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STEAM AND STEAM-ENGINES

mental principles of Energetics, and in particular the laws governing the transformation of energy from the form of heat to that of mechanical energy and vice versa. An all-comprehending law, of which the laws of energetics are in fact corollaries, the law of Existence, or of Persistence, is expressed thus: All that exists, whether matter or force or their resultant, energy, and in whatever form, is indestructible by finite power.

Unit for each 778 foot-pounds, or of one calorie for
each 427 kilogrammetres of energy or of work.
The mechanical equivalent of heat is the specific heat
of water at its temperature of maximum density ex-
pressed in dynamic units, as foot-pounds or kilogram-

metres.

The value of the mechanical equivalent of heat has been taken as first adopted by Joule, although recent and most carefully conducted investigations indicate a value higher, by perhaps one per cent, to be more ac this field to date, have, however, been based upon Many existing tables, and much work done in Joule's figure, 772, foot-pounds, 423, kilogrammetres. The figure, above given, 778 or 427, is now, however, generally accepted.

curate.

2. The total of any single effect of any given quan tity of heat acting in any thermodynamic operation is proportional to the total amount of heat-energy so act

ing.

This principle is substantially that first accepted by Rankine as the second law. Actual energy of vibration is understood.

Thus, of the whole quantity of heat passing from the heater to the working substance, one part is always transmuted into mechanical work, or energy; while the remainder goes to the refrigerator, and the ratio of the one quantity to the other is perfectly definite. Professor Wood expresses this law thus:

"If all the heat absorbed be at one temperature, and that rejected be at one lower temperature, then will the heat which is transmuted into work be to the entire heat absorbed in the same ratio as the difference between the absolute temperatures of source and refrigerator is to the absolute temperature of the source."

Matter may change its form and its chemical composition by rearrangement of its molecules or of its elementary atoms, but it cannot be destroyed; forces inhere and are persistent as characteristics of all matter and cannot be separated therefrom; energy, like matter, is constant in its total quantity in the universe and may be transferred and transformed, but cannot be extinguished. Transformation of energy, as of thermal into dynamic or mechanical, is simply the change of the kind of mass affected and consequent alteration of the kind of motion due to its action. A shot from a gun, stopped in its rapid flight by impact on the target, if not fractured, will exchange the thousands of foot-tons of mechanical energy sustaining its flight for precisely the same quantity of molecular motion and energy. Similarly, were a shot heated to a high temperature and then were all its molecules by some conceivable process of steering each into its path, made to take up simultaneously a definite rectilinear motion, it would become absolutely cold and would fly out into space with a dynamic mass-energy precisely equal and, in fact, with the identical energy at first displayed and as molecular. The heat-engine is a device for bringing about such a change for industrial purposes.

The laws of energetics, as usually enunciated, are:

1. The Law of Persistence, or of Conservation of Energy, namely: Existing energy can never be annihilated; and the total energy, actual and potential, of any isolated system can never change.

This is evidently a corollary of that grander law, asserting the indestructibility of all the work of creation, which has already been enunciated.

2. The Law of Dissipation, or of Degradation of Energy, namely: All energy tends to diffuse itself throughout space, with a continual loss of intensity, with what seems, now, to be the inevitable result of complete and uniform dispersion throughout the universe, and consequently of entire loss of availability.

It is only by differences in the intensity of energy, and the consequent tendency to forcible dispersion, that it is possible to make it available in the production of

work.

3. The Law of Transformation of Energy, namely: Energy may be transformed from one condition to another, or from any one kind or state to any other; changing from mass-energy to molecular energy of any kind, or from one form of molecular energy to another, with a definite quantivalence.

Thermodynamics, being a restricted energetic, in which only two energies, thermal and dynamic, are comprehended, its laws are, fundamentally, identical with the preceding and the enunciation just adopted is entirely accurate in this restricted science.

The Laws of Thermodynamics, in the special forms considered best for the purposes of the thermodynamist, are corollaries of the laws of energetics and of Newton's laws, which are a different method of expression of the same fundamental principles. They are usually stated thus:

1. Thermal and Mechanical Energy are mutually interconvertible in the proportion of one British Thermal

The second law finds important application simply in enabling us to ascertain the total quantity of work, external and internal, required to produce changes of volume and energy in fluids, like the vapors, in which we cannot measure directly the internal forces and internal work.

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If the change of sensible heat be called dS, that of "latent heat, dL, and of external work dU, then the first law of thermodynamics is expressed by the equa tions:

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where, in the last two expressions, dEdS+dL, and is d-dL+dU, and is the total work done, externally the variation of energy, actual and potential; while and internally. These are primary and general equa tions.

The quantity E is often called the intrinsic energy of the substance; L is evidently a potential energy; while S is a form of molecular kinetic, or actual, energy, which may sometimes be regarded as also in a senst potential.

The above are completely general expressions of the general fundamental equation of thermodynamics.

Internal work or energy, positive or negative, is the work performed in changing the relative distances between molecules, atoms or corpuscles, or in causing variation of their relative velocities, and within the mass and out of reach of the human senses. In the fundamental equation, it is measured by dL.

External work is that performed by mass or molecule, by atom or corpuscle against outside resistances, as where steam expands, doing work upon a piston. As indicated by the above laws, it must do so by surrendering an equivalent quantity of heat-energy. This is dW.

Heat-energy, thermal or dynamic, is of the same nature and may be measured in either thermal or dynamic units, foot-pounds and kilogrammetres, or in British or metric thermal units or "calories." One B. T. U., expressed in thermal units, is 778 foot-pounds expressed in dynamic units; one metric unit, the calorie, is 3.96832 times as great as the British, or the B. T. U. is 0.251996 of the metric unit. The engineer often conducts his thermoydyamic inves tigations in dynamic terms; the physicist and the chemist employ the thermal; the one often uses British, the other always adopts the metric.

STEAM AND STEAM-ENGINES

Where work is performed by an expanding fluid ternal energy is lost and gained by variation of upon a moving piston, the total work,

pistopet pi) as;

where a is the piston-area, and s is the space traversed by the piston; mean pressures corresponding to the external and the internal work being pe and pi while as=v, the volume traversed.

Corliss Engine Valve-motion (1850).

The Perfect Gas is a fluid within which no internal work is done with varying volumes and which may be defined by the equations, pv al; pv/Ta. In thermodynamic equations, the perfect gas has zero values of internal energy and work. T is absolute temperature, and the pressures and volumes at that temperature of unit mass.

Vapors are fluids in which the internal energy and work may be large, both absolutely and relatively, with changing volumes. Internal cohesive forces are often not only sensible but very great, the internal latent heat, which simply measures the internal work, when expanding water into vapor of one atmosphere pressure, as an example, is the equivalent of the work of elevation of the weight affected to a height of about 150 miles. These forces, however, as with the gases, do not prevent the free movement of molecules in any direction and to any extent; nor do they fix the volume and density of the substance.

Liquids are fluids in which the action of internal molecular forces gives stability of volume, but not of form, and the energies, internal and external, are thus limited to comparatively small ranges and to comparatively small values; while range and values are often enormously great when the liquid becomes vaporous, notwithstanding rapid diminution of molecular attractions.

Solids have stability, both of volume and of form; the ranges of internal forces and of energies are still more restricted than with liquids and their extent of action and their values are still less than in liquids. By accession of heat, all solids become at some definite point liquid, liquids become vapors and vapors, when "superheated," become gases. It is to be noted that, whenever a substance, of whatever class, alternately expands and contracts through a fixed range of volume, whatever its temperature or the pressure, precisely the same amount of in

volume against or with the constant effort of the internal forces.

Cycle is, thermodynamically, an operation in which a working substance passes through a series of changes of pressure, volume and temperature resulting in the final return of the substance to its initial physical state. In this operation, it is evident that the net change of internal energy is zero. This process is illustrated in heat-engines in which the working substance is confined within the working chamber and therein passes through repeated cycles with repetition of the kinematic cycle of the machine itself. Obviously, also, where a working fluid traverses a cycle, the presence or the absence of the quantity of internal energy becomes a matter of no importance when we seek only to determine the quantity of permanent thermodynamic transformation. The magnitude and effect of internal forces and energies have no influence upon the efficiency of transformation; but they have importance as affecting the relations of pressure, volume and temperature and the magnitude of the working cylinder and of the heat-engine itself. A steam, or other vapor, engine is vastly more compact than a gas-engine operating under similar thermal conditions, under similar limiting external pressures. internal forces affecting water and its vapor are large and confine the substance, at any stated temperature, to small volume and give it a high density, relatively to its gas. In the highest boiler pressures now usual, these forces are about ten times the gauge pressure. At atmospheric external pressure, they amount to thirteen atmospheres. These pressures cannot be measured by any gauge, but may be readily computed with precision from easily ascertainable

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data; they are perfectly well known, as are the specific volumes of the fluid, which are very difficult, but not impossible, of direct measurement.

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STEAM AND STEAM-ENGINES

The gas-engine has the advantage, in comparison with the steam-engine, in its higher available temperature range and consequent higher thermodynamic efficiency.

The exact treatment of the thermodynamics of the steam-engine requires the use of the higher mathematics, but the general principles have been given and the following will permit its applications to be understood:

A steam-engine is a thermodynamic system in which only thermal and dynamic energies are present and operative. Its action is to transform as large a proportion as possible of the heat supplied it into mechanical power and work. Each pound of steam from the boiler usually brings over the equivalent of about 0.4 horse-powerhour and each horse-power-hour is the ideal

Double-cylinder Pumping Engine (1878).

equivalent of the heat-content of about 2.3 pounds, a kilogram, nearly, of boiler steam, Of this heat, a part, which is precisely measured by the area of the indicator diagram, is converted into useful work and an "efficiency is attained measured by the ratio of the useful to the supplied energy in common units. Thus: where 23 pounds of steam per hour are demanded per horse-power developed, in the case assumed, the efficiency is 10 per cent; the heat supplied being that furnished from the fuel and measured by the difference between the "total heat" of the feed-water at condenser temperature and that of the steam in the boiler.

The nine tenths which fails of utilization is composed of a variety of wastes, including the thermodynamic, that portion of the heat reaching the steam-cylinder and actually acting upon the piston which is not converted into indicated work, the waste by conduction and radiation externally, and the waste by the transfer of heat between the metal of the cylinder and the working fluid. These quantities in a good example may be taken as follows, the friction wastes of the machine itself being included:

Available heat-energy
from the boiler.... . 100

Thermodynamic wastes. 70
Internal thermal loss.. 10
External waste...
Friction
Useful work..

5

This corresponds, for the ideal case, to an efficiency of 0.20, nearly.

The external waste of the steam-engine is usually considered to be covered by an allowance of about one B. T. U. per square foot per hour per degree range of temperature, Fahrenheit, or about three calories per square metre, although, on exposed metal having a rough surface, it may attain two to three times these figures. The exterior of the cylinder is commonly lagged and the heads, if not thus covered, are polished, thus minimizing the waste. The total waste, on even small engines, has been found capable of being reduced to less than 3.5 per cent, total, inclusive of engine and boiler, by the use of good non-conducting coverings. This loss is often quite unimportant on large engines.

The internal wastes are produced by heat-exchanges between metal and steam, at induction and eduction; the steam giving heat to the metal at its entrance into the cylinder and robbing the metal at exhaust, thus transferring heat often in large quantities from the steam to the exhaust side, very much as leakage carries the steam itself with its charge of heat. The effect on efficiency is precisely that of leakage. In this action, the cylinder-heads and the sides of the piston, being exposed to the widest range of temperature and for the longest periods, are most fruitful of waste; the cylinder, proper, and especially its middle portion, wastes least. The total loss is a function of the temperature range, the time of exposure to transfer, and the quality of steam, and of the ratio of expansion which measures rudely the quantity of steam per unit weight of

metal. In any one engine it may be stated, as a rough approximation, that the condensation is a constant quantity at all expansions. It may be treated as either a constant leakage or as a constant loss of work measurable by an equivalent back-pressure. A common value of this leakage may be taken, in pounds, as not far from 0.02 B. T. U., per square foot of surface exposed at cut-off, per minute per Fahrenheit degree of temperaturerange. As a fraction of the steam supplied, it is approximately proportional in any given engine to the square root of the ratio of expansion. With various types of engine, it ranges from 25 or 30 per cent, with simple engines of moderate size to 10 per cent, in multiple-cylinder engines of modern construction as a minimum. In steam pumps and very small engines, it may amount to more than the whole amount of steam taken in, for thermodynamic action. These machines, demanding 100, and even sometimes 150 or more pounds of steam per h. p. hr., waste three fourths or more by "leakage" of heat. The "record-breaking engines of large size and superior design demand as little as 10 to 12 pounds, approximating 200 B. T. U. per h. p. hr.

The velocity of heat-exchange in this manner is many times greater than in transfers across the boiler heating surfaces. It is the most rapid known form of condensation of steam, and is often 10 times as rapid as the pro100 duction of steam in the boiler supplying it.

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STEAM AND STEAM-ENGINES

The conditions of maximum efficiency are mainly two: the reduction to the practicable minimum of the thermodynamic waste by increasing in all possible ways the area of the indicator diagram per unit of steam supplied, and by minimizing the wastes of heat between boiler and engine-piston. The first includes the increase of the initial pressure, with decrease of back-pressure and adjustment of the ratio of expansion of the steam to the range thus secured; the second involves reduction of conduction and radiation by use of suitable non-conducting coverings of heated surfaces, protection from cooling influences and reducing "cylinder condensation" by drying and superheating the steam, by increasing the speed of engine and by diminishing the heat-exchanges between metal and steam by fine finish of surfaces, and, where practicable, by interposition of non-conducting material, as was done by Smeaton and attempted by later in

ventors.

"Mechanical efficiency," the ratio of work transmitted from the piston to the point of useful application, ranges from 95 per cent in

place and purpose of which the type is such that no practicable substitution will permit the supply of the demanded power at lower total operative costs, including interest on first cost, a sinking fund to provide for replacement at the end of its period of use, and annual operating expense; and that size of engine is on the whole best, variation from which in the direction of either increased or lessened size will increase that total expense of operation. In the latter case, the gain by reduction of size will be more than compensated by the loss due to its reduced efficiency. The best engine is that which will give largest returns on the capital invested, adding most effectively during its life to the dividends obtainable from the "plant" of which it forms a part.

The adjustment of the ratio of expansion of the steam to the requirements of maximum efficiency is the vital problem of the designing engineer and the purchaser of the engine. In the ideal case of the purely thermodynamic machine, this ratio is that of the initial to the backpressure, very nearly, and the terminal pressure

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direct-acting engines as a maximum, to 85 per cent with the older non-condensing engines. It is made a maximum and friction reduced to a minimum by careful design, and especially by securing constant, complete and free lubrication; usually, in the best cases, by a circulatory flow of oil, flooding the bearings and returned by pumps to the source, through a filter, to be again distributed to the rubbing surfaces of the engine. The lost work is the less, as the pressures are higher within limits determined by the nature of the materials, as the lubricant is better adapted to its intended purpose, and as the flow is more liberal where reaching the rubbing parts. The highest values of the coefficient of friction are often ten and sometimes twenty times the lowest and the careful attention of the engineer to this detail is always well compensated.

The ultimate limit of economy in operation, with any class of engine, is fixed by financial considerations, and the principle involved in determining the limit may be thus expressed :

That engine is most perfectly adapted to its

on the expansion-line should coincide with the back-pressure. For maximum economy of fuel, this expansion ratio should be reduced in proportion, closely, to the loss by heat-wastes between boiler and piston. For maximum efficiency from the financial point of view, a still further reduction is required in proportion to the relation of the operating costs apart from those of steammaking to those of engine-operation proper. Thus, in the thermodynamic case, with initial and final pressures, respectively, 10 atmospheres and one, the ratio is reduced, often from about ten to seven or eight by initial condensation and minor wastes, and to six by adjustment to that value, departure from which, in either direction, would increase total costs of the horse-powerhour.

With condensing engines, the ideal ratio might be 40 or 50, while the ratio for maximum duty would be not above 20, and the best ratio, from the point of view of the treasurer, might be not above 12 or 15. The accuracy with which the designing and constructing engineer determines the adjustment for

STEAM GAUGE - STEAM VESSELS

maximum financial efficiency is a measure of his ability and skill and a gauge of his success in solving his problem. With each standard construction, experience usually enables the engineer to satisfactorily determine the proper solution of this problem.

The case of the steam-turbine exhibits here one of its essential peculiarities. The ratio of expansion is fixed by the conditions of its design, construction and operation and is necessarily the ratio of initial to back-pressure if properly constructed. The maximum efficiency of the turbine is obtained at its maximum power and it possesses the same inherent inflexibility as the hydraulic turbine, if of other than the "partial" class, in which latter case power is adjusted to load by varying the number of nozzles or supply-passages in action. It has the same possibilities of adaptation as has the hydraulic with, further, available recourse to intermittent supply, as with the Parsons turbine, a plan unavailable with the hydraulic machine, as an element of regulation. The steam-turbine, also, is not subject to internal condensation as all its elements, when in steady operation, maintain a constant temperature. Its economic theory is thus greatly simplified. Its financial theory simply dictates the construction of a light, rapidly moving vane and a minimum cost of application to its work, to operation and to maintenance, as a total. See ROTARY STEAM ENGINE.

R. H. THURSTON, Cornell University. Steam-Engine Terms. The Construction and operation of the various appliances and principal parts of a steam-engine are specifically described, in their connection with and application to the locomotive, in the article under the title, LocoMOTIVE, DESIGN AND CONSTRUCTION OF THE MODERN, in this Encyclopædia.

Steam Gauge. - See STEAM-ENGINES.
Steam Hammer. See HAMMER.
Steam Heating. See HEATING AND VENTI-

LATION.

Steam Jacket, a space filled with steam surrounding the cylinder of a steam-engine; from it heat passes into the cylinder and prevents the condensation of steam which would otherwise take place during expansion.

Steam Navigation. See STEAM VESSELS. Steam-ships. See STEAM VESSELS. Steam Turbine. See STEAM AND STEAM-ENGANE; TURBINE.

Steam Vessels. The paddle wheel was in use for the propulsion of a vessel long before the application of steam to navigation. In the war galleys of the ancient Egyptians and Romans there were wheels operated by hand power through a windlass; and in one of the Punic wars the Romans transferred an army to Sicily upon vessels moved by wheels that were operated by oxen. Prince Rupert, after retiring from his military life, had a boat constructed on the Thames River, prior to 1680, that was propelled by paddle wheels, which were driven by horse power. It is thus clear that some form of paddle wheel for propulsion was made use of long before the steam-engine was in service. The Marquis of Worcester had experimented with the steam-engine from about 1655. He died in 1667 leaving a manuscript in

which he says: "By this I can make a vessel of as great burthen as the river can bear to go against the stream. . . And this engine is applicable to any vessel or boat whatsoever, without therefore being made on purpose. . It roweth, it draweth, it driveth, to pass London Bridge, against the stream at low water."

Early Steamboats.-The experiment narrated many years ago of Blasco de Garay in 1543 at Barcelona moving a vessel by steam power, has long since been looked upon with doubt. This was 100 years before the steamengine was put to any practical use even in its crude form. Denis Papin and Thomas Savary had mentioned the application of steam to navigation about 1690, and the former is said to have applied it on a model at a later date. In 1736 Jonathan Hull of England obtained a patent upon what would be termed a stern wheel boat for towing purposes; but as the steam-engine at that time was not in a form to adapt it for a vessel, and as it is said he never made a model of his invention, nor car

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ried on any experiments to develop his patent, it is not clear where the claim appears of his being the inventor of the steamboat. Experiments were made in France from 1759 to 1781 by Genevois and Perrier, when the Marquis de Jouffrey built on the river Saône a steamboat of 150 feet long by 15 feet wide, with which he made several experiments covering a period of over a year, but defects developed in the machinery so serious that caused the project to be abandoned. Patrick Miller of Scotland in 1788 had a double hull boat constructed 25 feet long and 7 feet broad, and fitted with a steam-engine, under the supervision of William Symington. It succeeded so well that he built the next year a larger double hull boat, and a trial was made on the Forth and Clyde Canal in the summer of 1789, when seven miles an hour was made. The boat, the wheels, and the engine were so ill proportioned to each other that the wheels were continually breaking, and the hull suffered so much from the strain imparted by the machinery as to be in danger of sinking. The trial was not considered to be a success, and the vessel was shortly after laid aside. It was now over 10 years before any further trials were made in Great Britain. It will be noted that John Fitch's experiments began in 1786, and Patrick Miller did not begin until some two years later. In 1802 Lord Dun

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