The electric reheating oven shown in the figure is used to heat a continuous she

Question

The electric reheating oven shown in the figure is used to heat a continuous sheet of metal from 25-1000C The metal speed is such that the strip of metal spends 2 hours inside this oven, The sheet thickness is 1cm and the ambient temperature is 25 C with the temperature of the outside of the oven a uniform 50C. Inside the oven use a and the metal sheet is 304 ss. Calculate the electric power input to the oven per unit oven width; q'. What percentage of this power is lost by convection to the outside air?

Explanation / Answer

Q1 = heat required per unit width to raise the temperature of the metallic strip from 25 - 1000 C ;

Q1 = mC dT ;

C = 27 W/m K

C : specific heat capacity of the metal;

Q1 =

Q c =m h A dT : Heat lost through convection;

Qc = 20 * 0.01 * (100-25);

Qc = 20 * .01 * 75 = 15 ;

Assuming unit mass for all the above cases;

Let W' be the work required by the oven per unit metal width;

so by the law of conservation of energy we have

Q1 = Qc + W';

C * 975 = 20 * 0.01 * 25 + W ;

W = 975 C - 5 ;

W net = 26230 J

Power = W /Tt;

here t = 2 hours ;

P = 26315 / (2*60*60);

P = 3.65 kW

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