Axial Fan Flowinator

thingiverse

I designed this device to boost the efficiency of axial part cooling fans. Axial fans excel at moving high volumes of air at low pressure. One problem with a ducted axial fan is the significant negative pressure vortex behind where the hub or motor is located. Filling that volume with a cone significantly smooths out airflow inside the duct. Another issue with axial fans is that efficiency drops more rapidly as back-pressure increases compared to radial fans. This occurs because air starts to spin around with the fan blades, rather than being pushed along the axis of the fan. To visualize this property, imagine blocking off both sides of the fan by laying something flat like card stock and turning it on. In this case, you have zero airflow, and what air is trapped between each blade simply spins around inside the fan housing with the blades. Adding some fins to the duct behind the fans helps reduce the amount that air swirls inside the duct. I tested out the first device in the pictures, and the airflow seems to have improved dramatically. Afterwards, I thought about increasing the size of the fins but haven't yet printed it. My anecdotal evidence is pretty meaningless. Lord Kelvin said it best: "When you can measure what you're speaking about and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is meager and unsatisfactory." So, I've looked and looked but haven't found a simple way to actually measure airflow. If anyone out there can do that and provide some comparative numbers, it would be greatly appreciated. I tore a small piece of paper and held it over and under the fan, with and without this device, and can definitely see a difference. I'd love to assign actual cfm numbers to it. I have included four versions. I have two different fans on my printer: a decent Sunon fan with an 18mm hub and some budget fans with 24mm hubs. For each hub size, I have one with small fins and one with large fins. I've tested the 24mm, short fin version.