0.001 to 1
0.6 to 120
0.5 to 5
120 to 400
✅ The correct answer is option B.
Engineering MCQs
A 10 cm dia steam pipe, carrying steam at 180°C, is covered with an insulation (conductivity = 0.6 W/m.°C). It losses heat to the surroundings at 30°C. Assume a heat transfer co-efficient of 0.8 W/m².°C for heat transfer from surface to the surroundings. Neglect wall resistance of the pipe and film resistance of steam. If the insulation thickness is 2 cms, the rate of heat loss from this insulated pipe will be
Greater than that for uninsulated steam pipe
Less than that of the uninsulated steam pipe
Equal to that of the uninsulated steam pipe
Less than the steam pipe with 5 cms insulation
✅ The correct answer is option B.
Prandtl number is the ratio of
Momentum diffusivity to mass diffusivity
Momentum diffusivity to thermal diffusivity
Thermal diffusivity to mass diffusivity
Thermal diffusivity to momentum diffusivity
✅ The correct answer is option B.
A 2-4 heat exchanger involves
Only counter-flow of fluids
Only parallel-flow of fluids
Both counter and parallel-flow of the fluids
Smaller pressure drop compared to 1-2 exchanger
✅ The correct answer is option C.
Thickness of thermal boundary layer is more compared to that of hydrodynamic boundary layer, when the value of Prandtl number is
1
< 1
> 1
> 5
✅ The correct answer is option B.
Multiple effect evaporators ar used to
Increase the steam economy & decrease the capacity
Increase the steam economy & the capacity
Decrease the steam economy & the capacity
Decrease the steam economy & increase the capacity
✅ The correct answer is option B.
When the ratio of the Grashoff number and to the square of Reynolds number is one, the dominant mechanism of heat transfer is
Free convection
Entry length problem in laminar forced conduction (developing thermal boundary layer)
Mixed convection (both free and forced)
Forced convection
✅ The correct answer is option C.
Heat transfer co-efficient equation for forced convection, Nu = 0.023 Re0.8 . Prn, is not valid, if the value of
N = 0.4 is used for heating
N = 0.3 is used for cooling
Reynolds number for the flow involved is > 10000
Reynolds number for the flow involved is < 2100
✅ The correct answer is option D.
The type of liquor circulation system to be ‘ employed in evaporators (viz. natural or forced circulation) is determined mainly by the __________ of the liquid.
Viscosity
Density
Thermal conductivity
Corrosive nature
✅ The correct answer is option A.
When vaporisation takes place through a blanketting film of gas, the phenomenon is termed as __________ boiling.
Pool
Nucleate
Transition
Film
✅ The correct answer is option D.