The effect of global cross flows on the flow field and local heat transfer performance of miniature centrifugal fans

Centrifugal fans are often integrated into thermal management solutions for a range of applications. Consequently, centrifugal fan designs can be subjected to varying environmental conditions, many of which can alter fan performance characteristics and ultimately influence the heat transfer performance of the cooling solution. Global cross flows are a commonly encountered practical operating condition, particularly in the cooling of electronics. Air-cooled electronic enclosures often incorporate miniature centrifugal fans to maintain reliable component operating temperatures at a local level, while larger system level fans are used to simultaneously control the ambient temperature within the enclosure. This type of operating condition has been investigated by introducing a uniform crossing air flow above a centrifugal fan inlet. Two scaled miniature centrifugal fan designs were selected to fundamentally assess the influence on local velocity field and heat transfer performance. This was achieved experimentally using Particle Image Velocimetry, and a combined infrared and heated-thin-foil technique developed for the accurate measurement of local heat transfer coefficients. the introduction of a crossing air flow above the fan inlet indirectly reduced both the local and global thermal performance of the centrifugal fan, and the resultant distorted inflow shifted the surface heat transfer distribution at the fan outlet from an axisymmetric to asymmetric profile. However, strategic positioning of components relative to a centrifugal fan can maintain the average component heat transfer coefficient at a similar level to a case without any cross flow. Results also indicate issues associated with the implementation of miniature centrifugal fan designs into crossing air flow environments, with reductions in thermal performance of over 30% observed.