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Mathematical analysis of dome geometry

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  • Lburou
    replied
    Re: Mathematical analysis of dome geometry

    Originally posted by Wiley View Post
    All in all one can probably model a theoretical WFO of any given construction. And I like what you have done, However, IMHO assumptions beyond broad generalizations are open to question. Still a fun exercise, and the graphs are cool in the fact they show no theoretical benefit from the lower dome shape. Empirical results may show something different. And of course getting followers of one type of WFO to give up preconceived ideas about one style being better than another for any stated purpose strictly on the basis of theoretical data/analysis might prove difficult. Some use insulated oven doors, some do not.

    Some imperical data would be nice as I read of people firing their WFOs for hours and I wonder at what point are they just wasting wood? Certainly there is an optimal time to fully saturate a given WFO. Burning more wood in an effort to increase that saturation is probably a futile exercise. I don't think it's a perfect analogy but if one likens it to a battery one can change the battery until it is fully charged no more. Further charging results in waste of charging energy as well as a degradation of the battery (damage to electrolyte). I don't know if over firing a WFO causes damage.

    This is probably just an issue of someone learning their WFO, still I cringe when I read of someone firing one of our domes for hours to get it to pizza temperature.

    Bests,
    Wiley
    Points well taken Wiley

    We see a LOT of member reports about time to a clear dome, and oven temperatures after 24, 48 and 72 hours. But we are most certainly comparing apples to oranges. Several of our best and most active members here have barrel ovens. Some have pompeii ovens built from early designs with varying insulation in the hearth and dome.

    We can compare apples to apples if each reporting member would include pertinent details of their build in their signature. Much like board members on car forums do (they will tell you everything about their car and what they did to make it faster). I propose we do the same here at FB.com. It would tell us a lot about the performance enhancements each finds successful.

    Below, in my signature, you see my attempt to start the trend
    I cite the FornoBravo pompeii plan V2.0 and note extra insulation under the oven floor, and any other departure from the plans.
    Last edited by Lburou; 01-31-2011, 09:34 AM.

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  • Wiley
    replied
    Re: Mathematical analysis of dome geometry

    All in all one can probably model a theoretical WFO of any given construction. And I like what you have done, However, IMHO assumptions beyond broad generalizations are open to question. Still a fun exercise, and the graphs are cool in the fact they show no theoretical benefit from the lower dome shape. Empirical results may show something different. And of course getting followers of one type of WFO to give up preconceived ideas about one style being better than another for any stated purpose strictly on the basis of theoretical data/analysis might prove difficult.

    Some imperical data would be nice as I read of people firing their WFOs for hours and I wonder at what point are they just wasting wood? Certainly there is an optimal time to fully saturate a given WFO. Burning more wood in an effort to increase that saturation is probably a futile exercise. I don't think it's a perfect anology but if one likens it to a battery one can change the battery until it is fully charged no more. Further charging results in waste of charging energy as well as a degradation of the battery (damage to electrolite). I don't know if over firing a WFO causes damage.

    This is probably just an issue of someone learning their WFO, still I cringe when I read of someone firing one of our domes for hours to get it to pizza temperature.

    Bests,
    Wiley

    Leave a comment:


  • mklingles
    replied
    Re: Mathematical analysis of dome geometry

    It's true the elliptical dome does appear to spread the height a bit better, although I don't quite have the apples to apples comparison yet.

    This shows a 42" hemispherical dome (h=21), a 42" spherical section (h=18) and a 42" ellipsoidal dome (h=15.5). The ellipsoidal dome does have slightly more even heat across the center section, and a bit more intensity for being a bit lower. I'm not sure the data indicates it's a significant difference.

    I'll compare a 15.5 inch hemispherical section to the ellipsoidal dome next week.

    Leave a comment:


  • Neil2
    replied
    Re: Mathematical analysis of dome geometry

    If they are both spherical, dome height will not matter much. If it is elliptical you will find a low dome spreads the heat better.

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  • GianniFocaccia
    replied
    Re: Mathematical analysis of dome geometry

    Thanks for the analysis, Michael. I put this study right up there with PizzaBob's heat flow analysis. In real terms, if correct, what this does is help remove some of the variables in oven design and construction, ie: kebwi's and drseward's compound angle indispensible tool. Relying on the fact that the dominant property in WFO-cooking is radiative, this would indicate there is no penalty for constructing a truly hemispherical dome, which is easier and more straightforward to build than a spherical cap, which is quite popular, given the number of builds with full-length soldiers.

    Leave a comment:


  • brickie in oz
    replied
    Re: Mathematical analysis of dome geometry

    Ok, Ill shut up now...

    Leave a comment:


  • Tscarborough
    replied
    Re: Mathematical analysis of dome geometry

    I know it will.

    Leave a comment:


  • brickie in oz
    replied
    Re: Mathematical analysis of dome geometry

    Originally posted by brickie in oz View Post
    Here are my scientific findings on wood fired ovens.

    If its too cold, add fuel.
    If its too hot, wait a while.

    Originally posted by Tscarborough View Post
    Now do the analysis for a barrel vault, please.
    I think itll be the same.

    Leave a comment:


  • mklingles
    replied
    Re: Mathematical analysis of dome geometry

    I'll add barrel vault to the list. Warning - it will take some time as I only get a few hours a week to play.

    Leave a comment:


  • Tscarborough
    replied
    Re: Mathematical analysis of dome geometry

    Now do the analysis for a barrel vault, please.

    Leave a comment:


  • Lburou
    replied
    Re: Mathematical analysis of dome geometry

    Originally posted by Polo View Post
    The OP's first post states that his figures do not take a fire or live coals into account. It seems that would negate the findings in regard to pizza cooking, which is done with a fire and live coals. As a matter of fact, I would think that the whole benefit from a low dome would result from the reflective nature of the dome during pizza cooking, which of course includes a fire and hot coals.

    The mathematics are interesting, but real practice may produce different results.
    Polo, I agree. But, that fact does not negate the questions the data raise, or deny the significance of the data. Therein lies the primordial clash between theory and practice. Sorting truth and fiction is what the scientific method does. Calculations are part of the scientific method. I worked in Military acquisition a few years and, believe me, I understand the balance between theory and practice.

    Originally posted by mklingles View Post
    @Lburou: your dimensions are close to the 42" w/ 21". It's going to take me some time to get things coded up for other then spherical surfaces.

    From everything I've read here, I've concluded that dome geometry isn't particularly important. Nobody has posted that they built an XYZ dome and it cooks poorly. I'm doing the math to back up the "dome geometry doesn't matter" conclusion.

    Insulation matters. Door opening for proper air flow matters.
    Thanks for the thoughts mklingles, I feel better about my plan to raise the dome height now. It will also increase the mass of the dome by 28 more half bricks.

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  • mklingles
    replied
    Re: Mathematical analysis of dome geometry

    @Polo. Certainly this is an analysis of only one factor in how the oven works for cooking. However, I believe it is the dominant factor in the effect of the dome shape on the cooking process.

    Leave a comment:


  • mklingles
    replied
    Re: Mathematical analysis of dome geometry

    @Lburou: your dimensions are close to the 42" w/ 21". It's going to take me some time to get things coded up for other then spherical surfaces.

    From everything I've read here, I've concluded that dome geometry isn't particularly important. Nobody has posted that they built an XYZ dome and it cooks poorly. I'm doing the math to back up the "dome geometry doesn't matter" conclusion.

    Insulation matters. Door opening for proper air flow matters.

    Leave a comment:


  • Polo
    replied
    Re: Mathematical analysis of dome geometry

    Originally posted by Lburou View Post
    mklingles, you have peaked my interest with these data. The calculations suggest a flaw in the asserted conclusion that a shorter dome has superior pizza cooking performance to a traditional hemispherical dome.....The calculations also show little or no difference in floor temperature!!
    The OP's first post states that his figures do not take a fire or live coals into account. It seems that would negate the findings in regard to pizza cooking, which is done with a fire and live coals. As a matter of fact, I would think that the whole benefit from a low dome would result from the reflective nature of the dome during pizza cooking, which of course includes a fire and hot coals.

    The mathematics are interesting, but real practice may produce different results.
    Last edited by Polo; 01-29-2011, 05:37 PM. Reason: added thought

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  • Lburou
    replied
    Re: Mathematical analysis of dome geometry

    mklingles, you have peaked my interest with these data. The calculations suggest a flaw in the asserted conclusion that a shorter dome has superior pizza cooking performance to a traditional hemispherical dome.....The calculations also show little or no difference in floor temperature!!

    The shorter dome is more difficult to build, must have a shorter door opening, and in general limits ease of use for anything but pizza and maybe some breads. If there is no REAL difference in the temperature pattern of the two designs, then your data has definite substantive significance.

    My goal is an oven to cook pizza, bread and roasts. The taller door is important to us. I plan a 39.25 inch oven floor and a 22-23 inch dome and a door 63% of the dome in height. Any thoughts? Would your calculations differ with the shape of the oven dome I propose?

    A calculation, or any research, is more valid when the variables within the calculation are controlled and equal when comparing one unit (oven height in this case) to another. Controlling the variables makes the data comparable from one condition to another. Generalizing the data to our oven builds could open the flood gates of debate about the best performing oven designs.

    I'm cutting bricks for my dome....And, very interested in these data.

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