Avaliação experimental do desempenho térmico e da pressão de vapor de um termossifão em diferentes inclinações

Abstract

Thermosyphons are highly efficient passive heat transfer devices capable of transferring thermal energy in small temperature gradients through the latent heat of vaporization, operating in a two-phase cycle. Such devices are basically composed of an evacuated metallic tube filled with a working fluid. They are composed of three regions: evaporator, adiabatic section, and condenser. Their applications vary from combustion air heaters, heat exchangers, heat regenerators, and solar collectors, among others. The objective of the present work was to experimentally investigate the influence of the slope on the thermal performance of thermosyphons and to verify the internal pressure variation. In this experimental study, the working fluid was distilled water. The device was manufactured in copper, with an external diameter of 9.45mm, internal diameter of 7.75mm, and a length of 500mm. The evaporator had a length of 210mm, while the adiabatic section and condenser had lengths of 20mm and 270mm, respectively. The thermosyphon was filled with 50% of the evaporator volume. The device was experimentally tested at different slopes (22.5, 45, and 90° from the horizontal) under heat charges ranging from 10 to 60W. The device also had a vacuum gauge attached, which allowed the evaluation of the pressure variation for the different slopes and thermal loads. The thermal analysis was based on the temperature distribution along the length, operating temperature, and thermal resistance. Given the results observed for thermal resistance, it was not possible to determine the best slope from the point of view of thermal performance, since all the results presented similar values when considering the experimental uncertainties. The internal pressure for the 45 and 90º slopes were very close, but lower than for the 22.5º slope, since in the latter the temperatures were higher.