The effect of fan operating point and location on temperature distribution in electronic systems

This paper investigates the effects of fan operating point and location on the temperature distribution in a simple test electronic system. First the investigation is performed with the fan mounted at the system outlet and drawing air through the system. Then the investigation is performed with the fan mounted at system inlet, pushing air through the system. Both cases were investigated at three flow rates within the fan's recommended operating range. In each case, Particle Image Velocimetry (PIV) was used to measure system air flow and infra red thermography was used to measure PCB surface temperature. At each flow rate examined, PIV showed the air velocity to be uniform in direction and magnitude in the system with the fan mounted at system outlet, with local velocities changing in proportion to the flow rate. PCB temperature increased with reduced flow rate. In the system with the fan mounted at inlet, flow had large tangential components, impingement onto the PCB and reverse flow. Mean PCB temperature was found to be unchanged by flow rate, due to the increased thermal mixing which occurred at lower flow rates. This paper illustrates the gains, which can be made through correct fan placement, and discusses how heat transfer coefficients within fan cooled electronic systems can be optimised throughout the fan operating range.