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  #91  
Old 05-05-2010, 05:37 PM
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Default Re: 81 Inch First Build (and first post)

Hi Roger, what is the material you used for the floor of the oven? Thanks
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  #92  
Old 05-05-2010, 06:10 PM
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Default Re: 81 Inch First Build (and first post)

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Originally Posted by lwalper View Post
I was really wondering about the possibility of hot steam belching back out through the open door. Doing the math, a cup of water expanding 1000 times its liquid volume to live steam, will displace a LOT of hot air. It's gotta go somewhere — don't stand in front of the open door when you squirt that water down the pipe. Yikes!

Some sort of heat exchanger/water heater would definitely be nice. Since this thing gets so hot, a coil seems like it would be counter intuitive with dependent loops bubbling and boiling and spitng steam as they are occasionally allowed to dry out. Maybe an "S" shaped arrangement would work — something that would drain completely?
This is a classic "steam hammer" heat exchanger design issue. You have to design it so that you do not heat the water to it's boiling point. Unless you have just a straight pipe where no water will collect; When it expands at the boiling point you will create a steam hammer which is powerful enough to blow a hole in the oven dome...or what ever contains the tubing.

Not sure how you can do it, but I would do some testing to see if your going to produce steam in the contraption. If so, you have to change the design in such a way that it does not produce steam. Ie, increase diameter of the pipe, increase water flow, etc. I would start with a 1" copper pipe and run a know length of pipe through an oven at a safer temp like 200F and see what temperature you get at the hot end of the pipe, at a constant water flow rate. This will tell you what kind of heat exchange to expect out of that length of pipe. Then increase the temp until the exiting water is no more than 180F. At this point you know whether or not you have the correct set-up.

Let's say your exit water temp is 100F (T2) when the oven temp is at 200F (T1). There will always be a delta btw the oven temp and and the exiting water temp; or you just made the perfect heat exchanger. So... hypothetically, if I raise the oven temp (T1) to 300F, what do you get for T2? maybe 200F? Raise T1 as high as possible until T2 =180F. If T1 can only reach 500F before T2 reaches 180F then you have to modify your setup. Shorter pipe, higher flow rate or bigger pipe diameter are your only options. Shorter pipe and higher flow rate primarily affect resonance time, pipe diameter affects surface area. Increasing pipe diameter will make the most difference in the design. Flow rate and pipe length will have less affect.

I don't know if you have access to and oven where you can do this testing but it is important that it is done for safety reasons. I would always start with a fully charged system before raising the temp to avoid water flashing into a hot empty pipe. This whole thing is a serious safety issue and should not be taken lightly. If done correctly it can be a great asset. Please be careful!!!
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Last edited by lwood; 05-05-2010 at 06:57 PM.
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  #93  
Old 05-05-2010, 08:23 PM
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Default Re: 81 Inch First Build (and first post)

lwood, the floor is soapstone, I cite the source earlier in this thread...seems like the perfect floor for pizza, though I have not tried it yet.

Interesting dynamics regarding the water/steam introduction, good science too! thanks!
Roger
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  #94  
Old 05-05-2010, 08:26 PM
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Default Re: 81 Inch First Build (and first post)

Agree, I will use soapstone on my next build. Hope that dissertation on the heat exchanger helps. John
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  #95  
Old 05-06-2010, 08:59 AM
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Default Re: 81 Inch First Build (and first post)

Thanks for those thoughts re: steam. All things to seriously consider. It just seems there ought to be a better way to introduce steam into the oven than throwing water on hot rocks. I saw an installation where an electric steam generator was actually plumbed into the oven. It was a takeoff from an electric deck oven. The owner/baker didn't seem to be real impressed with the setup. I've also seen a video showing steam injection in a large oven. When the button is pressed steam just roils out the door - pretty impressive.

I suppose, even if there is a flash of steam, that too can be controlled by regulating the volume of water running down the pipe. I may need only 1 or 2 ounces instead of 6 or 8. With the door closed there will be less steam loss than when flagging the door as per usual.

Cracking the dome? Don't want to do that!!
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  #96  
Old 05-13-2010, 09:55 AM
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Default Re: 81 Inch First Build (and first post)

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Originally Posted by windage View Post
perfect floor for pizza, though I have not tried it yet.

Roger
SWEET build, thanks for the time and pics....

What's the ETP? (estimated time 'till pizza?)

Jim
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  #97  
Old 05-14-2010, 09:03 PM
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Default Re: 81 Inch First Build (and first post)

Greetings from Western KY. Very impressive build. I'll be following your thread. I might even have to drive up for some pizza when you are open for business.

oven thread: http://www.fornobravo.com/forum/f21/...cky-12829.html (42" Pompeii in Kentucky)
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  #98  
Old 05-16-2010, 10:33 AM
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Default Re: 81 Inch First Build (and first post)

got any more pictures yet? I love your build
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  #99  
Old 05-22-2010, 07:37 AM
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Default Re: 81 Inch First Build (and first post)

I posted this in 2 other threads having to do with high temp mortar, especially calcium aluminate based;
Finally, success! After a long discussion with the US rep for the REFCON MG by Calcem, I was pointed in the right direction, 2 issues were giving me fits; lack of stickiness and short "pot time, or work time".
1) lime is the enemy of Calcium Aluminate based cements, the residue in my work tools was enough to set it off in 3 to 5 minutes, and the Forno Bravo formula posted as adding one part lime is REALLY off base. Bought a new tub, trowel and fresh blending buckets..now "work time" is as long as I need. No more lime contamination.
2) stickiness was a function of adding more sand for more "surface area" to hold the water. I also tried his tip of adding a few drops of dish soap to entrain air...not sure if that helped or not...so the mixture I am using to lay (soaked) brick; 6 sand, 2 cement, 1 clay. I may even drop cement to 1 part when I parge the outside of the dome.
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  #100  
Old 05-22-2010, 07:31 PM
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Default Re: 81 Inch First Build (and first post)

Thank you for sharing the info on the mortar, it will help many of us.
Don
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