WFO heat balancing and related issues (split)

[shuboyje]

Heat is gonna transfer from hot to cold no matter what the situation.  In an oven with the fire at the back the back will be the hottest and obviously the mouth of the oven will be the coolest, so it would only make sense the heat would travel forward.

[TXCraig1]

I don't disagree in principal Jeff. My question is will enough heat move by that mechanism to matter? I can put a blowtorch on one end of a fire brick and hold my hand on the other for quite a while.

[shuboyje]

There is a guy on fornobravo who cooks on coals only and has claimed for the last few years atleast he can maintain pizza temperatures that way for hours with the fire at the back.  From what I've seen I would believe that but do think you would need to add fuel as I mentioned.

[shuboyje]

I did an interesting experiment tonight.  I placed two basically identical bricks into the oven while waiting for the temp to drop for new york pies.  One was placed directly on the hearth and the other on top of perlcrrete.  After about 15 minutes I pulled them from the oven and allowed the temperature to even out for a few minutes.  The brick that was directly on the hearth measured just under 400F.  The brick that was on the perlcrete, and therefore only receiving radiant heat, was 181F.  This doesn't rule out the effect radiant heat may play, but I think it does show that conduction is a major player in transferring heat from the fire to the hearth.

[TXCraig1]

I did an interesting experiment tonight.  I placed two basically identical bricks into the oven while waiting for the temp to drop for new york pies.  One was placed directly on the hearth and the other on top of perlcrrete.  After about 15 minutes I pulled them from the oven and allowed the temperature to even out for a few minutes.  The brick that was directly on the hearth measured just under 400F.  The brick that was on the perlcrete, and therefore only receiving radiant heat, was 181F.  This doesn't rule out the effect radiant heat may play, but I think it does show that conduction is a major player in transferring heat from the fire to the hearth.

I don't see what this proves. Both bricks were exposed to the same air and radiant heat. One brick had a hot brick (the hearth) in direct contact with it and the other was insulated from the hearth. Why would you expect a result any different from what you got?

I'm guessing you heated your oven with the fire in the middle and then moved your coals to the back? If so, isn't it likely that the heat in the hearth that warmed the test brick was primarily from the fire previously above and not from the coals behind after being moved to the back?

[shuboyje]

I don't really think it "proved" anything, lol.  Maybe I misunderstood some of the comments from previous posts, but I was under the impression that you guys did not feel heat was transferring brick by brick via conduction in major quantities and instead felt the heat was transferring via radiation. 

I don't disagree in principal Jeff. My question is will enough heat move by that mechanism to matter? I can put a blowtorch on one end of a fire brick and hold my hand on the other for quite a while.

   

This quote basically hits at what I was testing.  Radiation alone brought the brick from ~50F to 180F(+130F).  Radiation + conduction brought the brick from ~50F to 400F(+350F).  Simple maths says conduction accounted for 220F as opposed to 130F for radiation.  The numbers themselves don't mean anything, but to me it does paint a picture that brick to brick conduction in the floor is feasible.

Now that I've hopefully somewhat explained my thought process I better get off the computer and on the phone to the Journal of Pizza and tell them to stop the presses pending further peer review, lol.  The things we do waiting to make more pizza.   

[TXCraig1]

I don't disagree that bricks conduct heat.

[scott123]

Jeff, I applaud your efforts. If you have any inclination to test this further (and I think you should), I'd really like to see a traditional fire on the side with a fairly active flame top licking flame for the test. It would also be nice if you could do the test near the end of the bake, just to make sure the super-heating of the center of the hearth during the initial fire isn't messing with the numbers. Lastly, could you take measurements of both the tops of the bricks and the fire facing sides?

Now that I've hopefully somewhat explained my thought process I better get off the computer and on the phone to the Journal of Pizza and tell them to stop the presses pending further peer review, lol.

You joke, but the real world ramifications of this information could be substantial. If conduction is the major player, then all these countless high dome oven owners could, in theory, place some sort of insulating layer (perlcrete) under their fires, go with larger, more aggressive fires and possibly end up with a more Neapolitan-ish top bottom heat ratio. This would most likely burn through a lot more wood, but... for a more Neapolitan-ish thermodynamic, I think it's a price many would be willing to pay.