1. Agitated film evaporator is sometimes more suitable because of which one of the following statement?
a) It has Low pressure operations
b) The temperature can be maintained as circulation is present
c) The flow velocity in the tubes and the liquid temperature can be controlled to suit the product requirements
d) Self cleaning because of presence of blades
Explanation: The agitated film evaporator has blades that move at a very close vicinity to the tube with the falling film renewing the film as well as removing the scaling produced; hence it can be regarded as self cleaning equipment.
2. Agitated film evaporator is also known as _______ film evaporator.
a) Wiped
b) Swiped
c) Flushed
d) Flash
Explanation: The agitated film evaporators are commonly known as Wiped surface evaporators because agitated film evaporator has blades that move at a very close vicinity to the tube with the falling film renewing the film as well as removing the scaling produced, hence it can be regarded as a self cleaning equipment.
3. Where does the agitation take place in an agitated film evaporator?
a) Before the liquid falls
b) At the film on the tube surface
c) At the upper end as fluid enters rest is turbulent
d) At the bottom-most point
Explanation: The agitation is carried out on the total length of the evaporator and not at parts, hence the option of agitation on the film is correct and others are incorrect (at the upper end as fluid enters rest is turbulent).
4. Which one of the following is not an advantage of agitated film evaporator?
a) Elevated heat transfer coefficients due to agitation.
b) Very low operation cost
c) Ability of working at high vacuum (down to 0.001 mbar)
d) Very low residence times (to avoid product degradation)
Explanation: The operation cost of agitated film is relatively high owing to the presence of pumps and motors for the agitators, hence this option (Very low operation cost) is wrong.
5. Which one of the following is not a disadvantage of agitated film evaporator?
a) Cost of motors for agitators
b) Higher cost compared to standard evaporation equipment
c) Absence of static pressure on the boiling liquid
d) Staging or vapour recompression for energy recovery are not possible
Explanation: The demerits of agitated film evaporator can be summarised as
i. Higher cost compared to standard evaporation equipment
ii. Staging or vapour recompression for energy recovery are not possible
Otherwise agitators are very useful and mostly preferred over others.
6.How can boiling point elevation be achieved in Evaporators?
a) Increasing pressure
b) Decreasing pressure
c) Increasing Temperature
d) Increasing concentration
Explanation: The boiling point of the solution increases as the water evaporates and the concentration increases, this is known as boiling point elevation.
7. Boiling point of the solution ________ as the evaporation process proceeds.
a) Increases
b) Decreases
c) Remains same
d) Becomes half
Explanation:The boiling point of the solution increases as the water evaporates and the concentration increases, this is known as boiling point elevation. Boiling point, melting point are few properties of liquids that depend on the concentration of solid.
8. Boiling point of a solution is a colligative property.
a) True
b) False
Explanation: The boiling point, melting point and osmotic pressure are few properties of liquids that depend on the concentration of solid in them, this is known as colligative properties
9. The boiling point of a solution is a colligative property because?
a) It depends on the temperature of solution
b) It depends on the concentration of solution
c) It depends on the applied pressure on the solution
d) It depends on the heat capacity of the solution
Explanation:The four properties of fluid that are colligative in nature are –
i. Vapour pressure depression
ii. Boiling point elevation
iii. Melting point depression
iv. Osmotic pressure.
Colligative properties are those properties of the liquid which change (either increase or decrease) with increasing the number of solute molecules (concentration) in the solvent.
10. Boiling point elevation causes the driving force of evaporation in the fluid to _________
a) Decrease
b) Increase
c) Remain same
d) Increase tenfold
Explanation:Boiling point elevation causes the boiling point of the solution to increase and hence the temperature now required to evaporate water also increases, thus the driving force decreases.