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Heat is a form of energy transferred from one body to another because of a temperature difference. The transfer of heat from one body to another is known as heat exchange or heat transfer. Heat always flows from a more heated to a less heated body and therefore heat exchange is a natural process.

There are three principal modes of heat transfer: by conduction, convection and radiation.

Conduction is the transfer of heat between bodies or parts which are in direct contact and does not depend on their motion.

Convection is heat transfer performed by particles of gas, vapour or liquid moving in space.

Radiation is heat transfer by thermal radiation.

In practice heat may be transferred by two or even all three modes simultaneously. For example, in a steam boiler it is important that the heat be transferred from the glowing surface of the burning fuel to the heating surface of the boiler. This process is performed by means of radiation. At the same time this surface receives heat from flue gases by convection while the heat in the wall itself, which forms a heating surface, spreads by conduction.

Упражнение 1. Переведите следующие словосочетания на английский язык:

поверхность нагрева, паровой котел, тепловое излучение, топочные газы, передача тепла.

Упражнение 2. Вставьте в предложение одно из пропущенных слов:

a. conduction; b. radiation; с. convection;

1. ............... is heat transfer performed by particles of gas, vapour and liquid moving in space.

2. ............... is a heat transfer between bodies in direct contact.

3. ............... is heat transfer by thermal radiation.

Упражнение 3. Ответьте на следующие вопросы.

1. What is heat transferred by?

2. What is conduction?

3. What is convection?

4. What is radiation?

General Information on Steam

Слова и словосочетания к тексту:

generate v	—	производить, вырабатывать
generation n	—	образование (пара)
saturated steam	—	насыщенный пар
moisture n	—	влага
specific heat	—	удельная теплота, теплоемкость
specific volume	—	удельный объем
superheated steam	—	перегретый пар
relative factor	—	относительная величина
depend upon	—	зависеть от
conversely adv	—	наоборот
exert v	—	оказывать давление, действие
gauge pressure	—	манометрическое давление
per cubic foot pcf	—	на кубический фут
pound per square inch psi	—	фунт на квадратный дюйм
exceed v	—	превышать
enthalpy n	—	энтальпия
evaporate v	—	испарять(ся), выпаривать
latent heat either … or	——	скрытое тепло или … или