# 11
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Re: Oven Fuel Consumption Quote:
I think that heat loss through the insulation of a well built oven will be almost negligible compared to heat loss through the oven opening. So the oven geometry and the door area compared to oven volume will determine most of the heat loss. I hope I find an article that addresses that. You raised an interesting point when you brought up the fact that specific heat and other parameters change with temperature rise inside the oven “(especially with a high change in temperature assuming you will be cooking at 500F+)” and this has been a confusing question to me. I mean how do I guarantee the validity of the equation Q = c m dt while c is no longer constant? I hope you tell me if you know. Thanks for being interested in my build. Search the thread (Brick oven reconstructed to a steel one). I’ll view your project too. Cheers. V12spirit |

# 12
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Re: Oven Fuel Consumption Quote:
Your guess is quite right. I did the search for running the oven on gas. I appreciate your generous contribution of the water pan experiment and would like to hear the results hopefully you will not hurt your neck. My calculations regarding gas give only the mass of consumed gas. I got (1634 g) of gas. If that doesn’t help, I’ll give you the number of Btus required so it might describe the appropriate burner. Btus required: (76514 )Btu Bests |

# 13
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Re: Oven Fuel Consumption Hey v12spirit, Heres a link to the derevations of specific heat equations: 2.4 Specific Heats Thermodynamics involves the use of partial differentials, thinking U as a function of time, volume, etc.. With various conditions (isobaric, isothermal, etc.), one can derive the fitting equation for their specific case. If this webpage looks like a foreign language, or even if you do not know what a partial derivative is, I suggest you not stress too much more on this analysis. I myself am not an expert in thermodynamics, but was just pointing out some flaws in the assumptions which arise from your equations. I think your best bet is to try to find some empirical evidence to analyze your design. Do some tests. Design your own experiment (similar to the water pan idea, but more controlled if possible). Right now I am gathering various refractory materials to decide which behaves the most fitting for my oven design. I plan to do a simple test of heating and cooling the refractory materials, measuring the temperatures during a time interval, and plotting the data in various ways. If you can not find your own data, all my suggestions are to find someone who has experience with the same materials. I am definitely new with wood/gas fired ovens and am learning as I find my own information also. I will definitely post my data and information I find out about the refractory materials I will test. Good luck, Adam |

# 14
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Re: Oven Fuel Consumption I just want to say, a good engineer knows when they have hit the point-of-diminishing returns is when it comes to trying to define the thermodynamic characteristics of something as fundamental as a wood-fired oven....If you need an equation, it all boils it down to this: combine firebrick + mortar + insulation with some blood/sweat/tears = WFO then add: (wood + oxygen + ignition source) to the WFO Done! |

# 15
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Re: Oven Fuel Consumption Hey jeeppiper, I like your formula haha. You have to realize as an engineering major I deal with the physics of things. It only comes naturally to me to try to exploit mathematical approximations, theories etc. in a design process. I realize many designs are proven completely functional and appropriate. However, my thoughts are always how a system could be improved in some area of concern. If you want a matrix equation corresponding to your equation : (firebrick, mortar, insulation) + (blood, sweat, tears) s.t. (blood, sweat, tears). Solve this equation for the eigenvalues and corresponding eigenvectors and you end up with a result of WFO. Just kidding, this is just a pure math joke. Adam |

# 16
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Re: Oven Fuel Consumption Quote:
What guarantees the equation Q = c m dt to be valid so long as c changes as the temperature rises? Thanks david for your careful notice. I hope somebody can find the answer. |

# 17
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Re: Oven Fuel Consumption Quote:
Thanks for the link. I'm supposed to manage with differential equations (I hope that) so long as I am currently developing a simulator for ski driving and it involves differential equations.. I opened the page but it will take a while to pick up some useful information from it due to being kind of sophisticated. I took a glance at your oven plan. It looks like being well engineered. Bests. |

# 18
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Re: Oven Fuel Consumption Adam, I hope I didn't offend you. I was just trying to keep you from spending a lot of time on something that might end up steering you down the wrong direction. Believe it or not, the WFO is a very complex and dynamic system. and trying to characterize it with some equations might mislead you and cause you to build an oven that doesn't function as expected. If you want to better understand your design, I would recommend downloading a copy of OpenFOAM and learning it. OpenFOAM is a free, open-source CFD package that will allow you to simulate the airflow in your oven. I would first start by a simple aerodynamic flow through your oven (no heat). This will allow you to see your mean flow path and where your might have stagnant flow (cold-spots). You can then expand your to estimate your heat transfer on the dome by simulating a combustion source. I'm sure OpenFOAM will have some sort of thermodynamic/heat-transfer capability. Doing a simulation will get you closer, however you will still need to understand its limitations. The WFO is a very dynamic system. The heat produced is highly coupled to the airflow. What I mean by this is that the more airflow you have, the more oxygen is sucked in, the more fuel is combusted, which creates more heat. The more heat in the chamber/chimney, the more temperature differential, the more pressure differential....E-I-E-I-OOOOO! So good luck finding an equation that will characterize the WFO! Personally, I would take advantage of the experience and know-how of the folks in the WFO community. Hope this helps. |

# 19
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Re: Oven Fuel Consumption Hey jeeppiper, You didn't offend me, don't worry about that haha. I will definitely look into OpenFOAM. I never did computer modeling of thermodynamics. Actually, I might even use a program next semester for my thermodynamics course. Thanks for the advise. Adam |

# 20
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Re: Oven Fuel Consumption Quote:
I just replaced the sphere volume (4/3)*(PI)*(r)^3 with (3/4)*(PI)*(r)^3 so I got this result: 4820 g that should have been: 6948 g The result is that my 3 factor is quite more safe so it can be reduced to a smaller factor that I hope one would one day do it.
__________________ Why is this thus? What is the reason for this thusness? I forgot who said that. |

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