Page:Steam turbines; a practical and theoretical treatise for engineers and students, including a discussion of the gas turbine (IA steamturbinespra00moyerich).pdf/28

CHAPTER II. THE ELEMENTARY THEORY OF HEAT.

NOTE. This short chapter may well be omitted, in reading, by those who are familiar with the thermodynamics of heat engines and with the use of entropy diagrams. It is intended primarily for practical engineers, who will find it particularly valuable for reference purposes, as the subject matter is completely indexed.

TECHNICALLY the steam turbine must be regarded as a heat engine, that is, a machine in which heat is employed to do mechanical work. From the viewpoint of the practical man its function, the same as that of any other heat motor, is to secure as much work as possible from a given amount of steam, or, going a step farther back, from the combustion of a given amount of fuel. Heat theory is, therefore, of first importance.

Heat is a form of energy like electrical, chemical, mechanical, potential, and kinetic. No doubt exists about the equivalence of the different forms of energy and their close relation to each other. Each, at will, can be changed into any of the other forms. The relative amount of heat in a observed, in common experience, by the sense of touch - whether the body is a solid, a liquid, or a gas. By such experience we have learned to recognize certain sensations as hot or cold; and then, with more accuracy, to speak of degrees of temperature. Now when a hot and a cold body are brought together their temperatures become equalized. The hotter body always loses heat. The colder body always gains heat.* This experience is the principal basis for all heat calculations.

When in the course of time it had been found that a more accurate method than that of the sense of touch was needed for heat determinations, methods utilizing the expansion of liquids
 * This phenomenon is called the second law of thermodynamics, that "heat energy always passes from a warm body to a cold body." 10