An inline separator idea

[alan m]

I've started accumulating some parts for more experiments on my end.

I have a couple of ideas for maximizing fines separation but need to get my test rig built.

im looking into getting parts so I can try this with 8" lines
im thinking of getting 12" y and reducers but they are expensive here in Ireland.

what ideas have you got.

[BernardNaish]

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!

[BernardNaish]

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.

[phil (admin)]

what ideas have you got.

Bunches of them.  I've been pondering some and realize how terrible they are.  By the weekend I'll hopefully be able to try a few out.

[alan m]

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.

some good insights Bernard.

im not sure what the relationship between slot size and the difference in diameters of the 2 pipes is yet.
I guess that you want the dust traveling as close to the outlet pipe as possible so that the dust just slips by . in the tests I did  I used a 4" inlet and outlet  with a 8" y. that 2" all around is probably too big for fines. most of my fines were bypassing.

[alan m]

what ideas have you got.

Bunches of them.  I've been pondering some and realize how terrible they are.  By the weekend I'll hopefully be able to try a few out.

come on phil . your teasing us

at least give us some of the bad ideas.
there might be some value in them ,
or at least tell us why you think its not worth trying

[phil (admin)]

Don't get your hopes up, this entire idea may turn out to be one of my worst.

[alan m]

Don't get your hopes up, this entire idea may turn out to be one of my worst.

keep your hopes up. all visionary's think their ideas are rubbish.

my gut tells me that this separator wont ever be as good as a top hat  separator but from my very rough playing with parts I had there is definitely merit to it . I got 50 % separation on the first decent try.

when all the brains come together and test the variables we should see a major increase in the efficiency.

[nucww]

Many thanks to all the contributors on this site. I have been planning a top hat and some thoughts have crossed my mind on this idea.  I think the wall friction is why the dust tends to collect there.  The dust has more frictional losses than the air. To enhance this design a spiral vane (propeller of sorts) inside the feed pipe will tend to spin the dust to the outside before it gets to the smaller pipe separator.  Depending on the extreme of the spiral, flow straighteners may be needed in the smaller receiving pipe to minimize pressure loss.  The other thought would be that the collector Y be much larger but retain the narrow clearance where the small end of the pipe is.  The larger volume will take the wind out of the dust and the back pressure may be less.  Also, the Y could be tilted so that the cavity of the Y uses gravity to keep the dust flowing down the Y.   

[alan m]

anyone get time to try it yet

[nucww]

I was planning to do a top hat, but this has me intrigued.  I do not have much spare time and may not have much time to experiment.  I may try a prototype that's a little different than whats proposed.  The question I have is if the air speed is reduced below ~45 mph, the theory says that the dust will not be picked up by the air flow.  So if the dust is on the wall traveling a speeds ~20 mph and the air flow is diverted from the wall to the center at speeds of ~20 mph, will the dust get pulled away from the wall or does it stay close to the wall if the pipes are vertical?  I also have concerns that with internal baffling (the spiral vanes) in the pipes that clogs may occur which means the design must come apart easily.  Any thoughts appreciated.

[alan m]

what prototype changes are you thinking about

[nucww]

A modification that I have been considering is to use a 5" base pipe and expand to a 10" wye.  Before the transition to the 10" pipe, place a 3" pipe inside the 5" pipe after the spiral vane. The 3" pipe goes into the 10" wye. At the end of the 3" pipe is a 5" or 6" pipe  that goes out of the other end of the wye.  At the transition from the 5" to 10" pipe add an internal transition on top of the 3" pipe that maintains a 1" channel between the outer transition and the inner transition.  When it is about  8" in diameter, collapse it back down to the 3" pipe inside the 10" wye.  If the dust stays on the outside surface, the dust flows outside the 3" pipe expands to 10", hopefully stays on the outside of the pipe and falls outside the 5" or 6" pipe with very low air flow and air flow without the dust is always moving forward and goes to the outside area between the 3" and the 5" to 6" pipe and hopefully has minimal pressure drop.  Without the transitions, I do not think there will be enough airflow to get the dust to the outside of the 10" pipe.  With these clearances, my main concern is dust hangups (on the spiral vane and the 1" channel) requiring frequent internal cleaning which means more design features to take it apart easily.

[phil (admin)]

A modification that I have been considering is to use a 5" base pipe and expand to a 10" wye.  Before the transition to the 10" pipe, place a 3" pipe inside the 5" pipe after the spiral vane. The 3" pipe goes into the 10" wye. At the end of the 3" pipe is a 5" or 6" pipe  that goes out of the other end of the wye.  At the transition from the 5" to 10" pipe add an internal transition on top of the 3" pipe that maintains a 1" channel between the outer transition and the inner transition.  When it is about  8" in diameter, collapse it back down to the 3" pipe inside the 10" wye.  If the dust stays on the outside surface, the dust flows outside the 3" pipe expands to 10", hopefully stays on the outside of the pipe and falls outside the 5" or 6" pipe with very low air flow and air flow without the dust is always moving forward and goes to the outside area between the 3" and the 5" to 6" pipe and hopefully has minimal pressure drop.  Without the transitions, I do not think there will be enough airflow to get the dust to the outside of the 10" pipe.  With these clearances, my main concern is dust hangups (on the spiral vane and the 1" channel) requiring frequent internal cleaning which means more design features to take it apart easily.

We're on the same page, someone just needs to do some testing.

[nucww]

For me right now I believe the top hat is going to be the solution for me and and don't have time to make two systems.  I'll continue to feed ideas for this for now.  Maybe later during the holidays when I'm off work I may experiment.