Source: Minutes of the Proceedings of the Institution of Civil Engineers, Vol 12, N° 897, p. 558
Date: May 17, 1853
Title: On the Caloric Engine
Author: Charles Manby, M. Inst. C.E.
At meetings of the Société d'Encouragement pour l'lndustrie Nationale, on the 26th January 1852, and at the Académie des Sciences, on the 2nd February of the same year, M. Galy Cazalat entered upon an examination of Ericsson's caloric-engine, assuming it to be composed of the following parts :
The two contrary successive currents, of the hot air which is cooled, and of the cold air which is heated, in their respective passages through the metallic web, are governed by a vessel called the "regulator."
In the preamble to his English patent, taken out under the name of Edward Dunn, December 26, 1850, Mr. Ericsson states that
the invention consists, in producing motive power by the application of caloric to atmospheric air, or other permanent gases, or fluids susceptible of considerable expansion by the increase of temperature,—the mode of applying the caloric being such, that after having caused the expansion, or dilatation which produces the motive power, the caloric is transferred to certain metallic substances, and again retransferred from these substances to the acting medium, at certain intervals, or at each successive stroke of the motive engine ; the principal supply of caloric being thereby rendered independent of combustion, or consumption of fuel accordingly ; whilst in the steam-engine the caloric is constantly wasted, by being passed into the condenser, or by being carried off into the atmosphere. In the improved engine, the caloric is employed over and over again, enabling me to dispense with the employment of combustibles, excepting for the purpose of restoring the heat lost by the expansion of the acting 'medium, and that lost by radiation also, for the purpose of making good the small deficiency unavoidable in the transfer of the caloric. (Repertory of Patent Inventions - Enlarged Series, Vol. XVIII., p. 93).
These passages would have led to the idea of a perpetual motion, but that the study of the well-known scientific laws applicable to the case, demonstrate the erroneous principle on which the presumed economy of the caloric engine is based. The elastic power of gases is solely due to the heat, which communicates a repulsive force to their particles.
Now, since the combination of a greater, or less quantity of caloric with a definite weight of gas, produces a greater, or less force, it is necessary, in order to remove mechanically this caloric from the gas, that a greater, or less, amount of power, should be employed. When, therefore, a volume of air is confined beneath a piston in a cylinder, an equilibrium exists between the force tending to press the piston against the air, and the caloric which imparts to the air the resistance opposed to the piston.
If the compressing force is increased by a quantity P, the air is compressed until its increase of resistance is equal to P, and a corresponding quantity of caloric is disengaged. This quantity measures exactly the increase of resistance ; for if the increase of force P is suppressed, the caloric disengaged becomes a reacting force equal to P, which causes the air to resume the volume it possessed under the initial pressure.
The increments of heat which measure the increments of resistance, in the states of equilibrium of gases, under increasing pressures, are equally found in the increments of resistance opposed to their velocity of efflux. It has been demonstrated by experiment, that the air which escapes from a reservoir, through an opening, under any given pressure, does not alter its temperature, although it may increase in volume. It follows, then, that heat is produced by the resistance which the atmosphere and the construction of the opening oppose to the efflux of the air, and that this heat is the more considerable as the difference between the pressure and the resistance (which difference produces the velocity of efflux) is greater ; hence, with the reciprocating motion of a piston in a cylinder, the caloric carried off by the motive fluid, air, or steam, in escaping, cannot be partly retained by a solid filter, without developing an equivalent resistance which annuls the anticipated economy.
This deduction from physical laws is directly at variance with the performance of the caloric ship "Ericsson," as asserted in the statements that have reached Europe. The engines of that vessel are said to be composed of two similar sets of apparatus, in each of which the working cylinder has a capacity of 915 cubic feet, the fire cylinder of 457 cubic feet, and the meshes of copper wire contained in the "regenerator," have a total surface of 4,900 square feet, and weigh 33,000 lbs. (All dimensions, weights, and temperatures are here expressed in equivalent English measures).
It is affirmed that this colossal engine, of 600 HP, only consumes 6 tons of coal in 24 hours ; whereas the engines of the best steam-vessels employ about ten times that quantity.
It is conceived that it will not be difficult to demonstrate, that this statement cannot have taken into account the fuel consumed in laying up a store of caloric, upon and by which the engines have been partly worked, during the evidently too short trials which have been made.
It is well known, that the caloric given out by 1 lb. of air, in cooling 1 degree, is sufficient to add 1° of temperature to 2'8 lbs. of copper. Assuming this as a principle, it is easy to calculate the caloric which the metallic gauze of the regenerator abstracts from the volume of air passing through it into the atmosphere, when the piston descends ; as well as the quantity which it restores to the current of compressed air, on returning in the opposite direction.
Suppose, first, that the regenerator receives no heat directly from the furnace, and that the motive air is maintained at the temperature of 521.5° F which is necessary to double its volume at 32°. Then let it be admitted, that the initial temperature of the wire-gauze, as well as the receiver of compressed air, and the atmosphere, is 32°. Finally, let the resistance encountered by the currents of air, and also the increase of temperature imparted by the small feed piston to the air, (incompressing it to the extent of two atmospheres, previously to injecting it into the recipient, namely, by raising it from 32° to 176°), be omitted from the calculation.
Then 915 cubic feet of air at 521.5° being equal in weight to half that bulk at 32°, and weighing 37.5 lbs. with the barometer at 30 inches ; when this volume of air is compressed to 2 atmospheres, it weighs 75 lbs.
Calculating according to what are contended to be the erroneous views of Captain Ericsson ; at the first descent of the working piston, the air expelled from the cylinders weighing 75 lbs. its temperature should diminish 486.5° in heating the 33,000 lbs. of copper web 3.08 degrees. When the piston re-ascends, the 75 lbs. of air which pass from the receiver through the wire-gauze at 35.08°, lower its temperature to 35.04°, in raising the air from 32° to 35.04°.
At the second stroke of the piston, the regenerator is raised to 38° by the air discharged, and is lowered to 37.96° by the entrance of the air from the receiver. And thus continually, until the metallic meshes impart to the current of cold air as much caloric as they abstract from the hot air.
Calculation demonstrates that this equilibrium will take place, when the temperature of the regenerator is at 277°, before the passage of the cold air. From this time, the action of the machine becomes regular, and it consumes at each stroke of the piston, 277 — 32 = 245° of heat, which the discharged air carries into the atmosphere.
To realize this considerable economy, much less, however, than that asserted, it would be necessary that the air discharged should traverse the wire gauze without cooling by expansion, i.e., should preserve the elastic force of two atmospheres, which it had in the working cylinder. Now this force diminishing to the sum of the resistances of the atmosphere and of the regenerator, opposed to it, the sensible heat which measures it must diminish, also, by the entire portion employed in augmenting the volume of the gas, without communicating itself to the copper-wire gauze.
It results from this, that every volume of air discharged, carries into the atmosphere nearly the whole of its caloric, which becomes latent in expanding to double its volume. The insignificant portion which it takes up in conjunction with the copper, in proportion to their respective weights and capacities, corresponds to the difference of the diminution of its volume.
To find the mean temperature of the regenerator, before and after the passage of the air:
t'' = [tP + T(C+P)]/(C + 2P)
t' = [TP + t(C+P)]/(C + 2P)
When the furnace heats, at the same time, the regenerator and the chamber, designated the expansion-heater, (chauffeur de detente,) the wire-gauze may be raised to the limiting temperature, which is 521.5° ; in this case the air of the receiver has imparted to it a greater amount of caloric, inasmuch as the wire-gauze is raised to a higher temperature, and it receives less from the furnace, to raise it to its ultimate degree of heat.
Notwithstanding these objections, which in the interest of science others deem incumbent to raise, after examining the description of these machines, and the accounts of their trial voyages, as transmitted to Europe, it must be admitted that Captain Ericsson has conferred a benefit on society, by this attempt to introduce heated air as a motive power, and he has, in following in the steps of the Messrs. Stirling, worthily maintained the reputation for ingenuity which he gained in his early labours in railway locomotion with the 'Novelty,' and in marine propulsion by his experiments ou the substitution of the screw for the paddle-wheel.
There appears to be at present so much doubt of the utility of the regenerator, that it would be wise to abandon its use for a time, and by trials with a more simple form of caloric engine, establish the fact either of the superiority, or of the inferiority of heated air, in comparison with steam, as a motive power.
In this sketch the views of M. Galy-Cazalat have been closely adhered to, and they have only been brought forward in deference to the expression of the wishes of the President at a previous meeting.