ICE MACHINES.
GENERAL PRINCIPLES--FREEZING MIXTURES--PERKINS’ ICE MACHINE, 1834--
PICTET’S APPARATUS--CARRÉ’S AMMONIA ABSORPTION PROCESS--DIRECT
COMPRESSION AND CAN SYSTEM--THE HOLDEN ICE MACHINE--SKATING RINKS--
WINDHAUSEN’S APPARATUS FOR COOLING AND VENTILATING SHIPS.
Very few people have any correct conception of the principles of
ice-making. Most persons have heard in a vague sort of way that
chemicals are employed in its manufacture, and many a fastidious
individual has been known to object to artificial ice on the ground that
he could taste the chemicals, and that it could not therefore be
wholesome. Such is the power of imagination, and such the misconception
in the public mind. Nothing could be more erroneous, nor more amusing to
the physicist, since no chemicals ever come in contact with either the
water or the ice. An intelligent understanding of the operations of an
ice machine involves only a correct appreciation of one of the physical
laws governing the relation of heat to matter, and the forms which
matter assumes under different degrees of heat. We see water passing
from solid ice to liquid water and gaseous steam, by a mere rise in
temperature, and conversely, by abstraction of heat, steam passes back
to water, and then to ice.
When one’s hands get wet they get cold. A commonplace, but convenient
proof of this is to wet the finger in the mouth and hold it in the air.
A sensible reduction of temperature is instantly noticeable. A more
pronounced illustration is to wet the hands in a basin of water, and
then plunge them in the blast of hot, dry air coming from a furnace
register. Instead of warming the hands, as many would suppose, this
will, as long as the hands are wet, produce a distinct sensation of
increased cold. It is due to rapid evaporation, which in changing the
water from a liquid to a gaseous form, abstracts heat from the hands.
Evaporation may be effected in two ways. The common one is by applying
extraneous heat, as under a tea kettle, in which case the evaporated
vapor is hot by virtue of the heat absorbed from the fire. The other way
is to reduce pressure or produce a partial vacuum over the liquid
without any application of heat, in which case the vapor is made cold.
As early as 1755 Dr. Cullen observed this, and discovered that the cold
thus produced was sufficient to make ice. An incident of evaporation is
the passing from the limited volume of a liquid to the greatly increased
volume of a gas. Water, for instance, when it changes to a vapor,
increases in volume about 1,700 times; that is, a cubic inch of water
makes about a cubic foot of steam, and when evaporation takes place from
a reduction of pressure, this involves a dissipation of heat throughout
the increased volume, and the corresponding production of cold. When,
however, matter changes from a liquid to a gas, or from a solid to a
liquid, a peculiar phenomenon manifests itself, in that a great amount
of heat is absorbed and, so far as the evidence of the senses goes,
disappears in the mere change of state. It is called _latent heat_. In
such case the heat becomes hidden from the senses by being converted
into some other form of intermolecular force not appreciable as sensible
heat, and producing no elevation of temperature. In illustration, if a
pound of water at 212° F. be mixed with a pound of water at 34° (both
being matter in the same state), there results two pounds of water at
the mean temperature of 123°. If, however, a pound of water at 212° be
mixed with a pound of _ice_ at 32° (matter in another state), there will
not be two pounds of water at the mean temperature of 122°, as might be
expected, but two pounds at 51° only, an amount of heat sufficient to
raise two pounds of water 71° being absorbed in the mere change of ice
to water without any sensible raise in temperature. This absorbed heat
is called latent heat, and it plays an important part in artificial
freezing. A familiar illustration of the absorption of heat in changing
from a solid to a liquid is found in the admixture of salt and ice
around an ice-cream freezer. These two solids, when brought together,
liquefy rapidly with an absorption of heat that produces in a limited
time a far greater degree of cold than that which could be obtained from
the ice by mere conduction, since the reduction of temperature proceeds
faster by liquefaction than can be compensated for by the absorption of
heat from the air. Were this not true, ice cream could not be frozen by
a mixture of salt and ice. Many such freezing mixtures are known, and a
few have been made commercially available, but they cannot be
economically employed in ice-making, and it is therefore only necessary
to consider the development of the more common principle of evaporation
and expansion, in which the change from a liquid to a gas occurs. The
volatile liquid which was first employed was water, but as it did not
vaporize as readily as some other liquids, more volatile substitutes
were soon found, among which may be named ether, ammonia, liquid
carbonic acid, liquid sulphurous acid, bisulphide of carbon and
chymogene, which latter is a petroleum product lighter and more volatile
than benzine or gasoline. As these liquids were expensive, it is obvious
that their vaporization could not be allowed to take place in the open
air, since the reagent would thus be quickly dissipated and lost, and
hence means were devised to condense and save this valuable volatile
liquid to be used over again. The vaporization of the volatile liquid to
produce cold, and its re-condensation to liquid form to be used over
again in an endless cycle of circulation, seems to have been first
effected by Mr. Perkins, of England, whose British patent No. 6,662, of
1834, affords a simple and clear illustration of the fundamental
principles of most modern ice machines. His apparatus is shown in Fig.
294. A tank _a_ is filled with water to be frozen or cooled. A
refrigerating chamber _b_, submerged in the water, is charged internally
with some volatile liquid, such as ether. When the piston of suction
pump _c_ rises a partial vacuum is formed beneath it, and the volatile
liquid in _b_ being relieved of pressure, evaporates and expands into
greater volume, the vapor passing out through pipe _f_ and upwardly
opening valve _e_. This vapor is rendered intensely cold by expansion,
and this cold is imparted to the water in tank _a_ to freeze it. A more
scientific statement, however, is that the cold vapor absorbs the heat
units of the water, and taking them away with it, lowers the temperature
of the water to the freezing point. When the piston of pump _c_
descends, valve _e_ closes, and the vapor, laden with the heat units
absorbed from the water, is forced through the downwardly opening valve
_e′_, and through pipe _g_ to a cooling coil _d_, around which a body of
cold water is continually flowed. This water, in turn, takes the heat
units from the vapor, and passes off with them in a constant flow, while
the vapor of ether is condensed into a liquid again by the cold water,
and passing through a weighted valve _h_, goes into the evaporating or
refrigerating chamber to be again vaporized in an endless circuit of
flow. It will be seen that the heat units from the water in tank _a_ are
first handed over to the cold ether vapors passing out from chamber _b_,
and by this vapor are then transferred to the flowing body of water
surrounding the coil _d_. The result is that the heat units carried off
by the water flowing around coil _d_ are the same heat units abstracted
from the water in tank _a_, which water is thus reduced to congealation.
[Illustration: FIG. 294.--PERKINS’ ICE MACHINE, 1834.]
Among later ice machines of this type the Pictet machine was a
conspicuous example. This employed anhydrous sulphurous acid as the
volatile agent, and is described in United States patent No. 187,413,
February 13, 1877; French patent No. 109,003, of 1875.
[Illustration: FIG. 295.--THE PICTET ICE MACHINE.]
In Fig. 295 is represented a vertical longitudinal and also a vertical
transverse section of a Pictet ice machine. A is a double acting suction
and compression pump, D and E are two cylinders which are similarly
constructed in the respect that they are both provided with flue pipes
and heads for a double circulation of fluids, one fluid passing through
the pipes while the other passes through the spaces between the pipes,
much like the condenser of a steam engine. The cylinder D is the
refrigerator where the volatile liquid is evaporated to produce cold,
and the cylinder E is the condenser where the gasified vapor is cooled
and condensed again to liquid form to be returned to the refrigerator.
The action is as follows: The pump A by pipe B draws from the chamber in
the refrigerator D containing the volatile liquid, causing it to
evaporate and produce an intense degree of cold which is imparted to the
liquid surrounding it and filling the tank. This liquid is either brine,
or a mixture of glycerine and water, or a solution of chloride of
magnesium, or other liquid which does not freeze at a temperature
considerably below the freezing point of water. Now, this
non-congealable liquid being below the freezing point, it will be seen
that if cans H be filled with pure water, and are immersed in this
intensely cold non-congealable liquid, the water in the cans will
freeze. This is exactly what takes place, and this is how the ice is
formed. As the volatile liquid is drawn out of the refrigerator D
through pipe B by the pump A it is forced by the pump through pipe C and
into the chamber of the condenser E. A current of cold water is kept
flowing around the pipes in E, coming in through a pipe at one end and
passing out through a pipe at the other end. The compressed and
relatively hot gases are by the contact of this cold water along the
sides of the pipes cooled and condensed into a liquid again, which
passes up the small curved pipe F and is returned to the refrigerator D,
to be again evaporated by the suction of the pump to continue the
production of cold. In large plants the non-congealable liquid and cans
of water to be frozen are (in order to get larger capacity) carried to a
large floor tank in a removed situation.
One of the earliest methods of producing ice in a limited quantity was
by evaporating water by a reduction of pressure and causing the vapor to
be absorbed by sulphuric acid, which has a great affinity for the water
vapor. Mr. Nairne, in 1777, was the first to discover the affinity that
sulphuric acid had for water vapor, and in 1810 Leslie froze water by
this means. In 1824 Vallance obtained British patents No. 4,884 and
5,001, operating on this principle, in which leaden balls were coated
with sulphuric acid to increase the absorbing surfaces, and which
apparatus was effective in freezing considerable quantities of ice.
The _carafes frappees_ of the Parisian restaurant were decanters in
which water was frozen by being immersed in tanks of sea water whose
temperature was reduced below freezing by the vaporization of ether in a
reservoir immersed in the sea water. Edmond Carré’s method of preparing
_carafes frappees_ involved the use of the sulphuric acid principle of
absorption, and to that end the aqueous vapor was directly exhausted
from the decanter by a pump, and the said vapor was absorbed by a large
volume of sulphuric acid so rapidly as to freeze the water remaining in
the decanter.
[Illustration: FIG. 296.--COMPRESSION PUMPS OF ICE PLANT.]
Probably the earliest practical ice machine to be organized on a
commercial basis was the _ammonia absorption machine_ of Ferdinand
Carré, which was a continuously working machine. It is disclosed in
French patents Nos. 81 and 404, of 1860, and No. 75,702, of 1867; United
States patent No. 30,201, October 2, 1860. In this case advantage is
taken first of the very volatile character of anhydrous ammonia, in the
expansion part of the process, and, secondly, of the great affinity
which water has for absorbing such gas. Strange as it may appear, the
production of ice in the Carré process begins with the application of
heat. It must be understood, however, that this forms no part of the
refrigerating process proper, but only a means of driving off or
distilling the anhydrous ammonia gas (the refrigerant) from its aqueous
solution. Ammonia dissolved in water, known as aqua ammonia, is placed
in a boiler or still above a furnace. The pure ammonia gas is thus
driven off from the water by heat under pressure, similar to that in a
steam boiler, and passes direct to a condenser, where, by cold water
flowing through pipes, the pure gas is liquefied under pressure. The
liquefied gas is then admitted to the evaporating or refrigerating
chamber, where it expands to produce the cold, and is afterward
re-absorbed by the water from which it was originally driven off in the
still, to be used over again. Machines of this type are known as
absorption machines, for the reason that the volatile gas is after
expansion re-absorbed by the liquid in which it was dissolved, and is
continuously driven off therefrom by the heat of a still. Absorption
machines were the outgrowth of Faraday’s observations in 1823. A bent
glass tube was prepared containing at one end a quantity of chloride of
silver, saturated with ammonia and hermetically sealed. When the mixture
was heated, the ammonia was driven over to the other end of the tube,
immersed in a cold bath, and the ammonia gas became liquefied. It was
found by him then that if the end containing the chloride was plunged in
a cold bath and the end containing liquid ammonia was immersed in water,
the heat of the water made the ammonia rapidly evaporate, the chloride
at the other end of the tube absorbed the ammonia vapors, and the water
around the end of the tube containing the liquefied ammonia was
converted into ice, by the loss of its heat imparted to the ammonia to
volatilize it. It only needed the substitution of water for the chloride
of silver, as an absorbing agent for the ammonia, and mechanical means
for economically working the process in a continuous way to produce the
Carré absorption machine. The most common form of ice machine to-day is,
however, what is known as the _compression_ or _direct_ system, in which
the absorption principle is dispensed with, the ammonia being compressed
by powerful steam pumps, then cooled to liquid form by condensers, and
then allowed to expand from its own pressure through pipes immersed in
brine in a large floor tank, in which cans containing pure water are
immersed, and the water frozen. Fig. 296[5] shows the compression pumps,
and Fig. 297 the floor tanks, of such a system. Many hundred cans
filled with pure water are lowered into the cold brine of the tank, and
their upper ends form a complete floor, as seen in Fig. 297. When the
water in the cans is frozen, the cans are raised out of the floor by a
traveling crane and carried to one of the four doors seen at the far end
of the room. The ice in the can is then loosened by warm water, and the
block dumped through the door into a chute, whence it passes into the
storage room below, seen in Fig. 298. In the can system the water is
frozen from all four sides to the center, and imprisons in the center
any air bubbles or impurities that may exist in the water. The plate
system freezes the water on the exterior walls of hollow plates, which
contain within them the freezing medium. In freezing the water
externally on these plates all impurities and air bubbles are repelled
and excluded, and the ice rendered clear and transparent.
[5] By courtesy of “Ice and Refrigeration.”
[Illustration: FIG. 297.--FLOOR TANK OF CAN SYSTEM.]
[Illustration: FIG. 298.--STORAGE ROOM OF ICE PLANT.]
An ice plant, employing what is known as the “can” system and capable of
producing 100 tons of ice in twenty-four hours, requires a building
about 100 feet wide and 150 feet long, on account of the great floor
space needed to accommodate the freezing tank, and the great number of
cans which are immersed in the same. A radical departure from this style
of plant is presented in the Holden ice machine. This does not require a
multitude of cans and a great floor space, but a lot 25 by 50 feet is
sufficient, for the ice is turned out in a continuous process like
bricks from a brick machine. The machine works on the ammonia absorption
principle, but the freezing is done on the outer periphery of a
revolving cylinder, from which the film of ice is scraped off
automatically and the ice slush carried away by a spiral conveyor to one
of two press molds, in which a heavy pressure solidifies the ice into
blocks, which are successively shot down from the presses on a chute to
the storage room, as seen in Fig. 299.
[Illustration: FIG. 299.--HOLDEN ICE MACHINE.]
The foregoing examples of ice machines give no idea of the great
activity in this field of refrigeration in the Nineteenth Century. Over
600 United States patents have been granted for ice machines alone, to
say nothing of refrigerating buildings, refrigerator cars, domestic
refrigerators, and ice cream freezers, etc. Among the earlier workers in
ice machines, in addition to those already named, may be mentioned the
names of Gorrie, patent No. 8,080, May 6, 1851, followed by Twining,
1853-1862; Mignon and Rouart, in 1865; Lowe, in 1867; Somes, in
1867-1868; Windhausen, in 1870; Rankin, in 1876-1877, and many others.
An application of the ice machine which attracted much attention and
attained great popularity for a while was that made in the production of
artificial _skating rinks_, in which a floor of ice was frozen by means
of a system of submerged pipes, through which the cold liquid from the
ice machine was made to circulate. The earliest artificial skating rink
is to be found in the British patent to Newton, No. 236, of 1870, but
it was Gamgee, in 1875 and 1876, who devised practical means for
carrying it out and brought it into public use. His inventions are
described in his British patents No. 4,412, of 1875, and No. 4,176, of
1876, and United States patent. No. 196,653, October 30, 1877, and
others in 1878.
The Windhausen machine was one of the earliest applications for
_cooling_ and _ventilating_ ships. This machine operated upon the
principle of alternately compressing and expanding air, and is described
in United States patents No. 101,198, March 22, 1870 (re-issue No.
4,603, October 17, 1871), and No. 111,292, January 24, 1871. To-day
every ocean liner is equipped with its own cold storage and ice-making
plant, refrigerator cars transport vast cargoes of meats, fish, etc.,
across the continent, and bring the ripe fruits of California to the
Eastern coast; every market house has its cold storage compartments, and
to the brewery the refrigerating plant is one of its fundamental and
important requisites.
The great value of refrigerating appliances is to be found in the
retardation of chemical decomposition or arrest of decay, and as this
has relation chiefly to preserving the food stuffs of the world, its
value can be easily understood. This branch of industry has grown up
entirely in the Nineteenth Century, and the activity in this field is
attested by the 4,000 United States patents in this class.