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   What is a perfect gas? It is one which behaves in accordance with the gas law,

PV = MRT, where P = absolute pressure, V = volume, M = mass, T = absolute temperature, and R is a constant for the particular gas depending on its molecular weight.

The volume is directly proportional to the temperature and inversely proportional to the pressure. Oxygen, nitrogen, air and hydrogen are examples of gases which are almost perfect at moderate temperatures and pressures. The gases commonly used in refrigeration are not perfect under normal operating conditions. With the exception of carbon dioxide, their deviations from the gas law are not great at the temperatures and pressures normally prevailing in the low pressure side of a vapor compression refrigerating plant.

  What is the difference between gas and vapor? The gaseous substance in contact with the liquid from which it is formed is known as a vapor and it is still called a vapor if superheated to some extent. At still higher temperatures it is known as a gas but there is no sharp line of demarcation.

  What is critical temperature? Although in general a vapor may be liquefied by increasing its pressure up to the saturation value corresponding to the temperature, this is not so if the temperature is above a certain level. For any vapor this temperature above which no pressure will produce liquefaction, is called its critical temperature.

 What is critical pressure? The critical pressure of a vapor is the pressure required to liquefy it at the critical temperature and is the highest pressure on the temperature – pressure graph for saturated vapor. At temperatures above critical the pressure exerted by a vapor depends on the weight of it in a given space.

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proportional, inversely proportional, oxygen, nitrogen, hydrogen, moderate, refrigeration, carbon dioxide, deviation, prevailing, gaseous, superheated, demarcation, saturated, exerted, condition, liquid, pressure.

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Demarcation (line), prevailing, proportional, moderate, inversely, superheated (gas), perfect (gas), oxygen.

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кислород

разграничение

идеальный

перегретый

пропорциональный

умеренный

преобладающий

обратно

От приведенных ниже слов образуйте однокоренные слова и

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Behave, refrigerate, operate, saturate, superheat, press, vapor, produce, liquid, form.

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1) temperature – critical, moderate, absolute, ground, indoor

2) gas – refrigerated, superheated, liquefied, city, dry, fuel

3) proportional – directly, inversely, mean

4) steam – dead, gaseous, dry, direct, wast

Ответьте на вопросы

1. What is gas?

2. What is a perfect gas?

3. What is the difference between gas and vapor?

4. What is critical temperature?

5. What is critical pressure?

Text 7.BOILING

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  What is boiling point? When a liquid contained in a vessel having an opening to permit the exit of vapor is heated, its vapor pressure rises and eventually reaches that of the surrounding atmosphere. When this happens, the liquid boils and the temperature at which it does so is known as the boiling point for that particular pressure. It is therefore the temperature at which the saturation pressure of the vapor equals that of the atmosphere. When the liquid is in a closed vessel or system in contact only with its own vapor, the term boiling point is not very appropriate. It is preferable to speak of the saturation temperature, which is the temperature of the liquid surface corresponding to the pressure of the vapor in contact with it.

   What happens to a gas which is allowed to expand in an engine cylinder? Conversely to the compression of a gas, the work done by an expanding gas is produced at the expense of the heat contained in the gas, which therefore falls in temperature.

What is the triple point? If a closed vessel containing only a pure liquid and its vapor is

cooled, the pressure will fall with the temperature in accordance with the pressure – temperature curve for saturated vapor. A temperature will be reached at which the liquid begins to freeze. Any further reduction in temperature will cause the transformation of

the liquid into solid. This temperature and its corresponding pressure are known as the triple point for the particular substance. Only at this temperature and pressure can the substance exist simultaneously in solid, liquid and vapor forms.

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Contained, opening, eventually, surrounding, appropriate, preferable, conversely, expanding, pure, triple, point, exist, simultaneously, curve, temperature, pressure, substance, transformation, corresponding.

Найдите в тексте 1: а) существительные, б) наречия, в) глаголы, г) прилагательные, д) причастия и выпишите их

Составьте сочетания из указанных ниже слов и переведите их на русский язык. Составьте предложения с этими словосочетаниями на английском языке

a) exit, appropriate, preferable, surrounding, curve.

б) pressure, temperature, gas, atmosphere, volume.

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1. Curve, in accordance with, the pressure, the pressure temperature, for, will, the temperature, fall, vapor, saturated, with.

2. Contained, the work, gas, done, is at, the expense, by, an, expanding, of , the, in, the, gas, produced, heat.

3. Saturation, the, is, the surface, to, the, of, the, in, vapor, with, it, corresponding, temperature, temperature, liquid, pressure, contact, of, the.

 6. Ответьте на вопросы

1. What is boiling point?

2. When does liquid boil?

3. What happens to a gas which is allowed to expand in an engine cylinder?

4. What is a triple point?

5. What will cause any further reduction in temperature?

6. When can the substance exist simultaneously in solid, liquid and vapor forms?

Text 8.THE JOULE-THOMSON EFFECT