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Axial fan / compressor for fluid bed?
Hi all, I'm looking into building a very compact fluid bed roaster and was curious if anyone has tried high static pressure axial fans - or if anyone has built a multi-stage axial compressor?

I think a general rule of thumb is that you need very roughly '1 in H2O' per inch of bean bed depth - though I could use help clarifying / verifying this rule of thumb.

So I think... very roughly - about 4 inches of beans in a bakelite 3.5" tube is 1 LB. (rounded up a bit for the funnel to the perf plate). To loft 1 lb of beans I guess we can assume that we need more than 4 in H20 static pressure rating.

There are several axial fans that meet this requirement out of the box - but specifically, I am looking at this:

I'm curious if the CFM rating would be too low to fluidize beans appropriately. Given near infinite static pressure rating, what would be the minimum CFM for good agitation?

Air Flow: 32.9 CFM (0.932m³/min)
Static Pressure: 6.830 in H2O (1701.2 Pa)

I think there are a few benefits of using an (this) axial compressor:

First, it keeps all motion in one direction - minimizing friction and turbulence losses typically seen in radial compressors.
Second, it is a bit quieter than a typical vacuum motor (70db vs 75-90db).
Third, it is SUPER small... This thing is 40mmx40mmx56mm.
Fourth, it is more energy efficient (at just 30W)
Fifth, it is powered with DC, which makes motor control a bit easier (and wiring a bit safer).
Sixth, since this fan is pulled from servers - it is regularly available on ebay for $10-20.
Seventh, the maximum operating temperature is 158F (70C), making it great for recirculation.

Edited by JackH on 10/14/2017 10:33 AM
Check out this post for a video of a build using an axial fan with a straight walled roast chamber.


To allow you to use a cone bottom design, I think you would have to stack a couple of axials in series to get enough static pressure. From all my reading, for a cone bottom RC, you will need at least 8-10" pressure but also depends on perf plate diameter, perf layout and bed depth.

1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
Hi Rob,
I can definitely see the benefits. I think you'll need the performance curve of the blower to decide on how big or how many.
Once you've achieved the pressure you need, how much cfm will be left?
Great idea!
Have fun,
Thanks for the link and encouragement. My plan right now is to feed the 40mm with an 80mm high pressure fan and to further increase pressure by adding a stator stage after each. So, the stack (bottom to top) would be 80mm fan + 80 mm stator to 40mm adapter + 40mm high pressure fan + stator on exit. I'll post results in this thread, ordered a fan from China so it will be a couple weeks.
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