Modeling Electronic Cooling Axial Fan Flows

Abstract

To address the requirement for prediction and understanding of airflow in forced convection cooled electronic systems, a detailed experimental investigation of the outlet flow of typical axial cooling fans has been performed. The flow is shown to be complex over much of the fans operational range, with significant radial and tangential velocities and regions with little or no flow. The effect of partially blocking a fan and running it at elevated temperatures are both shown to be significant. The effect of attaching a fan to an electronic system is then investigated. Flow drawn through a system is shown to be simple and well predicted by a standard CFD package. Flow blown into a system is far more complex, with large areas of recirculating flow, and less accuracy in the prediction. The paper gives valuable and novel design insight into forced cooling flows in electronic systems and shows that the industry is still some way from a reliable design method.

Local heat transfer performance and exit flow characteristics of a miniature axial fan

“…Yoon and Lee (2004) also used PIV to analyze the exit flow behavior of an axial fan, constructing a stereoscopic profile of the outlet flow. This highlighted the three-dimensional nature of the exit flow field, which has been shown by Grimes et al (2001) to be dependent on static pressure rise induced by the system resistance imposed on the fan. The influence of the common exit air flow trends noted in the referenced works (Yen and Lin, 2006;Yoon and Lee, 2004;Grimes et al, 2001), on heat transfer performance, was considered by Stafford et al (in preparation).…”

“…This highlighted the three-dimensional nature of the exit flow field, which has been shown by Grimes et al (2001) to be dependent on static pressure rise induced by the system resistance imposed on the fan. The influence of the common exit air flow trends noted in the referenced works (Yen and Lin, 2006;Yoon and Lee, 2004;Grimes et al, 2001), on heat transfer performance, was considered by Stafford et al (in preparation). Local heat transfer rates were examined over a heated flat plate which was cooled by an impinging axial fan air flow.…”

Model for predicting performance of cooling fans for thermal design of electronic equipment (Modeling and evaluation of effects from electronic enclosure and inlet sizes)

“…Grimes and Davies [10] reported on air flow and heat transfer in electronic equipment with a test circuit board cooled by a fan. Grimes et al [11] investigated flow fields in test electronic equipment with an axial fan and proposed guidelines for the choice of a numerical model. However, a detailed and systematic investigation of the effects of the electronic equipment itself on fan performance has not yet been carried out.…”

An Experimental Assessment of Computational Fluid Dynamics Predictive Accuracy for Electronic Component Operational Temperature

“…Fan-generated flows contain swirling flow patterns [44], while screen holes will produce jets downstream [24,45]. Such flow disturbances can generate unsteady or transitional flow conditions over electronic circuit boards, with attaching, separating and recirculating flow features [60], In addition, the component topology often generates multi-dimensional flow phenomena that include pulsating and vortical structures [60,61].…”

“…Physical uncertainties include, for example, power dissipation for the various system units, and grilles and vents pressure loss coefficients [34]. In addition, the capability o f the CFD code to predict complex flow phenomena, such as fan-induced, and their impact on heat transfer needs to be considered [24,44,45], This is often compounded by the fact that in the early design phase, the CFD user may have little or no a priori knowledge of the flow regime, whether laminar, transitional, turbulent, and whether steady or unsteady. Such an uncertainty typically arises from the absence o f a physical prototype, and the difficulty in defining a characteristic dimension, hence transition Reynolds number, that adequately describes the heat transfer characteristics over the PCB or sub-system considered.…”