E-PolyLearning

1. “The response of a thermocouple is defined as the time required for the thermocouple to reach the surrounding temperature when it is exposed to it”. Choose the correct answer
a. True
b. False
c. May be
d. Can't say
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Answer: (b).False

2. The sensitivity of thermocouple is defined as the time required by thermocouple to reach how much percentage of its steady state values?
a. 43.3
b. 53.2
c. 63.3
d. 73.3
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Answer: (c).63.3

3. The response time for different sizes and materials of thermocouple wires usually lie between
a. 0.04 to 2.5 seconds
b. 0.06 to 1.2 seconds
c. 0.02 to 0.04 seconds
d. 2.4 to 9.4 seconds
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Answer: (a).0.04 to 2.5 seconds

4. A thermocouple junction of spherical form is to be used to measure the temperature of the gas stream. The junction is at 20 degree Celsius and is placed in a gas stream which is at 200 degree Celsius. Make calculations for time required by the thermocouple to reach 197 degree Celsius temperature. Assume the thermos-physical properties as given below
k = 20 W/ m K

h = 350 W/m² K

c = 0.4 k J/kg K

p = 8000 kg/m³
a. 1.094 seconds
b. 2.094 seconds
c. 3.094 seconds
d. 4.094 seconds
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Answer: (d).4.094 seconds

5. An egg with mean diameter of 4 cm and initially at 25 degree Celsius is placed in an open boiling water container for 4 minutes and found to be boiled at a particular level. For how long should a similar egg boil at the same level, when refrigerator temperature is 5 degree Celsius? Use lumped parameter theory and assume following properties of egg

k = 12 W/m K

h = 125 W/m² K

c = 2 k J/kg K

p = 1250 kg/m³
a. 251.49 seconds
b. 261.49 seconds
c. 271.49 seconds
d. 281.49 seconds
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Answer: (c).271.49 seconds

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