Physics, 05.05.2020 17:44, vegasherlyn
13–86 A radiation shield that has the same emissivity e3 on both sides is placed between two large parallel plates, which are maintained at uniform temperatures of T1 5 650 K and T2 5 400 K and have emissivities of e1 5 0.6 and e2 5 0.9, respectively. Determine the emissivity of the radiation shield if the radiation heat transfer between the plates is to be reduced to 15 percent of that without the radiation shield.
Answers: 2
is the Stefan-Boltzmann constant which has a value 
![Q_2 = \frac{\sigma (T_1 ^4 - T_2 ^4)}{ [\frac{1}{e_1 } + \frac{1}{e_2 } - 1 ] + n [\frac{1}{e_3} + \frac{1}{e_3} -1 ]}](/tpl/images/0640/9277/c1c03.png)
the emissivity of the radiation shield and n is the number of radiation shield ![731.52 = \frac{5.67 *10^{-8} (650 ^4 - 400 ^4)}{ [\frac{1}{0.6} + \frac{1}{0.9 } - 1 ] + 1 [\frac{1}{e_3} + \frac{1}{e_3} -1 ]}](/tpl/images/0640/9277/79375.png)
![731.52 = \frac{1.4175*10^{-5}}{ [\frac{1}{0.6} + \frac{1}{0.9 } - 1 ] + 1 [\frac{1}{e_3} + \frac{1}{e_3} -1 ]}](/tpl/images/0640/9277/b6e34.png)
![[\frac{1}{0.6} + \frac{1}{0.9 } - 1 ] + 1 [\frac{1}{e_3} + \frac{1}{e_3} -1 ] = \frac{1.4175*10^{-5}}{731.52}](/tpl/images/0640/9277/83344.png)
![[\frac{1}{0.6} + \frac{1}{0.9 } - 1 ] + 1 [\frac{1}{e_3} + \frac{1}{e_3} -1 ] = 1.9377*10^{-8}](/tpl/images/0640/9277/b85e5.png)
![1 [\frac{1}{e_3} + \frac{1}{e_3} -1 ] = 1.9377*10^{-8} - [\frac{1}{0.6} + \frac{1}{0.9 } - 1 ]](/tpl/images/0640/9277/60847.png)
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13–86 A radiation shield that has the same emissivity e3 on both sides is placed between two large p...
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