Improvements in Air-compressors.
Year: 1899

page_text: Date of Application, 11th Oct., 1899-Accepted, 16th Dec., 1899
COMPLETE SPECIFICATION,
Improvements in Air-compressors.
I, JOHANN STUMPF, of 27, Rankestrasse, Berlin, in the German Empire,
Engineer, do hereby declare the nature of this invention and in what manner
the same is to be performed, to be particularly described and ascertained in and
by the following statement: —
Many attempts have heretofore been made to construct an efficient air-
compressor based on the principle of combining the air- and steam-cylinders.
Compressors of this kind have however never come into general use since it has
not been understood how the advantages which this system offers may be properly
utilized in their construction, and to properly develope this promising system.
How this can be done will be indicated in the following description.
If the pressure of the steam and the pressure of the air be assumed to be equal,
the steam and air-cylinders in an exhaust-compressor (i.e., an air-compressor
driven by a non-condensing steam-cylinder or engine) can be made of equal
size. This is always so, for example, in the compressors usually employed in
mines, in which, always assuming a free exhaust, the steam- and air-cylinders
are made of equal size. Consequently, without further discussion, the system
under consideration is applicable here. If we take તી compression of
the air of 9 atmospheres absolute, and the initial temperature at
20 degrees Centigrade, assuming moreover a steam pressure of 9 atmo-
spheres absolute, the temperature of the steam is 175 degrees C. and the
temperature of the compressed air 280 degrees C. From this, there results
difference of temperature of 105 degrees in favour of the compressed air. In
this calculation, the superheating is not considered, which is caused by drawing
the air into the heated valve-chest and the heated compression-cylinder. Neither
is the superheating considered which takes place by reason of the air being forced
through the narrow passages of the valve and so on. Measurements have shown
that the temperature is usually about 30 to 40 degrees higher than corresponds
to the temperature as calculated theoretically. We have therefore, in the above
assumption, to do with a difference of temperature of about 140 degrees C. This
circumstance can be advantageously utilized for heating the end of the com-
bination-cylinder, in which the steam acts.
In order to attain this object, one can proceed in various ways. In the accom-
panying drawing, two methods are shown by way of example.
In Figure 1, the cylinder a is surrounded by a jacket c into which the heated
air is conducted, for example. from beneath and carried away above, so that
the whole of the cylinder is always acted upon by the strongly-heated air. By
these means a very active heating of the steam cylinder is produced and the heat
of compression of the air utilized to the best advantage in the partial prevention
of cylinder-condensation. The compressed air here serves the purpose for which
boiler-steam would otherwise be employed.
Figures 2 and 3 show a second method of carrying out the present invention.
Instead of carrying off the heat of compression of the compressed air by allow-
ing it to act on the steam-cylinder in a jacket, the jacket can be dispensed with
and the transfer of heat effected by simple conduction, Figure 2. Experiments have

page_text: shown that this method of transferring the heat stands almost equal to the other,
if the construction is properly carried out. In this connection, attention is called
to Figure 3, where the construction of the common cylinder is indicated. In
order to obtain a high rate of transfer of heat, the cylinder a is made with ribs d;
these ribs are well covered with a material f which is a non-conductor of heat,
and the whole preferably enclosed in a casing g of sheet metal or wood. In this
manner, the cross-section of iron or other metal which transmits the heat, is
suitably increased and formed in an advantageous manner for the transfer of the
heat in the required direction and the said metal is moreover well lagged so
that no loss of heat can take place by radiation. By the cylinder-wall a alone a
considerable part of the heat of compression is transferred. By suitably forming
the cylinder as a ribbed heat-conductor, this effect can be considerably increased.
This form of construction has an advantage over the jacket form in that it is
simpler to manufacture. The useful effect is about the same in both cases.
'
A second advantageous effect of the conibination of the action of the steam and
air, lies in that the piston b, in its stroke, leaves behind a complete layer or
coating of condensation-water on the wall of the cylinder and moistens this
wall at each stroke. The water or moisture comes, in the succeeding air-com-
pression stroke, under the action of air heated to a very high. temperature and,
under this influence, is immediately quickly evaporated. In this connection,
it is to be taken into consideration that the condensed water is at a temperature
near the vaporizing point. In the much higher compression of the air, conse-
quently, a rapid evaporation of this hot water takes place immediately. The
evaporation however can only take place at the expense of the heat of compression
contained in the compressed air and consequently a cooling effect is obtained
which results in a favourable course of the compression line. In this con-
nection it is to be noted that hot, water, under some circumstances, can cool
better than cold, since the change in the state of aggregation comes in, whereby
a much greater quantity of heat can be fixed than by simple transfer of the heat.
The removal of the heat is also more rapid if it proceeds in conjunction with
change in the state of aggregation.
With combined steam and air- cylinders, consequently, a more advantageous
exchange of the heat is possible if they are provided with suitable arrangements
as above described. By the condensed water or deposit from the steam, the
air side is cooled, and by the product of the air side, that is the com-
pressed air, the steam side is heated: The heat of compression, which
would otherwise be lost in the pipes, as well as the water of condensation, which
would otherwise be forced out uselessly in the exhaust, are both employed use,
fully in their several ways.
"
J.
F
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what
I claim is:
An air-compressor wherein, in a common cylinder, the force of the steam is
developed on one side of the piston, and the work of compressing air is per-
formed on the other side, characterized in that, by jacketting or by conduction,
an exchange of heat is effected between the steam end and the air end of the
cylinder for the purpose of heating the steam end of the common cylinder by
the compressed air and cooling the compressor end of the common cylinder by
the water of condensation.
.
D. YOUNG & Co.,
11 & 12, Southampton Buildings, London, W.C., _
Agents for the Applicant.
f