Heat Transfer MCQs | AssignGuru

Q1 | Thermal conductivity of wood depends on

moisture

density

temperature

all of the above

Q2 | Heat conducted through unit area and unit thick face per unit time when temperature difference between opposite facesis unity,is called

thermal resistance

thermal coefficient

temperature gradient

thermal conductivity

Q3 | Emissivity of a white polished body in comparison to a black body is

higher

lower

same

depends upon the shape of body

Q4 | A grey body is one whose absorptivity

varies with temperature

varies with wavelength of the incident ray

is equal to its emissivity

does not vary with temperature and wavelength of the incident ray

Q5 | A non-dimensional number generally associated with natural convection heat transfer is

Grashoff number

Nusselt number

Weber number

Prandtl number

Q6 | LMTD in case of counter flow heat exchanger as compared-to parallel flow heat exchanger is

higher

lower

same

depends on the area of heat exchanger

Q7 | In counter flow heat exchangers

both the fluids at inlet (of heat exchanger where hot fluid enters) are in their coldest state

both the fluids at inlet are in their hottest state

both the fluids .at exit are in their hottest state

one fluid is in hottest state and other in coldest state at inlet

Q8 | Fourier's law of heat conduction is valid for

one dimensional cases only

two dimensional cases only

three dimensional cases only

regular surfaces having non-uniform temperature gradients

Q9 | All radiations in a black body are

reflected

partly reflected and partly absorbed

transmitted

absorbed

Q10 | According to Kirchoff's law, ratio of emissive power to absorptivity for all bodies is equal to the emissive power of a

grey body

brilliant white polished body

red hot body

black body

Q11 | The unit of overall coefficient of heat transfer is

W/m2

W/°C

W/m2 °C

W/m °C

Q12 | According to Stefan-Boltzmann law, ideal radiators emit radiant energy at a rate proportional to

absolute temperature

square of temperature

fourth power of absolute temperature

cube of absolute temperature.

Q13 | The unit of Stefan Boltzmann constant is

watt/cm2 °K

watt/cm4 °K

watt2/cm °K4

watt/cm2 °K4

Q14 | Stefan Boltzmann law is applicable for heat transfer by

conduction

convection

radiation

conduction and radiation combined

Q15 | The ratio of the emissive power and absorptive power of all bodies is the same and is equal to the emissive power of aperfectly black body. This statement is known as

Krichoff's law

Stefan's law

Wien' law

Planck's law

Q16 | The total emissivity power is .defined as the total amount of radiation emitted by a black body per unit

temperature

thickness

area

time

Q17 | The ratio of the energy absorbed by the body to total energy falling on it is called

absorptive power

emissive power

absorptivity

emissivity

Q18 | 40% of incident radiant energy on the surface of a thermally transparent body is reflected back. If the transmissivity ofthe body be 0.15, then the absorptivity of surface is

0.45

0.55

0.4

0.75

Q19 | The amount of radiation mainly depends on

nature of body

temperature of body

type of surface of body

all of the above

Q20 | The emissive power of a body depends upon its

temperature

wave length

physical nature

all of the above

Q21 | Two plates spaced 150 mm apart are maintained at 1000°C and 70°C. The heat transfer will take place mainly by

convection

free convection

forced convection

radiation

Q22 | In regenerative type heat exchanger, heat transfer takes place by

direct mixing of hot and cold fluids

a complete separation between hot and cold fluids

flow of hot and cold fluids alternately over a surface

indirect tr

Q23 | A perfect black body is one which

is black in colour

reflects all heat

transmits all heat radiations

absorbs heat radiations of all wave lengths falling on it

Q24 | If the temperature of a solid surface changes from 27°C to 627°C, then its emissive power changes in the ratio of

3

81

9

27