Vocabulary notes:

similar to -	схожий на
to assume -	визнати
pure ammonia -	аміак
at high (low) pressure -	під високим/низьким тиском
to leak -	витікати
a replacement -	Замінювач
harmful -	шкідливий

Text.

The refrigerator in your kitchen uses a cycle that is similar to the one described in the previous section. But in your refrigerator, the cycle is continuous. In the following example, we will assume that the refrigerant being used is pure ammonia, which boils at - 27 degrees F. This is what happens to keep the refrigerator cool:

The compressor compresses the ammonia gas. (Fig.1). The compressed gas heats up as it is pressurized (orange).

The coils on the back of the refrigerator let the hot ammonia gas dissipate its heat. The ammonia gas condenses into ammonia liquid (dark blue) at high pressure.

The high-pressure ammonia liquid flows through the expansion valve.

You can think of the expansion valve as a small hole. On one side of the hole is high-pressure ammonia liquid. On the other side of the hole is a low-pressure area (because the compressor is sucking gas out of that side).

The liquid ammonia immediately boils and vaporizes (light blue), its temperature dropping to -27 F. This makes the inside of the refrigerator cold.

The cold ammonia gas is sucked up by the compressor, and the cycle repeats.

Fig.1. The Refrigeration Cycle.

By the way, if you have ever turned your car off on a hot summer day when you have had the air conditioner running, you may have heard a hissing noise under the hood. That noise is the sound of high-pressure liquid refrigerant flowing through the expansion valve.

Pure ammonia gas is highly toxic to people and would pose a threat if the refrigerator were to leak, so all home refrigerators don't use pure ammonia. You may have heard of refrigerants know as CFCs (chlorofluorocarbons), originally developed by Du Pont in the 1930s as a non-toxic replacement for ammonia. CFC-12 (dichlorodifluoromethane) has about the same boiling point as ammonia. However, CFC-12 is not toxic to humans, so it is safe to use in your kitchen.

Many large industrial refrigerators still use ammonia. In the 1970s, it was discovered that the CFCs then in use are harmful to the ozone layer, so as of the 1990s, all new refrigerators and air conditioners use refrigerants that are less harmful to the ozone layer.

III. Comprehension check-up:

1. Make the right choice:

Home refrigerators use such refrigerant as… :

1. ammonia;

2. pure ammonia;

3. chlorofluorocarbons.

2) The compressor in a refrigerator compresses … :

liquid ammonia;

ammonia gas;

steam.

3) The ammonia gas condenses into ammonia liquid at … :

high pressure;

low pressure;

at the temperature –27 F.

4. A refrigeration cycle is … process:

hissing;

continuous;

c) toxic.

4. A non-toxic replacement for ammonia was originally developed by Du Pont in the … :

1970s;

1990s;

1930s.

High-pressure liquid flows through the … in the process of refrigeration cycle:

expansion valve;

coils on the back of the refrigerator;

a low-pressure area.

7) Pure ammonia gas would poses a … if the refrigerator were to leak:

question;

threat;

difficulty.

2. Put the sentences into the right order according to the text continuity:

Pure ammonia isn’t used in modern refrigerators.

The refrigeration cycle goes like this: ammonia gas is compressed, then it is converted into liquid, after boiling and vaporization the liquid becomes gas again.

It has been substituted by chlorofluorocarbons since Du Pont developed it in the 1930s.

A refrigeration cycle is a continuous process.

Dichlorodifluoromethane has about the same boiling point as ammonia.

Pure ammonia gas is highly toxic to people and would pose a threat if the refrigerator were to leak.

However, many large industrial refrigerators still use ammonia that can be harmful to the ozone layer.

3. Mark true (T) and false (F) statements. Correct the false ones:

Modern refrigerators use continuous refrigeration cycle.

The ammonia gas condenses into steam at high pressure.

The boiling point of pure ammonia is 100 degrees F.

The liquid ammonia is converted into ammonia gas again after boiling and vaporization.

Air conditioners use the same refrigeration cycle as refrigerators.

Home refrigerators are not dangerous, even if they leak.

Ammonia refrigerant could not be substituted and Du Pont invented a refrigerator without any refrigerant.

In the 1970s, it was discovered that the CFCs in use are harmful to the ozone layer.

IV. Vocabulary check-up:

Match the words with their definition:

similar to	at work
harmful	to replace; to change for
to drop	alike
to substitute	dangerous
running	to decrease; to fall

2. Fill in the missing prepositions where necessary:

A refrigeration cycle in any refrigerator is similar …the one in any air conditioner.

The ammonia gas condenses … ammonia liquid … high pressure.

The compressed gas heats … as it is pressurized.

A refrigerator, using ammonia, can be toxic … people if it leaks.

Refrigerants know … CFCs, were originally developed … Du Pont … the 1930s as a non-toxic replacement for ammonia.

An expansion valve is a small hole … one side …which there is high-pressure ammonia liquid and a low-pressure area … the other one.

When liquid ammonia boils and vaporizes, its temperature drops … -27 F.

Refrigerant CFC is non-toxic replacement ammonia.

3. Put the words into the right order to make up correct sentences:

Cycle, is, a, process, continuous, refrigeration, a.

Heats up, while, gas, pressurization, the, compressed.

Expansion, high-pressure, the, liquid, flows, through, ammonia, valve, the.

Refrigerators, use, home, ammonia, don’t, pure, it, is, because, toxic.

In, Du Pont, the, developed, 1930s, for, replacement, ammonia, a, non-toxic.

Boiling, has, CFC-12, ammonia, as, the, point, same.

Boils, pure, at, -27F, ammonia, degrees.

1970s, the, ozone, it, harmful, was, layer, in, are, discovered, the, CFCs, to, in use, the, that.

V. Controlled Practice: