I just got a fan for the den. It’s a cheap Honeywell-brand vertical fan. It works correctly, but I’ve been struggling to understand how it works. I don’t want to open the housing, so what I can gather from looking in through the grilles is that it looks something like this in cross-section :
Given that the rotating part (in blue) has rotational symmetry, I don’t see why the air is being drawn in from the intake grille and pushed out the output grille. I’ve drawn the housing as a featureless gray circle but I don’t know its shape on the inside; is that the secret ingredient?
I have a couple of those vertical fans. They work by FM.
Flippin’ magic.
Interesting article from a solid website.
Does the fan also blow out the back vent? From what I can gather the air is drawn into bottom and/or top area of the fan, then out the vents. A drum fan depending on the rotation direction draws air into the center and out the sides or the opposite. The tower fans seem to hide this in the case design. But in a furnace fan it is more obvious to see the way the air flows.
Maybe on the tower fan there is a difference in the fan blades angle at the top and or bottom sections. This may draw air in at those spots, then out over a longer center area.
Maybe.
The trick is that the fan barrel is not centred in the housing. These are known as tangential fans or cross flow fans.The other key thing is that air flows though the body of the barrel. On the inlet side the vanes steer the moving air into a near vortex that is situated near the vanes on the exit side, which essentially scoop the flow out into the outlet side.
I found this CFD blog with a few pics that might help visualise what is going on.
Thanks, @Francis_Vaughan , I think this is the correct explanation.
The noise varies when I walk around it, it gives the impression that the motor speed changes. It’s as if there were a mechanism in there ensuring that the vortex has the correct shape, but I find that hard to believe in a cheap device like this.
I’ve held a kleenex flat on the input grille, it gets sucked in mostly, although one edge of the tissue flaps a little bit, especially when the motor speed changes.
This is what I’m used to as well, I’ve seen kitchen or bathroom evacuation fans with that design. But no, this one has no openings at the top or the bottom, it’s all happening through the back and front grilles.
To be clear: this is not a Dyson-type air mover, with the large hole in the middle and the surprisingly high price tag. It’s an ordinary vertical fan (exact model).
The pictures on the site hint that the output grille is not symmetrical; mine has black grilles so it’s less apparent. On second look, the back grille is also off center. Also, yes, I can see through the drum when it’s spinning, so it’s not a solid cylinder. So, mad drawing skillz take 2:
