Author Topic: Comments on this design for LBE  (Read 7805 times)

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Offline shuboyje

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Re: Comments on this design for LBE
« Reply #50 on: August 25, 2012, 11:33:40 PM »
Ok home and at the computer.

Like I said before, I really think this design would struggle to get to temperature and would take a very long time to do so.  There simply is nothing directing heat at the hearth to heat the mass.  Putting the heat next to it like proposed all the heat will rise, the only thing heating the hearth will be very indirect hear from radiation and convection.  

I've got an idea I've been sitting on for a while, and I think this is the time to bring it up.  I personally think a directional burner(like I have posted links to building many times) on a pivot is a great solution for a single burner gas oven for home use.  For heat up the burner is pointed down at the hearth and blasting it directly with heat.  Once you have stored a bunch of energy in the thermal mass of the hearth stone and brought it up to temperature the burner is pivoted up where it will heat the top stone and provide hot convective flame like a wood fired oven.  If the hearth temp drops(not sure it would) you simply recharge it and keep going between pies.  Again I have added a crude drawing of the idea.

As for the safety concerns, I don't see where there is any more then with an LBE which are discussed daily here.  You are pumping explosive gases into a enclosed chamber.  Explosion is always a risk, but I've never seen an LBE built with a flame failure device and nobody flinches at that.
-Jeff


Offline Chicago Bob

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Re: Comments on this design for LBE
« Reply #51 on: August 25, 2012, 11:41:41 PM »

As for the safety concerns, I don't see where there is any more then with an LBE which are discussed daily here.  You are pumping explosive gases into a enclosed chamber.  Explosion is always a risk, but I've never seen an LBE built with a flame failure device and nobody flinches at that.
Your idea looks promising.
Safety concerns/talk is being expressed on this thread towards a beginner...please stay on topic.
"Care Free Highway...let me slip away on you"

scott123

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Re: Comments on this design for LBE
« Reply #52 on: August 26, 2012, 12:10:31 AM »
Jeff, the Drago burner heats the hearth with radiation that's a lot further away than what we're talking about here. It's incredibly inefficient and time consuming to use radiation to heat a hearth, but with enough BTUs it's entirely feasible.

That being said, I like your idea.  My only concern would be that, with this kind of single flame burner, the hearth would have hot spots that would be exponentially hotter than the cool areas.  You could add a rest period for the hearth to even out (for cordierite that could translate into as long as 30 minutes), but I think there's a more elegant approach.  I still like the all metal lazy susan under the hearth idea.  Another approach could be a hearth sandwich. The same way aluminum quickly spreads out the heat in cladded cookware, you could sandwich a layer of steel between thin cordierite stones. Another way might be grooves on the pivot that set different angles to the hearth- 5 minutes hitting the closest point on the hearth, then change the angle further out for 5 more minutes- and so on and so on.   By the time the flame is heating the outer most edge, the entire stone should be relatively evenly heated.

Btw, does one need to build a burner for this?  How about one of these?

http://www.northerntool.com/shop/tools/product_200203874_200203874

Offline shuboyje

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Re: Comments on this design for LBE
« Reply #53 on: August 26, 2012, 12:20:15 AM »
Don't take what I said the wrong way Bob, I think it's great that safety is being brought up, I have been the one voicing the same concerns many times both here and at fornobravo.  My point is simply that although there are safety concerns that should be taken seriously, they are no more so then those with an LBE, and beginners build LBE's all the time without those concerns ever being voiced.  The LBE thread is actually more dangerous because if you read it you can build an LBE from the information it holds without ever needing to ask a question, so countless "beginners" can build these ovens without anyone here ever knowing they exist, let alone explain the safety concerns to them.  The original LBE design was fairly safe due to the use of the grills original top vent, but once they went to the side vent configuration most use now you have a potentially explosive situation just like most other gas ovens.

Interesting stuff on the teflon tape, I'm gonna have to pay more attention around the jobsite and see what they are using, all I recall is the classic white tape in a blue container.  My (minimal)training on the topic was that the tapes only function was to act as a lubricant so the threads could be tighter and the natural function of the tapered thread pattern could be more effective.  Was I lied too? lol  

Your idea looks promising.
Safety concerns/talk is being expressed on this thread towards a beginner...please stay on topic.
-Jeff

Offline shuboyje

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Re: Comments on this design for LBE
« Reply #54 on: August 26, 2012, 12:33:26 AM »
I'm curious myself what type of temperature gradiant you would see.  I'm not so sure it would be any different then you see in a wood fired oven.  A couple turns and you might be good.  If not I think the options you mention are feasible. 

My $20 harbor freight weed burner was actually what began my thoughts about this idea.  So long as the burners air inlets where outside the oven it would probably work, but I do think a home built burner with a smaller diameter longer pipe would be a better fit for a small oven.
-Jeff

buceriasdon

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Re: Comments on this design for LBE
« Reply #55 on: August 26, 2012, 08:05:31 AM »
One of several sites calling out the use of teflon tape with propane fittings. I assumed this was common knowledge.
http://www.ehow.com/how_5984877_do-seal-propane-fittings_.html
Proper use of teflon tape:
http://yarchive.net/house/teflon_tape.html
However if you have acess to pipe dope by all means use it, I don't.
Don
« Last Edit: August 26, 2012, 08:49:57 AM by buceriasdon »

Offline Jet_deck

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Re: Comments on this design for LBE
« Reply #56 on: August 26, 2012, 08:47:48 AM »
All seriousnes aside, and having slept on it, I agree with Jeff.  There is no way that the burner at hearth level is going to heat the floor.  The top stone/steel will be responsible for 90% of the heat directed to the floor.

$.02
Her mind is Tiffany-twisted, she got the Mercedes bends

buceriasdon

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Re: Comments on this design for LBE
« Reply #57 on: August 26, 2012, 08:50:50 AM »
+1

All seriousnes aside, and having slept on it, I agree with Jeff.  There is no way that the burner at hearth level is going to heat the floor.  The top stone/steel will be responsible for 90% of the heat directed to the floor.

$.02

scott123

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Re: Comments on this design for LBE
« Reply #58 on: August 26, 2012, 09:16:45 AM »
The top stone/steel will be responsible for 90% of the heat directed to the floor.

That's exactly what I'm saying, Gene. Burners heat the ceiling, radiation from the ceiling heats the floor.  Did you see the video I posted?



The drago heats the ceiling and the radiation from the ceiling heats the floor.  All you need is a big enough flame and that floor will have no problem hitting the temp you need.

I'll put any amount of money on this  ;D
« Last Edit: August 26, 2012, 09:19:11 AM by scott123 »


Offline Jet_deck

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Re: Comments on this design for LBE
« Reply #59 on: August 26, 2012, 09:32:59 AM »
Yes. Scotty, the Drago is a monster burner.  We will need a good mass and insulation in the ceiling to catch and radiate the heat downward.  Your money is safe with me. :P
Her mind is Tiffany-twisted, she got the Mercedes bends

scott123

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Re: Comments on this design for LBE
« Reply #60 on: August 26, 2012, 09:54:28 AM »
We will need a good mass and insulation in the ceiling to catch and radiate the heat downward.

Actually, we don't need that much mass  :) I don't know anyone with a drago, so I can't say for certain how long it takes to heat a cold, fresh from the factory (or long vacation) oven, but Jeff has pointed out that it most likely takes a very long time, which I'm not disagreeing with.  A contributing factor to that time is the thermal mass in the dome.  As you scale it down, drop the thermal mass, lower the ceiling and go with a much higher BTU to mass ratio, the time shrinks considerably.

I'm not completely ruling out insulation here, but, as I told Bob yesterday, this is basically LBE thermodynamics.  In your average LBE, with the lid on, the proper size vent and a typically high BTU burner, the air foil/director stays plenty hot, regardless of the lack of insulation above it.

Now, I'm not necessarily backing the metal plate ceiling idea.  That could require insulation. I'm thinking some mass- 3/4" or thicker cordierite will, with enough BTUs glow cherry red and shower the hearth with all of it's radiative goodness.
« Last Edit: August 26, 2012, 10:18:16 AM by scott123 »

Offline shuboyje

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Re: Comments on this design for LBE
« Reply #61 on: August 26, 2012, 10:32:35 AM »
Scott,

When you use a frying pan in the kitchen do you put it on the burner and heat it up, or do you put a piece of steel on the burner, heat it to red hot and then hold it over the frying pan to heat it via radiation?  Get my point, lol.

If some part of this system was already built, or being repurposed in some way I could see trying to make it work.  Considering the poster is looking to build a custom burner in a oven that does not exist I don't see any reason to take such a round about approach when he can just blast the hearth with heat directly and be done with it.
-Jeff

buceriasdon

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Re: Comments on this design for LBE
« Reply #62 on: August 26, 2012, 10:59:24 AM »
Just throwing this out for the sake of conversation. Mount a 4" high pressure burner at the rear so it projects say an inch or so into the upper chamber. A slot cut in the lower kettle for the burner tube to set in and a mounted L bracket and hose clamp to hold it in position. Yes you lose that area but you still have fourteen inches of bake area. You must have a large enough vent in the top kettle because the air mixture at the venturi alone is not adequate to keep the flame going, the burner requires surrounding air also.
Don


 

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