Question #312192

Two large parallel planes having emissivities of 0.4 and 0.6 are maintained at temperatures of 846 K and 288 K, respectively. A radiation shield having an emissivity of 0.2 on both sides is placed between the two planes. Calculate (a) the heat-transfer rate per unit area if the shield were not present, (b) the heat-transfer rate per unit area with the shield present. If the emissivity of the shield is increased by 50%, how many shields are needed for the heat transfer rate per unit area as compared with the obtained results from (b)?

Expert's answer

**Solution;**

**(a)**

"\\frac{\\dot{Q}_{12}}{A}=\\frac{\\sigma(T_1^4-T_2^4)}{\\frac{1}{\\epsilon_1}+\\frac{1}{\\epsilon_2}-1}"

"\\frac{\\dot{Q}_{12}}{A}=\\frac{(5.67\u00d710^{-8}\u00d7(846^4-288^4)}{\\frac{1}{0.4}+\\frac{1}{0.6}-1}"

"\\frac{\\dot Q_{12}}{A}=9048.78W\/m^2"

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