Mini Cyclone

[silentC]

Here is my stab at a mini cyclone. It's made from two chlorine buckets, a funnel, a length of 40mm pipe and a 45% angle .

It works pretty well. I had one drum full of sawdust and I moved it to an empty one, with 99.9% of the dust ending up in the drum and not in the vacuum cleaner. However a small quantity of the very finest dust does end up in the bag and would clog it eventually. Considering that this was about 10kg of sawdust, I guess that's OK for what it is.

Does the length of the funnel have a dramatic affect on this? I've read that some people are able to do this with no dust at all in the vacuum bag. I might have to try it with a longer cone and see if that helps.

[Sturdee]

I don't think it is your funnel that is the problem but your outlet pipe.

The outlet pipe must protrude into the bucket beyond the inlet pipe otherwise some of the dust is sucked out immediately instead of spinning in a cyclonic motion and dropping into your container.

Have a look at the pictures I posted to give an idea of the lenght of the outlet pipe and how far it protrudes into the bucket.

Good luck,


Peter

[silentC]

Peter,

I had a look at your posting before I had a go at this. I got the idea from yours (forgot to say thanks - so thanks :)).

I tried varying how far the outlet protudes into the bucket but it didn't seem to make any difference. I understand what you are suggesting but I guess there is also a point where the proximity of the outlet will affect the cyclonic action. By removing the inlet, I could look inside and see what was going on. I found that I got a more evident whirlpool happening when the outlet was closer to the top.

I'll have another play with it tonight and see if I can't improve it.

Thanks,
Darren

[Sturdee]

Darren,


Ideally the cone ( funnel in this case ) is 1.6 times the lenght of the bucket but these ideal conditions are not possible with a mini system.

In my case the bucket is quite deep compared to yours, maybe you should use a deeper bucket and longer outlet pipe whilst keeping the inlet as high as possible and a longer cone will help.

It is possible to get all the dust into the container as I've used mine a lot since making it ( about 35 litres of sawdust) and to date the vacuum bag is still spotless.

Regards,

Peter

[silentC]

Well, after spending several fruitless hours tonight, I've decided that I've got the thing working as good as it's going to. I tried a taller bucket, longer outlet pipe, 90 degree inlet pipe (instead of 45 deg.) all with no real improvement. The best setup seems to be to have the inlet angled down at about 10 deg. from horizontal and to have the outlet more or less adjacent to it. Any lower and it starts picking up shavings.

I cut a window in the top of the bucket and put a piece of clear plastic over it so I could see what's going on. There's a very strong cyclone motion happening and you can see the dust being dragged in a spiral down the side of the bucket and into the funnel. When the dust is particularly fine, there's a bit of a cloud of it that sits in the top of the bucket and I think that this is where my problem is originating. One possibility is that my bucket has a keg shape, being fatter in the middle and this could be affecting the aerodynamics.

Anyway, it's a reasonably successful experiment but I'm now going to go visit my brother in law, who has a sheetmetal shop, and see what we can cook up.

[barnsey]

Hi SilentC,

For what it's worth I would try and get your inlet pipe to enter at the top as close to tangentialy to the inside wall of the container. This will give you better swirl around the walls of the container. At the moment you are getting to much flow interference having a bend in the inlet. There's a quick/rough graphic below to explain

I haven't made one yet but am reasonably familiar with the theory as detailed in Bill Pentz's site.
Cyclone Site (http://cnets.net/~eclectic/woodworking/cyclone/Index.html)

Make sure you look at this before you talk to your sheetie mate and I think you will have a better result.

My 2p worth anyway

Jamie

[silentC]

Barnsey,

Thanks for the tip, yes I see what you mean. I'll give it a go without the bend and see if it improves.

I've also got a copy of Sturdee's Triton bucket conversion plan (thanks Peter) and I'm going to give that a go. It just so happens that the bottom of my Triton bucket has a hole in it from where I dropped something on it, so I've got no qualms about hacking it up.

My bro-in-law is building a dust extraction setup for a local joinery (standard bag type) and he's managed to get me an old bag type extractor that they're not using anymore for $50, so I'm hoping to build a full scale jobbie using the blower out of that.

Cheers,
Darren

[harty]

Gents,
I've been in the mining game for years and we use cyclones to split slurry into a coarse and a fine cut. The coarse goes to the underflow and the fines to the overflow. I've been reading all the posts you've been writing on cyclones and thought I'd throw my bit in. Bear in mind I've never seen a sawdust cyclone so I might be talking crap here.

Sturdee is correct with the outlet comment. It's called a vortex-finder and should go into the cyclone body to pick up "clean" air.

Theoretically, the longer the cone, the finer the cut.

The other big variable that you could play around with is the spigot size. That is the size of the outlet hole at the bottom of the cone. The larger the spigot, the more coarse should go down there, and the finer the overflow should be. This all depends on how much vaccuum is being created.

Like I said, I deal with pumps pumping 5000m3/h of slurry into clusters of 10-12 cyclones producing 80kPa pressure, so maybe I'm heading in the wrong direction.

Anyway it might give you something to play with.

Regards
Harty

[Fantapantz]

Got me interested.......found this, might be of help.

Longer funnel, inlet more tangential to the side, outlet just past the straight section which would have to be longer to allow a more steady transition into the cone which has sides at about 20 degrees to the vertical..... I would say the diameter of the outlet would be important as well because a larger diameter would result in a lower pressure suction, this may reduce the size of the particles that are exhausted to your secondary filter (vacuum cleaner).

[soundman]

I am running a similar looking device, actually part of a built in vac system.

mine has a filter hanging into the chamber. A bit weird.


I have been diong some research int the subject (as have others here)

There are issues with air velocity. Entry velocity need to be kept high to sustain the cyclone action. however the exit velocity needs to be low to allow the finer dust to drop out.

Many cyclones I have seen have much larger exit pipes than inlet pipes.

You will also experience substantial suction loss with your current arrangement. I recon due to turbulent losses in the vortex.

the air is soo busy going round it don't want to come out!!!

There is some very serious stuff arround with all the math for designing cyclones.

cheers.