The Effects of Reynolds Number on the Aerodynamic Performance of Geometrically Similar Fans

The cooling of portable electronic devices has become paramount in the last number of years due to the simultaneous increase in power consumption and reduction in package size. This has lead to an increase in the amount of heat that needs to be dissipated by these devices. Passive cooling techniques will no longer provide an adequate solution and therefore active cooling solutions need to be implemented. The use of miniature radial fans in conjunction with heatsinks is a possible solution. These types of fans are especially suited as they can be deployed in a low profile format. However, little is known about the aerodynamic effects of reducing the fan scale and therefore Reynolds number to the extent necessary for use in portable electronic device cooling. This paper looks to quantify deviation of aerodynamic performance with Reynolds number from that predicted by the fan laws. Before tests were carried out experimental facilities were calibrated. Four radial fans with diameters of 80, 40, 18.3 and 10mm were then tested at a number of different rotational speeds with measurements of pressure rise and flow rates recorded for each of these speeds. The measurements presented show the need for a homogonous experimental setup with the exact conditions replicated each time a test is carried out. Results also show that there is good correlation between the experimental results for pressure rise and flow rate at high Reynolds numbers in accordance with trends from high Reynolds number theory. However at the lower Reynolds numbers a fundamental change in flow phenomena emerges which alters the maximum pressure and flow characteristics.