160 Important Heat And Mass Transfer MCQ Question and Answer | PDF Free Download
1.The critical radius is the insulation radius at which the resistance to heat flow is
- AMaximum
- BMinimum
- CV
- DNone of these
2.According to Stefan Boltzmann law, ideal radiators emit radiant energy at a rate proportional to
- AAbsolute temperature
- BSquare of temperature
- CFourth power of absolute temperature
- DFourth power of temperature
3.Two plates spaced 150 mm apart are maintained at 1000°C and 70°C. The heat transfer will take place mainly by
- AConvection
- BRadiation
- CForced convection
- DFree convection
4.Thermal conductivity of glass wool varies from sample to sample because of variation in
- AComposition
- BDensity
- CPorosity
- DAll of the above
5.Two balls of same material and finish have their diameters in the ratio of 2: 1 and both are heated to same temperature and allowed to cool by radiation. Rate of cooling by big ball as compared to smaller one will be in the ratio of
- A1:1
- B2: 1
- C1: 2
- D4: 1
6.The heat transfer from a hot body to a cold body is directly proportional to the surface area and difference of temperatures between the two bodies. This statement is called
- AFirst law of thermodynamics
- BNewton's law of cooling
- CNewton's law of heating
- DStefan's law
7.The use of heat exchangers is made in
- ARadiators in automobile
- BCondensers and boilers in steam plants
- CCondensers and evaporators in refrigeration and air conditioning units
- DAll of the above
8.The total radiation from a black body per second per unit area is ________ fourth power of the absolute temperature. This statement is known as Stefan Boltzmann law.
- AEqual to
- BDirectly proportional to
- CInversely proportional to
- DNone of these
9.Temperature of steam at around 540°C can be measured by
- AThermometer
- BThermistor
- CThermocouple
- DNone of these
10.Unit of thermal diffusivity is
- Am²/hr
- Bm²/hr °C
- Ckcal/m² hr
- Dkcal/m. hr °C
11.In free convection heat transfer, Nusselt number is function of
- AGrashoff number and Reynold number
- BGrashoff number and Prandtl number
- CPrandtl number and Reynold number
- DGrashoff number, Prandtl number and Reynold number
12.The 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. This statement is known as
- AWien's law
- BStefan's law
- CKirchhoff's law
- DPlanck's law
13.Joule sec is the unit of
- AUniversal gas constant
- BKinematic viscosity
- CThermal conductivity
- DPlanck's constant
14.The process of heat transfer from one particle of the fluid to another by the actual movement of the fluid particles caused by some mechanical means, is known as
- AConduction
- BFree convection
- CForced convection
- DRadiation
15.A perfect black body is one which
- AIs black in colour
- BReflects all heat
- CTransmits all heat radiations
- DAbsorbs heat radiations of all wave lengths falling on it
16.Thermal conductivity of a material may be defined as the
- AQuantity of heat flowing in one second through one cm cube of material when opposite faces are maintained at a temperature difference of 1°C
- BQuantity of heat flowing in one second through a slab of the material of area one cm square, thickness 1 cm when its faces differ in temperature by 1°C
- CHeat conducted in unit time across unit area through unit thickness when a temperature difference of unity is maintained between opposite faces
- DAll of the above
17.Planck’s law holds good for
- Ablack bodies
- Bpolished bodies
- Call coloured bodies
- Dall of the above
18.When α is absorptivity, ρ is reflectivity and τ is transmissivity, then for a diathermanous body,
- Aα = 1, ρ = 0 and τ = 0
- Bα = 0, ρ = 1 and τ = 0
- Cα = 0, ρ = 0 and τ = 1
- Dα + ρ = 1 and τ = 0
19.Heat transfer in liquid and gases takes place by
- AConduction
- BConvection
- CRadiation
- DConduction and convection
20.Which of the following would lead to a reduction in thermal resistance?
- AIn conduction, reduction in the thickness of the material and an increase in thermal conductivity.
- BIn convection, stirring of the fluid and cleaning the heating surface.
- CIn radiation, increasing the temperature and reducing the emissivity.
- DAll of the above