Improving the heat transfer characteristics of miniature two-phase thermosyphons with nanofluids based on Ukrainian natural alumosilicates

Abstract

In order to improve the heat transfer characteristics of miniature thermosyphons, a study of the processes of heat transfer by them using water and nanofluids as heat carriers was carried out. A water mixture based on nanoparticles of Ukrainian natural aluminosilicate - attapulgite with the addition of 0.1 % carbon nanotubes was used as nanofluids. The data of the study of the maximum heat flow and the minimum thermal resistance of copper thermosyphons with an internal diameter of 5 mm and a length of 700 mm are presented. Orientation of thermosyphons in space: vertical. The length of the heating zone varied from 50 mm to 200 mm, with the same amount of heat-carrier. The fill factor varied from 0.44 to 1.93. A comparison was performed of the heat transfer capabilities of thermosyphons with water and with a nanofluid with a mass concentration of 0.5 %. It has been shown that nanofluid thermosyphons transmit 53 % more heat flow compared to water, and thermal resistances are reduced by 25 %. The influence of the concentration of nanoparticles on the heat transfer characteristics of thermosyphons is shown. Nanofluids with concentrations (0.1 %, 0.5 %, 0.7 %) showed the same level of thermal resistances, with an increase in maximum heat flows compared to distilled water. Thus, when compared with the lowest concentration (0.1 %), the use of 0.5 % nanofluid gives an advantage of up to 40 %, and 0.7 % – an advantage of up to 51 %. This is explained by the appearance of a specific porous structure of anisometric nanoparticles on the heating surface, which contributes to the appearance of additional centers of vaporization during boiling and improves the heat transfer characteristics of thermosyphons. Thus, the use of such thermosyphons with nanofluids when cooling elements of electronic equipment could improve their functional characteristics