When heat transfer area required is very high
When heat transfer area required is very low, i.e (100-200 ft²)
Because it occupies less floor area
Because it is less costly
✅ The correct answer is option B.
Heat Transfer MCQs
A fluid is flowing inside the inner tube of a double pipe heat exchanger with diameter ‘d’. For a fixed mass flow rate, the tube side heat transfer co-efficient for turbulent flow conditions is proportional to
D0.8
D-0.2
D-1
D-1.8
✅ The correct answer is option B.
Boiling point elevation for a strong and concentrated solution is found by Duhring’s rule, which states that at the same pressure, the boiling point of a solution is a linear function of the __________ of pure water.
Boiling point
Dynamic viscosity
Kinematic viscosity
Density
✅ The correct answer is option A.
In evaporators, lowering the feed temperature
Increases the heating area required
Reduces the economy
Both A and B
Decreases the heating area required
✅ The correct answer is option C.
If all the conditions and dimensions are same, then the ratio of velocity through the tubes of a double pass heat exchanger to that through the single pass heat exchanger is
1
2
1-Feb
4
✅ The correct answer is option B.
The inner wall of a furnace is at a temperature of 700°C. The composite wall is made of two substances, 10 and 20 cm thick with thermal conductivities of 0.05 and 0.1 W.m-1.°C-1 respectively. The ambient air is at 30°C and the heat transfer co-efficient between the outer surface of wall and air is 20 W.m⁻².°C-1. The rate of heat loss from the outer surface in W.m-2is
165.4
167.5
172.5
175
✅ The correct answer is option A.
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.