heat transfer objective questions with answers part4

Q1. Heat conducted througfi unit area and unit thick face per unit time when temperature difference between opposite faces is unity,is called
(A) thermal resistance
(B) temperature gradient
(C) thermal conductivity
(D) heat transfer

Q2. The rate of energy emission from unit surface area through unit solid angle, along a normal to the surface, is known as
(A) emissivity
(B) reflectivity
(C) intensity of radiation
(D) absorptivity.

Q3. Emissivity of a white polished body in comparison to a black body is
(A) higher
(B) lower
(C) same
(D) depends upon the shape of body

Q4. A grey body is one whose absorptivity
(A) varies with temperature
(B) varies with wavelength of the incident ray
(C) is equal to its emissivity
(D) does not vary with temperature and. wavelength of the incident ray

Q5. Two balls of same material and finish have their diameters in the ratio of 2 : 1 and both are heated to same temperature and allowed to cool by radiation. Rate of cooling by big ball as compared to smaller one will be in the ratio of
(A) 01:05:00
(B) 02:01:00
(C) 01:02:00
(D) 04:01:00

Q6. .A non-dimensional number generally associated with natural convection heat transfer is
(A) Grashoff number
(B) Weber number
(C) Prandtl number
(D) Reynold number.

Q7. LMTD in case of counter flow heat exchanger as compared-to parallel flow heat exchanger is
(A) higher
(B) lower
(C) same
(D) depends on temperature conditions.

Q8. In heat exchangers, degree of approach is defined as the difference between temperatures of
(A) cold water inlet and outlet
(B) hot medium inlet and outlet
(C) hot medium outlet and cold water inlet
(D) hot medium outlet and cold water outlet

Q9. In counter flow heat exchangers
(A) both the fluids at inlet (of heat exchanger where hot fluid enters) are in their coldest state
(B) both the fluids at inlet are in their hottest state
(C) both the fluids .at exit are in their hottest state
(D) one fluid is in hottest state and other in coldest state at inlet

Q10. A steam pipe is to be insulated by two insulating materials put over each other. For best results
(A) better insulation should be put over pipe and better one over it
(B) inferior insulation should be put over pipe and better one over it
(C) both may be put in any order
(D) whether to put inferior OIL over pipe or the better one would depend on steam temperature

Q11. 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

Q12. According of Kirchhoff’s law,
(A) radiant heat is proportional to fourth power of absolute temperature
(B) emissive power and absorptivity are constant for all bodies
(C) ratio of emissive power to absorptive power is maximum for perfectly black body
(D) ratio of emissive power to absorptive power for all bodies is same and is equal to the emissive power of a perfectly black body.

Q13. All radiations in a black body are
(A) reflected
(B) refracted
(C) transmitted
(D) absorbed

Q14. 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

Q15. The concept of overall coefficient of heat transfer is used in case of heat transfer by
(A) conduction
(B) convection
(C) radiation
(D) conduction and convection

Q16. Joule sec is the unit of
(A) universal gas constant
(B) kinematic viscosity
(C) thermal conductivity
(D) Planck’s constant

Q17. The value of Prandtl number for air is about
(A) 0.15
(B) 0.35
(C) 0.7
(D) 1.7

Q18. The value of the wavelength for maximum emissive power is given by —
(A) Wien’s law
(B) Planck’s law
(C) Stefan’s law
(D) Fourier’s law

Q19. Log mean temperature difference in case of counter flow compared to parallel flow will be
(A) same
(B) more
(C) less
(D) depends on other factors

Q20. 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