Curved Inlet

[Mike F]

Hi,

After reading through a large number of threads, I feel time is right to start making one of these wonderful contraptions. In my introduction, made just a few hours ago, I mentioned that I am into composites and it is these skills that I wish to use in my construction. Unfortunately, probably due to an age thing, I cannot remember which of the many threads I have read that mentioned the possibility of a curved inlet, the idea of which was to force the particles against the outside of the inlet before entering the separator. One of the problems mentioned was the construction of such an item. Using composite techniques, this is not a problem and I have drawn up such an inlet as shown in the attached.

My question would be; does anyone know or can guess at a reasonable radius for such a curved inlet? Incidentally, I will also be making a composite bell mouth for the outlet.

A word of warning - I am not the speediest of workers so don't expect too much too soon :)

Mike

[BernardNaish]

Sounds as though you probably already know how to generate an elliptical former for your bell mouth but if not see here:

http://www.jpthien.com/smf/index.php?topic=1098.0

Please let us know how you get on and measure if you can. GOOD LUCK.

[retired2]

Mike, you might be referring to what is called a scrolled inlet.  There have been a couple of discussions about this, but I don't know if "search" can find them. 

In any case, a scroll design is not just a curved inlet pipe, as I recall the design effects the shape of the separator chamber, it is no longer a true circle - it becomes eccentric.  Not sure if anyone has ever really built one because it complicates the construction task.  And if anyone has built one, I don't ever recall any test data to see if it improves performance.

[BernardNaish]

These are all the links I could find to scroll inlets.

http://www.jpthien.com/smf/index.php?topic=492.msg2625#msg2625
http://www.jpthien.com/smf/index.php?topic=1085.msg5880#msg5880
http://www.jpthien.com/smf/index.php?topic=492.msg2920#msg2920

Bill Penz also talks about a curved inlet pipe but you will have to plough through his rather complex site here:

http://billpentz.com/woodworking/Cyclone/Index.cfm

[Mike F]

Hi guys,

Thanks for responding.

Retired; I am pretty sure it was in one of your threads or replies that the curved entry was mentioned but I cannot find the reference. It was discussing how to ensure the particles were as close to the wall as possible on entry and it was postulated that if the flow were directed to the outside of the entry, by forcing the air to travel in an arc, this may help. I know what you mean about the scrolled inlet and this was not quite the same thing but was trying to achieve something similar.

Bernard; Yes, the elliptical bell mouth is very easy to achieve using composites but the procedure is not everybody's cup of tea. I would use male formers/plugs for making the laminates for both the bell mouth and the entry as this will give me a very smooth inner surface. I remember trying to plough through Bill Pentz' site some time ago but I will re-visit for a refresher.

It's past midnight here so that's it for today. I'll do some more CAD work tomorrow and maybe start cutting plugs/patterns soon. If no one can answer the question of radius, I will just have to suck it and see. The problem with the composite solution is that there is a little more work to do for each iteration. The beauty is that once there, you can produce as many identical pieces as you or others wish.

Cheers,

Mike

[retired2]

Maybe this is the discussion you were remembering:

http://www.jpthien.com/smf/index.php?topic=536.msg2813#msg2813

[Schreck]

I believe Phil raised the issue of a curved entry and the benefits it would offer in encouraging particles to move towards the side before entering the central ring.  Makes sense to me.  Seems you would get some of the benefit of a scroll inlet without the complicated construction.  This is also related to the issue of an off-center outlet that both Retired2 and Phil have mentioned.  In the CFD thread, replies #16 and 17 show why an off-center outlet should improve separation - you are moving the outlet away from the region where particle-laden air is entering the ring and has yet to be forced to the side.  Perhaps a curved inlet transition from round to rectangular, combined with an off-center outlet, would be a good combination. 

Regarding the OP question of dimensions, I'm not sure about the the radius of the curve, but I would think the piece needs to mate with a 20" diameter top hat.  The 32 gallon Brute has an inner diameter of 20" and is commonly used. 

The image below shows a curved inlet on the left and a typical straight inlet on the right.   Might as well curve it!

[galerdude]

Mike, I would imagine, if you are thinking of retailing your round to rectangle adapter, that an outside radius would need to be similar to a 32 gallon garbage can. That seems to be what the majority of the forum top hat users use. Myself using an even smaller collection container would be interested in an adapter as you have proposed. Have any idea at this time what one might be able to purchase one for? I have some other ideas for a new Thien top hat separator and this would certainly make it easier to incorporate those ideas.
Thanks for posting!

[AndyF]

I can confirm that a curved inlet does force the particles to the outside of the separator.

I haven't tired to photograph it, but the intersection of the particle flows looks like a "merging traffic" sign and no apparent turbulence where the flows meet.


Andy

[Mike F]

Retired; you are correct, that was the thread I read about the idea and, Schreck, it was Phil who posed the question.

My application would be fitted to a standard, British dustbin of 460mm (18inch), internal diameter so the dimensions will not be too far away from your standard 20inch drum. I will re-draw the inlet and make sure the curve meets the wall tangentially while giving enough clearance at the circular end. I will also try and model the whole thing and post the result here for criticism.

Galerdude; I have no intention of retailing the inlets or bell mouths but am prepared to make a few as long as my costs are covered and if they are wanted/needed/prove to make a difference. However, I will not be inclined to make lots of different models for different diameters of drum or inlet. We will have to see how it goes. If I document my progress here then other folk with some composite know how could easily pick up the cudgel. Early days yet but I do need to get this thing made as I have some huge moulds to make that will create oodles of dust and chips and I don't want to start without this system in place. I will try and take some shots of my current DC to show how inefficient it is at trapping the sort of debris I am creating.

Thanks Andy for confirming this is worth continuing with. I don't recall seeing a thread where anybody has tried this. Did you document your build? If so could you give me a link to it?

Cheers,

Mike

[BernardNaish]

Hi fellow Brit.  You may have already considerd this but it has just occured to me that you might want to wait a short while to see if this produces some usefull results:

http://www.jpthien.com/smf/index.php?topic=1105.0

We have not had a post on this link for a while which is a pity as it looked as though the model work could be usefull if it got close to retired2's data:

By the way what make of dustbin are you going to use? Presumably you also found that the usual Brute bin costs an arm a leg here!

Regards.

[AndyF]

Build thread:

http://www.jpthien.com/smf/index.php?topic=1085.msg5880#msg5880

I too would like to see how these variations affected the computer model,


Andy

[Mike F]

Hi Bernard,

I have been watching that particular thread with a lot of interest but it strikes me that there are just too many wanted variables for Supertrucker to model, despite trying to tie him down to a specific model. If we now throw in a few different inlet variations, he may blow the proverbial gasket :)

I have a bin that is very similar to the American Brute and it's been in my garden for many many years and I have no idea how it got there. It has a bit of garden rubbish in it at the moment but nothing that cannot be cleaned up.

Attached are some more CAD presentations, for criticism, drawn up in lieu of the previous replies. One of them shows the projected circular, internal diameter of the bin and the proposed entry trajectory. It now has a cuff on the inlet side to accept 100mm duct.

Andy; thanks for the link.

Cheers,

Mike

[BernardNaish]

Hi Mike, I had not thought to make the modelling more complex. I believe that ithat nteresting work should stick to modeling retired2's build until it gives results similar to his. THEN we can try out lots of lovely ideas. I too hope we have not put superptrucker in a bad position. I think we all got so excited with the possibilities that we may have overloaded him.

[AndyF]

Mike,

That last picture is very similar to mine.  Except your round-to-rectangle transition is more graceful.


BernardNaish: I definitely agree to get the current CFD model to where we understand it before we start making changes like eccentric shapes, chamber heights, and inlet angles.

I hope we didn't run off superptrucker........

Andy