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Low-dome design questions - Forno Bravo Forum: The Wood-Fired Oven Community

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Low-dome design questions

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  • Low-dome design questions

    I'm researching low-dome design for Neapolitan pizza. My objective is an evenly cooked pizza not only top vs. bottom but also all around.

    Neapolitan pizza ovens that currently do this best appear to:
    - be ellipsoidal in the top half
    - be cylindrical in the bottom half
    - have a low, ~30% height/diameter ratio

    Why is an ellipsoidal curvature good for even heating? Because ellipsoids focus radiation at foci, wouldn't ellipsoids produce hot points instead of evenly spreading fire heat?

    Why cylindrical in the bottom half instead of say running the ellipsoidal curvature down to the floor?

    What's so magical about a height/diameter ratio of 30%? I've read two explanations for this, one that the lower dome cooks the top of the pizza faster (why?) and another that the lower dome eliminates space for steam to collect (so what?).

    Welcome any thoughts from folks who understand some of the physics behind even heating. Thanks.

  • #2
    Re: Low-dome design questions

    Great questions all.

    I have such mixed feelings about Naples pizza ovens. Caputo flour (Naples) is by far the best, San Marzano tomatoes (Naples) are incredible, authentic Mozzarella (Naples) and Provola (Naples) are great and Italian pizzaioli (many trained in Naples) are fantastic.

    But do you need a low dome oven to make great Pizza Napoletana? Do you need an aggressively low domed Naples-style oven to fully and perfectly bake an Italian pizza in 90 seconds? I don't think so.

    A majority of the best wood-fired pizzerias around the world -- including most Italian pizzerias outside of Naples (and many VPN certified pizzerias) use modern wood-fired ovens, such as the FB Modena, which have a slightly higher dome and more curved shape than the steep wall/flat dome shape of the Naples oven. They bake great pizza.

    It makes intuitive sense to me that having vertical space in the dome that is higher than the oven opening acts as a heat reservoir, and improves the oven's efficiency with fuel, without diminishing its ability to bounce heat down onto the cooking floor and cook pizza. That is part of the logic behind the more modern design.

    From a practical point of view, it is probably a little more difficult to build an aggressive low dome oven -- but that said, folks have done it, and really enjoyed the process.

    Maybe it's an inkblot test. We choose to see what we want in a Naples oven.

    I can't wait to hear other folks input on the physics of heat transfer and pizza.
    James
    Pizza Ovens
    Outdoor Fireplaces

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    • #3
      Re: Low-dome design questions

      I don't have the experience with different designs to comment on 'this one is better - because'.

      What I can say is that I built a Pompeii oven, with a shape that is detailed in the plans on this web site, and can make a pretty darn fine pizza.

      I would not look forward to the work involved in making a dome that is 'shorter' than the one I did build. At some point you begin to loose the inherent strength of the 'arch' shape that is part of the design.


      JED

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      • #4
        Re: Low-dome design questions

        To me the bigger problem is keeping the 63 % ratio of height of interior to height of entrance. Lower ceiling height makes for a lower entrance. A 40 inch diameter hemispherical dome has a ceiling height of 20 inches and 63 % of that is approximately 12 5/8 inches, which is enough to allow most pots and roasters to fit easily inside. Reduce that interior dome height to say 14 inches and the entrance height goes to a bit over 8 3/4 inches; now my turkey roaster wouldn't fit thru that low an entrance.

        So if one is simply going to cook pizza and little else then perhaps it isn't a problem. I prefer an oven with more versatility than that.

        Or doesn't the 63% "sweet spot" ratio apply to low dome ovens?

        Wiley
        Last edited by Wiley; 01-23-2009, 12:34 PM.

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        • #5
          Re: Low-dome design questions

          A hemisphere has one focus - the center. An ellipsoid has two (in three dimensions this is a ring), so it will spread the radiated heat from the dome more evenly.

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          • #6
            Re: Low-dome design questions

            There are some advantages and some disadvantages to a higher dome oven. For one thing, a higher dome holds a lot of wood on startup, so you only need two or three trips out to the yard to feed it when starting it up. It also supports a taller door, for easier access, not to mention fitting in the annual obligatory turkey.

            I do think a lower dome gives more top heat to the pizza, and this may promote more even cooking. Make no mistake, the heat comes from the top. Tonight i threw in a pan of chicken pieces at pizza heat with the fire going. They browned on the top, and the bottoms stayed white until the pieces were turned.
            My geodesic oven project: part 1, part 2

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            • #7
              Re: Low-dome design questions

              Originally posted by scpizza View Post
              Why is an ellipsoidal curvature good for even heating? Because ellipsoids focus radiation at foci, wouldn't ellipsoids produce hot points instead of evenly spreading fire heat?

              I would think the ellipsoid shape may have originally been the result of the joining of the dome rings to the doorway arch and may have just resulted in a difference in cooking

              What's so magical about a height/diameter ratio of 30%?

              I don't know if it is magical but man that is low!!!...a 36 inch diameter with a 12 inch ceiling height and an 8.5 inch door height...not too mention how aggressively that arch would have to be sprung
              Just a few thoughts from me...our barrel vault has a pretty low dome at 14 inches...but it is a barrel vault and therefore has a good bit of concrete cladding...and it is abit of a squeeze to get the big turkey in in November
              Best
              Dutch
              Last edited by Dutchoven; 04-01-2009, 06:02 AM.
              "Making the simple complicated is commonplace; making the complicated simple, awesomely simple, that's creativity. " Charles Mingus
              "Build at least two brick ovens...one to make all the mistakes on and the other to be just like you dreamed of!" Dutch

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              • #8
                Re: Low-dome design questions

                As a compromise, I built my dome at 18 inches for a 40 inch oven. This is 90% of the radius (or 45% of the diameter). The door height is 11 1/2 inch.

                It works well for pizzas and the door is easily large enough to put in a turkey.

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                • #9
                  Re: Low-dome design questions

                  Why is an ellipsoidal curvature good for even heating? Because ellipsoids focus radiation at foci, wouldn't ellipsoids produce hot points instead of evenly spreading fire heat?

                  Why cylindrical in the bottom half instead of say running the ellipsoidal curvature down to the floor?
                  Question 1 is already answered by Neil2. Question 2 may be answered by the fact that the focus ring is centered above the oven floor rather than on the oven floor.

                  karl

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