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Due to ever increasing consumer demand, today's marketplace is full of portable computing devices such as notebook computers, gaming machines, personal digital assistants, and smart phones. In each of these technologies, processing power and functionality levels are continuing to increase, resulting in increased thermal management issues. The former of these technologies already use an active cooling solution with a profile of 10-15mm while the latter two are quickly approaching the limits of passive cooling. Since a common characteristic in each of these technologies is the desire to reduce profile height, there exists a need to develop low profile cooling solutions that are capable of supporting this growing market. However, a prerequisite to developing such solutions is an accurate understanding of how the noise level characteristics of the driving fans scale with height. This paper experimentally addresses the acoustic scaling of low profile fans. The rotor heights range from 0.5mm to 15mm with diameters from 15mm to 32mm, giving an aspect ratio of height relative to diameter of 0.03-0.6. The results can be used as a foundation for the development of active cooling in mobile devices where both correlations for noise levels and basic design criteria are identified. [ABSTRACT FROM AUTHOR]

The noise produced by cooling air passing through electronics packages arises from two sources. One source is the noise of the air-moving fan of either an axial or centrifugal type. This noise may have both tonal and random components and is strongly dependent on the way that the fan is placed in the unit and on where its operation is on the fan's operating curve. Often, fans are the dominant noise sources. The flow of air produces random noise due to the turbulence generated throughout the unit. Because the turbulent airflow is also responsible for heat transfer between the components and the air stream, we can regard this part of the noise as the irreducible noise due to cooling. If fan noise were eliminated, this part of the noise would remain. There is a relation, therefore, between the irreducible noise and the cooling of the unit. But the fan noise must also be considered. The relation between total airflow related noise and cooling requirements is developed in this paper for the irreducible noise. [ABSTRACT FROM AUTHOR]