Effects of Electronic Enclosure and Inlet Area on P - Q Curves of Installed Axial Cooling Fans

This paper describes the effects of the enclosure and its inlet on the performance of axial air-cooling fans installed in electronic equipment. The performance of an air-cooling fan is defined by its P - Q (pressure difference — flow rate) curve. Recent studies have reported that the P - Q curve of cooling fans depends on their operating environment. P - Q curves are normally used to define the performance of fans in the computational fluid dynamics (CFD) codes. Therefore the change of the P - Q curve may cause inaccurate CFD analyses to be performed in the thermal design of electronic equipment, including cooling fans. In this study, we measured the performance of test fans in an enclosure and explored the effects of the inlet size and shape while varying the speed of revolution of the fan. In particular, the static pressure difference between the front and rear of fans installed in a test enclosure was investigated. Our experiments clarified the effect of the enclosure on fan performance. The level of decrease of the maximum flow rate was found to be determined by the size of the inlet area, and was independent of the shape of the inlet and the revolution speed of the fan.