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Why black? Rough or smooth?

  1. May 5, 2005 #1
    Hello everyone,

    I have read on the Internet that you can get the "brick oven effect" -- uniform heat distribution and crisp bread crusts -- from a regular gas or electric oven by placing tiles and/or firebricks under the food, and tiles above the food (bricks are too heavy to go above).

    1. Why does a brick oven cook more evenly than a modern gas or electric oven, which has a pronounced heat gradient from front to back?

    2. It is always said that black radiates better than white. What is the physical explanation for that?

    3. Firebrick have a rough texture, almost as rough as cinderblock. Would there be a difference due to the difference between the surfaces of black firebrick or black glazed tile? (Firebricks have more thermal mass, so after being opened for a peak, the oven will regain its temperature more quickly with firebrick than with tile. Here, however, I'm asking about the effect of the surface texture.)

    Thanks for your help!

    Rocky
     
  2. jcsd
  3. May 5, 2005 #2

    Andrew Mason

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    Perhaps it has to do with temperature stability and uniformity even at high temperatures. That is hard to achieve if the gas or electricity is on all the time (in order to achieve high temperatures).

    For a body in thermal equilibrium, the heat being absorbed has to equal the heat being emitted. Since a black body is a good absorber of heat (none of the incident radiation is reflected so all is absorbed), it is also a good emitter of heat. So, for a given temperature, the black body emits more radiation (in this case, heat) than a white body.

    AM
     
  4. May 6, 2005 #3
    Thanks and...

    Thanks, Andrew.

    Excellent explanation for #2.

    I didn't understand #1. Uh...on second thought...once the fire is removed from the brick oven, it has a chance to equilibrate it's internal temperature by radiating more from the hotter parts and absorbing more in the cooler parts.

    I hope someone will check in on #3.

    Rocky
     
    Last edited: May 6, 2005
  5. May 8, 2005 #4

    FredGarvin

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    In #3, the surface texture simply gives you more surface area from which to absorb and radiate. Also, the glazing will undoubtedly have a reflective quality to it. So with an unglazed, you are imparting heat to the bricks as well as heat to the air inside the box. This way you envelop the food in a hot box as well as hot air.

    In #1, the answer is thermal mass of the bricks plust the construction of modern ovens. The bricks have quite a bit of mass that also helps insulate and retard the heat transfer to the surroundings. In a fired oven, you also have a relatively constant source of heat. This means that more heat stays in the oven. With gas and electric there are two things that you are fighting. 1 the oven box is metal with fiberglass or somekind of insulation around it. That is not going to reduce the heat going to the surroundings as well as the brick does. Also, the controls of modern ovens actually have the temperature in the box oscillating about a mean temperature. The better the quality of the oven, the less overall deviation in extreme temperatures in the box.
     
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