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A Simplified but Limited Formula.-A convenient formula for a pressure of 175 lb. per sq. in., the approximate pressure involved in steam turbine operations, has been worked out by the mechanical engineering students at the University of California for superheat between fifty and six hundred degrees and is as follows:
Wherein t, is the number of degrees superheat. The accuracy of this formula is within one-half of one per cent. for the range of superheat above set forth.
Other Relationships Exist.-By making use of certain theoretic considerations in thermodynamics many other equations might be written setting forth still other relationships involved in the determination of steam constants, but sufficient illustrations have now been given the reader for a thorough introduction to such formulas. Perhaps after all the most important lesson one derives from their use is that their application is often so tedious and their range of accuracy often so questionable, that one had better stay on well trodden paths and master to their fullest extent the application of the steam tables and diagrams in the solution of all steam engineering problems.
THE FUNDAMENTALS OF FURNACE OPERATION IN FUEL OIL PRACTICE
FIG. 57.-Air ducts for furnace
ANY of us are familiar with the famous painting that pictures James Watt as a boy gazing in wide-eyed amazement at the homely tea-kettle spouting forth its hitherto unharnessed power generating vapors. The eyes of the youth are illuminated with that strange and wonderful light that set forth in a measure some of the dreams of constructive imagination which must have been filling his consciousness at that time.
The great inventor of the steam engine undoubtedly saw in the teakettle before him, not the homely object of the kitchen, but in its expanded form one of the most necessary mechanisms for modern industrial development-namely,
the steam boiler.
Let us then examine the fundamental operation and construction of the steam boiler, and consider this great giant of modern industrial aggrandizement to see wherein it varies from its progenitor the homely tea-kettle of Watt's boyhood dream.
The Fundamentals of the Tea-Kettle and the Boiler are the Same. The tea-kettle in its construction and operation may be considered under three separate discussions. First, there must be some means of generating and imparting heat; secondly, a container for the water and steam must be constructed with physical characteristics to meet the stresses and strains involved;
and, thirdly, the cycle of physical operations through which the water and steam pass in the generation of steam is of vast importance.
The tea-kettle operation in its simplest analysis consists of a flame placed beneath a metal container. This metal container absorbs the heat from the flame and transmits it to the water within the container. When sufficient heat has been absorbed by the water within the container to raise its temperature to the boiling point corresponding to the external pressure of the atmos
phere, the tea-kettle boils or in the language of the steam engineer the tea-kettle generates steam.
In its fundamental makeup, the boiler too, quite closely follows this familiar and homely object-the tea-kettle. For in the modern boiler heat is first generated in a furnace. This heat is then imparted to a metallic drum or tubes through which water is passed. When sufficient heat is thus imparted to raise the temperature of the water to the boiling point for the pressure involved, steam generation takes place.
Inefficiency of Tea Kettle Operation. In modern kitchen economics but little attention is paid to the manner in which the heat is imparted to the tea-kettle. Usually the stove lid is taken off and the kettle placed over the fire space thus created. Some minutes later, the house-wife, ignorant of the vast heat losses that have taken place, returns to draw off the hot water thus inefficiently obtained as convenience may require. As a matter of fact, the slightest and most casual investigation shows that in the United States millions of dollars are wasted every year for
lack of reasonable care in the kettle operation. This loss is, however, so widely distributed over thousands of homes that it is not felt in any concentrated form.
Efficiency in the Modern Steam Boiler a Necessity. In the case of the modern central station, however, efficiency is the cry of the day. For with competition on all sides and regulating commissions to limit the prices charged for the power supply, the utmost in economic steam generation is essential.
Hence, in modern steam boiler operation, especially in its
heat generating properties, a wide variation from tea-kettle operation is in vogue, not so much in fundamental principles involved as in efficiency of methods employed in the heat generating mechanisms
Efficient Furnace Construction of Utmost Importance.-To accomplish this efficiency an enclosed compartment beneath the boiler proper is built. This is known as the furnace. In this furnace heat generating substances such as coal, wood, and crude petroleum are burned. In the study of chemistry it has been found that certain primary elements, notably carbon, hydrogen,
FIG. 60.-Typical boiler front in fuel oil practice.
In this illustration may be seen the fuel oil atomizer in the ash pit entrance, the covered steam pipes for supplying steam used in atomization, the fuel oil supply pipes, the damper control, the draft gage and other accessories for fuel oil operation.
and sulphur, upon coming in contact with heated oxygen undergo a chemical reaction and in doing so give out enormous quantities of heat. It is the generation of this heat and its ultimate absorption by the water in the boiler that makes the modern steam engine and steam turbine the giants in commercial enterprise that today they represent.
Fuels Defined.-In nature, substances such as coal, wood and crude petroleum are found in vast quantities and since these contain large amounts of free carbon and hydrogen, they make excellent articles for heat generation and are called fuels.
An Air Supply Essential.-It has been mentioned that a supply of oxygen is absolutely necessary so that a chemical reaction