J. Phil Thien's Projects

@retired2

One other thing I believe was in this article was a description of the optimal ratio of dimensions (but I've been reading alot).  If the pipe diameter is x then bell rim diameter is 2X and optimal length of pipe is also X.  So if I plan an 8" wide pipe outlet (inlet to fan/vacuum) then the pipe should be 8" long.  I haven't found any research on the distance below the bell, to the baffle.  I know yours is about 3" or so but that seemed really low to me.  I'm going to try 8" above the bell and >1x below.  We will see. 


Maybe we should bite the bullet and do a computational analysis of the design.  Any current University Engineering students lurking?

.
Rob

So in my extensive readings while waiting for my motor, fan and other parts to arrive (which takes many days here in Canada during xmas) I've come across answers to both of the 'challenges', or at least more information.  Sadly I can't provide references, so google away.

1) humidity - not really an issue with room temperature air, and if you are concerned, commercial designs use a thin layer of mineral oil or 'silicon' oil (whatever that is) on the top of the water.
2) don't put the exhaust outlet IN the water, leave it a few inches ABOVE the water.  This is called a dust trap.  You can buy these for venting a dryer in the winter.  These do have a problem with humidity but this is due to the moisture in the dryer air not from the cool water surface.

I learned that in the early days of automobiles, the air filters were exactly this oil based dust trap design, even VW's into the 50's had them apparently.  The claim is they are more efficient than paper type filter material.  And they never clog.  And a pail of water is going to be cheaper than fancy spun polyester pleated HEPA filters.  And a water trap may be more effective trapping the smallest particles - exactly what we want.

As an aside, dust trap filters went away in cars because paper was cheaper, smaller, lighter, more rugged and didn't require so much vertical height to be effective.

Has anybody tried this?  Perhaps somebody that has already built could try this.  Even better if you have a Dylos to measure before and after.  And a way of measuring motor current to compare to high end filters.

Not asking too much am I? :)

Rob

http://www.profblairandassociates.com/pdfs/RET_Bellmouth_Sept.pdf

Contains a CFD analysis of Bell openings that applies to this thread.