State of the art review of conventional and anti-gravity thermosyphons: Focus on two working fluids

Abstract This paper presents a critical overview of operating principles and features of conventional and anti-gravity thermosyphons (TSs), which have led to the development of anti-gravity TSs with two working fluids. It has been demonstrated that the heat fluxes transferred by vapour and liquid heat carriers are comparable in discussed systems. The hydraulic head, which must be overcome in antigravity TSs, is much less when liquid heat carrier is used rather than vapour. A certain temperature difference between heated and cooled working fluids always occurs in anti-gravity TSs, and thus it makes possible to contain sensible heat in liquid heat carrier and create a pressure difference in the saturated vapour necessary for fluid circulation. Despite its good thermodynamic properties, water is a difficult-to-use working fluid within a temperature range of 30÷100 °C and is replaced with low-boiling substances (refrigerants). However, it is undesirable to use large amounts of these substances, and that is why it has been suggested to introduce a system in which water transfers heat and a low-boiling substance sets water in circulation. Two variants of such anti-gravity TSs with two working fluids are presented. They have been patented and successfully tested in a laboratory, as well as in a structure of solar installation. Vertical heat transfer was correspondingly over 1.5 and 18 m, and the thermal power varied from 300 to 1500 W.