Impact of Silica Nanofluid Deposition on Thermosyphon Performance
Agnieszka Kujawska, Robert Mulka, Matthias H. Buschmann, Z. Królicki, Bartosz Zajączkowski
Abstract
Thermosyphons are among the most efficient passive heat transfer devices known nowadays. Due to heat and mass transfer limitations of working fluids, much effort is invested in developing a new generation of enhanced fluids, such as nanofluids. Previous studies reported improved thermal capacity when water was replaced by nanofluid. The interplay between nanoparticles and the evaporator surface is crucial here. However, the details of the deposition mechanism and its impact on boiling are still not known. This paper focusses on determining how the boiling process in the thermosyphon affects the inner wall of the evaporator and the nanofluid itself, and how it influences the thermal performance. For that purpose, we conducted the experimental study on a thermosyphon filled with silica nanofluid and then analyzed the samples of evaporator surface and silica nanofluid under a scanning electron microscope. Silica deposited into a porous layer during boiling, which enabled capillary wicking. This in turn decreased the overheating of the evaporator wall. Moreover, silica nanofluid increased heat transfer efficiency and transferred more thermal energy at low heat loads. After opening the thermosyphon, the deposited layer dried and split up. Based on two methods of crack pattern analysis, the mean thickness of the layer was estimated.