Chemical Heat Transfer Mcqs - Set 12

1)   The rate of heat transfer from a vertical plate by natural convection depends upon the temperature differences (ΔT) between wall and outside bulk. The proportionality is given as______________?

a. (ΔT)1/4
b. (ΔT)1/2
c. (ΔT)5/4
d. (ΔT)3/4
Answer  Explanation 

ANSWER: (ΔT)3/4

Explanation:
No explanation is available for this question!


2)   If average heat transfer co-efficient is ha and the local coefficient at the end of the plate is hl then in case of heat transfer to a fluid flowing over a flat plate, heated over its entire length________________?

a. ha = hl
b. ha = 2hl
c. ha = 0.5 hl
d. ha = 0.75 hl
Answer  Explanation 

ANSWER: ha = 2hl

Explanation:
No explanation is available for this question!


3)   Harmonic mean temperature difference is given by_________________?

a. √(ΔT1 . ΔT2)
b. 2 (ΔT1 . ΔT2)/(ΔT1 + ΔT2)
c. 2 (ΔT1 . ΔT2)/(ΔT1 – ΔT2)
d. (ΔT1 – ΔT2)/(ΔT1 . ΔT2)
Answer  Explanation 

ANSWER: 2 (ΔT1 . ΔT2)/(ΔT1 + ΔT2)

Explanation:
No explanation is available for this question!


4)   200 kg of solids (on dry basis) is subjected to a drying process for a period of 5000 seconds. The drying occurs in the constant rate period with the drying rate as, Nc = 0.5 × 10-3 kg/m2.s. The initial moisture content of the solid is 0.2 kg moisture/kg dry solid. The interfacial area available for drying is 4 m2/1000 kg of dry solid. The moisture content at the end of the drying period is (in kg moisture/kg dry solid)?

a. 0.5
b. 0.05
c. 0.1
d. 0.15
Answer  Explanation 

ANSWER: 0.1

Explanation:
No explanation is available for this question!


5)   Fourier’s law of heat conduction applies to _____________ surfaces?

a. Isothermal
b. Non-isothermal
c. Both A. and B.
d. Neither A. and B.
Answer  Explanation 

ANSWER: Both A. and B.

Explanation:
No explanation is available for this question!


6)   Which of the following is generally considered as opaque surface towards radiations ?

a. Gases
b. Solids
c. Liquids
d. Both B. and C.
Answer  Explanation 

ANSWER: Both B. and C.

Explanation:
No explanation is available for this question!


7)   Steam is to be condensed in a shell and tube heat exchanger, 5 m long with a shell diameter of 1 m. Cooling water is to be used for removing the heat. Heat transfer co-efficient for the cooling water, whether on shell side or tube side is the same. The best arrangement is_____________?

a. Vertical heat exchanger with steam on tube side
b. Vertical heat exchanger with steam on shell side
c. Horizontal heat exchanger with steam on tube side
d. Horizontal heat exchanger with steam on shell side
Answer  Explanation 

ANSWER: Vertical heat exchanger with steam on shell side

Explanation:
No explanation is available for this question!


8)   The steam ejector is used to__________________?

a. Remove condensate from the steam pipelines
b. Create vacuum
c. Superheat the steam
d. None of these
Answer  Explanation 

ANSWER: Create vacuum

Explanation:
No explanation is available for this question!


9)   Heat flux is the time rate of heat transfer per unit_______________?

a. Length
b. Area
c. Volume
d. None of these
Answer  Explanation 

ANSWER: Area

Explanation:
No explanation is available for this question!


10)   The actual temperature drop across the heating surface in an evaporator depends on the_________________?

a. Feed
b. Depth of liquid over heating surface
c. Pressure difference between steam chest and vapour space
d. All A., B. and C.
Answer  Explanation 

ANSWER: All A., B. and C.

Explanation:
No explanation is available for this question!


11)   Extended heat transfer surface like fins are used to increase the heat transfer rate. Fin efficiency is defined as the ratio of heat transferred across the fin surface to the theoretical heat transfer across an equal area held at the________________?

a. Surrounding temperature
b. Average temperature of the fin
c. Temperature of the fin end
d. Constant temperature equal to that of the base
Answer  Explanation 

ANSWER: Constant temperature equal to that of the base

Explanation:
No explanation is available for this question!


12)   Thermal conductivity of a conducting solid material depends upon its_______________?

a. Temperature
b. Porosity
c. Both A. & B.
d. Neither A. nor B.
Answer  Explanation 

ANSWER: Both A. & B.

Explanation:
No explanation is available for this question!


13)   When vaporisation takes place directly at the heating surface, it is called________________?

a. Film boiling
b. Nucleate boiling
c. Vapour binding
d. None of these
Answer  Explanation 

ANSWER: Nucleate boiling

Explanation:
No explanation is available for this question!


14)   As per Kirchoff‟s law, the ratio of the total radiating power to the absorptivity of a body depends on the_______________?

a. Temperature of the body only
b. Wavelength of monochromatic radiation
c. Both A. and B.
d. Nature of material of body
Answer  Explanation 

ANSWER: Temperature of the body only

Explanation:
No explanation is available for this question!


15)   Fourier’s law applies to the heat transfer by__________________?

a. Convection
b. Radiation
c. Conduction
d. All A., B. & C.
Answer  Explanation 

ANSWER: Conduction

Explanation:
No explanation is available for this question!


16)   The heat transfer by radiation from a mild steel surface is to be reduced by reducing the emissivity of the surface. This can be best achieved by__________________?

a. Painting the surface black
b. Painting the surface white (with aluminium paint)
c. Giving the surface a mirror finish
d. Roughening the surface
Answer  Explanation 

ANSWER: Painting the surface white (with aluminium paint)

Explanation:
No explanation is available for this question!


17)   Heat produced when a steady state current, I passes through an electrical conductor having resistance, ‘R’ is___________________?

a. IR
b. I2R
c. IR2
d. I2R2
Answer  Explanation 

ANSWER: I2R

Explanation:
No explanation is available for this question!


18)   In a multipass shell and tube heat exchanger, tube side return pressure loss is equal to _____________ the velocity head?

a. Twice
b. Four times
c. Square root of
d. Square of
Answer  Explanation 

ANSWER: Four times

Explanation:
No explanation is available for this question!


19)   The heat flux (from outside to inside) across an insulating wall with thermal conductivity, K = 0.04 W/m.°K and thickness 0.16m is 10 W/m2. The temperature of the inside wall is – 5°C. The outside wall temperature is___________________?

a. 25°C
b. 30°C
c. 35°C
d. 40°C
Answer  Explanation 

ANSWER: 35°C

Explanation:
No explanation is available for this question!


20)   Dittus-Boelter equation cannot be used for molten metals mainly due to its very low_____________________?

a. Prandtl number
b. Grashoff number
c. Thermal conductivity
d. Viscosity
Answer  Explanation 

ANSWER: Prandtl number

Explanation:
No explanation is available for this question!


21)   Steam consumption in kg/hr in case of an evaporator is given by (where, C & E are capacity the economy of the evaporator respectively) ?

a. C/E
b. E/C
c. CE
d. 1/CE
Answer  Explanation 

ANSWER: C/E

Explanation:
No explanation is available for this question!


22)   Which of the following is unimportant in forced convection ?

a. Reynolds number
b. Prandtl number
c. Grashoff number
d. None of these
Answer  Explanation 

ANSWER: Grashoff number

Explanation:
No explanation is available for this question!


23)   Convective heat transfer co-efficient in case of fluid flowing in tubes is not affected by the tube length/diameter ratio, if the flow is in the _____________ zone?

a. Laminar
b. Transition
c. Both A & B
d. Highly turbulent
Answer  Explanation 

ANSWER: Highly turbulent

Explanation:
No explanation is available for this question!


24)   The number of kg vaporised per kg of steam fed to the evaporator is defined as____________?

a. Capacity
b. Rate of evaporation
c. Economy
d. Rate of vaporisation
Answer  Explanation 

ANSWER: Economy

Explanation:
No explanation is available for this question!


25)   Vacuum is generally maintained in the vapour space of an evaporator mainly to__________________?

a. Get economical temperature difference by using moderate pressure steam
b. Facilitate forward feeding in multiple effect evaporation
c. Concentrate heat sensitive materials
d. Achieve very high concentration of the final product
Answer  Explanation 

ANSWER: Get economical temperature difference by using moderate pressure steam

Explanation:
No explanation is available for this question!


26)   With increase in porosity, the thermal conductivity of a solid substance__________________?

a. Increases
b. Decreases
c. Remains unchanged
d. May increase or decrease; depends on the solid
Answer  Explanation 

ANSWER: Decreases

Explanation:
No explanation is available for this question!


27)   Which type of heat exchanger is preferred for heavy heat loads ?

a. Double pipe
b. Plate fine
c. Series and parallel set of shell and tube
d. None of these
Answer  Explanation 

ANSWER: Series and parallel set of shell and tube

Explanation:
No explanation is available for this question!


28)   The unit of heat transfer co-efficient in SI unit is____________________?

a. J/M2°K
b. W/m2°K
c. W/m°K
d. J/m°K
Answer  Explanation 

ANSWER: W/m2°K

Explanation:
No explanation is available for this question!


29)   If the baffle spacing in a shell and tube heat exchanger increases, then the Reynolds number of the shell side fluid_________________?

a. Remains unchanged
b. Increases
c. Increases or decreases depending on number of shell passes
d. Decreases
Answer  Explanation 

ANSWER: Decreases

Explanation:
No explanation is available for this question!


30)   Fouling factor_____________________?

a. Is a dimensionless quantity
b. Does not provide a safety factor for design
c. Accounts for additional resistances to heat flow
d. None of these
Answer  Explanation 

ANSWER: Accounts for additional resistances to heat flow

Explanation:
No explanation is available for this question!