Heat Transfer Operations Practice Test 6

1. The blades of the agitated film evaporator have a self cleaning effect on the evaporator and hence give us the freedom to use fouling fluids.

True

False

2. What are the names of the axes in the plot by Duhring?

X –Boiling Point of pure water, Y- Boiling Point of solution

X –Boiling Point of solution, Y- Boiling Point of pure water

X –Boiling Point of Solution, Y- Concentration of solution

X –Concentration of solution, Y- Boiling Point of solution

3. What is the overall heat transfer coefficient of an evaporator setup of internal diameter is 30cm and 1m length cylinder in order to evaporate 10kg of water from a feed of 50kg at a temperature of 25℃ to a final temperature of 150℃? Saturated temperature of steam = 160℃
Latent heat of vaporization of water = 2,260 kJ/kg
Specific heat capacity of solution = 4 KJ/Kg K

5053 kJ/m² K

503 kJ/m² K

5553 kJ/m² K

553 kJ/m² K

4. Recognize among the following which is an agitated film evaporator.

heat-transfer-operations-questions-answers-agitated-film-evaporator-q12c

heat-transfer-operations-questions-answers-agitated-film-evaporator-q12a

heat-transfer-operations-questions-answers-agitated-film-evaporator-q12b

heat-transfer-operations-questions-answers-agitated-film-evaporator-q12d

5. Which one of the following is not an advantage of agitated film evaporator?

Very low residence times (to avoid product degradation)

Elevated heat transfer coefficients due to agitation.

Ability of working at high vacuum (down to 0.001 mbar)

Very low operation cost

6. Forced convection boiling is also known as __________

Bubble boiling

Partial nucleate boiling

Flash boiling

Nucleate boiling

7. The Duhring’s rule is used to determine _______

Boiling point elevation

Vapour pressure depression

Osmotic pressure

Surface tension

8. The boiling that takes place in forced convection boiling is popularly known as surface boiling.

False

True

9. What is the pressure used for thermal desalination of water in climbing film evaporators?

Very high around 3-4atm

Just below 1atm

Atmospheric pressure

Close to zero

10. Why is the calculated heat transfer area more than the inner surface heat transfer area of the evaporator?

Area is more than outer surface area

Because the area is outer surface area

Because the area is on a diameter between outer and inner diameter

Because the area is equivalent to a large diameter