I started this thread to collect thoughts on why a Neapolitan oven is designed the way it is and perhaps to do some quantitative analysis. I've been considering looking at the impact of the view factor (as affected by dome height and shape) on energy delivered to the pie, but Iím not sure when Iíll get around to it.
I hope to hear otherís thoughts on why the different design elements are the way they are. Here are some of the things Iíve thought about recently. Impact of dome height on floor heating
I wonder if the low Neapolitan dome is as much about heating the floor as about providing heat to the pie from above? As noted above, I've been experimenting with just how fast I can increase the deck temperature with the fire size and flames rolling across the dome.
Both convection and radiation are heating the floor. Based on what I wrote above, I'm convinced that conduction from the coals plays zero role in heating the deck other than directly under the fire. Of course conduction is the main heat source for the deck until you move the fire to the other side of the oven.
With a high dome and a large door, there may be a significant reduction in heat reaching the floor. A high dome has a lower view factor which reduces radiant energy on the deck while a high dome combined with a large door may prevent a meaningful amount of convection from reaching the floor Ė instead a lot of heat may flow right out the door. (Adapted from my post here http://www.pizzamaking.com/forum/index.php/topic,24542.msg248474.html#msg248474
)Floor heating via conduction
I would say the fraction of heat coming from the fire through the floor is even lower Ė probably well under 0.5%
Consider the typical WFO floor. It has very low thermal conductivity Ė probably in the range of 0.6 to 1.1 W/m*K in the biscotto or bricks, but there are also air gaps Ė particularly in a brick floor, so the conductivity of the floor system is even lower. But letís call it 1 W/m*K to be conservative.
Low carbon steel, like people are using for pizza, by comparison, is about 50. Letís say we had a Neapolitan oven with a similar steel floor and we made the unrealistic assumption that 100% of the heat in the floor where the pie is baked comes from the coals through the steel. Our brick floor is only 2% as conductive, so at most 2% of the heat could be coming from the coals through the floor material. Aluminumís conductivity is over 200 W/m*K, and it still would not deliver 100% of the floor heat, but if it did, our bricks would be down to 0.5%.
My observations seem to support this analysis. The floor directly under the coals will heat to north of 1200F, yet I can easily increase or decrease the temperature of the deck by +/- 150F (825F Ė 975F) in a matter of perhaps 30 minutes to an hour by simply changing the intensity of the flames. Changing the size of the coal pile has no such similar effect. (From a post I made in Omidís thread http://www.pizzamaking.com/forum/index.php/topic,14506.msg240367.html#msg240367
If Biscotto di Sorrento is ~0.3W/m*K and typical fire brick is 1.1W/M*K, the absolute difference is small, but it's almost 4 times as conductive. I'd bet it's at least 2X as conductive. This allows for much higher [low] dome temperatures while maintaining thermal balance.