# Mechanical Engineering MCQs [Quiz 39]

Q1. In counter flow heat exchangers
(a) both the fluids at inlet (of heat ex¬changer where hot fluid enters) are in their coldest state
(b) both the fluids at inlet are in their hot¬test 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
(e) any combination is possible depending on design of heat exchanger.

Q2. 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
(e) unpredictable.

Q3. 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.

Q4. According of Kirchhoff’s law,
(a) radiant heat is proportional to fourth power of absolute temperature
(b) emissive power depends on temperature
(c) emissive power and absorptivity are constant for all bodies
(d) ratio of emissive power to absorptive power is maximum for perfectly black body
(e) ratio of emissive power to absorptive power for all bodies is same and is equal to the emissive power of a perfectly black body.

Q5. All radiations in a black body are
(a) reflected
(b) refracted
(c) transmitted
(d) absorbed
(e) partly reflected and partly absorbed.

Q6. 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.

Q7. The concept of overall coefficient of heat transfer is used in case of heat transfer by
(a) conduction
(b) convection
(d) conduction and convection
(e) convection and radiation.

Q8. The unit of overall coefficient of heat transfer is
(a) kcal/m2
(b) kcal/hr °C
(c) kcal/m2 hr °C
(d) kacl/m hr °C
(e) kcal/m3 hr °C.

Q9. Joule sec is the unit of
(a) universal gas constant
(b) kinematic viscosity
(c) thermal conductivity
(d) Planck’s constant
(e) none of the above

Q10. The value of Prandtl number for air is about
(a) 0.1
(b) 0.3
(c) 0.7
(d) 1.7
(e) 10.5

Updated: 22nd August 2019 — 9:07 PM