Numerical study on prediction, evaluation and restraint mechanisms of geyser boiling phenomenon in two-phase closed thermosyphons

Abstract

This paper numerically investigates the formation mechanism of geyser boiling inside a two-phase closed thermosyphon (TPCT) with inclined orientations of 0°, 30° and 60°, filling ratio varying from 0.25 to 1.25 and heat flux ranging from 25 to 150 W. The regional flow patterns of geyser boiling phenomenon (GBP) are illustrated and the thermal resistance is regarded as the evaluation criterion. The volume of fluid (VOF) method with Lee model are applied and the condensation time relaxation coefficient is corrected and benchmarked with experimental data reported in existed literatures. Result shows that a significant precision improvement on the TPCT wall temperature prediction can be achieved when employing the condensation time relaxation coefficient of 100. Meanwhile, the GBP is more likely to occur at low power inputs (1) which will be pronouncedly alleviated by the inclined orientation due to the acceleration of bubble departures. For further erasing GBP, the stationary bended structures are investigated with bending angles ranging from 0 to 60°. A new criterion based on the liquid level fluctuation is also proposed to evaluate the intensity of GBP. It is found that the TPCT with bended structures present much more prominent effect on GBP alleviation compared to cases with inclined orientations due to the lower bubble departure resistance at the evaporation region and the abrupt pressure variation at the bending site. The case with the bending angle of 45° shows the lowest liquid level of 0.32, indicating the optimal effect on GBP restraint.

Keywords

• TPCT
• Geyser boiling phenomenon
• Inclined orientation
• Bending angle
• Liquid level promotion number