A loaf of bread is being baked in an oven. The oven walls and the air are at 477

Question

A loaf of bread is being baked in an oven. The oven walls and the air are at 477.4 degree K. The surface temperature of the bread is at 373 degree K. The bread is on a conveyor belt moving through the oven. The bread is a rectangular solid, which is 0.1143 m high, 0.1143m wide and 0.330 m long with a total surface area for radiation of 0.17701 m3 (two sides, top, bottom, and two ends). Heat is transferred by both radiation and convection. For the surfaces, the simplified convective Heat Transfer Coefficient equations given in Table 4.7-2 ,page 28 may be used. (Use the Convective Heat Transfer Coefficients given in the Data below.) For the top surface, use the Equation for a cooled plate facing upward. For the bottom plate, use the Equation of a cooled plate looking downward. Calculate the radiation heat transfer coefficient, hr, in W/(m -K). Calculate the heat transferred by radiation, Watts Calculate the convective heat transfer coefficients, hc, for the vertical sides, top, and bottom, in W/ (m2-K). See Data below. Calculate the heat transferred by convection, Watts. Calculate the total heat transferred to the bread in Watts. Data: Emissivity of the bread, = 0.85. For the two vertical sides and two ends, hc = 1.37 ( T/L)1/4, W/ (m2-K), For L use the height, and the total area of the two sides and two ends, L = 0.1143 m A total, is 0.10157m2. For top plate, cooled looking upward, hc = 0, 59 ( T/L)14, W/ (m2-K) For top plate, for L, use the average of the width and the length, L = 0.22222 m, and A total is 0.03772m2 For bottom plate, cooled looking downward, hc = 1.32( T/L)1/4, W/(m2-K). L = 0.22222 m, and A total is 0.03772m2

Explanation / Answer

Ans. q = 278.4 W (950 Btu/h)

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