Heat and Mass Transfer
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

One
Three
Two
Four

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Heat and Mass Transfer
The time constant of a thermocouple is

Determined by the time taken to reach 100°C from 0°C
The time taken to attain 50% of the value of initial temperature difference
The time taken to attain the final temperature to be measured
The time taken to attain 63.2% of the value of initial temperature difference

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