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This set of Thermal Engineering 1 Multiple Choice Questions & Answers (MCQs) focuses on Heat Transfer

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