Avaliação experimental do desempenho térmico de termossifões com nanofluido como fluido de trabalho

Abstract

Thermosyphons are passive devices used in the enhancement of heat transfer, operating in two-phase cycle. Such devices are capable of transferring large amount of thermal energy through heat transfer, even with a small temperature gradient. In the industry, its applications are in heat regenerators, combustion air heaters, heat exchangers, solar collectors, among others. Thermosyphons are composed of three regions, the evaporator, the adiabatic region, and the condenser, each one with their respective functions. The objective of this work was to analyze experimentally the influence of the nanofluid’s use, based on gold, in function of enhance the thermal conductivity of the thermosyphon, compared its performance with deionized water, besides of study which nanofluid’s concentration is presented the best thermal behavior. It was also objective of this work evaluate the best work’s tilt of the thermosyphon. The thermosyphons were made from a copper tube with outer diameter of 9.45 mm, and inner diameter of 7.75 mm, with total length of 200 mm, characterized by the evaporator with 80 mm, the adiabatic region with 20 mm and the condenser with 100 mm. The working fluids used were deionized water and gold nanofluid in concentration of 10% and 20% in water, which the tubes’ filling ratio were 40% of the volume of the evaporator. The evaporator heating was done from an electric potential applied on a ribbon’s nickel-chromium alloy type, and the condenser cooling occurred by forced convection of air. The test were carried out in vertical and 45º positions, with increasing thermal loads between 5W until the maximum power of the working fluid and then decreasing, consecutively, the loads until the initial one. From the showed results, it was verified that all the thermosyphons presented appropriate behavior, besides of verify the potentiality of this devices. It was also noticed that the nanofluid’s application as heat booster, showed superior values than the deionized water, and the concentration of 20% in water have the best values, in order of 238% superior when compared the thermal resistance of the device with water. Regarding the tilt, it was noticed that the tilt of 45º had the best values of thermal resistance.