Investigation of increased performance of close series stacked tube axial fans due to inclusion of diffuser element

The increased performance of close series stacked tube axial fans due to the introduction of a diffuser element between the primary and secondary fan is investigated in this paper. Experimental results showed that there was a 15% increase on average in the performance of two stacked Delta AFB0412VHN 40 mm fans across their operating range when a diffuser element was introduced between the two fans. It was also observed that the performance approximately increased by an additional 4% when the space between the diffuser and primary fan was increased from 0.3Dh to 0.5Dh. Numerical simulation of the flow between the primary and secondary fans was used to probe the cause of the increased performance. The area-averaged secondary kinetic energy (SKE) was used in the presented study as an indicator of the swirl decay. The numerical results showed that the introduction of a diffuser element reduced the SKE/SKEinlet ratio dramatically. It was also found that the SKE/SKEinlet ratio was further decreased when the distance between the diffuser and primary fan was increased to 0.5Dh, which is consistent with the experimental observation.