Pellvac virvelvind (whirlwind)

[phil (admin)]

Well, I've explained why bigger is better for baffles, while smaller is better for slots.

You mentioned following the VV design and adding a baffle below it (I assume some inches).  The baffle, in that case, would act like a false bottom, slowing the passage of debris to below the baffle.  Any debris that hangs above the baffle (above the fill line of the unit) will get scrubbed from the unit more than if you just allowed it to fall to the bottom of the drum.

Give it a shot, though.  Just don't blame the baffle when it makes things worse, as you won't be using it as intended.

It isn't too difficult to "mentally model" this stuff, BTW.

Imagine, for example, someone blowing a cigarette smoke cloud in a room.  Now, imagine taking a straw and blowing into the cloud of cigarette smoke.

Do you blow a hole through the cloud equal to the diameter of the straw?  No.  Instead, your breath coming out of the straw expands in every direction and blows a sort of clean-air bubble in the cloud.  And as you blow a clean bubble into the cloud, the clean air you're blowing also siphons smoke from behind you and starts to blow that along with the clean air bubble, and after a breath or two, you're just mixing the smoke with the clean air.

Likewise, as soon as air enters the separator and is no longer constrained by the inlet, it fans out in every direction, looking for the path of least resistance.  As soon as the airstream finds a slot, it wants to move through that slot (where the resistance is lower) and mix with whatever is there.

So we need to focus it, make the air do what we want it to do.  If the slot is too soon, the fast moving air will siphon debris, just like our straw did with the smoke.  So we want to give the air a chance to expand a bit, and slow down, before showing it the slot.  Once the airstream has spread-out and slowed-down, we have a slot, and we allow the slowing air with debris to expand into the slot.  As it comes around full circle, we want to take the slot (and any debris down below) away and direct the now clean air to the outlet tube.

Just think through that when you're doing your experiments.  There may be a better way to do it, but I sure haven't found it.

Good luck and post-back some pictures when you come up with something.

[alan m]

thats a very good analogy phil
it explains the solid part of the slt very well . i never thought about it like that.

[jalar]

I do understand that your construction is not a cyclone. Your construction allows the air to slow down and expand a bit, so that the debris has time to sink into the slot. This is a sound idea. But as you say, with the inlet close to the baffle, there will inevitably be some turbulence there. So the baffle needs a solid part that hinders the turbulence from influencing the air mass (and debris) below the aperture to re-enter the air flow above the baffle.

But the Virvelvind is a (short) cyclone, that tries to keep airspeed as high as possible, pressing the dust out to the outer wall. This is why a stepped construction might work without a big baffle. The inlet is, relatively speaking, far from the step (and vortex breaker). The inventor talks about airspeeds of 180 km/h (50 m/s or 110 mph) in the cyclone. I don't know about that, but the idea behind a cyclone is just that: high airspeed.

The lower part of the cyclone ("above the fill line") allows the air to slow down and expand a bit. Therefore, I was thinking that your baffle might help. But you seem to be saying no.

Anyhow, since people seem to be happy with the performance, I'll risk it and buy one. Given some time I'll experiment with it too.

[phil (admin)]

I do understand that your construction is not a cyclone.

They're both technically centrifugal separators, they could be referred to as cyclonic separators.  But neither the VV or my design is really a "cyclone," I suppose, as that term is used in industry and typically refers to a more conventional unit featuring a cone.

[jalar]

Agreed.

[phil (admin)]

I do understand that your construction is not a cyclone. Your construction allows the air to slow down and expand a bit, so that the debris has time to sink into the slot. This is a sound idea. But as you say, with the inlet close to the baffle, there will inevitably be some turbulence there. So the baffle needs a solid part that hinders the turbulence from influencing the air mass (and debris) below the aperture to re-enter the air flow above the baffle.

The turbulence isn't there because of the baffle, the baffle is there because of the turbulence.  The turbulence exists in the VV design, too (incoming air running into an already spinning air mass causes turbulence).  The designer of the VV just didn't do enough to address it (IMHO).

Spinning air masses undulate (they move in waves).  Cyclonic separators are full of turbulence.  They need to tame the turbulence to adequately separate.

But the Virvelvind is a (short) cyclone, that tries to keep airspeed as high as possible, pressing the dust out to the outer wall. This is why a stepped construction might work without a big baffle. The inlet is, relatively speaking, far from the step (and vortex breaker). The inventor talks about airspeeds of 180 km/h (50 m/s or 110 mph) in the cyclone. I don't know about that, but the idea behind a cyclone is just that: high airspeed.

"Short cyclone" is merely a label that could just as easily be applied to my design.  Calling the VV a "short cyclone" does not make it unique in any way.

The lower part of the cyclone ("above the fill line") allows the air to slow down and expand a bit. Therefore, I was thinking that your baffle might help. But you seem to be saying no.

You could always try it.

Anyhow, since people seem to be happy with the performance, I'll risk it and buy one. Given some time I'll experiment with it too.

Sounds good.

Do many people use them for woodworking?  I wonder because I haven't come across it before.

[jalar]

The turbulence isn't there because of the baffle, the baffle is there because of the turbulence.

I agree with you on this, perhaps I was unclear in the previous comment.

The turbulence exists in the VV design, too (incoming air running into an already spinning air mass causes turbulence).  The designer of the VV just didn't do enough to address it (IMHO).

There certainly is turbulence there too, but I think that he has put some thought into this. He went about solving this differently (IMHO).

"Short cyclone" is merely a label that could just as easily be applied to my design.  Calling the VV a "short cyclone" does not make it unique in any way.

True. I do suspect that the airspeed is higher in the Virvelvind, though, but see below.

Do many people use them for woodworking?  I wonder because I haven't come across it before.

No, and I think your design might be more suitable for woodworking, with large(ish) shavings and sawdust. There is a sweet spot size like you said, and that is porbably larger in your separator. Many here use the Virvelvind to protect their vacuum cleaner when they clean out ash in their wood-pellet burner. That is why I'm so focused on small-sized dust. The down side is probably a larger pressure drop (less air flow).

[alan m]

i take it jalar that you are swedish or in that area.
im in ireland

where can you buy this
i dont see any way on the site . i could contact them

how much is it
i could do with a seperater for ashs

[phil (admin)]

I found catalog outfits in the US that sell them, do services like google/bing shopping work for you guys, maybe you can find a catalog or mail order house?

[jalar]

Yes, I'm in Sweden. The retailers are too far from me, I can tell from the retailer map on the swedish pages. :( For me it's probably simplest to call the manufacturer directly, but email would be an option I guess. I wonder what they charge for the transport...

[alan m]

i was looking for a retailer so i could see how much they wanted for it and how much to ship
it would probably be too expencive to buy and better off building  one

[jalar]

The ash cyclone with bucket and heat resistant hose is SEK 956. Not cheap.

[alan m]

that seams a little high.
thats about 110 euro. plus shipping etc

aldi are selling their bucket with a moter set up. for 40 euro
it has a fire rated hose and metal bucket.
my neighbour has a broken one . i might liberate it and build my own version and see what hapens

[jalar]

What's a "moter"?

[alan m]

sorry motor