Determining the influence of geometric factors and the type of heat carrier on the thermal resistance of miniature two-phase thermosyphons

Abstract

This paper reports experimental data on the total thermal resistance of copper two-phase thermosiphons with internal diameters of 3 mm, 5 mm, and 9 mm, 700 mm long. Water, ethanol, methanol, and freon-113 were used as heat carriers. During the study, thermosiphons were located vertically. The length of the heating zone varied from 45 mm to 200 mm while the length of the condensation zone was constant and equaled 200 mm. The filling coefficient of thermosiphons varied from 0.3 to 2.0. Two series of experiments were conducted. The first series was distinguished by the fact that the filling coefficient of three thermosiphons with an internal diameter of 9 mm varied from 0.3 to 0.8 with the same length of the heating zone of 200 mm. The second series of experiments was carried out on thermosiphons with internal diameters of 3 mm and 5 mm. With the same amount of heat carrier, the length of the heating zone changed from 45 mm to 200 mm. As a result of research, it was determined that the total thermal resistance of thermosiphons is influenced by both their geometric factors (internal diameter and filling coefficient) and the type of heat carrier. The main factor that influenced the value of thermal resistance was also the transmitted heat flux. An increase in heat flow led to a significant decrease in thermal resistance. The maximum heat flux was determined with minimal thermal resistance. To calculate the value of the thermal resistance of thermosiphons, two dimensionless dependences were derived, which hold for two ranges of Reynolds numbers. For small Reynolds numbers (until 2000), which characterize the beginning of the action of vaporization centers and their gradual increase, the degree indicator was –0.8, and for larger Reynolds numbers, up to critical phenomena, the degree indicator was at the level of –0.3.