Heat and Mass Transfer MCQ – Set 05

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All questions answers in the last paragraph

Q1. 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.

Q2. Total heat is the heat required to

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

Q3. In heat transfer, conductance equals conductivity (kcal/hr/sq.m/°C/cm) divided by

(A) Hr (time)
(B) Sq. m (area)
(C) °C (temperature)
(D) K.cal (heat)

Q4. Heat transfer by radiation mainly depends upon

(A) Its temperature
(B) Nature of the body
(C) Kind and extent of its surface
(D) All of the above

Q5. Film coefficient is defined as Inside diameter of tube

(A) Equivalent thickness of film
(B) Thermal conductivity Equivalent thickness of film Specific heat × Viscosity
(C) Thermal conductivity Molecular diffusivity of momentum Thermal diffusivity
(D) Film coefficient × Inside diameter Thermal conductivity

Q6. Thermal diffusivity is a

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

Q7. The ratio of the thickness of thermal boundary layer to the thickness of hydrodynamic boundary layer is equal to (Prandtl number) n, where n is equal to

(A) -1/3
(B) -2/3
(C) 1
(D) -1

Q8. In a heat exchanger with one fluid evaporating or condensing, the surface area required is least in

(A) Parallel flow
(B) Counter flow
(C) Cross flow
(D) All of these

Q9. In counter current flow heat exchanger, the logarithmic temperature difference between the fluids is __ as compared to parallel flow heat exchanger.

(A) Same
(B) Less
(C) Greater
(D) None of these

Q10. The heat transfer by conduction through a thick cylinder (Q) is given by (where T₁ = Higher temperature, T₂ = Lower temperature, r₁ = Inside radius, r₂ = Outside radius, l = Length of cylinder, and k = Thermal conductivity)

(A) Q = [2πlk (T₁ – T₂)]/2.3 log (r₂/r₁)
(B) Q = 2.3 log (r₂/r₁)/[2πlk (T₁ – T₂)]
(C) Q = [2π (T₁ – T₂)]/2.3 lk log (r₂/r₁)
(D) Q = = 2πlk/2.3 (T₁ – T₂) log (r₂/r₁)

Q11. 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

Q12. Cork is a good insulator because it has

(A) Free electrons
(B) Atoms colliding frequency
(C) Low density
(D) Porous body

Q13. The amount of heat flow through a body by conduction is

(A) Directly proportional to the surface area of the body
(B) Directly proportional to the temperature difference on the two faces of the body
(C) Dependent upon the material of the body
(D) All of the above

Q14. Thermal diffusivity is

(A) A dimensionless parameter
(B) Function of temperature
(C) Used as mathematical model
(D) A physical property of the material

Q15. In convection heat transfer from hot flue gases to water tube, even though flow may be turbulent, a laminar flow region (boundary layer of film) exists close to the tube. The heat transfer through this film takes place by

(A) Convection
(B) Radiation
(C) Conduction
(D) Both convection and conduction

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