# Heat and Mass Transfer MCQ – Set 04

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## Q1. In free convection heat transfer transition from laminar to turbulent flow is governed by the critical value of the

(A) Reynold’s number
(B) Grashoff’s number
(C) Reynold’s number, Grashoff’s number
(D) Prandtl number, Grashoff’s number

## Q2. The automobile radiator is a heat exchanger of

(A) Parallel flow type
(B) Counter flow type
(C) Cross flow type
(D) Regenerator type

(A) h = k/ ρS
(B) h = ρS/k
(C) h = S/ρk
(D) h = kρ/S

## Q4. According to Newton’s law of cooling, the heat transfer from a hot body to a cold body is

(A) Directly proportional to the surface area
(B) Directly proportional to the difference of temperatures between the two bodies
(C) Either (A) or (B)
(D) Both (A) and (B)

## Q5. The value of the wave length for maximum emissive power is given by

(A) Kirchhoff’s law
(B) Stefan’s law
(C) Wine’s law
(D) Planck’s law

## Q6. Thermal conductivity of solid metals with rise in temperature normally

(A) Increases
(B) Decreases
(C) Remain constant
(D) May increase or decrease depending on temperature

## Q7. Which of the following is a case of steady state heat transfer?

(A) I.C. engine
(B) Air preheaters
(C) Heating of building in winter
(D) None of the above

## Q8. The concept of overall coefficient of heat transfer is used in heat transfer problems of

(A) Conduction
(B) Convection
(D) Conduction and convection

## Q9. According to Prevost theory of heat exchange

(A) It is impossible to transfer heat from low temperature source to t high temperature source
(B) Heat transfer by radiation requires no medium
(C) All bodies above absolute zero emit radiation
(D) Heat transfer in most of the cases takes place by combination of conduction, convection and radiation

## Q10. Heat conducted through per unit area and unit thick face per unit time when temperature difference between opposite faces is unity, is called

(A) Thermal resistance
(B) Thermal coefficient
(D) Thermal conductivity

## Q11. Which of the following statement is wrong?

(A) The heat transfer in liquid and gases takes place according to convection
(B) The amount of heat flow through a body is dependent upon the material of the body
(C) The thermal conductivity of solid metals increases with rise in temperature
(D) Logarithmic mean temperature difference is not equal to the arithmetic mean temperature difference

## Q12. Which of the following would lead to a reduction in thermal resistance?

(A) In conduction, reduction in the thickness of the material and an increase in thermal conductivity.
(B) In convection, stirring of the fluid and cleaning the heating surface.
(C) In radiation, increasing the temperature and reducing the emissivity.
(D) All of the above

## Q13. The use of heat exchangers is made in

(B) Condensers and boilers in steam plants
(C) Condensers and evaporators in refrigeration and air conditioning units
(D) All of the above

## Q14. Reynolds number is the ratio of

(A) Energy transferred by convection to that by conduction
(B) Kinematic viscosity to thermal diffusivity
(C) Inertia force to viscous force
(D) None of the above

## Q15. The heat is transferred by conduction, convection and radiation in

(A) Melting of ice
(B) Boiler furnaces
(C) Condensation of steam in condenser
(D) None of these

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