Geyser boiling experiments in thermosyphons filled with immiscible working fluids

Abstract

This paper presents an experimental study on the Geyser Boiling phenomenon in two-phase thermosyphons operating with two working fluids simultaneously: distilled water and thermal oil. The Geyser Boiling is a periodic phenomenon that occurs during some specific thermosyphon operation conditions and is associated with instabilities due to the nucleated pool boiling. The amplitude and frequency of this phenomenon are related to the conditions in which the device is subjected. In this work, the thermal performance of a thermosyphon operating in Geyser Boiling with these two fluids is studied. The influence on the amplitude and frequency of the Geyser Boiling phenomenon is experimentally verified, considering the following parameters: volume ratio of the two working fluids, power input into the evaporator and condenser cooling conditions. Higher amplitudes are usually related to lower frequencies. It was observed that, when a single fluid is used, the height of the liquid column (hydrostatic pressure) is directly associated with the intensity of the phenomenon. Besides, the presence of oil tends to reduce the Geyser Boling effects, with the exception of when the device operates with a thin oil layer over the water. It was concluded that the Geyser Boiling in two-phase thermosyphons, with single or mixture of working fluids, can be characterized by the numbers: Reynolds, Jakob and Bond. Furthermore, two extreme low and high performance conditions were observed in the Geyser Boiling regime operation.