Heat and Mass Transfer
The time constant of a thermocouple is

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

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Heat and Mass Transfer
Thermal conductivity of a material may be defined as the

Heat conducted in unit time across unit area through unit thickness when a temperature difference of unity is maintained between opposite faces
All of these
Quantity of heat flowing in one second through a slab of the material of area one cm square, thickness 1 cm when its faces differ in temperature by 1°C
Quantity of heat flowing in one second through one cm cube of material when opposite faces are maintained at a temperature difference of 1°C

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Heat and Mass Transfer
In counter flow heat exchangers

Both the fluids at inlet are in their hottest state
Both the fluids at exit are in their hottest state
Both the fluids at inlet (of heat exchanger where hot fluid enters) are in their coldest state
One fluid is in hottest state and other in coldest state at inlet

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