160 Important Heat And Mass Transfer MCQ Question and Answer | PDF Free Download
1.Heat is closely related with
- ALiquids
- BEnergy
- CTemperature
- DEntropy
2.Thermal conductivity of water in general with rise in temperature
- AIncreases
- BDecreases
- CRemain constant
- DMay increase or decrease depending on temperature
3.Thermal conductivity of air with rise in temperature
- AIncreases
- BDecreases
- CRemain constant
- DMay increase or decrease depending on temperature
4.The emissivity for a black body is
- A0
- B0.5
- C0.75
- D1
5.The thickness of thermal and hydrodynamic boundary layer is equal if Prandtl number is
- AEqual to one
- BGreater than one
- CLess than one
- DEqual to Nusselt number
6.The value of the wavelength for maximum emissive power is given by
- AWien’s law
- BPlanck's law
- CStefan's law
- DFourier's law
7.The heat transfer by conduction through a thick sphere is given by
- AQ = 2πkr1 r2 (T1 - T2)/ (r2 - r1)
- BQ = 4πkr1 r2 (T1 - T2)/ (r2 - r1)
- CQ = 6πkr1 r2 (T1 - T2)/ (r2 - r1)
- DQ = 8πkr1 r2 (T1 - T2)/ (r2 - r1)
8.The ratio of surface convection resistance to the internal conduction resistance is known as
- AGrashoff number
- BBiot number
- CStanton number
- DPrandtl number
9.Moisture would find its way into insulation by vapour pressure unless it is prevented by
- AHigh thickness of insulation
- BHigh vapour pressure
- CLess thermal conductivity insulator
- DA vapour seal
10.A cube at high temperature is immersed in a constant temperature bath. It loses heat from its top, bottom and side surfaces with heat transfer coefficients of h₁, h₂ and h₃ respectively. The average heat transfer coefficient for the cube is
- Ah₁ + h₂ + h₃
- B(h₁.h₂.h₃)1/3
- C1/h₁ + 1/h₂ + 1/h₃
- DNone of these
11.An ordinary passenger aircraft requires a cooling system of capacity
- A2 TR
- B4 TR
- C8 TR
- D10 TR
12.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)
- ARN = hl/k
- BRN = μ cp/k
- CRN = ρ V l /μ
- DRN = V²/t.cp
13.Metals are good conductors of heat because
- ATheir atoms collide frequently
- BTheir atoms are relatively far apart
- CThey contain free electrons
- DThey have high density
14.Kirchhoff's law states that
- AThe total radiation from a black body per second per unit area is directly proportional to the fourth power of the absolute temperature
- BThe wave length corresponding to the maximum energy is proportional to the absolute temperature
- CThe ratio of the emissive power and absorptive power of all bodies is the same and is equal to the emissive power of a perfectly black body
- DNone of the above
15.If the temperature of a solid surface changes form 27°C to 627°C, then its emissive power changes in the ratio of
- A3
- B9
- C270
- D81
16.Reynolds number is the ratio of
- AEnergy transferred by convection to that by conduction
- BKinematic viscosity to thermal diffusivity
- CInertia force to viscous force
- DNone of the above
17.A heat exchanger with heat transfer surface area A and overall heat transfer coefficient U handles two fluids of heat capacities Cmax and Cmin. The number of transfer units (NTU) used in the analysis of heat exchanger is specified as
- AA.Cmin/U
- BU/A.Cmin
- CA.U.Cmin
- DA.U/Cmin
18.In a shell and tube heat exchanger, baffles are provided on the shell side to
- AImprove heat transfer
- BProvide support for tubes
- CPrevent stagnation of shell side fluid
- DAll of these
19.Fourier's law of heat conduction gives the heat flow for
- AIrregular surfaces
- BNonuniform temperature surfaces
- COne dimensional cases only
- DTwo dimensional cases only
20.Radiation is the process of heat transfer in which heat flows from a ________, in a straight line, without affecting the intervening medium.
- ACold body to hot body
- BHot body to cold body
- CSmaller body to larger body
- DLarger body to smaller body