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Staggering performance

Better enclosure cooling from a new fan layout. By Tom Perazzo.

If tough reliability and redundancy requirements are not enough, today¡¦s systems dissipate more power than ever and power loads continue to rise.

Based on Newton¡¦s law of cooling ¡V Q = hAƒ|T ¡V and assuming temperature T is constant, the only ways to extract the higher heat load, Q, are to increase the heat transfer coefficient, h ¡V by providing more airflow ¡V or increase the surface area, A, with more heat sinks.

Conventional cooling systems use axial fans or impellers/blowers to move air through a card cage. Problems arise when the air mover close to a set of cards fails ¡V the lack of air movement can mean cards can fail in a matter of minutes. This is avoided, as far as possible, through redundancy.

One approach to redundancy is a push/pull fan configuration ¡V one set of fans pushes air into the card cage, whilst another set pulls air out. But, in the event of a failure, the locked fan introduces higher impedance to airflow, causing airflow to bypass some card slots. It is also difficult to achieve high flow rates with this arrangement. With two fans installed in series, maximum airflow is limited to that of one fan. Two fans installed in parallel may provide twice the volume of a single fan, but the drawbacks here are increased space requirements and loss of redundancy.

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Graham Pitcher

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