# Dairy Engineering Questions and Answers – Evaporator – 1

This set of Dairy Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Evaporator – 1”.

1. Statement related to the process of evaporation that is incorrect is?
a) Evaporation occurs at any temperature
b) Evaporation takes place within liquid
c) Temperature may change during evaporation
d) No bubbles are formed in liquid during evaporation

Explanation: Some of the salient features of evaporation are it occurs at any temperature, It might lead to temperature change. It has been noted that no bubbles are formed in liquid during evaporation.

2. Rate of evaporation is______
a) directly proportional to temperature of liquid
b) inversely proportional to temperature of liquid
c) independent of temperature of liquid
d) directly proportional to humidity of surrounding air

Explanation: Evaporation depends directly on temperature of liquid. Higher the temperature of the substance the greater is the kinetic energy of the molecules at its surface and therefore the faster the rate of their evaporation.

3. Rate of evaporation increases as?
a) exposed surface area of liquid increases
b) exposed surface area of liquid decreases
c) movement of air above surface of liquid decreases
d) atmospheric pressure increases

Explanation: A substance that has a larger surface area will evaporate faster, as there are more surface molecules per unit of volume that are potentially able to escape.

4. Rate of evaporation decreases as?
a) temperature increases
b) humidity of surrounding air increases
c) movement of air above surface of liquid increases
d) atmospheric pressure decreases

Explanation: Humidity is the amount of water vapor present in the air. The air around us cannot hold more than a definite amount of water vapor at a given temperature. If the amount of water in air is already high, the rate of evaporation decreases.

5. Which of the following factors do not affect the rate of evaporation?
a) Temperature of liquid
b) Humidity of surrounding air
c) Depth of liquid
d) Surface of liquid

Explanation: The rate of condensation increases if the temperature of the gas is decreased. On the other hand, the rate of evaporation increases if the temperature of the liquid is increased. It is also increased if: the surface area of the liquid is increased.
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6. Evaporation occurs only _____
a) after boiling
b) after extreme cooling
c) at surface of a liquid
d) if boiling occurs at atmospheric pressure

Explanation: Evaporation takes place at a surface and below the boiling point. The surface atoms or molecules gains energy from surroundings and overcome the attractions of other molecules & get to vaporize.

7. Compounds evaporating easily and giving off a smell are?
a) ionic compounds
b) covalent bonds
c) metallic bonds
d) dative bonds

Explanation: ‘Hospital smells’ are really covalent compounds floating in the air and these attacks our noses. This means that molecules can escape from the liquid fairly easily and evaporate.

8. When heating begins in miscible solutions, vapors formed will be?
a) of liquid lower in boiling point
b) of liquid higher in boiling point
c) vapors will be of both liquids with a higher concentration of liquid having low boiling point
d) collected in a gas syringe

Explanation: Vapors will be of both liquids with a higher concentration of liquid having low boiling point as the heating starts in miscible solution.

9. Evaporation of solution of CuSO4 helps in?
a) making it concentrated
b) crystallization of CuSO4
c) evaporation of salt CuSO4
d) concentration and crystallization

Explanation: The solution turns blue because of diffusion. On heating the solution nothing will happen. Evaporation of solution of CuSO4 leads to its concentration and crystal formation.

10. Crystallization, evaporation and distillation are a means of?
a) separating soluble substances in solution
b) separating insoluble substances in solutions
c) separating filtrate from solution
d) concentration

Explanation: Crystallization, evaporation and distillation are methods of separation of soluble substances in a solution.

11. Concentration is different than drying.
a) True
b) False

Explanation: Concentration of a liquid means removal of a solvent, in most cases water; concentration is distinguished from drying in that the final product – the concentrate – is still liquid.

12. Which of the following is not the reason for the concentration of food liquids?
a) reduce the cost of drying
b) induce crystallization
c) reduce costs for storage and transportation
d) increase water activity in order to increase microbiological and chemical

Explanation: There are several reasons for concentrating food liquids, e.g. to reduce the cost of drying, induce crystallization, reduce costs for storage and transportation, reduce water activity in order to increase microbiological and chemical stability and to recover by-products from waste streams.

13. Evaporation in dairy industry is a preliminary step to which of the following process?
a) Drying
b) Flavoring
c) Watering
d) Pasteurization

Explanation: Dairy industry evaporation is used for concentration duties such as milk, skim milk and whey. It is also used as a preliminary step to drying. Milk products intended for milk powder are normally concentrated from an initial solids content of 9 – 13% to a final concentration of 40 – 50% total solids before the product is pumped to the dryer.

14. Evaporation in dairy industry is done under __________
a) Vacuum
b) Heater
c) Dryer
d) Pasteurizer

Explanation: The products to be evaporated are normally heat sensitive and can be destroyed by adding heat. To reduce this heat impact, evaporation takes place under vacuum, sometimes at temperatures as low as 40°C.

15. Which evaporators can be used when a low degree of concentration is required?
a) Falling film evaporator
b) Circular type evaporator
c) Tubular type evaporator
d) Plate type evaporator

Explanation: Circulation evaporators can be used when a low degree of concentration is required or when small quantities of product are processed. In yogurt production, for example, evaporation is utilized to concentrate milk 1.1 to 1.25 times, or from 13% to 14.5% or 16.25% solids content respectively. This treatment simultaneously de-aerates the product and rids it of off-flavors.

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