Optical measurement of electronic system air flow and temperature distribution

Measurements of air flow and heat transfer in electronic systems are rare. The majority of those which have been performed are point-based and as a result, do not lead to a very good understanding of the flow structures or heat transfer patterns which are present. This paper describes techniques used to perform full field measurements of air flow and heat transfer in a fan-cooled electronic system. Particle image velocimetry (PIV) is used to measure air flow velocity distribution, while infrared thermal imaging is used to measure the temperature distribution on a printed circuit board (PCB). The accuracy of each of these techniques is assessed and described in detail. The techniques are used to perform measurements in two electronic systems: one system with an inlet mounted fan and the other with an outlet mounted fan. The measurements show that the physics of flow in both of the systems are in marked contrast with one another. In the system with the outlet mounted fan, the flow was found to be steady and uniform, while in the system with the inlet mounted fan, the flow was found to be swirling and unsteady. Temperature distributions, which were measured, were explained in terms of the measured velocity distributions. The unsteady, swirling flow encountered in the inlet mounted fan system was found to give rise to significantly lower temperatures than those resulting from the steady, uniform flow in the system with the outlet mounted fan.