Working backwards from bell to burner

[peterberg]

Cramer,
Whether or not the "broken riser" of Matt is usable in a J-tube remains to be seen. But when it does work I do suspect you has to respect the ratio between feed, tunnel and riser. Not the length of the riser does count but how high it is above the feed instead.

The most elegant way to calculate those is using the following rules: feed from top to halfway tunnel height, tunnel from halfway feed to halfway riser, riser from half height tunnel to top. The ratio using this calculation should be about 1, 2, 4. The question which isn't answered still is how much lower the riser can end, for a large part depending on the quality of the chimney.

When is does work however, the fire won't rise vertically from the riser's mouth, but it will keep going in the same direction as the riser tube is pointing instead. Acting like a flame thrower, so to speak.

But it's your first build, why are you trying to walk this untrodden path?

[matthewwalker]

I suspect Peter is right, and Cramer, to answer your question directly, I don't know.

[satamax]

What about digging a bit to put the burn tunel in the ground

[Cramer]

What about digging a bit to put the burn tunel in the ground

Two words... concrete floor.

[Cramer]

Dec 28, 2013 14:23:28 GMT -8 Cramer said:

But it's your first build, why are you trying to walk this untrodden path?

The million dollar question!  The application calls for a long narrow short bell.  I am trying to ascertain whether or not I can do this without a "pop up" section on the bell making the bell about belt high for the entire surface would be a best case scenario.

Not the length of the riser does count but how high it is above the feed instead.

Well then the concept of the angled riser becomes less useful except for directing the flow.  Okay then, I would like to contribute to research into the concept of the angled (not broken but truly angled) riser.  Hypothesize that as long as the gasses from pyrolysis remain contained in a well insulated riser for the proper distance (dictated by the 1:2:4 ratio) and have at least some upward angle, a (complete as possible) burn can be achieved.  Burner Rev1.skp (145.43 KB) (revised with proper ratio) The length of the feed tube has been shortened and the 1:2:4 ratio is maintained. 

When is does work however, the fire won't rise vertically from the riser's mouth, but it will keep going in the same direction as the riser tube is pointing instead. Acting like a flame thrower, so to speak.

I believe your assumption that the double helix of the exiting gasses causes this has validity here.  That dual spiral would tend to hold itself together over a fairly long distance.


Has anyone ever lengthened a riser?  If the ratio is not the magic and the distance above the feed tube/burn tube is (that is if the proposed design does not work as is) then either the riser will need to be lengthened or a longer riser (new one) would have to be used.  I have no problem re-building the burner if the design is flawed but if nobody tries this how will we all know whether it will work or not?

A little background on me.  I have worked in the HVAC industry for the last 16 years so I am not devoid of at least a bit of knowledge of thermodynamics.  Many years ago I was also a high rise fire safety Marshall with training in fire science but that training was long ago and far away.  Using what I can recall of that training I very much believe the ratio is the main driving factor rather than the rise in the riser tube.  I am willing to test that hypothesis but not without input from as many sources as I can get.

Thanks to you all, if I can borrow a Testo and someone can tell me what methodology to use to run the numbers after the build I would be glad to do so.

[satamax]

Dec 28, 2013 17:50:35 GMT -8 Cramer said:

What about digging a bit to put the burn tunel in the ground

Two words... concrete floor.

And?

[Cramer]

LOL! Not going to happen! Too funny though!

[morticcio]

That dual spiral would tend to hold itself together over a fairly long distance.

Has anyone ever lengthened a riser?

With my 8" J-tube and 6" batch box test rockets, I used a 1500mm (59") vertical riser. In both cases when the rocket was roaring hard there was a 12" to 18" long flame coming out the end. This was best viewed in the dark and there wasn't any spiral to speak of, just a vertical flame tapering to a point similar to a thick marker pen.

So from my experience I would say the neat tight spiral you see at the bottom of the riser rapidly "uncoils itself" (for want of a better description) as it travels up/along the riser. The longer the riser, the more the spiral uncoils? Rather like stretching one of those Slinky toys. Maybe Karl could help on this one?

[Cramer]

One more question. Does the surface area of the portion of the burner assembly inside a bell count toward the total ISA of the bell?  I am kind of right on the edge at 50.79 ft^2 for a 6 inch J Tube burner. I could shorten the length of the bell by the 2 1/2 inch dimension of a brick if need be.  or the 4 1/2 inch dimension or if really need be the 9 inch dimension but I think that would be going too far.

Here is the latest iteration if anybody wants to take a look at it.  Bell and burner together with the proposed layout.  I am wondering if anyone thinks the chimney might be in the wrong place considering the way the riser is pointed?  Okay make that two more questions then.

Bell and burner together.skp (165.27 KB)

[morticcio]

You could face the area you are referring to. If it is the same material and thickness as the surrounding bell I can't a problem. Just ensure the J-tube is well insulated.

Sometimes the exit on the bell is determined by the location of the chimney itself. If it's the only place for an exit you could include a length of flue pipe running along the back so the inlet is behind the riser exit.


BTW, you are going to build and test the J-tube in this configuration before installing in a bell aren't you??

[Cramer]

You could face the area you are referring to. If it is the same material and thickness as the surrounding bell I can't [see] a problem. Just ensure the J-tube is well insulated.

By this you mean yes it should be included in the ISA calculation or no, it should make no difference?   It seems to me that even if it is well insulated it would be conducting heat from combustion and be radiating it rather than taking it in and thus it would NOT figure in to the ISA calculation?

Sometimes the exit on the bell is determined by the location of the chimney itself. If it's the only place for an exit you could include a length of flue pipe running along the back so the inlet is behind the riser exit.

I have pondered on the efficacy of this solution.  Has this been done before?  It seems to me that there is a pressure differential between the bell and the chimney once the expanding heated gas stream begins, making this a viable solution.  I suppose I could do a redesign of the burner and have it angle to the left, placing it at the same end as the chimney outlet thus eliminating the need for the extra pipe inside the bell.  That might be a better solution?

BTW, you are going to build and test the J-tube in this configuration before installing in a bell aren't you??

It was suggested that I do a mock up using expendable materials before fabricating the real thing.  I have yet to figure out just how I am going to be able to do that and still simulate the load of the bell on the burner.  A prudent thing to do for sure, I just have not figured out the logistics as yet.

I also have not yet come up with a method to fabricate the casting (for the real thing, should testing prove fruitful in the mock up design) so that I can attach the riser tube to the burner after it has been installed (slid into place) in the opening of the bell.  I have been thinking of the possibility of casting a depression into the burner body that will accept a 9 inch ceramic flue liner with three inches of kaowool or superwool with a rigidizer inside leaving a 6 inch inside diameter riser.  In case of a riser failure in the future sometime this would provide the opportunity to replace that section of the burner without having to rework anything. Is there such a thing as a 9 inch flue liner?

With my 8" J-tube and 6" batch box test rockets, I used a 1500mm (59") vertical riser. In both cases when the rocket was roaring hard there was a 12" to 18" long flame coming out the end. This was best viewed in the dark and there wasn't any spiral to speak of, just a vertical flame tapering to a point similar to a thick marker pen.



So from my experience I would say the neat tight spiral you see at the bottom of the riser rapidly "uncoils itself" (for want of a better description) as it travels up/along the riser. The longer the riser, the more the spiral uncoils? Rather like stretching one of those Slinky toys. Maybe Karl could help on this one?

Interesting, I wonder if the spiral is still there and just not visible to the naked eye.  I cannot think of a way to test for this though.  It may be that the invisible spiral, devoid of burnable gasses at the perimeter are the cause of the neat taper of the exiting flame? 

 

[morticcio]

There are a lot of "I can't", "I cannot" and "I have yet to"s in your replies. Like Peter said you're walking down an untrodden path.

I think the best thing you can do now is go build the J-tube with the angled heat riser. Get that working. Feed it small sticks and big sticks. Find out what makes it stall and what makes it roar. When you have done that then add the bell. Details like chimney exits and additional steel pipe are things that can be dealt with as and when you get to that stage.

Look forward to hearing how you get on.

[Cramer]

Look forward to hearing how you get on.

And you shall. material acquisition begins as soon as I get some time off to procure some things.

Thanks!

[Robert]

Keep posted Cramer. Kinds of interesting idea with the bent riser. i am interested how it will perform.

[Cramer]

Okay, got some 6 inch and 10 inch duct from work along with some 6 and 10 inch elbows to make a test rocket of the slanted riser variety. I will use perlite in between for insulation purposes. Expendable materials for the trial run. I might just dig a hole in the ground to stabilize everything and try the 40 degrees up from horizontal to see what happens. If that appears to work I will go down to 30 degrees and see what happens. If 40 does not work I will go up ten degrees at a time to gauge just how much of an angle seems to work other than true vertical. Wish me luck guys!