WATER RESOURCES OF THE USA

The USA is one of the first countries whose developing economy has met with a shortage of pure fresh water. Such conflicting situations have been caused by the exceptionally rapid growth of water consumption and by the constancy of the size of river runoff. The water crisis began to show at the beginning of the 60s. It was then when the gigantic projects were born to transport fresh water from Canada and Alaska to the main territory of the USA. At the end of 60s it became evident that the problem could not be solved by purifying utilized water.

By spending large sums of money on developing gigantic desalination plants it became clear that by channeling the runoff from the neighbouring territories and from the ocean an increase in the volume of polluted water would be brought about, which even at present overfills the rivers and lakes of the country.

It is the runoff which can be used without a full regulation of rivers by hydrotechnical installations. It is possible by recycling the same volume of water, which claims great requirements to the quality of their purification.

The main increase in water consumption takes place in that sphere of national economy, where water is necessary principally for cooling purposes – in industry, especially in heat-power engineering.

How can water losses be replenished? It is necessary to note the evergrowing consumption of ground water. The removal of considerably greater volumes of ground water that are taken at present will not diminish their total storage for a long time. Water supply at the expense of ground water is also convenient to satisfy the every day necessities of the population.

Other reserves that can be used are the water of the ocean. A wide substitution of fresh water for salt water for cooling purposes is assumed, mainly in heat-power engineering.

Over one quarter of the whole consumption of water will become possible due to the use of seawater. As concerning the abovementioned projects according to which fresh water is to be transported from Canada and Alaska and the entailed possibility to use the great reserves of hydropower of the western part of the continent, they have been cancelled.

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ТЕКСТЫ ДЛЯ САМОСТОЯТЕЛЬНОЙ РАБОТЫ (II семестр)

ТГВ, ВИВ, БТП и ПТ

ПРЕДТЕКСТОВЫЕ УПРАЖНЕНИЯ

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transmission 1.основной

occupants 2. составные части

comfort 3. удобство

components 4. доля, часть

fundamental 5. жители

locate 6. передача

generate 7. вырабатывать, производить (энергию)

component 8. размещать

proportion 9. понятия

concepts 10. составляющий элемент

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PANEL HEATING

(1) Heating and ventilation are two branches of engineering which are very closely connected and concerned with providing a required atmospheric environment, former with respect to heat supply to produce a desired temperature for maintaining comfort and health, the latter with supply and removal of air often with emphasis on contamination of the air.

(2) Heating prevents the too rapid loss of heat from the body. By heating the ambient air of walls, ceiling or floor the rate of heat loss from the body is controlled. The determination of the capacity or size of the various components of the heating system is based on the fundamental concept that heat supplied to a space equals heat lost from the space. The most widely used system of heating is the central heating, where the fuel is burned in one place – the basement or a specially designed room and from which steam, hot water or warm air is distributed to adjacent and remote spaces to be heated.

(3) There two most common systems of heating – hot water and steam. Both systems are widely used nowadays. A hot-water system consists of the boilers and a system of pipes connected to radiators. They are suitably located in rooms to be heated. The pipes, usually of steel and copper, feed hot water to radiators or convectors which give up their heat to the room. The cooled water is returned to the boiler for reheating.

(4) As for steam systems, steam is generated usually in the boiler and then led to the radiators through or by means of steel or copper pipes. The steam gives up its heat to the radiators and the radiator to the room and the cooling of the steam condenses it to water. The condensate is returned to the boiler either by gravity or by a pump. The air valve on each radiator is necessary for air to escape. Otherwise it would prevent steam from entering the radiator.

(5) Recent efforts to conceal heating equipment have resulted in an arrangement where hot water or steam is circulated through distribution units embedded in the building construction. Panel heating is a method of introducing heat to rooms in which the emitting surfaces are completely concealed in the floor, walls, or ceiling. The heat is disseminated from such panels partly by radiation and partly by convection, the relative amounts depending on the panel location. Ceiling panels release the largest proportion of heat by radiation and floor panels - the smallest. The proportion of heat disseminated by radiation and convection is also dependent on panel-surface temperatures. The basic advantage of a panel heating system is that of comfort.

(6) Application of certain panels is frequently restricted by structural details. Other factors to be considered are type of occupancy, furniture or equipment location, large glass areas, heat-storing capacity of building construction, room height, climate and first cost.

As for fuels used for heating buildings they include coal, oil, manufactured and natural gases and wood. There are two other sources: electricity and steam. Nowadays gas fuel is being used on an increasing level.

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