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Two long parallel surfaces each of emissivity 0.7 are maintained at different temperatures and accordingly have radiation heat exchange between them. It is desired to reduce 75% of the radiant heat transfer by inserting thin parallel shields of emissivity 1 on both sides. The number of shields should be

Two long parallel surfaces each of emissivity 0.7 are maintained at different temperatures and accordingly have radiation heat exchange between them. It is desired to reduce 75% of the radiant heat transfer by inserting thin parallel shields of emissivity 1 on both sides. The number of shields should be Correct Answer Three

$$\frac{{{\text{Q with shield}}}}{{{\text{Q without shield}}}} = \frac{1}{{{\text{n}} + 1}}.$$
N = number of parallel shields
0.25n + 0.25 = 1
0.25n = 0.75
n = 3.

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