ACD-2.1 HTRI Air Cooler Performance Evaluation - Effect of Fan Tip Clearance

R. B. Ritter, T. P. Cham, and J. Taborek

The HTRI air cooler research plant, described in Report ACD-1, was operated to determine the effect of the clearance between the tip of the fan blades and the surrounding fan ring. This clearance ranged from 0.72 in. (18.3 mm) to zero. A difference of 27 percent in the efficiency for the air cooler was found for the extremes of fin tip clearance. This indicates that extreme care should be given to the fan tip clearance design.

The above values refer to a 60-in. (1.524-m) diameter fan. It is speculated that larger fan diameters will not produce such drastic differences but, nevertheless, the inefficiencies due to the fan tip clearance are relatively large and can be corrected inexpensively with a simple plastic strip technique described in this report.