Performance analysis of axial fans in unitary air-conditioning systems

Abstract

The design and performance analysis of axial fan blades in unitary air conditioning systems are investigated numerically. The effect of propeller diameter, number of blades and blade pitch (angle of attack) on the air flow rate, static pressure rise and static efficiency are examined by solving the full three-dimensional flow equations across the fan blade. The tested configurations included 18 [46 cm] to 24 [61 cm] propeller diameters, 2 to 4 blade propellers, and a pitch range of 25 to 35 degree. It was found that peak static efficiency was highest in the pitch range of 40 to 45 degree. The static efficiency decreased with the increase in number of blades. The static efficiency was insensitive to the propeller diameter, resulting in a flat curve in the range of the tested diameters. The increase in propeller diameter had the most pronounced effect in increasing the air flow rate. The increase in blade pitch, in the optimum pitch range, delivered the maximum increase in the static pressure rise. The results show that the best performance of the propeller occurs at the maximum possible diameter, within the physical constraint of the unit, using the least number of blades at the optimum pitch range.