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.Management Sciences
Category: Heat Transfer
In regenerator type heat exchanger, heat transfer takes place by___________________?
A. direct mixing of hot and cold fluids
B. a complete separation between hot and cold fluids
C. flow of hot and cold fluids alternately over a surface
D. generation of heat again and again
E. indirect transfer
Which of the following property of air does not increase with rise in temperature ________________?
A. thermal conductivity
B. thermal diffusivity
C. density
D. dynamic viscosity
E. kuiematic viscosity
According to Kirchoff’s law, the ratio of emissive power to absorptivity for all bodies is equal to the emissive power of a _________________?
A. grey body
B. brilliant white polished body
C. red hot body
D. black body
E. none of the above
The thermal diffusivities for gases are generally_____________________?
A. more than those for liquids
B. less than those for liquids
C. more than those for solids
D. dependent on the viscosity
E. same as for the liquids
When heat is transferred from one particle of hot body to another by actual motion of the heated particles, it is referred to as heat transfer by ___________________?
A. conduction
B. convection
C. radiation
D. conduction and convection
E. convection and radiation
Fourier’s law of heat conduction is valid for_________________?
A. one dimensional cases only
B. two dimensional cases only
C. three dimensional cases only
D. regular surfaces having non-uniform temperature gradients
E. irregular surfaces
The thermal diffusivities for solids are generally__________________?
A. less than those for gases
B. jess than those for liquids
C. more than those for liquids and gases
D. more or less same as for liquids and gases
E. zerci
Thermal conductivity of glass-wool varies from sample to sample because of variation in ________________ ?
A. composition
B. density
C. porosity
D. structure
E. all of the above
The energy distribution of an ideal reflector at higher temperatures is largely in the range of ___________________?
A. shorter wavelength
B. longer wavelength
C. remains same at all wavelengths
D. wavelength has nothing to do with it
E. none of the above
Thermal conductivity of non-metallic amorphous solids with decrease in temperature __________________?
A. increases
B. decreases
C. remains constant
D. may increase or decrease depending on temperature
E. unpredictable
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