### Multiple Choice Questions and Answers (MCQs) on Heat and Mass Transfer

01. Unit of thermal conductivity in M.K.S. units is

(A) K cal/kg m² °C
(B) K cal m/hr m² °C
(C) K cal/hr m² °C
(D) K calm/hr °C

02. Thermal diffusivity is a

(A) Function of temperature
(B) Physical property of a substance
(C) Dimensionless parameter
(D) All of these

03. Unit of thermal conductivity in S.I. units is

(A) J/m² sec
(B) J/m °K sec
(C) W/m °K
(D) Option(B) and (C) above

04. 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.

05. 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

06. 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

07. Thermal conductivity of non-metallic amorphous solids with decrease in temperature

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

08. According to Dalton’s law of partial pressures, (where Pb = Barometric pressure, pa = Partial pressure of dry air, and pv = Partial pressure of water vapour)

(A) Pb = pa – pv
(B) Pb  = pa + pv
(C) Pb = pa × pv
(D) Pb = pa/pv

09. Heat transfer takes place as per

(A) Zeroth law of thermodynamics
(B) First law of thermodynamic
(C) Second law of the thermodynamics
(D) Kirchoff’s law

10. The heat transfer by conduction through a thick sphere is given by

(A) Q = 2πkr1 r2 (T1 – T2)/ (r2– r1)
(B) Q = 4πkr1 r2 (T1 – T2)/ (r2 – r1)
(C) Q = 6πkr1 r2 (T1 – T2)/ (r2 – r1)
(D) Q = 8πkr1r2 (T1 – T2)/ (r2 – r1)

11. 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
(D) Conduction and convection

12. Fourier’s law of heat conduction is (where Q = Amount of heat flow through the body in unit time, A = Surface area of heat flow, taken at right angles to the direction of heat flow, dT = Temperature difference on the two faces of the body, dx = Thickness of the body, through which the heat flows, taken along the direction of heat flow, and k = Thermal conductivity of the body)

(A) k. A. (dT/dx)
(B) k. A. (dx/dT)
(C) k. (dT/dx)
(D) k. (dx/dT)

13. When heat is transferred from hot body to cold body, in a straight line, without affecting the intervening medium, it is referred as heat transfer by

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

14. Reynolds number (RN ) is given by (where h = Film coefficient, l = Linear dimension, V = Velocity of fluid, k = Thermal conductivity, t = Temperature, ρ = Density of fluid, cp = Specific heat at constant pressure, and μ = Coefficient of absolute viscosity)

(A) RN = hl/k
(B) RN = μ cp/k
(C) RN = ρ V l /μ
(D) RN = V²/t.cp

15. Sensible heat is the heat required to

(A) Change vapour into liquid
(B) Change liquid into vapour
(C) Increase the temperature of a liquid of vapour
(D) Convert water into steam and superheat it

16. Heat transfer in liquid and gases takes place by

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

17. The heat transfer takes place according to

(A) Zeroth law of thermodynamics
(B) First law of thermodynamics
(C) Second law of thermodynamics
(D) Kirchhoff’s law

18. Which of the following is the case of heat transfer by radiation?

(A) Blast furnace
(B) Heating of building
(C) Cooling of parts in furnace
(D) Heat received by a person from fireplace

19. Thermal conductivity of water ________ with rise in temperature.

(A) Remain same
(B) Decreases
(C) Increases
(D) May increase or decrease depending upon temperature

20. Heat is closely related with

(A) Liquids
(B) Energy
(C) Temperature
(D) Entropy

21. The thickness of thermal and hydrodynamic boundary layer is equal if Prandtl number is

(A) Equal to one
(B) Greater than one
(C) Less than one
(D) Equal to Nusselt number

22. Pick up the wrong case. Heat flowing from one side to other depends directly on

(A) Face area
(B) Time
(C) Thickness
(D) Temperature difference

23. The critical radius is the insulation radius at which the resistance to heat flow is

(A) Maximum
(B) Minimum
(C) Zero
(D) None of these

24. Metals are good conductors of heat because

(A) Their atoms collide frequently
(B) Their atoms are relatively far apart
(C) They contain free electrons
(D) They have high density

25. The automobile radiator is a heat exchanger of

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