Earthstone 110 or FGM?

[scott123]

Also, remember that you can only count the dome space in the vicinity of the door, not the back of the oven.

While the front of the dome gets hotter than the rear, the whole dome is heated by the superheated air.  If the whole dome is heated, the dome in the back gets counted.

Fabricate an insert, and pre-heat the oven with and without it. If the insert doesn't trim off at least 1/4 of the pre-heat time (and use at least 1/4 less wood to reach the same temps), I'll eat my hat.

[TXCraig1]

Tom, the exhaust layer isn't trapping heat, it's the top of the dome that's trapping the heat as it rises. This really isn't all that complicated.  Hot air rises.  Cooler exhaust air sinks.  The rolling layer of smoke we've all seen at the door level is cooler then the air above it.

Are you sure about that? My recollection is that the smoke after adding a log to a hot oven is at the upper level of the oven. Isn't that why there is a layer? The cooler, denser air below traps the particulate matter in the upper part of the oven?

[TXCraig1]

In a perfectly cylindrical 42" oven, a 2" lower door translates into 264 square inches of additional brick surface area contacting the hot air

And 264in² of additional brick surface area and who knows how much additional mass that must be heated.

and 2772 cubic inches (19 cubic feet) of additional hot air volume.  That triples the volume of the 1" head space created by the original door.  

Triple sounds impressive, but consider the numbers. (N.B. 2,772 in³ = 1.6ft³)

Let’s say the superheated air is 1500F/1089K

2,772in³ = 0.0454m³

At 1089K, the density of air is .3243kg/m³, so you have 0.0147kg of air in the extra 2”

At 1089K, the specific enthalpy of air is 1,149kJ/kg, so the energy of the extra 2” of air is 16.9kJ or 0.017MJ

There is about 10.4MJ/kg recoverable energy in oak firewood, so the energy in the air in the extra 2” is about the equivalent of 0.0016kg or 0.06oz of oak.

Here is what that looks like (paper clip for scale):

[Chicago Bob]

Fabricate an insert, and pre-heat the oven with and without it. If the insert doesn't trim off at least 1/4 of the pre-heat time (and use at least 1/4 less wood to reach the same temps), I'll eat my hat.

Mmmm....

[Reep]

Craig is giving me nightmares of may P-chem courses in graduate school.

It will be a while, but I will have a way to test the oven under both conditions.  I'll weigh out the same amount of wood, burn it under the same conditions and at the same time point after lighting I will take a temp measurement of the dome and floor and compare them.  It will be a while though, so Scott better not salt his hat yet.

[TXCraig1]

It will be a while, but I will have a way to test the oven under both conditions.  I'll weigh out the same amount of wood, burn it under the same conditions and at the same time point after lighting I will take a temp measurement of the dome and floor and compare them.  It will be a while though, so Scott better not salt his hat yet.

Remember the most important of the "same conditions" are the moisture content of the wood, the ambient air temperature, and the initial heat content of the oven which, of course, is at least partially a function of the ambient air temperature. If there has been a big swing in ambient temperature (particularly if there is also wind) before the test, the starting temperature of the oven might not be a reliable indicator of heat content. Small differences in moisture content of the wood will make a big difference in the test.

[Reep]

Remember the most important of the "same conditions" are the moisture content of the wood, the ambient air temperature, and the initial heat content of the oven which, of course, is at least partially a function of the ambient air temperature. If there has been a big swing in ambient temperature (particularly if there is also wind) before the test, the starting temperature of the oven might not be a reliable indicator of heat content. Small differences in moisture content of the wood will make a big difference in the test.

Yeah, I can use the same lot of wood, and in SoCal we have a lot of very mild days, so consistency isn't a problem.  I can even take starting surface temperatures to make sure it's the same.  I have a Ph.D. in science so I think I can eliminate most variables and get a good result.  I will wait until the oven is well broken in too so we don't get any variation from that.

Now, off to order my oven.

[TXCraig1]

Yeah, I can use the same lot of wood, and in SoCal we have a lot of very mild days, so consistency isn't a problem.  I can even take starting surface temperatures to make sure it's the same.  I have a Ph.D. in science so I think I can eliminate most variables and get a good result.  I will wait until the oven is well broken in too so we don't get any variation from that.

Now, off to order my oven.

I look forward to the results.

[JConk007]

Holy Moly way too complicated Lost me on the first X2?  I prefer results
The first 2 pictures  are from ? oven and second 2 are from ?
same Batch of wood !
options are Mobile , Earthstone , and Four Grand Mere  
John

[Chicago Bob]

Gorgeous pies John...you deserve an icy cold Margareta...top shelf. 

[JConk007]

its  about the different ovens and all the hoopla on heat loss, floor temp gases.... 
Boggles my mind you cant go wrong with either as I said before. Build 1 . go to italy for a month and train ? come back its done and have some fun !

[Reep]

its  about the different ovens and all the hoopla on heat loss, floor temp gases.... 
Boggles my mind you cant go wrong with either as I said before. Build 1 . go to italy for a month and train ? come back its done and have some fun !

Yeah.  Your first hand experience with all these was very valuable.  I still want to play with the door opening out of curiosity, but I know I will love my oven. 

Okay, so I like the bottom pie the best.  Which oven?

[JConk007]

The Bottom Pie was from the  Four Grand Mere Party I did for RickM now a member here andcame over last night. You can confirm it in my FWF thread toward end  before bacholorette party same pics are there 

[Reep]

The Bottom Pie was from the  Four Grand Mere Party I did for RickM now a member here andcame over last night. You can confirm it in my FWF thread toward end  before bacholorette party same pics are there 

Sweet.  I know the look of the top is mostly the skill of the chef, but both top and bottom looked great. 

[scott123]

Triple sounds impressive, but consider the numbers. (N.B. 2,772 in³ = 1.6ft³)

Let’s say the superheated air is 1500F/1089K

2,772in³ = 0.0454m³

At 1089K, the density of air is .3243kg/m³, so you have 0.0147kg of air in the extra 2”

At 1089K, the specific enthalpy of air is 1,149kJ/kg, so the energy of the extra 2” of air is 16.9kJ or 0.017MJ

There is about 10.4MJ/kg recoverable energy in oak firewood, so the energy in the air in the extra 2” is about the equivalent of 0.0016kg or 0.06oz of oak.

According to this calculator, the ideal flow rate for an 8" diameter 2' high chimney at 800F is .05799 m³/s.  In other words, the superheated air volume that we're discussing (0.0454m³) is being replaced every second (give or take). Based on your numbers, for a six hour preheat, the necessary energy to maintain that 1089K temp in that 2" of volume would translate into 81 lb. of wood. Now, this is an ideal flow rate for one chimney.  Even if the chimney is only drawing 1/4 of that, you're still talking 20 lb. of wood.

That's a lot of wood. A lot of energy.  If the draw keeps that superheated air in contact with the additional 2" wide surface area for a second (or more), over the course of six (or more) hours, that's a substantial amount of heat transfer, especially considering the convective impact of the perpetually moving air.

[scott123]

Holy Moly way too complicated Lost me on the first X2?  I prefer results

John, buddy, we're talking about wood consumption here, along with peak dome temps. All your beautiful pizza photos prove is that just about any WFO can make stunning pizza.  That's not being argued here.  It wouldn't be easy, but I have no doubt that your stunning pies could be reproduced in a Mugnaini. And yet, no one here would ever recommend a Mugnaini to the original poster.

It's not about whether or not an oven can make great Neapolitan pizza, it's about whether or not it can make great Neapolitan pizza in the easiest and most efficient way possible.  The lower dome of the FGM is a critical part of that equation, but the door height (and potential insert to correct it) is a contributing factor as well.

[TXCraig1]

According to this calculator, the ideal flow rate for an 8" diameter 2' high chimney at 800F is .05799 m³/s.  In other words, the superheated air volume that we're discussing (0.0454m³) is being replaced every second (give or take). Based on your numbers, for a six hour preheat, the necessary energy to maintain that 1089K temp in that 2" of volume would translate into 81 lb. of wood. Now, this is an ideal flow rate for one chimney.  Even if the chimney is only drawing 1/4 of that, you're still talking 20 lb. of wood.

Scott,
Your calculation represents the amount of wood necessary to maintain the temperature of that 2” if you replaced the air every second with air at 0K. I also think the idea of replacement of that 2” is conceptually wrong. Say you have two ovens identical in every respect except that one has a 2” higher dome.  The flow rate is going to be virtually identical.

That's a lot of wood. A lot of energy.  If the draw keeps that superheated air in contact with the additional 2" wide surface area for a second (or more), over the course of six (or more) hours, that's a substantial amount of heat transfer, especially considering the convective impact of the perpetually moving air.

You make it sound like if you don’t have “superheated air” on that 2”, the air contacting it will be at ambient temperature. I would think that it would be only marginally cooler than the “superheated air.”   How big do you think the temperature differential is?

I believe the air temperature much smaller factor than the radiant energy coming off the fire with respect to heating the oven. For example, When I bring the fire down and move it from the middle to the left rear, the right side wall is usually about 925-950F. Within 30 minutes, that right wall will have cooled to 875F.

[TXCraig1]

It's not about whether or not an oven can make great Neapolitan pizza, it's about whether or not it can make great Neapolitan pizza in the easiest and most efficient way possible.  The lower dome of the FGM is a critical part of that equation, but the door height (and potential insert to correct it) is a contributing factor as well.

How do you know that the extra radiant energy put on the pie from the improved view factor of the lower dome doesn't more than compensate for 2" less "superheated air" whatever that is?

How do you know that by restricting the airflow into the FGM as you have proposed, you won't more than offset any gains from the extra "superheated air" with losses in combustion efficiency?

How do you know the energy differential between "superheated air" and the other hot air in the upper part of the oven is even meaningful?

[TXCraig1]

Scott, you may be right. I'm not trying to be combative. I'm just having a hard time seeing the basis for some of the assumptions that are being made.

[scott123]

Your calculation represents the amount of wood necessary to maintain the temperature of that 2” if you replaced the air every second with air at 0K. I also think the idea of replacement of that 2” is conceptually wrong. Say you have two ovens identical in every respect except that one has a 2” higher dome.  The flow rate is going to be virtually identical.

Yes, the 0K was an error. All my figures are pretty rough. It still translates into a lot of wood using ambient temps for the replacement air.

The flow rate will be virtually identical. I'm not talking about two different rates, just two different flow distances. Car A is going 65 mph and Car B is going 65 mph, but Car B (the lower door) is on a slightly longer track.