J. Phil Thien's Projects

Here in UK it is possible to buy second hand steel bins that have been used to ship fruit juices. Sometimes they have small holes in the bottom to allow the plastic liners to be installed but these are easily sealed.

http://stores.ebay.co.uk/J-S-Simcox-Ltd?_trksid=p2047675.l2563

sploo, acryllic was called Plexiglass by one manufacturer.

I believe that retired2 came to the conclusion that the threaded rod he used to support the baffle was probably not needed. I do not like it being in the airstream, only because some long shavings might hang up on it. Your idea of a sort of scaffolding sounds OTT. Glueing a thicker piece of material to the underside while making sure there is at least 2" of clearance will certainly make it certain that it does not vibrate.

I do not think that angling the inlet duct downwards would improve performance very much and it just makes construction more complex.

Let us know how you get on.

sploo,

Perhaps you have not seen this:

http://www.jpthien.com/smf/index.php?topic=563.msg3034#msg3034

You could leave the outlet of your fan rectangular and attach it to the inlet rectangle of the Top Hat as in retired2's design. If I have understood you correctly this means:

     20" overall diameter Thats fine
    14" tall (2x height of the 7" tall inlet) 1 1/2 x would do because gains not huge but may stop hang up of big shavings
    Side inlet mounted just under the top lid (called a "Top hat" design?)  your fan outlet tight to the top
    Inlet maybe protruding into the separator like a Pentz cyclone.  No. It will cause turbulence and degrade separation
    6" round outlet pipe, protruding ~10.5" down from the underside of the lid (inlet height + 1/2 of inlet height)  OK
    1/4" thick material for the baffle - preferably something very smooth               OK
    1.25" wide slot in the baffle         OK

I hope this helps and if so I would love to hear how well it performs......or otherwise.

It has been noted many times that the baffle needs to be as thin as possible. Frequently 1/4" oil tempered hardboard has been used.

I do not think the debris is hiding from the air so much , it is more likely being elbowed out of the way by the greedy air slamming down the pipe, pushing the "weaker" particles out of the way – the bullies.

My second question is: - do the fines get spun closer to the pipe wall than the coarse? Clearly large lumps will be prevented from getting as close to the wall as fine dust because of the curve of the wall. Secondly each particle of dust weighs less than a larger piece of debris so presumably larger particles take more energy to move them? Hence are larger bits more likely to stay towards the centre of the pipe? If this happens does it mean that a cross section of the vortex would show an outermost layer composed of fine dust getting progressively coarser towards the centre?

It is not as simple as that as there are many other things going on. Friction, surface areas,etcetera, etcetera. It may be that the only way to find out is to "look" at some mixed dust and shavings spinning down a pipe. I cannot get to my shop to do it myself so if anyone knows for sure I would be gladdened to hear from them.

This idea is exciting. I am too ill to get to my work shop just now or I would be there playing and measuring but it does give me time to think about it.

Some of us use DC systems fitted with very fine filters to keep dangerous wood dust out of our lungs. The important but secondary function is to keep the shop and machines clear of shavings, chips and dust. A Thien baffle or a cyclone is used to remove the dust to keep filters as clean as possible. This keeps the air flowing at effective levels for longer before having to clean the filters.

Separating out fine dust takes precedence over coarser debris.

With the in-line separator (ILS)  is the space between the vortex finder and the outer "Y" fitting equivalent to the width of the slot in the Thien baffle? If so the narrower the gap in an ILS the more efficient the separation of fines!

One such did some work that he presented here. When it was pointed out that the assumptions he had made did not match real life he just disappeared!

This was a pity as it looked as though that would have been a fabulous resource, saving a hugh amount of time and perhaps the only way to optimise these designs.

If you look at this build it covers most of what you need to know to make a good tophat :

http://www.jpthien.com/smf/index.php?topic=563.msg3034;topicseen#msg3034

Ask if anything not clear and let us know how you get on with your build.

Dado is the word used in the USA. In England it is a groove if along the grain and a housing if across the grain. Then again a rabbet is a small furry animal that is very good to eat.

Sounds as though you might be thinking of an in-bin separator. If so I suggest you go the top hat route instead. The best build is retired2's here:

http://www.jpthien.com/smf/index.php?topic=563.msg3024#msg3024

If I have misread your thoughts then I appologise and no harm done.

If you go this route then use polycarbonate and not acrylic sheet as acrylic is too brittle, think PlexiGLASS.

Yes r2 is right about standardisation. However sportflyer has a specific need and has found an improvement, albeit subjective. Some quick weighing with and without the ply strips should quickly establish if he is on the right path for his application.

I mean angled at 70 degrees in the direction of air flow. I was thinking the dust would be "screwed" downwards. I would have thought thin battens were flexible enough to twist and follow the curved wall. You might even be able to use balsa wood if it were coated with a hard finish. If this proves impossible then changes in the width, thickness and spacing of the vertical battens may be the only variables that can be tried.

I think the rectangular section of your battens could be why you are getting different results from Phil. Washboard ripples are quite different from an abrupt castellation. There are all sorts of possible turbulent flows around the "square" edges. My "lash up" bin has quite acute changes in angle of the stiffening indents around its circumference. Not at all like corrugated roofing. This does remove fine dust. Cannot say how much because I have not measured it but a significant layer of fine dust sits in the bottom of my bin every time I empty it.

What we are trying to do is slow up the very fine dust so that it will fall downwards through the slot. It has little mass so are we trying to "draw" the energy out somehow? The micro turbulent flows across abrupt changes in section might do this. Of course r2 is right to remind us that this will be at the cost of air velocity.

Another thought! Are these particles so small as to be attracted to electricaly charged plates. The words electrical precipitators floated slowly in so I searched and found: "An electrostatic precipitator (ESP) is a filtration device that removes fine particles, like dust and smoke, from a flowing gas using the force of an induced electrostatic charge minimally impeding the flow of gases through the unit." Just a thought.

Electronic postage or kitchen scales are remarkable accurate – not laboratory standard but good enough particularly if comparing before and after.

A useful experiment. It looks as though you are on to something here. I wonder what would happen if yours strips were angled down towards the slot? Again what would happen if the strips were thicker? Sorry - my mind is racing ahead of my concern for your work load.

I think you are getting into a lot of electronic complexity. How about cutting a window ang glazing it with clear plastic. This link also gives a low tech solution:

http://www.jpthien.com/smf/index.php?topic=170.msg954;topicseen#msg954

Please let us know how you get on.

That report sounds interesting and I would very much like to read it. Can anyone point to it?

BTW the link to r2's build is here:

http://www.jpthien.com/smf/index.php?topic=563.msg3034;topicseen#msg3034