Flow fields with tip leakage vortex in a small axial cooling fan

Abstract

In order to improve the fan characteristics, especially efficiency and noise level of a small axial cooling fan with a large tip clearance, the internal flow measurements with tip leakage vortex were carried out at fan rotor outlet using an I-type hot-wire probe. The probe was set toward two directions, parallel and normal to the meridional plane of test fan, and the two directional velocity components were measured. From the result of fan test it was found that the test fan didn't have the unstable characteristic with a positive gradient on its pressure -flow-rate curve. From the results of velocity measurement it was observed that the tip leakage vortex exited at maximum efficiency flow-rate and large flow-rate conditions. However, at small flow-rate conditions the tip leakage vortex was not observed and it was found that the flow field were enlarged toward radial outwards

Factors affecting small axial cooling fan performance

“…The impeller diameter is 85 mm, hub ratio is 0.69, tip clearance is 1.5 mm, number of blades is 5, and the rotating speed is 3000 revs/min [2]. For the purpose of modeling, the reverse direction method was used for three outlet blade stagger angles θ=30.5°, 37.4°and 44.5°, as shown in Fig.1.…”

“…Little research for small axial flow fans has been undertaken. In Japan, there has been some research using small scale wind tunnels [2]. In this paper, the setting of inlet and outlet is according to the static characteristics line [2].…”

Heat transfer and performance characteristics of axial cooling fans with downstream guide vanes

“…The overall operational performance of small axial cooling fans in terms of pressure drop and heat transfer removal capabilities can be affected by many parameters. For example, blade metal angles [12] and tip leakages [13] can be a critical factor in determining how well a cooling fan will perform since the position of the fan blades within the axial flow fan housings affects the flow conditions. A new concept for further improvement of the performance and efficiency curves includes contra rotating fan impellers [14] however the increase in noise has to be considered [15].…”