pipes.