Refrigeration And Refrigerators

Refrigeration and RefrigeratorsRefrigeration and Refrigerators

1.1. ProportionProportion: the relation of one part to another or to the whole.

WORD STUDY:WORD STUDY:

There is a high proportionproportion of nitrogen in the atmosphere.

2.2. BurstBurst : break open by force.

You can burstburst a car tyre by sticking a nail

in it.

3.3. EssentialEssential:: vital, very important.

Proteins and vitamins are

essentialessential to good health.

4.4. InsulatedInsulated : : encased in a poor conductor material.

An insulatedinsulated container is encased in a material that is a poor conductor of heat, so that the temperature inside remains

unaffected by the temperature outside.

5.5. Blasting Blasting :: blowing very hard with high-pressure air.

Food can be frozen by placing it in an insulated container and blastingblasting it at high speed with air cooled below -30°C.

Vegetables and meat can be preserved in brinebrine.

6.6. brinebrine : salt water.

7.7. freezerfreezer : It is a refrigerator which keeps its contents at temperatures well below freezing point.

A freezerfreezer is a type of refrigerator which we use for long storage.

8.8. thawed outthawed out : unfrozen

Frozen food is thawed outthawed out simply by raising its temperature over O°C.

When snow thawsthaws, it melts.

9.9. poultrypoultry : domestic birds such as hens, ducks, geese and turkeys.

PoultryPoultry can usually be eaten.

PoultryPoultry is a collective word which is uncountable and has no plural.

10.10.cooling agentcooling agent: a substance which cools other substances.

An agentAn agent is the active substance in a process.

Certain chemicals are used as drying agentsagents.

11.11. cycle:cycle: a a continuing process in which continuing process in which certain actions and reactions are certain actions and reactions are repeated over and over again, e.g. the repeated over and over again, e.g. the water cycle.water cycle.

12.12. thermostatthermostat : an instrument which maintains a constant temperature.

A A thermostatthermostat usually consists of a usually consists of a bimetallic stripbimetallic strip and and two contacttwo contact pointspoints, one to a , one to a heaterheater and one to and one to a a coolercooler. The heater is switched on when the . The heater is switched on when the temperature falls below the required level and the temperature falls below the required level and the cooler is activated when the temperature rises cooler is activated when the temperature rises above the required level. Brass and iron are the above the required level. Brass and iron are the two metals usually used.two metals usually used.

QUESTIONS ON THE TEXTAnswer these questions:

a) How do sub-zero temperatures affect harmful micro-organisms?

Micro-organisms cannot grow or multiply at sub-zero temperatures.

b. What does most food consist of?

Most food consists of animal or plant cells containing a high proportion of water.

c) Why is food spoilt if it is frozen gradually?Food is spoilt because Food is spoilt because the water expands and the water expands and forms large crystals of forms large crystals of ice whichice whichburst the cell burst the cell membranes and membranes and destroy the structure destroy the structure of food.of food.

d) What do the d) What do the stars on a stars on a refrigerator refrigerator indicate?indicate?The stars on a The stars on a refrigerator refrigerator indicate the indicate the minimum minimum temperature the temperature the refrigerators can refrigerators can reach.reach.

e- Which property of ammonia makes it a suitable cooling agent?

Ammonia condenses and re-evaporates quickly when the pressure on it varies.

f. What would happen if the temperature in a refrigerator rose too high?

If the temperature in a refrigerator rose too high, a thermostat would switch off the refrigerator.

a)a) The faster food is frozen, the smaller The faster food is frozen, the smaller the ice crystals formed.the ice crystals formed.

b)b) The freezing point of brine is lower The freezing point of brine is lower than that of water. than that of water.

c)c) If you have a freezer you can pick If you have a freezer you can pick strawberries in summer and eat them strawberries in summer and eat them in mid-winter.in mid-winter.

d)d) Certain gases such as ammonia can Certain gases such as ammonia can be used as a cooling agent in a be used as a cooling agent in a refrigerator.refrigerator.

TrueTrue and and FalseFalse Statements Statements::TrueTrue and and FalseFalseStatements Statements ::