Thermal management of a laptop computer with synthetic air microjets

This paper discusses experiments conducted to determine the effectiveness of synthetic air microjets in cooling packaged thermal test chips and a laptop computer processor. The details of the experiments may be found in Reference 1. A small electromagnetic actuator was used to create the jets. When AC voltage was applied to the assembly, or microjet, a pulsating jet of air was forced out through an orifice in one face of the actuator. Design variables included the number and diameter of the orifices. The magnitude and frequency of the input signal were held constant. Initially, a microjet was used to cool a heated, packaged thermal test chip. The setup was such that the jet(s) of air impinged directly on the package, and the distance between the microjet and the heated surface was varied. For the remaining experiments, the microjet was used to cool the processor of a laptop computer. In these tests, the air jet(s) impinged on the plate covering the processor. Various orifice plate designs and methods of baffling and sealing were employed to increase the cooling efficiency. Occasionally, the microjet was used in conjunction with a small 5-V fan to determine the effect of global cooling on the microjet effectiveness. Synthetic air microjets were shown to be effective in cooling both the test chips and the laptop processor. For the former tests, the microjet produced an average 26 percent reduction in chip temperature rise compared to the temperature rise that existed under natural convection conditions. For the latter tests, the processor temperature rise was decreased by 22 percent compared to the temperature rise without microjet cooling.