Author Topic: Thoughts on Neapolitan oven design  (Read 1648 times)

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Offline TXCraig1

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Thoughts on Neapolitan oven design
« on: April 14, 2013, 04:39:34 PM »
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):

Floor material
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.
I love pigs. They convert vegetables into bacon.


Offline nyyankees325

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Re: Thoughts on Neapolitan oven design
« Reply #1 on: April 15, 2013, 09:24:29 PM »
do you have any idea why they use chalk (gesso) to build the ovens ? i see in the pictures of Ferrara he has alot of it. do you think he puts it in his mortar mix ?

Offline dirk3000

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Re: Thoughts on Neapolitan oven design
« Reply #2 on: April 21, 2013, 05:19:00 PM »
That's gypsum, it sets in an hour. Don't know if its in the mortar, it's not known to be used for mortars in traditional building.

TXCraig1: interesting observations! Thanks for sharing

Offline nyyankees325

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Re: Thoughts on Neapolitan oven design
« Reply #3 on: April 21, 2013, 05:35:30 PM »
Yea the gypsum stefano ferrara has bags of it in one picture he might add it in his refractory mortar I'm not sure.  You didn't mention the chimney design , it seems ferrara builds his chimney right on the dome while forni Grimaldi puts it on a layer of blanket. I think the most important thing in the oven is the biscotto Di sorrento

Offline shuboyje

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Re: Thoughts on Neapolitan oven design
« Reply #4 on: April 21, 2013, 07:23:56 PM »
Yea the gypsum stefano ferrara has bags of it in one picture he might add it in his refractory mortar I'm not sure.  You didn't mention the chimney design , it seems ferrara builds his chimney right on the dome while forni Grimaldi puts it on a layer of blanket. I think the most important thing in the oven is the biscotto Di sorrento

Ceramic fiber blanket is a fairly modern product, that would suggest the Ferrara method is more traditional.  Using ceramic fiber there really makes no sense.  By insulating a Neapolitan style vent you have simply created a poorly design standard vent with two extra near 90 degree turns to decrease draw.  At that point the vents  only purpose is aesthetics.  That may matter to some but for me form without function is a waste, form that detracts from function is a mistake.  This is an artisan product, but it ins't a piece of art that only needs to hang on a wall, it is a piece of commercial equipment that needs to function. 

 
-Jeff

Offline TXCraig1

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Re: Thoughts on Neapolitan oven design
« Reply #5 on: April 21, 2013, 08:17:46 PM »
By insulating a Neapolitan style vent you have simply created a poorly design standard vent with two extra near 90 degree turns to decrease draw.  At that point the vents  only purpose is aesthetics.

Maybe maybe not. I don't have a strong opinion either way at the moment. I don't think the two turns have a material effect on the draw however - at least not in my oven. I'm not arguing the effect of bends in a flue; rather, the flue cross-section in my oven narrows from ~100in^2 at the mouth of the flue (~250in^2 at the oven opening) to 79in^2, in the 10"ID chimney AFTER the second bend, and we know 10" ID is plenty. What the flue may give up in the bends, it more than makes up for in volume.
I love pigs. They convert vegetables into bacon.

Offline Tscarborough

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Re: Thoughts on Neapolitan oven design
« Reply #6 on: April 21, 2013, 08:30:22 PM »
If it doesn't smoke it works, but the real loss is in heat when not firing.  Not a big deal, but certainly a trade off.  I didn't realize they used gypsum, I will have to study on that one.

Offline shuboyje

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Re: Thoughts on Neapolitan oven design
« Reply #7 on: April 21, 2013, 08:52:30 PM »
Craig, realize most of the things I talk about are from the view point of an idealist, which I am too a fault.  In the day to day most of them will be very minute differences.

In theory the friction loses from the two turns in your vent are mitigate by the increased flow caused by the energy added to the system via the dome.  My point is that with the blanket in place you now lose that energy.  Since we can NEVER eliminate all friction and a bend will always have greater friction then straight pipe it goes without saying an oven with a straight up vent of the same volume would have better draw. 

I do agree the Neapolitans don't mess around when it comes to flue volume, and the classic design creates a nice long transition to the round pipe which is very good for reducing friction.
-Jeff

Offline nyyankees325

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Re: Thoughts on Neapolitan oven design
« Reply #8 on: April 21, 2013, 09:48:30 PM »
If it doesn't smoke it works, but the real loss is in heat when not firing.  Not a big deal, but certainly a trade off.  I didn't realize they used gypsum, I will have to study on that one.


Sotto: Pizza Oven Being Built

Here's the pic if you zoom in you can see its written on the bag , gesso da muro rapida presa

Offline nyyankees325

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Re: Thoughts on Neapolitan oven design
« Reply #9 on: April 21, 2013, 10:03:34 PM »
Sotto: Pizza Oven Being Built

Here's the pic if you zoom in you can see its written on the bag , gesso da muro rapida presa


http://pizza.it/content/x-marco-forno#uwzbfxy9ksm

If you go to this post here on pizza.it marco told this guy vincenzone to put the"gesso" on the oven before the insulation


Offline shuboyje

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Re: Thoughts on Neapolitan oven design
« Reply #10 on: April 21, 2013, 10:10:19 PM »
My guess is it serves as an expansion gasket between the oven and the stucco exterior.  Gypsum is going to be soft.
-Jeff

Offline Tscarborough

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Re: Thoughts on Neapolitan oven design
« Reply #11 on: April 21, 2013, 10:36:49 PM »
Yes, gypsum is like perlcrete without the insulating qualities:  good compressive but practically no flexural or shear strength.

Jeez, looking at that link, I would run those guys off my job.  I don't give a crap about tradition, that is sloppy, poor workmanship.

They use the the gypsum as a a plaster and fill for the joints they leave open when building the dome, then use the tufa as insulation and to buttress.  On that build at least, they do not rely on the stucco monocoque.  Other builds I have seen use either ground tufa, or maybe the gypsum as insulation and buttress and do use the shell as a monocoque.
« Last Edit: April 21, 2013, 10:41:19 PM by Tscarborough »

Offline nyyankees325

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Re: Thoughts on Neapolitan oven design
« Reply #12 on: April 22, 2013, 10:19:48 AM »
Ceramic fiber blanket is a fairly modern product, that would suggest the Ferrara method is more traditional.  Using ceramic fiber there really makes no sense.  By insulating a Neapolitan style vent you have simply created a poorly design standard vent with two extra near 90 degree turns to decrease draw.  At that point the vents  only purpose is aesthetics.  That may matter to some but for me form without function is a waste, form that detracts from function is a mistake.  This is an artisan product, but it ins't a piece of art that only needs to hang on a wall, it is a piece of commercial equipment that needs to function.


http://www.fornigrimaldi.com/fasi-di-lavorazioni/forno-mobile/?lang=en#!lightbox[auto_group1]/8/

In this picture you can see some type of blanket on the dome, I haven't see Ferrara put a blanket but I assume he does this as well.

Offline shuboyje

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Re: Thoughts on Neapolitan oven design
« Reply #13 on: April 22, 2013, 07:30:28 PM »
Looking closer at those pictures, that vent is entirely different then I've seen on other Neapolitan builds, it is nearly straight up.
-Jeff

Offline Tscarborough

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Re: Thoughts on Neapolitan oven design
« Reply #14 on: April 22, 2013, 09:16:52 PM »
Code on flues is 30 degree bends.  It has nothing to do with draw, it is because of soot buildup and flue fires.  I am not sure how applicable this is to wood fired oven appliances, but I would think it would be safe to say that it does apply.

Offline TXCraig1

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Re: Thoughts on Neapolitan oven design
« Reply #15 on: April 22, 2013, 09:29:26 PM »
Code on flues is 30 degree bends.  It has nothing to do with draw, it is because of soot buildup and flue fires.  I am not sure how applicable this is to wood fired oven appliances, but I would think it would be safe to say that it does apply.

I would say that the vast majority of WFOs I've seen in restaurants have a 90 degree bend coming out of the oven (or back-to-back 45's anyway). Both ovens shown being built in the link nyyankees325 posted a couple posts above show this as well.
I love pigs. They convert vegetables into bacon.

Offline shuboyje

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Re: Thoughts on Neapolitan oven design
« Reply #16 on: April 22, 2013, 09:53:43 PM »
I was referencing the actual masonry portion of the vent.  Where the others I have seen don't go vertical until they reach the center of the dome this one goes vertical at the very front of the oven, it's essentially just a small S curve.  This looks like exactly what Marco was advising against in his now famous(amongst this forum) description of a proper Neapolitan oven.  What I find even more interesting is that at one point Marco endorsed Grimaldi saying they made the best ovens but where very pricey.  Later without ever mentioning names(that I saw at least) he mentioned that his opinions on builders had changed after learning some of them were not doing things correctly.
-Jeff

Offline Tscarborough

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Re: Thoughts on Neapolitan oven design
« Reply #17 on: April 22, 2013, 10:02:08 PM »
I think they do a lot of things wrong personally.  There is no doubt about the ability of the ovens to produce a 40, 50, or 90 second pizza, but I do not admire their construction techniques or their efficiency.  I guess I will have to build one more the way I think it should be built to prove it.

Offline shuboyje

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Re: Thoughts on Neapolitan oven design
« Reply #18 on: April 22, 2013, 10:03:56 PM »
I agree with you completely Tom.  That was my goal in my oven, taking the basic form of their ovens and combining them with better materials and methods.
-Jeff

Offline nyyankees325

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Re: Thoughts on Neapolitan oven design
« Reply #19 on: April 22, 2013, 11:00:47 PM »
I was referencing the actual masonry portion of the vent.  Where the others I have seen don't go vertical until they reach the center of the dome this one goes vertical at the very front of the oven, it's essentially just a small S curve.  This looks like exactly what Marco was advising against in his now famous(amongst this forum) description of a proper Neapolitan oven.  What I find even more interesting is that at one point Marco endorsed Grimaldi saying they made the best ovens but where very pricey.  Later without ever mentioning names(that I saw at least) he mentioned that his opinions on builders had changed after learning some of them were not doing things correctly.


Quote
Please let me clarify again that I am not associated with sfallestimenti and I made the mistake of recommending them in the past based on wrong information and very much regret so.  Since then, after further and more solid investigation, I would only recommend Forno Napoletano and that is the main reason I AM associated with them and part of this project.

Before signing up to this idea I have throughly tested and verify the ovens made by the master behind Forno Napoletano and have seen 70+ years old oven made by the previous generations of the same family.


http://www.pizzamaking.com/forum/index.php?topic=6655.0 reply 5





 

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