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.Management Sciences
Category: Heat Transfer
In convection heat transfer from hot flue gases to water tube, even though flow may be turbulent, a laminar flow region (boundary layer of film) exists close to the tube. The heat transfer through this film takes place by___________________?
A. convection
B. radiation
C. conduction
D. both convection and conduction
E. none of the above
The time constant of a thermocouple is_______________?
A. the time taken to attain the final temperature to be measured
B. the time taken to attain 50% of the value of initial temperature difference
C. the time taken to attain 63.2% of the value of initial temperature difference
D. determined by the time taken to reach 100°C from 0°C
E. none of the above
The amount of radiation mainly depends on___________________?
A. nature of body
B. temperature of body
C. type of surface of body
D. all of the above
E. none of the above
The value of Prandtl number for air is about _______________________?
A. 0.1
B. 0.3
C. 0.7
D. 1.7
E. 10.5
Planck’s law holds good for________________?
A. black bodies
B. polished bodies
C. all coloured bodies
D. all of the above
E. none of the above
Total emissivity of polished silver compared to black body is___________________?
A. same
B. higher
C. more or less same
D. very much lower
E. very much higher
Two plates spaced 150 mm apart are maintained at 1000°C and 70°C. The heat transfer will take place mainly by ___________________?
A. convection
B. free convection
C. forced convection
D. radiation
E. radiation and convection
Heat flowing from one side to other depends directly on ___________________?
Pick up the wrong case?
A. face area
B. time
C. thickness
D. temperature difference
E. thermal conductivity
The unit of Stefan Boltzmann constant is ____________________?
A. watt/cm2 °K
B. watt/cm4 °K
C. watt2/cm °K4
D. watt/cm2 °K4
E. watt/cm2 °K2
Unit of thermal conductivity in S.I. units is__________________?
A. J/m2 sec
B. J/m °K sec
C. W/m °K
D. A. and C. above
E. B. and C. above
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