2.2. Refplant cycle of operation

A simple refrigerator circuit is illustrated diagrammatically in Fig. 1.

The evaporator coils may consist of grids on the walls and ceiling of the chamber to be cooled or may be in the form of an air cooling battery placed behind a screen or, again, in the form of coils in a vessel containing brine, water or other fluid.

The evaporator itself is first cooled by the refrigerant and then it in turn cools the surrounding air or other medium. This absorption of heat by the evaporator causes the refrigerant to evaporate (change from a liquid to gas) until finally at the end of the circuit only dry gas at the pressure shown on the gauge should remain to pass into the compressor.

If the regulator is passing an excess of refrigerant, then the gas entering the compressor will still contain some liquid which will cause the crankcase to become cold or frosted, with a cold delivery pipe. If the regulator is insufficiently open, all the liquid will have evaporated before reaching the end of the circuit with the result that only part of the evaporator coil can do useful work.

A regulator which is properly adjusted only passes liquid refrigerant at the rate at which it is formed in the condenser, and preserves the right proportion of the total charge in the condenser and in the evaporator.

In the compressor the gas is recompressed to the pressure necessary for condensation, after which it passes into the condenser.

In the condenser the heat of evaporation and compression is extracted by the condenser cooling medium (water), resulting in the gas again becoming a liquid.

The pressure in the condenser will correspond to the temperature of condensation and this relationship is shown on the gauge.

A receiver or liquid reservoir is supplied with some plants to act as a storage vessel for surplus refrigerant resulting from variations in the demand on the plant.

After leaving the condenser the liquid refrigerant passes back to the regulator to repeat the whole cycle of operation.

Words to be Learnt

simple – простой; medium – среда; absorption – поглощение; coil - змеевик, кольцо; to cause - быть причиной, заставлять; chamber камера; screen – экран; to evaporate – испарять, испаряться; vessel - емкость; brine – рассол; finally – наконец; fluid – жидкость; dry - сухой; to surround – окружать; gauge – прибор, измеритель; to remain – оставаться; to pass – пропускать; excess – избыток; to preserve – сохранять; crankcase - картер (компрессора); charge – заряд; frosted - заиндевевший; покрытый инеем; to extract – отбирать;to correspond to – соответствовать; delivery pipe - нагнетающий, to supply - снабжать, подавать, подающий патрубок; plant – установка; insufficiently – недостаточно; to act as - действовать в качестве; to reach – достигать; storage - хранилище, склад; useful – полезный; surplus - лишний, избыточный; properly - должным образом; demand – потребность

to adjust - регулировать, настраивать

LABORATORY WORK

Remember the following word combinations. Give their equivalents.

cycle of operation, evaporator coils, air cooling battery, in its turn, surrounding air, surrounding medium, to change from liquid to gas, dry gas, pressure gauge, to become cold, to become frosted, delivery pipe, useful work, properly adjusted, right proportion, total charge, heat is extracted, cooling medium, pressure corresponds to the temperature, liquid reservoir, storage vessel, surplus refrigerant, to repeat the cycle.

Ask questions as if you want to know the place.

Model. The circuit is illustrated in Fig. 1. Where is the circuit illustrated?

The air cooling battery is placed behind a screen. 2. The liquid refrigerant is formed in the condenser. 3. The gas is recompressed in the compressor. 4. The relationship pressure/temperature is shown on the gauge. 5. The heat of evaporation is extracted in the condenser.

Say the following sentences with the verb in the passive voice.

Model. The refrigerant cools the evaporator. The evaporator is cooled by the refrigerant.

1. The evaporator cools the surrounding air. 2. The evaporator absorbs the heat. 3. The gauge shows the pressure. 4. The condenser extracts the heat of compression. 5. The engineer adjusts this regulator.

Listen to these questions beginning with does and translate them. Begin your translation with становится ли . . ., проходит ли ... . Give short answers expressing agreement.

Model. Does the refrigerant pass back to the regulator? Yes, it does. It does pass back.

1. Does the gas become a liquid again? 2. Does the pressure in the condenser correspond to the temperature of condensation? 3. Does the condenser cooling medium extract the heat of evaporation? 4. Does the gas after the compressor pass into the condenser? 5. Does the regulator preserve the right proportion of charge in the condenser and evaporator? 6. Does the absorption of heat cause the refrigerant to evaporate?

Pay attention to the translation of the «ing-forms.

the gas entering the соmpressor газ, поступающий в комnpeccop

the vessel containing brine емкость, содержащая рассол

the regulator passing the refrigerant регулирующий вентиль пропускающий хладагент

the gas becoming a liquid газ, превращающийся в жидкость

the surplus refrigerant resulting from variations- избыточный хладагент, появляющийся в результате изменений

Translate the following words adding the prefix re-.

Mоde1: to adjust регулировать, настраивать to readjust настраивать вновь

to compress, to liquefy, to construct, to heat, to form, to expand, to charge, to place, to open, to produce, to move, to circulate.

Change the verb of each sentence to the Future Indefinite Tense. Use the model.

Model. The gas entering the compressor contains some liquid.

The gas entering the compressor will contain some liquid.

1. The liquid in the compressor causes the crankcase to become frosted. 2. Sometimes the liquid evaporates before reaching the end of the circuit. 3. The, refrigerant changes from a liquid to gas. 4. The dry gas in the evaporator remains to pass into the compressor. 5. The pressure in the condenser corresponds to the temperature of condensation.

Memorize the terms in Fig. I.

suction to compressor всасывание компрессора

L.P. liquid (low pressure liquid) жидкость при низком давлении

evaporator испаритель

regulator регулирующий вентиль

superheat removal снятие перегрева

liquid cooling охлаждение жидкости (конденсата)

delivery valve нагнетательный, подающий клапан

suction valve всасывающий клапан

WORK IN CLASS

I. Translate the text.

II. Make up 5 sentences of your own using word combinations from Ex. 2 (Lab. Work).

III. a) Find in the text the passage describing the operation of the regulator.

b) Pick out the phrases containing the future tenses; analyze these forms and translate them.

IV. Write out from the text the words naming essential parts of the equipment described in this text.

V. Choose the right word in the list and complete the sentences. gauge, regulator, evaporator, compressor, receiver, condenser

Is it right to say that...

1. A device where the heat of compression is extracted is the ... . 2. A device where the gas is recompressed is the ... . 3. A device which acts as a storage vessel is the ... . 4, A device which passes liquid refrigerant only at the proper rate is the ... . 5. A device that cools the surrounding air is the ... . 6. A device that shows the pressure is the ... .

VI. Answer the following questions on the text.

One student asks questions, the other answers them with a short response.

M о d el. What is illustrated in Fig. 1? - A refrigerator circuit.

1. What do the evaporator coils consist of? 2. Where are the grids? 3. Where is the air cooling battery placed? 4. What may a vessel contain? 5. By what medium is the evaporator cooled first? 6. What device cools the surrounding air? 7. What process causes the refrigerant to evaporate? 8. When does the dry gas remain in the evaporator? 9. Under what conditions will the gas in the compressor contain some liquid? 10. Why does the compressor crankcase become frosted? 11. What will happen if the regulator is insufficiently open? 12. What is the function of the regulator? 13. Does the regulator preserve the right proportion of charge in the condenser and evaporator? 14. To what pressure is the gas recompressed in the compressor? 15. When does the gas pass into the condenser? 16. By means of what medium is the heat extracted in the condenser? 17. When is the gas again becoming a liquid? 18. Where is the relationship pressure/temperature shown? 19. How does a receiver act? 20. For what purpose does the liquid refrigerant pass back to the regulator?

VII. Say what you can about the cycle of operation in a refrigerating plant. Use Fig. 1 and the following plan:

1. The evaporator. Its construction and function.

2. The role of the regulator in the system.

3. Function of the compressor.

4. The heat and the condenser.