From what has been said, it will have been seen that, so far as the
mere application is concerned, there is no difference whatever between
the absorption and compression processes. The following
considerations, therefore, which chiefly relate to the application of
refrigerating apparatus, will be dealt with quite independent of
either system. The application of refrigerating apparatus may roughly
be divided into the following heads:
a. Ice making.
b. The cooling of liquids.
c. The cooling of stores and rooms.
_Ice Making._--For this purpose two methods are employed, known as the
can and cell systems respectively. In the former, moulds of tinned
sheet copper or galvanized steel of the desired size are filled with
the water to be frozen, and suspended in a tank through which brine
cooled to a low temperature in the refrigerator is circulated. As soon
as the water is completely frozen, the moulds are removed, and dipped
for a long time into warm water, which loosens the blocks of ice and
enables them to be turned out. The thickness of the blocks exercises
an important influence upon the number of moulds required for a given
output, as a block 9 in. thick will take four or five times as long to
freeze solid as one of only 3 in. In the cell system a series of
cellular walls of wrought or cast iron are placed in a tank, the
distance between each pair of walls being from 12 to 16 in., according
to the thickness of the block required. This space is filled with the
water to be frozen. Cold brine circulates through the cells, and the
ice forms on the outer surfaces, gradually increasing in thickness
until the two opposite layers meet and join together. If thinner
blocks are required, the freezing process may be stopped at any time
and the ice removed. In order to detach the ice it is customary to cut
off the supply of cold brine and circulate brine at a higher
temperature through the cells. Ice frozen by either of the above
described methods from ordinary water is more or less opaque, owing to
the air liberated during the freezing process, little bubbles of which
are caught in the ice as it forms, and in order to produce transparent
ice it is necessary that the water should be agitated during the
freezing process in such a way as to permit the air bubbles to escape.
With the can system this is generally accomplished by means of arms
having a vertical or horizontal movement. These arms are either
withdrawn as the ice forms, leaving the block solid, or they are made
to work backward and forward in the center of the moulds, dividing the
block vertically into two pieces. With the cell system agitation is
generally effected by making a communication between the bottom of
each water space and a chamber below, in which a paddle or wood piston
is caused to reciprocate. The movement thus given to the water in the
chamber is communicated to that in the process of being frozen, and
the small bubbles of air are in this way detached and set free. The
ice which first forms on the sides of the moulds or cells is, as a
rule, sufficiently transparent even without agitation. The opacity
increases toward the center, where the opposing layers join, and it
is, therefore, more necessary to agitate toward the end of the
freezing process than at the commencement. As the capacity for holding
air in solution decreases if the temperature of the water is raised,
less agitation is needed in hot than in temperate climates.
Experiments have been made from time to time with the view of
producing transparent ice from distilled water, and so dispensing with
agitation. In this case the cost of distilling the water will have to
be added to the ordinary working expenses.
_Cooling of Liquids._--In breweries, distilleries, butter factories,
and other places where it is desired to have a supply of water or
brine for cooling and other purposes at a comparatively low
temperature, refrigerating machines may be advantageously applied. In
this case the liquid is passed through the refrigerator and then
utilized in any convenient manner.
_Cooling of Rooms._--For this purpose the usual plan is to employ a
circulation of cold brine through rows of iron piping, placed either
on the ceiling or on the walls of the rooms to be cooled. In this, as
in the other cases where brine is used, it is employed merely as a
medium for taking up heat at one place and transferring it to the
ammonia in the refrigerator, the ammonia in turn completing the
operation by giving up the heat to the cooling water during
liquefaction in the condenser. The brine pipes cool the adjacent air,
which, in consequence of its greater specific gravity, descends, being
replaced by warmer air, which in turn becomes cold, and so the process
goes on. Assuming the air to be sufficiently saturated, which is
generally the case, some of the moisture in it is condensed and frozen
on the surface of the pipes; and if the air is renewed in whole or in
part from the outside, or if the contents of the chamber are wet, the
deposit of ice in the pipes will in time become so thick as to
necessitate its being thawed off. This is accomplished by turning a
current of warm brine through the pipes. Another method has been
proposed, in which the brine pipes are placed in a separate
compartment, air being circulated through this compartment to the
rooms, and back again to the cooling pipes in a closed cycle by means
of a fan. This plan was tried on a large scale by Mr. Chambers at the
Victoria Docks, but for some reason or other was abandoned. One
difficulty is the collection of ice from the moisture deposited from
the air, which clogs up the spaces between the pipes, besides
diminishing their cooling power. This, in some cases, can be partially
obviated by using the same air over again, but in most instances
special means would have to be provided for frequent thawing off, the
pipes having, on account of economy of space and convenience, to be
placed so close together, and to be so confined in surface, that they
are much more liable to have their action interfered with than when
placed on the roof or walls of the room.
In addition to the foregoing there are, of course, many other
applications of ammonia refrigerating machines of a more or less
special nature, of which time will not permit even a passing
reference. Many of these are embraced in the second class, cold water
or brine being used for the cooling of candles, the separation of
paraffin, the crystallization of salts, and for many other purposes.
In the same way cold brine has been used with great success for
freezing quicksand in the sinking of shafts, the excavation being
carried out and the watertight tubing or lining put in while the
material is in a solid state. In a paper such as this it would be
quite impracticable to enter into details of construction, and the
author has therefore confined himself chiefly to principles of
working. In conclusion, however, it may be added that in ammonia
machines, whether on the absorption or compression systems, no copper
or alloy of copper can be used in parts subjected to the action of the
ammonia. Cast or wrought iron and steel may, however, be used,
provided the quality is good, but special care must be taken in the
construction of those parts of absorption machines which are subjected
to a high temperature. In both classes of apparatus first-class
materials and workmanship are most absolute essentials.
* * * * *
[Continued from Supplement, No. 646, p. 10319.]