Geyser boiling in a thermosyphon with nanofluids and surfactant solution

Abstract

Experiments with a two-phase closed thermosyphon are carried out with the aim of investigating the influence of different working fluids on geysering. The length of the analysed device is 1.800 mm and its inner diameter is 20 mm. It is filled with various working fluids: from pure deionised-water and deionised-water plus sodium dodecyl sulphate (surfactant) as reference fluids to two different gold nanofluids, a silica nanofluid, and a nanofluid with nanohorn nanoparticles. Thermal performance of the thermosyphon is investigated with respect to time averaged parameters, such as amount of heat transferred, thermal resistance, and temperature distribution in the working fluid sump, but also with respect to geysering frequency and time dependent internal pressure. The inlet temperature of heating water is controlled between 35 °C and 85 °C and of the cooling medium between 15 °C and 25 °C.The most important conclusion is that geysering is strongly affected not only by nanoparticles, but also by chemical stabilisers like sodium dodecyl sulphate or polyvinylpyrrolidone. It is shown experimentally that nanofluids consisting of base fluid, chemical stabiliser, and nanoparticles in some cases diminish or even completely suppress geysering. Effects related to the nanoparticles alter the solid-vapour interface (a nanoporous layer on the evaporator wall) and the vapour-liquid interface (bubble surface). The influence of nanoparticles is restricted to the evaporator section. Replacing water with one of the other studied solutions/suspensions shifts the working point of the thermosyphon, changing the amount of transferred heat (increase even up to 80% for low evaporator temperature) and operating temperature levels.