160 Important Heat And Mass Transfer MCQ Question and Answer | PDF Free Download
3.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
- C1
- D-1
4.Heat flows from one body to other when they have
- ADifferent heat contents
- BDifferent specific heat
- CDifferent atomic structure
- DDifferent temperatures
5.In regenerator type heat exchanger, heat transfer takes place by
- ADifferent heat contents
- BA complete separation between hot and cold fluids
- CFlow of hot and cold fluids alternately over a surface
- DGeneration of heat again and again
6.Which of the following property of air does not increase with rise in temperature?
- AThermal conductivity
- BThermal diffusivity
- CDensity
- DDynamic viscosity
7.Thermal conductivity of water _________ with rise in temperature.
- ARemain same
- BDecreases
- CIncreases
- DMay increase or decrease depending upon temperature
8.The rate of energy transferred by convection to that by conduction is called
- AStanton number
- BNusselt number
- CBiot number
- DPeclet number
9.The highest thermal diffusivity is of
- AIron
- BLead
- CConcrete
- DWood
10.Film coefficient is defined as the ratio of
- AThermal conductivity to the equivalent thickness of the film of fluid
- BTemperature drop through the films of fluids to the thickness of film of fluids
- CThickness of film of fluid to the thermal conductivity
- DThickness of film of fluid to the temperature drop through the films of fluids
11.The ratio of the energy absorbed by the body to total energy falling on it is called
- AAbsorptive power
- BEmissive power
- CAbsorptivity
- DEmissivity
12.Which of the following is the case of heat transfer by radiation?
- ABlast furnace
- BHeating of building
- CCooling of parts in furnace
- DHeat received by a person from fireplace
13.The rate of energy emission from unit surface area through unit solid angle, along a normal to the surface, is known as
- AEmissivity
- BTransmissivity
- CReflectivity
- DIntensity of radiation
14.Thermal conductivity of wood depends on
- AMoisture
- BDensity
- CTemperature
- DAll of the above
15.According of Kirchhoff's law
- ARadiant heat is proportional to fourth power of absolute temperature
- BEmissive power depends on temperature
- CEmissive power and absorptivity are constant for all bodies
- DRatio of emissive power to absorptive power for all bodies is same and is equal to the emissive power of a perfectly black body
16.Thermal diffusivity of a substance is given by (where h = Thermal diffusivity, ρ = Density of substance, S = Specific heat, and k = Thermal conductivity)
- Ah = k/ ρS
- Bh = ρS/k
- Ch = S/ρk
- Dh = kρ/S
17.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)
- AQ = [2πlk (T₁ - T₂)]/2.3 log (r₂/r₁)
- BQ = 2.3 log (r₂/r₁)/[2πlk (T₁ - T₂)]
- CQ = [2π (T₁ - T₂)]/2.3 lk log (r₂/r₁)
- DQ = = 2πlk/2.3 (T₁ - T₂) log (r₂/r₁)
18.The amount of radiation mainly depends on
- ANature of body
- BTemperature of body
- CType of surface of body
- DAll of the above
19.Wien’s law states that the wave length corresponding to ________ is proportional to the absolute temperature.
- AMinimum energy
- BMaximum energy
- CBoth (A) and (B)
- DNone of these
20.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
- AConvection
- BRadiation
- CConduction
- DBoth convection and conduction