Ukraine, Kyiv, ¹National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute”; ²ISEE SSU.

Thermosyphons are two-phase closed heat exchange systems that contain a certain amount of liquid and utilize the latent heat of vaporization and condensation to transfer heat between the heat source and the heat sink without any external devices. They are a type of heat pipe that lacks a capillary structure, so the return of the condensed coolant from the condensation zone to the heating zone is driven by gravitational forces. Due to the absence of a capillary structure, thermosyphons exhibit lower resistance to the movement of the vapor-liquid mixture from the heating zone to the condensation zone, as well as to the return flow of the condensate.
A distinctive feature of such systems is their high equivalent thermal conductivity, which is several orders of magnitude greater than that of natural metals (such as copper or silver). Because of their superior heat transfer characteristics, thermosyphons are widely used in various technical fields, including the chemical and petroleum industries, electronics, telecommunications devices, energy storage systems, and geothermal heating systems, among others.
This paper presents experimental data on the heat transfer characteristics of two-phase thermosyphons with an internal diameter of 9 mm and lengths of 500, 700, and 1000 mm, using water as the coolant. The filling ratio (Fr) varied from 0.3 to 1.2. The length of the condensation zone was the same for all thermosyphons. The study was conducted with the thermosyphons oriented vertically at an angle of 90° relative to the horizontal. The influence of the filling ratio and the effective length of the thermosyphons on the minimum thermal resistance, the maximum heat flux, and the equivalent thermal conductivity is analyzed.

Keywords: thermosyphon, effective length, thermal resistance, heat flux, equivalent thermal conductivity, spatial orientation.

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