Thread: Square and Hexagonal Cyclones?

Originally Posted by QC Inspector

I think the idea, if they do perform, might be easier for many people to make in their home shop/shed. 90º and 60º angled cuts on a table saw being a breeze using MDF or plywood, familiar materials. Lots of calculators exist to get the angles for the cones.

Well spotted Pete

And, yes, that construction method would be relatively easy for those with a background in woodworking. I made a number of the components of my ducting that way. In my case I was using octagonal (which wasn't tested by the experimenters) but the hexagonal design that they did test would be equally easy to construct...

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Something else to be considered is that someone making a kit of pre-cut materials would be able to ship them much cheaper than round cyclone parts or assemblies. The flat pack box being much more compact.

Pete

Originally Posted by QC Inspector

Something else to be considered is that someone making a kit of pre-cut materials would be able to ship them much cheaper than round cyclone parts or assemblies. The flat pack box being much more compact.

Another good point there, Pete.

It's the large volume, not the weight, of the cyclone bodies that is the killer with shipping them about.

An interesting area that could be played with but how about making a round cyclone in the fashion of wooden barrels which would be round without the angles. I rarely visit the forum these days as my interests have changed and a PM by Pete alerted me to this thread.

Chris I was looking at it from the perspective of being easy to make with few manageable parts. A 510mm radius round type (CV sized) made with 65mm wide staves would have 25 to assemble and that wouldn't count the work needed to make the inside fully round if you wanted to take it that far. The hexagonal just the 6 pieces and one could use body filler applied in the corners with a rounded trowel or can lid to "soften" the corners further.

I find it fascinating that there are cyclones made with flat panels that work and it got me wondering how close they perform to a Pentz cyclone. The one in the paper I linked was called a Hoffmann Cyclone that looks much like a Pentz with a longer cone. I figure the hexagonal can't be worse than a short cone and if made of common sheet materials woodworkers are familiar with would be affordable to those with less disposable cash.

Pete

Originally Posted by Chris Parks

An interesting area that could be played with but how about making a round cyclone in the fashion of wooden barrels which would be round without the angles.

Chris, et al

A staved cyclone would be a work of art, but I know which one I would prefer to build in terms of speed and cost... a hexagonal or octagonal one with a mix of ply and MDF would be the way I would go, especially if it could to be flat packed for transport.

Ply and MDF would also lend itself to some production efficiencies such as laser (or whatever) CNC cutting and distributed through IKEA...

The paper you referred to presented mathematical modelling for 3 hexagonal cyclones and a square design. The Hoffman round cyclone referred to is quite small: casing OD 200, INLET 100X40, OVERALL HEIGHT 800mm.
The Clearview design has a casing OD of 457 mm. Smaller cyclones apparently need more power to produce adequate flow.

The paper gives detailed flow diagrams, showing higher flow in and below the outlet pipe for the round type, while the hex one has lower flow in the outlet pipe, with lower tangential velocity.

Comparing pressure drop from inlet to outlet pipe, the round design has greater pressure drop and than the hex one.

The common blower characteristic of lower flow at higher pressure is consistent with these findings.

Separation efficiency is better for the round design, but the authors suggest that fine particles might be separated more efficiently by the hex model, while particles in the 2.5 - 5 um might be removed more effectively by the round model.

No detail is given of internal geometry, such as an air ramp, which would reduce turbulence.

The square design performed significantly worse than the 3 hexagonal ones.

The Pentz design (round) outer casing and cone are not too difficult to make in sheet metal, but the angled (down) inlet and internal air ramp are more troublesome.
Cyclones generally reduce air flow, as do blocked filters, but the Pentz design minimizes this disadvantage. To get the 1200 CFM we are told to aim for, a hexagonal cyclone would need to be at least as big as Pentz Clearview.

For people who would rather work in wood, I can see the appeal of the hexagonal design, and this paper suggests that its performance might be ok.
The proportions of a hex cyclone might be best copied from the Pentz design - diameter and cone length particularly, as the Hoffman shape is tall/narrow, and might not fit under the ceiling of small workshops.

Rob

We don't tend to think out of the box but it has just occurred to me that a CNC could cut pieces to build the body and nothing has to be folded and the accuracy of the cut parts would be very good. Do it in plywood or even in MDF and epoxy the inner surface to prevent surface erosion and there is no reason to think it would not have a long service life. Build the cone and the circular part of the body separately and fibreglass the joint between them to form the body.

Originally Posted by robgran

The paper you referred to presented mathematical modelling for 3 hexagonal cyclones and a square design. The Hoffman round cyclone referred to is quite small: casing OD 200, INLET 100X40, OVERALL HEIGHT 800mm.
The Clearview design has a casing OD of 457 mm. Smaller cyclones apparently need more power to produce adequate flow.

The paper gives detailed flow diagrams, showing higher flow in and below the outlet pipe for the round type, while the hex one has lower flow in the outlet pipe, with lower tangential velocity.

Comparing pressure drop from inlet to outlet pipe, the round design has greater pressure drop and than the hex one.

The common blower characteristic of lower flow at higher pressure is consistent with these findings.

Separation efficiency is better for the round design, but the authors suggest that fine particles might be separated more efficiently by the hex model, while particles in the 2.5 - 5 um might be removed more effectively by the round model.

No detail is given of internal geometry, such as an air ramp.

The Pentz design (round) outer casing and cone are not too difficult to make in sheet metal, but the angled (down) inlet and internal air ramp are more troublesome.

For people who would rather work in wood, I can see the appeal of the hexagonal design, and this paper suggests that its performance might be ok.

Rob

I understand the testing of the Hoffman was with a small lab sized unit, the results of which may not scale up to ones we would use. I can't remember whether it was this paper or another I looked at but they were testing the lab units at half or less than the velocities our shop sized cyclones. I don't know how that would translate to a bigger unit we might want.

I had assumed they weren't playing with inlets although did find another paper where the duct before the inlet was radiused with square cyclones improving the flow. No inlet ramp that I recall. Performance assessment of a square cyclone influenced by inlet section modifications | Journal of the Brazilian Society of Mechanical Sciences and Engineering.

I certainly feel a hexagonal cyclone is worth more investigation and it can't be worse than the overpriced short cyclones everyone is selling these days.

There are other papers on the net, easily found by searching square or hexagonal cyclone separators etc. Unfortunately some only available to institutions of higher learning which I can't get my grubby fingers on to. Science Direct seems to be blocking me now as all I see is a blank screen.

Pete

Originally Posted by Chris Parks

We don't tend to think out of the box but it has just occurred to me that a CNC could cut pieces to build the body and nothing has to be folded and the accuracy of the cut parts would be very good. Do it in plywood or even in MDF and epoxy the inner surface to prevent surface erosion and there is no reason to think it would not have a long service life. Build the cone and the circular part of the body separately and fibreglass the joint between them to form the body.

I was thinking if one used kitchen countertops, smooth surface not pebbled, the laminate facing inside would likely outlive most of us and we wouldn't have to use stinky, sticky resins unless you like that sort of stuff. Or one could buy the sheet goods with high pressure laminate or melamine coating already on it. The outside would look nicer than the chipboard of a countertop.

I should have said I thought using a CNC in post #3 to make the flat pack kits would be something a person could market to others. For someone that already owned a CNC, cutting to order or making small batches could be a nice sideline that wouldn't involve a huge investment over and above what they already had.

Pete

Originally Posted by Chris Parks

Do it in plywood or even in MDF and epoxy the inner surface to prevent surface erosion and there is no reason to think it would not have a long service life.

I built my ducting with a mix of ply and MDF with a coating of waterproof PVA on the inside surfaces and side seams. It has withstood any impact and abrasion I have thrown its way over the last the last 15yrs.

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The flanges were just bolted together with a foam gasket at the join. I did make the cyclone itself from sheet metal (seen in last photo), but knowing now about the performance of the hexagonal design I may gone that way. Octagonal as seen in first photo above may even give a better performance that hexagonal.

As already pointed out, the flat pack option for shipping is the big upside at the cost of some performance.

IMG_20230920_152809.jpg
This is the air ramp or baffle which reduces turbulence as the air+dust stream enters the cyclone, and that maintains the best possible air flow. The cylindrical outlet was removed for the pic.
The baffle is attached to the outer casing and the join sealed with polyurethane. The inside edge of the baffle does not need to be sealed as air velocity is low nearer to the centre.
The inlet is angled down for the same reason - better air flow due to less turbulence.

For a hexagonal cyclone, a groove could be routed into each stave before assembly, to hold the metal ramp in place. This would involve some geometry to get the grooves to line up at the desired angle.

A basic point to be aware of is that the direction of air rotation in the cyclone must be the same as in the blower. So the blower rotation dictates which side of the cyclone the inlet is inserted.

The research paper covering hex cyclones was published in 2015, and the Hoffman cyclone was first sold around 60 years ago. The comparison might not relate to more recent designs. more recent research is presented in this paper

Processes | Free Full-Text | CFD Investigation on the Performance of Cyclone Separators with Divergent or Convergent Insertion Pipes

Thanks robgran

I had given a little thought to the ramp. I figured that with all the hex pieces laid side by side one could take a ruler and draw a line from the start of the ramp to the end across all six pieces. That would make for a reasonable ramp with the understanding that rather than a ramp being single smooth piece it would be made of 6 small flat pieces joined together. Some sanding and filling would make it better. You would have the choice of cutting a groove or cutting the tops right off to resemble the Dust deputy type ramp instead of a flat top. Separate impeller verses one integrated into the top of the cyclone like Bill's and imitators are.

I also figured one could use Bill's design spreadsheet to get the dimensions to adapt for a hexagonal which has decent performance in a shorter cyclone, important in home shops. If one had access to a proper Pentz cyclone a side by side comparison would be possible to see how the two compare.

Thanks for the link. Admittedly mostly way beyond my understanding. Still very interesting and the Recommended Articles on the top left of the first page has already sent me to some other articles.

Pete

Originally Posted by robgran

IMG_20230920_152809.jpg

This is the air ramp or baffle which reduces turbulence as the air+dust stream enters the cyclone, and that maintains the best possible air flow. The cylindrical outlet was removed for the pic.
The baffle is attached to the outer casing and the join sealed with polyurethane.

And, here is another pic of the helical ramp in one of the Pentz design cyclones I built and also the inlet tube that fits inside the ramp...

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Those were made from sheetmetal and the ramps were soft soldered to the body of the cyclones. Pop rivets and caulk would have done the job equally as well with those

With a stave construction I see no reason why a smooth sheetmetal or plywood or plastic sheet ramp couldn't be slotted into grooves running down the inside of a hex/oct cyclone. Getting the exact position and angles of the slot would be more readily done with CNC while cutting the panels, but simply running a piece of string around the outside of the cyclone and drilling small 'pilot' holes through to the required inside position would also work. However, the hex panels would need to be thick enough in the ramp area so the ramp slot didn't break through. Less so with octagonal staves, but they would also need to be thicker than otherwise required.

I like Pete's suggestion better of just cutting off the top of the cyclone at ramp height, like done on some dust deputy models, and just screwing the ramp to the helical topped cyclone body. The downside of doing this is that it would make attaching the impeller unit to the top of the cyclone more of a challenge and less elegant.

The downside of locating the impeller unit next to the cyclone is that it takes up valuable floor space in small footprint workshops. However, for various reasons, I have never mounted the impeller assembly on the top of the cyclones I've built. If you have the floor space there are some advantages of doing it that way, not least of which is locating the noisy impeller unit elsewhere, including outside and venting the exhaust unfiltered there.

Originally Posted by robgran

A basic point to be aware of is that the direction of air rotation in the cyclone must be the same as in the blower. So the blower rotation dictates which side of the cyclone the inlet is inserted.

Also, keeping in mind that the direction of air rotation reverses inside the cyclone...

Reverse air flow in cyclone lg.jpg


Source: Just a moment...

At least one of the Clearview cyclones has had this the wrong way around for optimum performance.