spacers

[Don]

Phil,
Why do simply use wood dowels as spacers?

[phil (admin)]

That would work fine.  Someone else suggested all-thread or carraige bolts through thinner PVC pipe.  Whatever gets the job done w/o being too much wider would be just fine.

[eliphant]

I notice that your spacers are round and you say that you are looking for non-turbulent flow. Have you considered some sort of air foil shape to your spacers? I don?t remember the exact number, but you can be 5 times bigger on the air foil before you have the resistance of the round shape which should help create smoother air flow. You will have to calculate the reynolds number and find the right shape, but it would be interesting to see the results.  I also notice that you are using a corrugated metal can, I believe using a smooth plastic can could help create less turbulence. What is the pressure and velocity drop in the system with the can installed? 

[phil (admin)]

I notice that your spacers are round and you say that you are looking for non-turbulent flow. Have you considered some sort of air foil shape to your spacers? I don?t remember the exact number, but you can be 5 times bigger on the air foil before you have the resistance of the round shape which should help create smoother air flow. You will have to calculate the reynolds number and find the right shape, but it would be interesting to see the results.  I also notice that you are using a corrugated metal can, I believe using a smooth plastic can could help create less turbulence. What is the pressure and velocity drop in the system with the can installed? 

I'm satisfied with the round spacers and standard steel can.  I'm trying to apply the 90-10 rule, hoping for 90% of the performance of a cyclone with 10% of the effort (and cost).  But you're right, having a smooth-walled can is important.  Thankfully, the walls at the top of the can (where it matters most) are fairly smooth.  The stamped, or corrugated sections start further down and that is okay.

In terms of pressure/velocity drop, I guess the answer is, it depends.  I've seen anywhere from a low of a 22% hit to CFM (which is incredible) to a high of approx. 40%, and a lot depends on the blower being used.  As one might expect, blower units w/ more static lift fair better.

Right now I'm experimenting w/ a mod that moves a blower directly to the top of the unit.  So instead of being connected via a hose to a center outlet, the blower IS the center outlet and is bolted right to the top (much like a typical two-stage DC).  This has required moving the outlet off-center by approx. 2" to accommodate the width of the blower assembly.  So far I can say that the #'s kinda surprise me.  I think the unit worked better with the hose connection instead of having it directly coupled.  This, of course, is counter-intuitive.  And there are lots of variables, too (like how well the new top seals, etc.).

Suffice it to say, I have more research to do.