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  #31  
Old 02-06-2011, 12:47 PM
Il Pizzaiolo
 
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Default Re: Mathematical analysis of dome geometry

Thanks, mklingles!

Would be interesting to do a conical oven also - easy shape to specify. I think you will find all of the options are very similar for the no fire case.

I believe the biggest advantage of the lower oven for pizza lies in the flame being closer to the pie - and wrapping more over the top of the pie. If we assume the flames are say 16 inches "tall" they will reach an inch or two further across a "low" dome compared to a taller one and will be several inches closer. We are all familiar with the fact that the side of a pizza cooks faster than the "dark" side (which is receives less flame radiation and more black body refractory radiation from a cooler source than the flame). As a note, for small flames there would be little difference.

Thanks for bringing up the topic and for your calculations!
Jay
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  #32  
Old 02-06-2011, 02:59 PM
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Default Re: Mathematical analysis of dome geometry

To sum it up then, for pizza cooking:

For smaller ovens a hemispherical shape will do fine and provide the opportunity for a somewhat higher door (maintaining the 63% door/dome ratio).

For a larger oven, say 40 inches or more, an elliptical or low dome shape might be more efficient for cooking pizza.
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  #33  
Old 02-06-2011, 03:43 PM
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Default Re: Mathematical analysis of dome geometry

Quote:
Mathmatically:

- A parabola will focus radiant heat at a single point somewhere above the floor.
- A hemisphere will focus at a single point on the floor (center)
- An ellipse will focus on two points on the floor (or in three dimensions, a ring).
What Neil2 is describing here is the behavior of photons that are reflected off of the surface. For that fraction of the inferred radiation that is not absorbed and re-admitted the reflective properties would apply. This article at wikipedia has a good description of specular reflection from curved mirrors. Wikipedia - Curved Mirrors

I have not been able to find a reliable source of data on the amount of energy absorbed by fire brick vs the amount reflected. I believe from the numbers I have found that ~80% of the energy is absorbed and only 20% reflected.

Also the roughness of the firebrick will greatly distort any reflected "image
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  #34  
Old 03-01-2011, 07:49 AM
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Thumbs up Re: Mathematical analysis of dome geometry

I thought we had a good beginning for this discussion....Are we done? Ready to read more
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  #35  
Old 03-02-2011, 04:31 PM
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Default Re: Mathematical analysis of dome geometry

I'm working on adding the door opening to the calculation. Maybe a week or so, I'll get the next round of math done.
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  #36  
Old 10-17-2011, 06:09 PM
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Default Re: Mathematical analysis of dome geometry

mkingles, as an engineer I salute you sir! I liked your quote from a while back 'The maths keeps me out of trouble'

Surely there must be an engineer on this Forum with access to some professional thermal modelling software, three dimensional modelling of radiated heat is fairly complicated, and it doesn't take the effect of convection into account - even in a sealed dome there will be a surface temperature differential between the floor and the walls, which would set up a circulating air flow within the oven. Would this be considered negligible in this situation?
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  #37  
Old 10-17-2011, 06:47 PM
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Default Re: Mathematical analysis of dome geometry

For sure the Convection is a dominant factor in heating the oven and distributing the heat within the oven. For cooking, I think the radiation factor dominates. However, I don't know that to be the case.

I did talk to one physics professor about handing this off to have a student do some more work on it, but haven't even followed up on that. (To busy cooking pizzas, building wood shed, etc).
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  #38  
Old 10-17-2011, 06:54 PM
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Default Re: Mathematical analysis of dome geometry

It is not too complicated.

An elliptical oven has a lower dome than a hemisphere of the same diameter. The heat from the ceiling bricks is closer to the top of the pizza.
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  #39  
Old 10-18-2011, 04:35 AM
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Default Re: Mathematical analysis of dome geometry

This also applies to small ovens. The dome and flame from the active fire are much closer to the pizza. My own oven has the interior height at only 10 and a half inches. It still cooks much the same 90 sec to 2min pizzas. The larger the oven, the larger the fire so I guess it all evens out.
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  #40  
Old 08-31-2013, 03:42 AM
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Default Re: Mathematical analysis of dome geometry

A late first entry to this thread.

In the first post on this thread mklingles said:

Quote: "If anyone knows the absorption / reflection coefficients for fire brick at ~800degF please post."

No one answered...,

On the last page of posts mklingles posted:

Quote: "For sure the Convection is a dominant factor in heating the oven and distributing the heat within the oven. For cooking, I think the radiation factor dominates. However, I don't know that to be the case.

I did talk to one physics professor about handing this off to have a student do some more work on it, but haven't even followed up on that. (To busy cooking pizzas, building wood shed, etc)."


The post runs out at that point.

mklingle (I think) is on the right path as regards the investigation of how items are baked within a wood fired oven. Little, if any, quantitative study has been done on why this combination is able to produce such amazing gastronomic results.

The most likely candidate is the effect of radiant energy on water molecules - especially the distribution of radiant energy excitation on those water molecules...,

Has anyone added to this discourse anywhere else on the site?

Wild-Yeast

P.S. I have ulterior motives on this subject - that's for later...,
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