Dome design/shape

[grone]

Everyone in here seems to use a spherical dome as opposed to an elliptical shape. Is there a reason for this? I've noticed a few threads whereby people suggest lifting your pizza towards the top of the oven when you are done (well, almost done) to crisp the top up a bit more; but wouldn't the same affect be achieved by building a lower dome?

I am currently drawing plans up on paper (I can't work out how to use QCad... if only Ubuntu had a mechanical drafting program) to work out the brick count and taper angles on the bricks, and need to decide on a dome shape before I can continue. I thought a round based elliptical vault dome would be good because it provides a more even heat from the top of the oven. What are the advantages and disadvantages of available designs? What -are- the available designs?

[BackyardPermaculture]

Re: Dome design/shape

Remember that the size of the opening is around 63% of the dome height; reducing the dome height significantly will also reduce the doorway - too low and you won't be able to get certain foods in and out. It will also reduce the space for the fire, and at some point will affect the airflow - cold air must flow in the bottom, circulate around the top, and out the chimney. A very low dome will also have an increased risk of collapse and will be much more difficult to build.

Not every oven has an imbalance of heat either; mine has so far proved to be very well balanced, with even cooking on base and top of pizza.

Cheers, Mick

[david s]

Re: Dome design/shape

The best combustion chamber is the hemisphere, although departure from this will not make too much difference. With an ellipse you will have to reach further into your oven to get to the back, which means longer handled tools. All design changes are a compromise. Depends what you want.

[grone]

Re: Dome design/shape

So perhaps just a slightly lower dome, but not a severe ellipse?

And to david, I mean the height of the dome rather than the length/depth. Still a regular circle shape for that.

EDIT: And I imagine a hemisphere or parabolic curve would be terrific for cooking with a directional heat (if you wanted to cook something in a specific spot), but how directional is the radiant heat stored in the bricks? Or is the raised hemisphere a good design because it provides a more even heat to more locations in the oven?

[fxpose]

Re: Dome design/shape

So perhaps just a slightly lower dome, but not a severe ellipse?

If you go through some of the build threads here you'll find that a lot of us have gone with the slightly lower dome design.
My floor radius is 17" and my dome height is 15".

George

[grone]

Re: Dome design/shape

I've noticed that some are slightly lower. Haven't managed to read a whole lot of the build threads as of yet. I am getting there, and it's all helping (I think).

[shuboyje]

Re: Dome design/shape

There are a few of us around with low domes. As I argued out here:

http://www.fornobravo.com/forum/6/ne...t-12735-2.html

I feel most of the advantages of the hemisphere that get tossed around here are make believe, but they do have a few big advantages. They are stable and need no support in the horizontal plane, but if that was your only concern a oven with a catenary section would be stronger still, but I don't see anyone building those. They are also much easier to build because you can use a dome gauge thanks to the constant radius. Their last advantage in my mind is the fact that there are tons of them built and being used and functioning great. All you have to do is follow the group and your oven will be great. With a low dome you roll the dice a bit.

Spherical ovens do not provide more even heat, and they do not provide a perfect combustion chamber. A car engine is under compression, our oven are not, and even then being from Detroit I happen to know(check wikipedia) that the hemi makes it's gains from the valve size and placement of both the valves and the spark plugs, and not at all due to it's shape leading to better combustion.

I hope to be building a bigger better oven in the near future at a new house, and if I do it will again be a low dome, but this time it will be in the form of a 3 centered arch.

[grone]

Re: Dome design/shape

Thanks for the reply, I hadn't read the other thread. I was thinking along similar lines in building a higher soldier course and then the shallowest possible dome with what-ever re-enforcing was necessary in the horizontal plane (Just a strap of hoop iron around the bricks?). It seems to make sense that it would provide a more even heat in the oven. I've been trying to read up on thermal radiation and heat convection currents but really I think it would take years of study to be able to work out how it can be incorporated in to choosing a pizza oven design.

[Tscarborough]

Re: Dome design/shape

Electric and gas ovens are either flat ceiling or have a very shallow arch. I can only assume that if there were any advantage to it they would be produced with a higher arch.

The main problems I see with a shallow arched wood fired oven are:

1. The opening will also be very low.
2. The fire will be harder to build and maintain, simply because of the depth.
3. The oven design will need to be engineered to a much greater extent because of the greater forces at play in the walls.

[GianniFocaccia]

Re: Dome design/shape

I can't help but think that anyone who builds a Pompeii-style oven will eventually migrate from their beloved pizza to bread, roasts, casseroles and smoked/grilled dishes, etc. In the event this occurs, I would think a higher-dome oven would provide a higher-degree of control of fire-management, food placement, and a suitable height to grill steaks/chicken.
Of course if all one is going to cook is pizza, I'd opt for a slightly lower dome.

[Neil2]

Re: Dome design/shape

The optimum shape for a pizza oven is an ellipse. Use an 85-90% height to radius ratio.

This is not really that "shallow", but is sufficient to spread the single point focus of a hemisphere out to a 8-10 inch ring. This will give a more even and higher heat to the top of the pizza.

[Hasan]

Re: Dome design/shape

i have a very small barrel oven

with inner dome height of 11.25 and a width of 18

is that too small? or will that make a nice neopolitan oven
- btw its also steel with firebricks lined outside