A thermocouple in the form of a long cylinder of 2 mm dia initially at 30 C is used to measure the temperature of a cold gas at –160 C. The convection coefficient over the surface is 60 W/m 2 K. The...

A thermocouple in the form of a long cylinder of 2 mm dia initially at 30C is used to measure the temperature of a cold gas at –160C. The convection coefficient over the surface is 60 W/m²K. The material properties are: density = 8922 kg/m³, specific heat = 410 J/kgK, conductivity = 22.7 W/mK. Determine the time it will take to indicate –150C and also the time constant of the thermocouple.

Then use Eq. (3.3),

Find t. This can be reduced by using smaller wire diameter or higher value of h. The time