The MICROFAN programme which is underway at Stokes since 2002 supersedes an extensive investigation of macro scale fan aerodynamics which concluded in 2001. The motivation for the work is the forecasted increase in heat dissipated in a range of electronic devices. This will threaten reliability at package level, whilst in portable electronic devices, case temperature will compromise user comfort. With these needs in mind, Stokes is developing its novel micro fan technology.

Micro-scale Fans: Axial Fan (6mm f) and Radial Fan (10mm f)

The initial phase of this programme looked at the fundamental changes in fluid dynamics which take place as fan geometric scale is reduced from the macro to the micro scale. The concept of operating fans with diameters as small as 6mm was then demonstrated. The initial phases of the programme investigated both radial and axial flow geometries, and demonstrated radial flow geometries to be most suitable from aerodynamic, fabrication and dynamic stability perspectives. The findings of the initial phases can be found in the publications listed below.

The programme has progressed through the initial fundamental and proof of concept phases to its current technology development and commercialisation phase, where the focus is on the development of integrated micro fan/heat sink products for two target applications:

Product-level cooling for portable electronic devices. Numerical simulations of a novel integrated micro fan/heat sink indicate gains in heat transfer of approximately 20% over a heat sink which employs conventional features.

Package-level cooling for a range of electronic systems. Experimental measurements on an initial micro fan prototype indicate that the novel SRI design outperforms conventional fan designs by up to 25% in terms of flow rate and pressure rise.

The MICROFAN team at Stokes comprises seven researchers, with expertise in heat transfer, mechanical design, reliability prediction, aerodynamics and numerical simulation. The programme employs a range of analytical, numerical and experimental techniques. Entropic analysis has been used to investigate the reduction in aerodynamic efficiency with reduced scale. Constructal theory was used to optimise the geometry of radial flow heat sinks. Numerical modelling using Fluent software was used to identify detailed fan outlet and blade passage flow structures, whilst these predictions were validated using Particle Image Velocimetry measurements. This combination of techniques has given the MICROFAN team at Stokes a unique understanding of micro fan technology, and paves the way for the development of an exceptional range of micro fan products to meet the thermal demands of a variety of electronic devices.

Relevant Publications

Grimes R., Walsh E, Quin, D., and Davies, M., 2005 “The Effect of Geometric Scaling on Aerodynamic Performance”. Accepted for publication, AIAA Journal.

Hanly, K., Grimes, R., Walsh, E., Rodgers, B. and J Punch, J., 2005, “The Effect of Reynolds Number on the Aerodynamic Performance of Micro Radial Flow Fans”, presented at the American Society of Mechanical Engineers Heat Transfer Conference, HT2005-72514,San Francisco, CA, July.

Quin, D., Grimes, R., Walsh, E., Davies, M. and Kunz, S., 2004, “The Effect of Reynolds Number on Microfan Performance”, Proceedings of the 2nd International Conference on Microchannels and Minichannels, Rochester, NY, USA, June.

Grimes, R., Quin, D., Walsh, E., Davies, M. and Kunz, S., 2003, “A Theoretical and Experimental Investigation of the Scaling of Micro Fan Performance”, ASME International Mechanical Engineering Congress and Exhibition, Washington D.C., USA, November.

Grimes, R., Walsh, E., Kunz, S., Davies, M. and D. Quin, 2003, “Scaling the Performance of Micro-Fans”, Proceedings of the 1st International Conference on Microchannels and Minichannels, Rochester, NY, USA, April.