Scaling the Performance of Micro-Fans

Pumping of liquids and gases in micro fluidic systems has been the focus of much attention in recent times. Miniaturisation of traditional rotating pumps such as axial and radial flow designs, has been limited by the fabrication techniques employed. As a result of these limitations, the geometry of the majority of rotating micro pumps has been two-dimensional. This paper addresses issues of scaling in micro axial flow fans. The anticipated primary application will be in cooling compact electronic systems, but the results are applicable to a much wider range of pumping applications. Using novel fabrication techniques a series of geometrically similar three dimensional fans were fabricated, ranging in size from the macro to the micro scale. Experimental techniques are described which will be used for the characterisation of these fans. A scaling analysis is used to show how reduced fan scale causes increased local loss as fan dimensions are reduced to the micro scale. Numerical simulations of flow in the channels between the fan blades were performed to investigate the validity of the scaling theory, the results of which give confidence in the scaling analysis. The fundamental finding of this work is that a reduction in scale is accompanied by a reduction in efficiency and thus fan performance.