J. Phil Thien's Projects

My experience with polycarbonate is that it does not snap, but I only have 2mm sheet. I suspect that it was not poly.

Also, poly is very temperamental about what you use to clean it with, paint thinners, acetone etc, will cloud the surface. WD40 is good for removing stains. Keep a few offcuts in a draw for testing cleaning products.

Dave

Very tidy. I'm looking forward to reading the results.

Dave

Quote from: johna on August 12, 2011, 06:10:57 AM
If that does not work, I guess all I can do is to take off say 1/2" at a time from the metal exit pipe.

I think you may need to extend, not shorten.

Dave

I agree with Retired2. Explore what you have already built. First I would experiment with the exit pipe height. Start too low and gradually raise it.

Dave

Yes, but I do not have the luxury of a lathe. If you have the capability to turn such large blocks, you could turn a bell mouth, but it would be cheaper to buy one I guess.

Fibreglass is very easy to work with and done right, would offer a good, strong solution. Lots of Googling first, to get the feel for the process.

Dave

The hot oil method works and was my first thought. I make fishing lures and we use this method for shaping polycarbonate. I have never tried it with anything this big though, but definately works.

I would probably make a male former and lay up some fibreglass, with some wood ribs laid in, to add some stiffness to the shape. The trick is making the former, but it is not that difficult.

Great links, I love seeing mans inginuity at work. This is what we do.

Dave

I think that the bell mouth idea is valid input and worth posting. I am assuming that unproven ideas are acceptable here. The bell mouth would definately be on my list of ideas to try. The improved efficiency might even cause more problems than it solves. Certainly the height above the baffle plate would have to be reduced.

Interesting input, thanks for posting.

Dave

On another forum, I was prevented from posting links or pics, until I had made ten posts. I now understand the reason why. I think ten is a bit excessive. Something similar could be done here, were the new user has to gain permission to post links for say the first five posts. More work for you though.

I guess it is possible to install software that scans the early posts for links and prevents the post from being submitted, but I don't know much about this.

Dave

What ever it is, it is not good. This vibration could reduce the life of the bearings over time.

I am thinking resonant frequency, like the vibration you get in some old cars at certain frequencies. What happens if you open a third gate or partially close one of the two open gates?

If it is resonant frequency and the above two tests stop the vibration, probably the next improvement that you make to the system will clear it. On a positive note, any changes you make, you will be able to hear the difference ;D

Just theorizing here.

Dave

Quote from: RCOX on July 27, 2011, 08:38:35 PM
R&R the accumulator with a 6" hvac wye. A little improvement but would not have been worth the trouble if I did not plan to switch the main trunk to a 6" line also. This is something we discussed and you don't know the outcome until you do it. Now I know. I tried opening both lines with the thought that a 6" line (from the wye through the separator to the dc) being 2.25 times larger than a 4" line should be able to pull that much with a little to spare. WRONG. There was at least a 30% loss of suction on the "working" line when I opened the gate on the second line. This is not really an obstacle as I am the only person using the system, just stating my observations. I hope it will be worth my effort to switch out the 4" mains that I have now and go with 6". This will be a project for the future.

The other thing I noticed. When I opened a second gate there was a mild hammering sound coming from the impeller area. With only 1 gate open this did not happen. It only happened with 2 gates open. I did not try a 3rd gate to see what happened, just occured to me as I typed this. Does anyone have a thought on what this could be? I do not recall it doing this when I had the accumulator in place but it would do it if I ran the system with the separator disconnected from the rest of the system.

I also started taping seams on my ductwork. Trying to stop as many airleaks as possible. None were serious but several small ones add up to the same as a big one.

Now it is time to start making some saw dust and really test these changes.

Thoughts or questions, let me know.

I am sorry you did not get the improvement in performance that you were looking for after replacing the accumulator with a Y, but you did get an improvement. Maximizing the efficiency of your system is going to be lots of small improvements, like straightening out runs and removing elbows, sealing leaks etc. The fact that you actually noticed a change is significant, some improvements may only register on instrumentation, but the cumulative improvement is there.

There was always going to be a large drop when you open the second line, I don?t see how this can be avoided.

The vibration problem is interesting. Is that happening with two gates opened on the same line or one gate on each line.

Dave

These are only my ideas and opinions and should not be taken as fact or gospel. I throw them out there for discussion only.

First off, great post, full of good information.

Accumulator – here is a highly speculative and over simplified diagram of what I think is happening inside the accumulator. On the left, a single inlet open, on the right, both inlets open.



When the flow passes a sharp corner, edge or even a sharp bend, a low pressure is generated on the lee side. This is caused by the air having momentum. The air wants to travel in a straight line. However, some of the air is pulled over by the low pressure, effectively reducing the diameter of the inlet pipe. This peeled off air has nowhere to go and quickly degenerates into chaotic flow or turbulence (red). All the sharp edges on the lee side of the accumulator just make things worse, churning up the air. Some of this turbulent flow will oppose the main flow and slow it down some. The same thing happens at the edges of the inlet and outlet pipes (blue). Even a regular ‘Y’ will have this turbulence, it cannot easily be avoided.

With both inlets open, the main turbulence (red) is replaced by a different pattern. It is more organized and so appears to be less of a problem, but it is still destructive to the flow efficiency. This flow is called vortex shedding and it alternates left and right (this should be visible). If you Google ‘wiki vortex shedding’ the first entry on the list will be a Wikipedia page, at the top of that page, you will see an animation of what is happening.

Here is the link: http://en.wikipedia.org/wiki/Vortex_shedding

As the vortices flow downstream, they constrict the middle of the outlet pipe (until they eventually merge into the flow), effectively reducing the diameter. Even though they look harmless, this is probably causing more of a problem than the single inlet in the left diagram.

There are things that can be done to reduce the problems: Extending the inlet pipes in at an angle, until they touch, should remove the vortex shedding problem. Filling/fairing all the corners will reduce the blue disturbances, but the best solution would be to fit a proper ‘Y’.

Inlet and outlet relative height – I am not convinced that this is significant. The inlet flow will take the easiest route, which is down the centre of the chamber. If the inlet is aligned with the chamber centre then there is no change of direction. Probably below centre is more accurate, as the outlet will tend to pull the overall flow downwards.

What I think is critical, is the height of the outlet relative to the flow centre or indirectly, to the baffle. Every build will have a slightly different flow, so any numbers provided can only be considered a starting guide. You will have to adjust or tune the height to find the most efficiency.

Dave

 :D me in a nut shell. Proud to be an engineer.

Dave

Thanks Chuck.

Retired2 - I do agree. Quantifying results is the problem. I don't think a bank of pressure gauges is going to help either. I don't think anything can beat measuring dust in and dust out, repeated several times for consistency. I just wish I had the funds, as this is the kind of stuff that I love doing, ideas, building, prototyping and testing is my full time hobby. I am an amateur inventor, which means I don't get paid.

Even though we cannot prove any of the ideas, I still think that we should continue to collect them. Occasionally someone will suggest and idea that maybe seems insignificant, but will jump off the page. Also ideas generate ideas. So I say keep 'em comming.

Dave

Fascinating discussion.

We bend over backwards to eliminate turbulence, rightly so, but sometimes vortices can be used to our advantage. Consider this for discussion purposes:



Maybe a block is a bit too much, a bump may be better. If you force or compress the flow inwards, after the bump, it will spring back. Positioned correctly, its inertia will force the incomming flow towards the outside of the chamber.



Dave

You mentioned turbulence in the accumulator. This is obviously causing some losses as turbulence is never a good thing. It may be prudent to fix this first, as you do not know to what extent the accumulator losses are affecting things.

One step at a time. If you fix everything at once, you will never find out what worked and we (the viewers) learn nothing from your experiences ;D

Dave