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MAKING STEAM WORK HARDER
CHARLES FREDERICK CARTER
IVEN a chance to save a mile that before a man gets hold of the next
lion dollars in one lump anyone he has plenty of time to figure out American would acquit him- that it only takes a hundred centimes to self creditably, if not bril- make a franc; and that when he gets
liantly. But no free-born enough francs he will have a million. In American citizen would so demean him- these few sentences is contained the esself as to save a paltry hundred dollars. sence of all the reasons why those felAs for saving a nickel the man who lows on the other side of the Atlantic would even hint at such a thing would can beat us so badly in building small disgrace himself and his family to the motors that we do not deserve to be inthird generation. But in countries where cluded “Among those Present” in the the unit of the monetary system is the competition. franc or the lire, which are but the fifth It was in Germany that the first pracpart of a dollar, or the mark or the shil- tical gas engine was evolved. It was a ling, which are a shade less than a German, too, who invented and develfourth of a dollar, things are different. oped the Diesel oil engine, which seems In Europe it is so long between francs to have landed on the solar plexus of the steam engine, not merely for use on land, perheating will increase the pressure. In but for the propulsion of ships. Also, it ordinary practice superheating increases was the Germans who recently developed the volume so slightly that the rise in the small steam engine to such a marvel- pressure is not appreciable. Steam at 200 ous degree that the gas engine and the pounds pressure when superheated 100 oil engine have almost been counted out. degrees will have a temperature of 487 As a result of all this there has developed degrees and still remain at 200 pounds across the water about the loveliest three pressure. Superheated steam partakes of cornered contest for supremacy between the nature of a perfect gas. Like a gas these various types of prime movers that it is a poor conductor of heat. At 170 one could wish to see. First the gas en- pounds pressure with 200 degrees of sugine forges ahead, then the oil engine perheat it takes 3.27 cubic feet of steam gets a pfennig or two the best of the gas to weigh one pound, while only 2.47 engine, and then the steam engine downs pounds of saturated steam at the same them both.
pressure will weigh one pound. At the present time the honors appear The object in superheating is chiefly to be with the steam engine, but by so to eliminate wasteful condensation and narrow a margin that only an expert ac- consequent loss of heat in the cylinders. countant could measure it. At all events This can only be done by admitting the the small steam engine has been devel- steam at such a temperature that it can oped in Europe to an extent that is worth give up enough heat to raise the tempertalking about.
ature of the cylinder walls and still not In England the new type of steam en- lower its own temperature below the gine is spoken of, at least among engi- point of evaporation. Opinion differs neers, as an “Overtype superheat steam regarding the most economical degree of engine.” The Germans, economical of superheat, though it is well understood breath as of other things, name it the that a small amount is not worth while. "lokomobile,” while the French call it In practice the amount of superheat vathe “Demi-fixe” and let it go at that. ries from 100 to 200 degrees. The highWhatever the name, the new engines are est superheat yet attempted is 250 deidentical in principle and nearly so in de- grees, which means an actual temperatails of construction. They are portable, ture of nearly 650 degrees. If the temor semi-portable steam engines equipped perature was carried any higher it would with superheaters and other improve- result in the rapid reduction of the ments.
strength of the steel. Lest those foreigners should become The apparatus by which this wondertoo conceited about their achievements ful improvement in the quality of steam it may be well to say, first of all, that we is effected is nothing more than a series know just as much about engines as they of small pipes in the smokebox. The ardo. If some of those gentlemen from rangement of the coils of pipe varies, and Germany who spend all their lives build- so does the style of the header in which ing small engines were to come over here all the coils terminate. But all alike are they would be speechless with awe upon so arranged as to expose the whole surseeing some of our enormous power face of pipes and header to the hot gases plants. Both in size of plants and in the from the furnace. In an internally fired degree of economy realized in these large boiler the heating surface of the superplants we lead the world. Only in heater is usually about thirty times the smaller power plants, say up to a thou- grate area; and in a watertube boiler sand horse power, do European builders about ten times the grate area. To make excel.
a different comparison, the superheater's The superheater is the essential fea- heating surface ranges all the way from ture of the lokomobile. Superheated half that of the boiler to as large an area steam is defined as “Steam having a tem- as the boiler has. After being generated perature higher than that due to its pres- in the boiler the steam is conducted to sure.” In superheating steam expands the superheater where it lies in wait for to a slight degree if the pressure is con- the wasted heat rushing through the flues stant; but if the volume is constant su- and captures it before it can seize an
opportunity to escape up the smoke builders have left us far behind by the stack.
simple expedient of casting the cylinder Superheated steam can travel twice as and the steam dome all in one piece, with fast as saturated steam. It is possible to the former inside the latter, so that the transmit superheated steam a distance of walls of the cylinder are always sursix to ten thousand feet without a loss of rounded by steam at boiler temperature. more than ten per cent in pressure; and Only the heads are outside, where they by the use of separators to get rid of are as readily accessible as those of any what condensation there may be, to de- other type of engine. liver the steam in every way satisfactory It is well known that a compound enfor use. But no such formidable journey gine under proper conditions is more is ahead of the steam in a lokomobile; economical than a simple engine. So the and this brings up the second important lokomobile usually has a compound enfeature which makes the new type of gine. After expanding the steam in the engine so superior to the American high pressure cylinder until its temperahome-made kind.
ture is reduced to about 235 degrees it The great problem before the steam is returned to a second edition of the engineer is to prevent waste of the heat superheater where its temperature is after it has been put into the steam. As raised to about 360 degrees before being one means of preventing this loss the admitted to the low pressure cylinder. engine is mounted on the boiler of the From the low pressure cylinder the steam lokomobile. This eliminates the neces- is exhausted into a condenser where it sity of providing outside steampipes with gets down into water again. In some their enormous possibilities for waste of factories using lokomobiles of the larger heat by radiation. American engines of size the exhaust steam is used for heatsmall size are commonly mounted on the ing the building before it goes to the boiler, to be sure; but the European condenser. From the condenser the late