A spherical thermocouple junction of diameter 0.706 mm is to be used for the measurement of temperature of a gas stream. The convective heat transfer coefficient on bead surface is 400 W/m2K, Thermophysical properties of thermocouple material are k = 20 W/mK, c = 400 J/kgK and = 8500 kg/m3. If the thermocouple initially at 30 C is placed in a hot stream of 300 C, the time taken by the bead to reach 298 C, is

A spherical thermocouple junction of diameter 0.706 mm is to be used f

1.	A spherical thermocouple junction of diameter 0.706 mm is to be used for the measurement of temperature of a gas stream. The convective heat transfer coefficient on bead surface is 400 W/m2K, Thermophysical properties of thermocouple material are k = 20 W/mK, c = 400 J/kgK and = 8500 kg/m3. If the thermocouple initially at 30 C is placed in a hot stream of 300 C, the time taken by the bead to reach 298 C, is
A.	2.35 s
B.	4.9 s
C.	14.7 s
D.	29.4 s
Answer» C. 14.7 s

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