IMPROVEMENTS IN REFRIGERATING MACHINES
Year: 1871

page_text: PROVISIONAL SPECIFICATION left by Hunter Henry Murdoch at
the Office of the Commissioners of Patents, with his Petition, on
the 14th April 1871.-A communication from abroad by Edward
Roettger, of Lille, France, Civil Engineer.
I, HUNTER HENRY MURDOCH, of No. 7, Staple Inn, in the County
of Middlesex, Patent Agent, do hereby declare the nature of the said
Invention for "IMPROVEMENTS IN REFRIGERATING MACHINES," to be as
follows:-
:-
This Invention relates to machines for the production of cold by
means of compressed air. It is well known that if compressed air
be cooled to, say, the temperature of the atmosphere and then allowed
to expand cold will be produced. Hitherto in all applications of this
principle the expansion of the compressed air has taken place freely,
without having to overcome any resisting pressure.
Now this Invention is based upon a series of experiments which have
lead to the discovery that in order to produce cold economically by
means of compressed air the expansion of the said compressed air
must take place under pressure equal to the expansive force of the
said air.

page_text: According to this Invention an air pump provided with a double
casing, through which water is allowed to circulate, is connected by its
piston rod and a connecting rod with a crank upon a shaft supported
in suitable bearings in the frame of the machine. Upon the said shaft,
at a suitable distance from the air pump crank, is another crank
connected by means of a connecting rod with a piston rod, the piston
of which rod works in a cylinder, which may be termed the "expansion
cylinder," the said expansion cylinder being provided with ports for the
entry and outlet of air, and also with a slide valve and variable expansion
gear, such as would be fitted to an ordinary steam engine, wherein the
steam is intended to work expansively. The air pump is made to draw
air from the vessel or apparatus in which refrigeration is to be produced,
the said air is then forced by the said pump into an air-tight reservoir
or chamber, in which water circulates through suitable pipes. From
the said reservoir or chamber the compressed air passes into a second
reservoir or holder, so arranged that the communication between it and
the first-mentioned reservoir or chamber may be cut off when required.
From the said second reservoir or holder the compressed air passes into
the expansion cylinder, in which it acts as a motive power, giving a
reciprocal motion to the piston as in a steam engine, and giving rotatory
motion to the crank shaft and thereby working the air pump.
The relative positions of the cranks of the air pump and expansion
cylinder are such that when the compressed air is admitted to the
expansion cylinder the piston of the air pump will be exerting its
greatest amount of pressure upon the air. Thus if the air is to be
compressed by the air pump to a pressure, say, of four atmospheres,
it is when the piston of the said air pump has completed three-fourths
of its stroke that the compressed air is admitted to the expansion
cylinder, and the said compressed air is fed into the said expansion
cylinder till all the air in the air pump is forced into the air-tight
reservoir or chamber. During this latter portion of the stroke of the
air pump piston the communication between the said air-tight reservoir
or chamber, and the second reservoir or holder is cut off by means of a
cam or excentric, or other suitable mechanical contrivance acting on
a suitable valve or stop-cock. During the first portion of the stroke
of the air pump piston, when the said piston begins to compress the
air, the compressed air in the expansion cylinder is allowed to work
expansively, the feed of compressed air to the said cylinder being cut
off by the expansion gear. By this arrangement the compressed air in

page_text: the expansion cylinder as it expands is opposed constantly by a pressure
equal to its own expansive power; the heat it still contains is converted
into useful effect, and cold is produced. The length of stroke of the air
pump is equal to that of the expansion cylinder, but the diameter of the
said expansion cylinder is somewhat larger than that of the air pump
in order to compensate for the loss of power absorbed by friction and
other causes, and as the said expansion cylinder thus requires a larger
supply of compressed air than is forced into the reservoirs or holders by
the air pump, a small extra air pump is used to force air into the said
reservoir to complete the necessary supply.
The working of the machine is as follows:-The air is compressed
and partially cooled in the air pump. It is then forced into the first
reservoir or chamber, where it is further cooled by contact with the
water pipes. It then is admitted into the second reservoir or holder,
from which it passes at intervals, as required, into the expansion cylinder
in which it expands, and by its action on the piston of the said
cylinder it works the air pump, compressing therein a volume of air
nearly equal to its own volume, and forcing the said compressed air into
the reservoir herein-before described. The power thus exerted by the
compressed air during its expansion effectually deprives it of its remaining
caloric, and the cold expanded air thus produced is then discharged
into the refrigerating chamber or apparatus for use.