The Nonuniform Rotation Non-evacuated Wickless Heat Pipe Within Nanofluid Vortex Field

The evaporator of the rotating wickless heat pipe (WHP) is vertically placed in the central core of the nanofluid vortex, while its finned condenser transfers heat to ambient air. The vortex of nanofluid (Al₂O₃ nanoparticles and water) is previously heated and establishes a vortex movement inside a cylindrical vertical vessel. Thus, the saturation of the working fluid inside the WHP is enabled, provided that the temperature of the nanofluid is higher than the saturation temperature of the working fluid (ethanol) in the WHP. The angular speed of the rotating WHP is changed in a controlled manner, with the aim of establishing its influence on the nanofluid temperature and WHP efficiency. The tangential velocity of the vortex nanofluid motion changed, by the controlled change in the angular speed of the stir bar at the bottom of the vessel placed. By changing the angular speeds of WHP and stir bar, and the volume fractional ratio of Al₂O₃ nanoparticles inside the base fluid, it aims to obtain the transient values of nanofluid temperature and WHP efficiency. Analytical modeling and experimental testing were established to achieve the stated goal. As a result of the conducted analysis, nanofluid temperatures and WHP efficiency at nonuniform rotation non-evacuated wickless heat pipe within the nanofluid vortex field were obtained. This work indicated the possibility of various changes in WHP efficiency. Based on the conducted analysis, the rotation of WHP affects the intensity of heat exchange of its evaporator and condenser. The nanofluid temperature decreases by a value of 0.5% after 200 s, when accelerating the WHP and stir bar, while the required nanofluid temperature, under the same conditions, increases by 2.1%. In the case of deceleration of WHP and stir bar, the required nanofluid temperature decreases by 3.8%, after 140 s. Furthermore, the direction of rotation and nonuniform rotation affects the cooling rate of the nanofluid. WHP efficiency for accelerating WHP and stir bar, if their rotation directions are opposite, has a 16.2% higher value after 100 s from the start of nanofluid cooling.