Abstract: Axial microfan is widely used as cooling equipment for electronic devices such as PCs. Currently, the PC size becomes smaller and smaller while their operating speed becomes faster and faster, which calls for better cooling performance of axial microfan. As an important and effective design approach, the similitude design has been widely used in the design of large and medium fans, but not yet in the design of axial microfan. One main reason is that the flow inside the microfan is located in non self-similitude area for Reynolds number, which results in the poor performance of the microfan designed by those similitude criterions that are surely effective for the design of large and medium fans, where the flow is located in self-similitude area for Reynolds number. By using the similitude principle for aerodynamics, the aerodynamic similitude conditions for axial microfan are proposed. Compared to large and medium fans in self-similitude area, a new criterion called ‘chord Reynolds number’ is proposed and is numerically validated with the discussions on its applicability and limitation. Results indicate that ‘chord Reynolds number’ can well realize the aerodynamic similitude for the axial microfan but it requires that the revolution speed of the impeller should be in direct proportion to the square of the reduced scale, so the reduced scale of model impeller shall not be too large, otherwise new non similitude factors may occur again due to too high revolution speed.

Key words: Aerodynamic performance, Axial microfan, Similitude criterion