160 Important Heat And Mass Transfer MCQ Question and Answer | PDF Free Download
1.In free convection heat transfer transition from laminar to turbulent flow is governed by the critical value of the
- AReynold's number
- BGrashoff's number
- CReynold's number, Grashoff's number
- DPrandtl number, Grashoff's number
2.A grey body is one whose absorptivity
- AVaries with temperature
- BVaries with wavelength of the incident ray
- CIs equal to its emissivity
- DDoes not vary with temperature and. wavelength of the incident ray
3.The automobile radiator is a heat exchanger of
- AParallel flow type
- BCounter flow type
- CCross flow type
- DRegenerator type
4.LMTD in case of counter flow heat exchanger as compared to parallel flow heat exchanger is
- AHigher
- BLower
- CSame
- DDepends on the area of heat exchanger
5.Sensible heat factor is given by (where S.H. = Sensible heat, and L.H. = Latent heat)
- AS.H/(S.H + L.H)
- B(S.H + L.H) /S.H
- C(L.H - S.H)/S.H
- DS.H/(L.H - S.H)
6.Unit of thermal conductivity in M.K.S. units is
- AK cal/kg m² °C
- BK cal m/hr m² °C
- CK cal/hr m² °C
- DK calm/hr °C
7.The critical thickness of insulation for a sphere is
- Ak/h₀
- B2k/h₀
- CV
- Dh₀/2k
8.Free convection flow depends on
- ADensity
- BCoefficient of viscosity
- CGravitational force
- DAll of these
9.Which of the following has maximum value of thermal conductivity?
- AAluminium
- BSteel
- CBrass
- DCopper
10.Which of the following is expected to have highest thermal conductivity?
- ASteam
- BSolid ice
- CMelting ice
- DWater
11.According to Kirchoff's law, the ratio of emissive power to absorptivity for all bodies is equal to the emissive power of a
- AGrey body
- BBrilliant white polished body
- CRed hot body
- DBlack body
12.The transfer of heat by molecular collision is known as
- AConduction
- BConvection
- CRadiation
- DNone of these
13.Heat transfer by radiation mainly depends upon
- AIts temperature
- BNature of the body
- CKind and extent of its surface
- DAll of the above
14.The thermal diffusivities for solids are generally
- ALess than those for gases
- BLess than those for liquids
- CMore than those for liquids and gases
- DMore or less same as for liquids and gases
15.The process of heat transfer from one particle of the body to another is called conduction, when the particles of the body
- AMove actually
- BDo not move actually
- CAffect the intervening medium
- DDoes not affect the intervening medium
16.An electric cable of aluminium conductor (k = 240 W/mK) is to be insulated with rubber (k = 0.15 W/mK). The cable is to be located in air (h = 6 W/m²). The critical thickness of insulation will be
- A25 mm
- B40 mm
- C100 mm
- D200 mm
17.The concept of overall coefficient of heat transfer is used in heat transfer problems of
- AConduction
- BConvection
- CRadiation
- DConduction and convection
18.The natural convection air cooled condensers are used in
- ADomestic refrigerators
- BWater coolers
- CRoom air conditioners
- DAll of these
19.Fouling factor is used
- AIn heat exchanger design as a safety factor
- BIn case of Newtonian fluids
- CWhen a liquid exchanges heat with a gas
- DNone of the above
20.In heat exchangers, degree of approach is defined as the difference between temperatures of
- ACold water inlet and outlet
- BHot medium inlet and outlet
- CHot medium outlet and cold water inlet
- DHot medium outlet and cold water outlet