Reduction in flow rate of small cooling fans by an obstruction

Abstract

A compact air-cooling device often encounters high-density mounting environment, which may reduce a flow-rate of a cooling fan. In this work, the PQ characteristics of a cooling fan was investigated which varied by placing an obstacle in close proximity of a fan. Small axial-flow fans of 30-80 mm in side length and small centrifugal fans of 35-52 mm in side length were tested here. As a result, it was found that the maximum flow rate for the free air-flow begin to decrease when the opening area of the gap-flow between the fan and the obstacle becomes smaller than twice the fan flow area, and decreases suddenly if it becomes smaller than the fan flow area. This relation was almost independent of type and size of a fan, rotation speed of impeller, and shape and position of an obstacle.