Calculating Heat Transfer by Radiation: Copper Block at 250 C and 1200 sq cm

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Homework Help Overview

The discussion revolves around calculating heat transfer by radiation from a copper block at 250°C with a surface area of 1200 square centimeters. The participants are exploring the application of the Stefan-Boltzmann law and the implications of emissivity in their calculations.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants discuss the formula for heat transfer and its components, questioning the dimensions of the result and the necessity of converting temperatures to absolute values. There is also an exploration of the heat flux calculated and its relation to the surrounding environment.

Discussion Status

The discussion is ongoing, with participants providing insights and corrections regarding the calculations and assumptions. Some participants have offered guidance on the importance of absolute temperature and the need to consider the surrounding radiation when calculating heat flux.

Contextual Notes

There is a noted lack of additional information about the water involved in the heat transfer, which may affect the calculations. Participants are also working under a time constraint, as the problem is due soon.

annedi
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Homework Statement



How much heat is radiated in water per sq cm, from a block of copper at 250 C and 1200 .

Homework Equations


e= 0.6

Hr= (Area)(e)(5.67x10^-8 W/m^2K^4)(temperature)^4

The Attempt at a Solution


i'm sorry, i don't know how to solve this one...
 
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annedi said:
Hr= (Area)(e)(5.67x10^-8 W/m^2K^4)(temperature)^4

Do you know what this formula says (what the result of it is) and what the dimension of the result could be?
 
The answer must be in joules per second
 
annedi said:
The answer must be in joules per second

Correct, J/s (=W). So it is a heat flux. If you plug in the temperature(s) and the the emissivity from the statement (there is no area), what heat flux have you calculated?
 
is this correct. i computed the Hr as a function of area

132.89 W Area /m^2
70543 W Area/m^2
 
annedi said:
is this correct. i computed the Hr as a function of area

132.89 W Area /m^2
70543 W Area/m^2

According to the statement you posted the temperatures of the copper are given in °C. The formula only works with the absolute temperature, so the values are not correct.

What do you mean with "W Area/m^2"? If you don't know a value for the area and you calculate the formula without it, what would the dimension of the result be?
 
I'm sorry, I forgot to convert the temperature

what i meant by W (area)/ m^2

whatever the area is, you'll plug it in the equation.. so W (x)m^2/m^2 will cancel out thus leaving W as the unit
 
annedi said:
I'm sorry, I forgot to convert the temperature

what i meant by W (area)/ m^2

whatever the area is, you'll plug it in the equation.. so W (x)m^2/m^2 will cancel out thus leaving W as the unit

Okay, then if you plug in all the values you have, what heat flux would you have calculated? (I mean from where to where or from which object to which object)
 
the heat flux from copper to water is 2548.23 W/m^2 at 250C.. is this what you mean..
 
  • #10
annedi said:
the heat flux from copper to water is 2548.23 W/m^2 at 250C.. is this what you mean..

That is basically what I meant, but it is not the heat flux to the water. It would be the heat flux, if all the objects around the copper wouldn't emit radiation at all (at which temperature would that be?). All the objects around, also emit radiation and you need to calculate the difference of the exchanged heat fluxes. Is there any other information about the water?
 
  • #11
there is no more information stated here.. thanks for the help stockzahn. I really appreciated it. this was due today
 
  • #12
annedi said:
there is no more information stated here.. thanks for the help stockzahn. I really appreciated it. this was due today

If that should be the solution, then sorry. I obviously misunderstood the statement. Just one more thing: I think you have to calculate the heat flux for one cm^2 not m^2. That has to be still transformed.
 
  • #13
oh yeah. i just realized that just now.. THANKS AGAIN :)
 

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