J. Phil Thien's Projects

Did anyone notice that this collector looks a lot like the ideas in " An inline separator idea  "?

Another look at your pictures and another thought came to mind.  The seal between the trash can lid and the trash can must be air tight.  I can't see inside the lid or edge of the trash can to see if you have any insulating material.  The cyclone effect is greatly diminished when there are even small leaks in the cyclone area according to others.  It will also reduce your air flow at the inlet where you are collecting dust.

Another thing to consider is the alignment of the baffle slot relative to the inlet pipe.  There is no clear view but the open slot should end right before the inlet pipe.  The view I saw looked like it was open 40-60 degrees after the pipe inlet.

I struggled several months over a Thien baffle design. My system (described in "HF DC spiral collector with flow redirection") had to fit under a 74" ceiling shelf.  I only wanted to do it once so I put all the features that I thought would enhance flow with my cheap HF DC.  If you look at the computer generated flow patterns in a Thien baffle type collector linked in one of these posts, the velocity is high on the outside surface, slows down until it gets close to the outlet pipe.  The vortex speed in the center becomes huge which is why I think the flow straighteners work.  I am guessing that the high vortex is not productive in the center because the dust is collected on the outside and the flow inward negates the outward movement of fine dust. In contrast to a cyclone that can use that spin to separate the fines to continue to drop into the container.  To minimize the turbulent losses from the vortex, I added flow redirection between the baffle and the outlet pipe since flow doesn't like to hit a perpendicular wall.  My system works well for now but I would like to test the different outlet designs but its not easy to take apart.  In some respects, I regret not putting in some flexibility to test different configurations but on the other hand I have allergies and needed a  DC system.  So if you are inquisitive and enjoy the ride, go for it.  If you need a DC, keep it simple, wrap it up and start collecting dust; in my opinion the basic Thien design works very well.

I agree with retired2 that the internal walls are an additional source of friction.  The dust is slowed by the friction of the walls and hence the collection by the outer walls is quite effective with the Thien concepts. The proposed design has almost two revolutions of dust on the wall without a collection hole. Its not clear what is accomplished with these walls.   As you noted, you have two sections in the waste can to prevent cross flow in the can. If the holes did exist on all the spiral walls there isn't much to prevent the flow from going down into the can and back up again.  The cross flow and the pressure drop were reasons for me not to look at this type of design.  Also, it seems like there will be a dead spot on the bottom plate near the outlet tube that may collect dust and require periodic cleaning.  This spiral design does seem to allow more time for the fine dust to get the the walls so as retired2 says if you have the hp to drive it go for it.

I simply use wedges at three locations under the can.

AndyF,
Thanks for the compliment.  I remember looking at your post and was intrigued and was a reason I incorporated the spiral design.  I did not mean to imply that the significant differences that I used were my own ideas.  The only new idea is the flow redirection below the widemouth outlet.

Some general comments for those interested.
The Plexiglas at the top has shown an interesting behavior of the fine dust.  The fine dust collects on the Plexiglas while it is running and some dust does remain there.  It appears to be there because of the static caused by the moving dust.  It has a interesting spiral pattern.  When I touch the plexiglas with my whole hand, the dust moves away from my hand.  I wonder whether the circular section could be made of metal and a voltage applied to act like a electrostatic collector to enhance fine dust collection.  Once the flow is off, the voltage could be removed to drop the dust in the collection can.

Does this occur on the top of other designs made of MDF?

A correction to the velocity with the separator installed.  I was measuring the velocity of two different 5" pipes.  The separator pipe was  made to slide inside a standard 5" pipe so its area was less.  I can't measure it now but it could be a 1/4" OD difference which would reduce the relative flow by ~10%.  I am guessing it would make the 45mph to 40.5mph.

Bird's eye view.

Picture of completed system.

Copied from inline separator.
Most of the design and credit comes from the contributors of the topic:5", Rectangular Inlet, Bellmouth Outlet with Air Straightener, Top Hat Separator.
This is being used with a HF DC so the design was trying to minimize pressure drop to maximize flow.
Some of the significant differences are:
-  spiral chamber with the spiral starting ~6" before chamber entry.  The spiral lost ~2 1/4" per revolution.
-  a high narrow rectangular inlet (10"x2.25") so that entry dust is already close to the outer surface
-  Plexiglas on the top and formica for the spiral sides
-  Baffle slot was extended to ~320 degrees since the spiral design should minimize turbulent entrance.
-  a 3/4" MDF baffle with the slot edges tapered to ~1/4".
-  5" outlet pipe with a X flow straightener
-  a commercial bellmouth outlet pipe with the flat part of the rim cut off resulting in ~7.25" OD mouth for a 5" base pipe
-  flow diverters at the bottom of the wide mouth to divert the flow up rather than spinning around. Some CFD simulations show that vortex in the center is huge and is likely causing significant pressure losses.
I had a anemometer to measure airspeed to test some of the differences.
With the standard HF setup, 10' HF flex pipe and a 4" to 5" transition, the airspeed at the surface of the 5" transition was 48 mph. (airspeed with a 4" pipe was off scale max of 67 mph)  With the same piping and with the dust separator installed, the speed was 45mph.  So this design only lost 3 mph.
Installed a .5micron wynn filter, put the motor on top of the collector, patched some leaks in the impeller housing, and put a foam insulation strip between the bottom bag and the housing.  With the dust separator installed, the speed improved to 51mph with the same piping as the previous test.   So getting rid of the 5" flex pipe and adding the extra area of the wynn filter gained about 6 mph as noted by others on this web site and elsewhere giving me a net gain with the dust collector of ~3 mph .
I used hvac 5" ducts for the main line and all drops from the ceiling are 4" pipe.  I made my own wyes since the commercial ones were expensive and the cheaper hvac ones had the wrong end crimped.  The longest run of 5" was about 16'.  For all 90 degree turns, I used 2 elbows at 45 to make more gradual turns.  After installing the pipe I tested the longest run of 5" pipe and the speed was only 38 mph.  Taping all the joints made a huge difference.  The speed was now 54mph.  A gain of ~3 mph changing the 10' - 4" flex pipe with the metal duct.
I allowed a cup of flour to be sucked into the inlet to the collector and ~ 2/3 of it ended up in the trash can.  There was some visible in the chamber and the edges of the trash can.  Some made it to the bag after the impeller.
Attached is a picture that better shows what I am describing.  I will reply to this and add other pictures it seems that I can only add one of this size at a time.

I agree. I'll copy it so it doesn't clutter this one.  This was the forth time I time to post it and I did not know why it was not working so I added it to an existing thread.  While doing this I got a message saying that I could only load one picture of this size at a time.

This is summary of my dust collector that I spoke of in an earlier response.  Most of the design and credit comes from the contributors of the topic:5", Rectangular Inlet, Bellmouth Outlet with Air Straightener, Top Hat Separator.
This is being used with a HF DC so the design was trying to minimize pressure drop to maximize flow.
Some of the significant differences are:
-  spiral chamber with the spiral starting ~6" before chamber entry.  The spiral lost ~2 1/4" per revolution.
-  a high narrow rectangular inlet (10"x2.25") so that entry dust is already close to the outer surface
-  Plexiglas on the top and formica for the spiral sides
-  Baffle slot was extended to ~320 degrees since the spiral design should minimize turbulent entrance.
-  a 3/4" MDF baffle with the slot edges tapered to ~1/4".
-  5" outlet pipe with a X flow straightener
-  a commercial bellmouth outlet pipe with the flat part of the rim cut off resulting in ~7.25" OD mouth for a 5" base pipe
-  flow diverters at the bottom of the wide mouth to divert the flow up rather than spinning around. Some CFD simulations show that vortex in the center is huge and is likely causing significant pressure losses. 
I had a anemometer to measure airspeed to test some of the differences.
With the standard HF setup, 10' HF flex pipe and a 4" to 5" transition, the airspeed at the surface of the 5" transition was 48 mph. (airspeed with a 4" pipe was off scale max of 67 mph)  With the same piping and with the dust separator installed, the speed was 45mph.  So this design only lost 3 mph. 
Installed a .5micron wynn filter, put the motor on top of the collector, patched some leaks in the impeller housing, and put a foam insulation strip between the bottom bag and the housing.  With the dust separator installed, the speed improved to 51mph with the same piping as the previous test.   So getting rid of the 5" flex pipe and adding the extra area of the wynn filter gained about 6 mph as noted by others on this web site and elsewhere giving me a net gain with the dust collector of ~3 mph .
I used hvac 5" ducts for the main line and all drops from the ceiling are 4" pipe.  I made my own wyes since the commerical ones were expensive and the cheaper hvac ones had the wrong end crimped.  The longest run of 5" was about 16'.  For all 90 degree turns, I used 2 elbows at 45 to make more gradual turns.  After installing the pipe I tested the longest run of 5" pipe and the speed was only 38 mph.  Taping all the joints made a huge difference.  The speed was now 54mph.  A gain of ~3 mph changing the 10' - 4" flex pipe with the metal duct.
I allowed a cup of flour to be sucked into the inlet to the collector and ~ 2/3 of it ended up in the trash can.  There was some visible in the chamber and the edges of the trash can.  Some made it to the bag after the impeller.
Attached is a picture that better shows what I am describing. Evidently, I can only send one of these at a time.

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.

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.