Investigation of effect of a mechanical agitator on pool boiling heat transfer

In this study, effect of a mechanical agitator on heat transfer at pool boiling is investigated experimentally and numerically. An axial agitator without/with blades is used as the mechanical agitator, which is mounted on the lower surface of the heater. Pure water is used as the working fluid. The bubble departure diameter is determined using the image processing technique. Computations are performed via ANSYS FLUENT. Effects of the speed of the agitator, the number of blades of the agitator and the distance between the agitator and the heater on heat transfer and bubble departure diameter are investigated. It is obtained that the convective heat transfer coeffi-cient is increased by increasing the number of agitator blades from three to seven about 47% at minimum heat flux (17 kW/m2) and maximum speed (187.5 rpm) considered. At the same time, the bubble departure diameter has been detected a decrease by about 6%. It is also shown that the maximum increase in heat transfer is observed at the distance of 20 mm. It is obtained that when the distance between the agitator and the heater surface is reduced from 40 mm to 20 mm, the convective heat transfer coefficient increases by 58%, and the diameter of the vapor bubble decreases by 20%.