TRANSPORT PROCESSES (HEAT TRANSFER, DIFFUSION, GAS ABSORPTION)

The driving force in heat transfer is

a. concentration gradient

b. temperature gradient

c. viscosity gradient

d. thickness of the solid in question

b. temperature gradient

Thermal diffusivity of a material

a. has the unit m2/sec.

b. is defined as k/ρ x Cp.

c. is the ratio of thermal conductivity to thermal capacity.

d. all of these

d. all of these

Under the same temperature gradient across various metal

plates of the same thickness, the heat conducted per unit of

surface area will be largest across

a. lead c. iron

b. copper d. nickel

b. copper

If a man touches two metals which were kept together at room

temperature, why would one metal feel colder than the other

a. one has a high heat transfer coefficient

b. one has a high thermal conductivity

c. one has a lower temperature

d. one has a higher heat capacity

b. one has a high thermal conductivity

Cork is a good insulator because it has

a. free electrons

b. atoms colliding frequency

c. low density

d. porous body

d. porous body

The insulation ability of an insulator with the presence of

moisture would

a. increase c. remains unaffected

b. decrease d. none of the above

b. decrease

The critical radius ‘r’ of insulation on a pipe is given by

a. r = 2k/h c. r = k/h

b. r = k/2h d. r = h/k

c. r = k/h

The critical radius of insulation for a spherical shell is (where k

= thermal conductivity of insulating material and ho = heat

transfer coefficient of the outer surface)

a. k/ho c. ho/k

b. 2k/ho d. ho/2k

b. 2k/ho

Heat transfer occurs by natural convection because change in

temperature causes differences in

a. viscosity c. thermal conductivity

b. density d. heat capacity

b. density

In a heat exchanger with steam outside the tubes, a liquid gets

heated to 45°C, when its flow velocity in the tubes is 2 m/s. If

the flow velocity is reduced to 1 m/s, other things remaining

the same, the temperature of the exit liquid will be

a. less than 45°C

b. more than 45°C

c. equal to 45°C

d. initially decreases and remains constant thereafter

b. more than 45°C

Heat transfer in turbulent flow may be described by an

empirical equation correlating

a. Nusselt, Peclet, Prandtl numbers

b. Nusselt, Prandtl, Stanton numbers

c. Nusselt, Prandtl, Reynolds numbers

d. Nusselt, Graetz, Schimdt numbers

c. Nusselt, Prandtl, Reynolds numbers

When heat is transferred from hot body to cold body, in a

straight line, without affecting the intervening medium, it is

referred as heat transfer by

a. conduction c. radiation

b. convection d. convection and radiation

c. radiation

An ideal surface that absorbs all incident radiation, regardless

of the wavelengths and direction and is also considered to be

a perfect emitter is referred to as a

a. gray body c. black body

b. black hole d. pin hole

c. black body

In thermal radiation, for a black body

a. α= 1 and ε is not equal to 1

b. α is not equal to 1 and ε= 1

c. α and ε are not equal to 1

d. α= 1 and ε= 1 where α is absorptivity and ε is emissivity.

d. α= 1 and ε= 1

where α is absorptivity and ε is emissivity.

37. In what flow region is the Dittus-Boelter equation valid?

A. Natural convection
B. Laminar
C. Turbulent
D. Forced convection

C. Turbulent

38. What property in heat transfer accounts for the thermal conductivity, density, and specific heat of a material?

A. Heat transfer coefficient
B. Thermal conductivity
C. Thermal expansivity
D. Thermal diffusivity

D. Thermal diffusivity

40. What happens to liquid water if dropped on a pan at 193°C (Leidenfrost point)?

A. Will vaporize instantly
B. Will bounce like balls
C. Will freeze temporarily
D. Will fall flat

B. Will bounce like balls