In order to conserve energy, the inner surface of double-glazed windows are treated with a low emissivity coating that reduces the emissivity of the uncoated surface from 0.95 to 0.5 for the coated surface. If the temperatures of the two glass panes are 20°C and 0°C, respectively, determine the reduction in heat transfer in a coated double-glazed window as compared with the uncoated one.
GIVEN
? Double glazed windows treated with low emissivity coating that reduce emissivity of uncoated
surface from ??1 =0.95 to ??2= 0.5.
? Temperature of glass pane 1 (T1)= 20°C = 293 K
? Temperature of glass plane 2 (T2) = 0°C = 273
FIND
Reduction in heat transfer in coated double glazed window as compared to uncoated one.
PROPERTIES AND CONSTANTS
From Appendix 1, Table 5, the Stephan-Boltzmann constant
When the double glazed window is not coated heat transfer between the surfaces is
When the double glazed window is coated heat transfer between the surfaces is
Thus the reduction in heat transfer
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