This paper investigates the thermal and fluid dynamic characteristics due to multiple miniature axial fans with blade chord and span length scales less than 10 mm, impinging air onto finned surfaces. A coupled approach, utilizing both experimental and numerical techniques, has been devised to examine in detail the exit air flow interaction between cooling fans within an array. The findings demonstrate that fans positioned adjacently in an array can influence heat transfer performance both positively and negatively by up to 35% compared to an equivalent single fan—heat sink unit operating standalone. Numerical simulations have provided an insight into the flow fields generated by adjacent fans and also the air flow interaction with fixed fan motor support structures downstream. A novel experimental approach utilizing infrared thermography has been developed to locally assess the validity of the numerical models. In particular, an assessment on implementing compact lumped parameter fans and fans modeled with full geometric detail is shown for two configurations that are impinging air onto finned and flat surfaces. Overall, the study provides an insight into fan cooled heat sinks incorporating multiple miniature axial fans and general recommendations for improving current numerical modeling approaches.
Abstract. Thermal performance characteristics are assessed for multiple miniature axial fans of 24.6 mm diameter that provide impingement cooling on a finned surface. Combined experimental and numerical analyses indicate that fans positioned adjacently in an array can influence heat transfer performance both positively and negatively by up to 35% compared to an equivalent single fan -heat sink unit operating standalone. However the level of thermal performance reductions, coupled with greater geometrical flexibility, makes the design approach a viable alternative to current single fan -heat sink units. Experimental measurements also suggest that for a fixed spacing, fan operating point is a sensitive criterion for ensuring optimal thermal performance over an equivalent single fan unit. Numerical simulations, modelled using experimental inputs, have provided an insight into the flow fields produced by the interaction between adjacent fans and the finned geometry. Fluid recirculation occurs beneath the fan hub of the centrally located fan in the array, with the adjacent fans on the periphery experiencing cross flow in the hub region. A novel experimental approach utilising infrared thermography has been developed to assess the validity of the numerical model. Indeed, the previously stated flow features were confirmed using this assessment, while limitations in the modelling assumptions have been outlined. Overall, the results provide recommendations in the design of fan cooled heat sinks utilising multiple axial fans for jet impingement and an understanding of the flow physics which occur within this compact cooling solution design.
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