Refrigerator

Refrigerators are used to store foods which deteriorate at ambient (окружающий) temperatures. Devices described as "refrigerators" maintain a temperature a few degrees above the freezing point of water; similar devices which maintain temperatures below the freezing point of water are called "freezers". The refrigerator is a relatively modern invention; it replaced the common icebox (ледник) which had been a household item for almost 150 years before. Freezers keep their contents, usually foods, frozen. They are used both in households and in commercial enterprises. Most freezers operate at -18 °C.

Commercial fridge and freezer units were in use for almost 40 years prior to home models. They used toxic ammonia gas systems, making them unsafe for home use. Practical household refrigerators were introduced in the 1920s and gained wider acceptance in the United States in the 1930s as prices fell and non-toxic, non-flammable synthetic refrigerants such as Freon or R-12 were introduced. 60% of households in the US owned a refrigerator by the 1930s; the same figure was achieved in the UK only some 40 years later, in the 1970s.

What facts from the history of refrigerators did you learn?

Unit VII

Exercise I. Make sure you pronounce the following words correctly:

Process, vessel, fluid, combustion, tube, turbine, source, surface, flue gas.

Steam boilers

In all power plants, power generation process is based on the work of a boiler. A boiler is a vessel in which water or other fluid is heated under pressure. The fluid is then circulated out of the boiler for use in various processes or for heating applications. The source of heat in a boiler is combustion of such fuels as wood, coal, oil or natural gas. An essential function of a boiler is to produce an efficient flow of heat from the heat source to the feed water or steam. This heat flow is due to conduction from the hot gases and radiation from the flames. The simplest structure consists of one or more steel drums and boiler tubes. Steam boilers have become more complex with the development of power generation. As steam turbines need superheated steam, the steam boiler incorporates a superheater, which is a heat transfer surface, to form superheated steam from saturated steam. Waterwalls have been added to the unit. They are boiler tubes connected with the water circulation system. The theoretical limit to which flue-gas temperature may drop is the temperature of the saturated steam. With higher boiler steam pressures a further extension to the heating surface is made in the form of an economizer. Here, feed water, which is lower in temperature than boiler steam, is heated by the flue gases as they leave the boiler surface. The economizer also sets a limit to which the temperature of the flue gases may drop. Further surface in the form of an air heater can be used to reduce the flue-gas temperature by warming the air needed for combustion.

When elementary drums and tubes of the steam boiler are added to its design in the form of waterwalls, superheater, economizer, air preheater, and possibly other heating surfaces, we have the steam generating unit. In addition to the heating surface, the steam generating unit includes the furnace, combustion and draft equipment for controlling combustion and steam formation. Several accessories for safety and maintenance are also part of the complete unit.

There are two types of boilers in general use: the fire-tube and the water-tube boiler, with the latter predominating.

Exercise II. Translate the following attributive groups into Russian:

Power plant work, power generation process, steam boiler function, heat gas flow, water circulation system, steam generating unit, flue gas temperature, boiler steam pressure, heat recovery ventilation system, ventilation air excess moisture.

Exercise III. Match the words in A with the words in B:

a) steam, power, gas, steel, boiler, heating, draft, safety, water, feed

b) circulation, plant, drums, pressure, tubes, boiler, flow, surface, equipment, accessories.

Exercise IV. Complete the sentences according to the text:

1) The two general types of boilers are … .2) An essential function of a steam boiler is to produce …. 3) The simplest structure of a steam boiler includes … . 4) In an economiser, the feed water is heated by … .5) A further extension of the heating surface is made in the form of … or ….. 6) A steam generating unit consists of …. .

Exercise V. Translate the sentences paying attention to the Participial construction. Find a sentence with one in the text.

1) Steam turbines are becoming more complex, boilers developing into complicated units. 2) A refrigerator is a relatively modern invention, a common icebox having been replaced some 150 years ago. 3) The evaporator operating at a temperature below dew point, moisture is collected at the evaporator section.

4) Open windows disrupting the work of the HVAC system, air-conditioned buildings often have sealed windows. 5) Ceiling fans are widely used in small spaces, with the air circulating within a room.

Exercise VI. Translate the following sentences into Russian. Mind that “ing-forms” can have different functions in a sentence.

1) In Roman hypocausts, the floors and walls were warmed up quickly, hot air from fires circulating through flues and ducts. 2) When a ceiling fan is in operation, the air is circulating within the room, hot air rising to the ceiling.

3) Hot water circulating in the pipes is an essential part of an under-floor heating system. 4) The circulating of the air in a natural ventilation system is provided by the stack effect. 5) Circulating through the boiler tubes the water absorbs heat.

Exercise VII. Tasks to the text:

1) What is the main function of a steam boiler? 2) What are the main types of boilers? 3) Describe the main units of a boiler and their functions.

Exercise VIII. Read the following text without a dictionary and give a short summary.