Thermodynamics is that branch of physics which deals with the conversion of mechanical energy into thermal energy and the reverse process of transforming heat into work.
The production of heat by mechanical means may be illustrated by the phenomenon of friction. For example, fire may be started while rubbing together two sticks of wood. Heat is developed when compressing a gas. The transformation of heat into work may be illustrated by operation of a steam or gas engine by means of which heat may be transformed into mechanical energy.
So a heat engine is a machine for transforming heat into mechanical energy, the most important of the practical heat engines being the steam engine and the internal combustion engines.
To transform energy from any of its numerous forms into heat is a comparatively simple process. To transform heat into work is a different matter. Experience shows that any actual physical process, as the change of state of a system, is irreversible and is accompanied by a frictional effect. A strictly reversible frictionless process being an ideal, it may be approached but never attained. In the case of the ideal reversible process, there is no change in the quantity of available energy. But an actual irreversible process is always accompanied by a decrease of the amount of energy available for transformation. All transformations of energy are subject to two far-reaching laws:
1) The general law of conservation of energy, of which the following is a statement: the total energy of an isolated system remains constant and cannot be increased or diminished by any physical process whatever.
2) The law of degradation of energy. According to this law, the result of any transformation of energy is the reduction of the quantity of energy that may be usefully transformed into mechanical work.
The first law of thermodynamics is merely the law of conservation applied to the transformation of heat into work. It may be stated as follows: when work is expended in producing heat the quantity of heat generated is equivalent to the work done. And conversely, when heat is employed to do work, a quantity of heat precisely equivalent to the work done disappears.
The second law of thermodynamics is essentially the law of degradation of energy. Whereas the first law gives a relation that must be satisfied in any transformation of energy, it is the second law that gives information regarding the possibility of transformation and the availability of a given form of energy for transformation into work. A general statement of the second law is: «No change in a system of bodies that takes place of itself can increase the available energy of the system».
Упражнение 6. Опираясь на содержание прочитанного текста, закончите предложе-ния, используя предлагаемые варианты.
1. A heat engine is...
a) a machine for transforming heat into mechanical energy.
b) a machine for defining the amount of mechanical energy.
c) a machine for solving physical problems.
2. The production of heat by mechanical means may be illustrated by...
a) the phenomena of potential energy of a body which it possesses due to its position.
b) the phenomena of conservation of energy which can neither be created nor destroyed in any physical effects.
c) the phenomena of friction.
3. The first law of thermodynamics is...
a) the law of degradation of energy.
b) the law of conservation of energy.
c) the law of transformation of energy.
Упражнение 7. Расположите предложения в той последовательности, в которой они даны в тексте.
1. The production of heat by mechanical means may be illustrated by the phenomenon of friction.
2. Experience shows that any actual physical process is irreversible and is accompanied by frictional effect.
3. Whereas the first law gives a relation that must be satisfied in any transformation of energy, it is the second law that gives information regarding the possibility of transformation.
4. Thermodynamics is that branch of physics which deals with the conversion of mechanical energy into thermal energy and the reverse process.
5. A heat engine is a machine for transforming heat into mechanical energy.
Упражнение 8. Используя материал текста, ответьте на вопросы.
1. What does thermodynamics deal with?
2. The phenomenon of friction is the illustration of the production of heat by mechanical means, isn't it?
3. What are the most important heat engines?
4. Are there two or three laws of transformation of energy?
5. Will you explain the essence of the 1st law of thermodynamics?
6. What does the law of degradation of energy state?
Упражнение 9. Составьте план по прочитанному тексту и перескажите текст согласно этому плану.
Упражнение 10. Скажите, каким образом вы можете использовать информацию, содержащуюся в тексте, при работе по специальности?
Дата добавления: 2015-09-11; просмотров: 240 | Поможем написать вашу работу | Нарушение авторских прав |