Air regenerator using an oxygen jet venturi

An air regenerator is provided comprising, in a cylindrical duct 4 communicating laterally with filtering cartridges 5, a venturi 1 whose outlet horn 1a is connected to a regenerated air outlet tube 3. The end of the inlet horn 1a is open and emerges inside duct 4. At a given distance with respect to horn 1b emerges a nozzle 2 whose mouthpiece is bored with a calibrated orifice of a diameter between 0.15 and 0.25 mm and whose thickness at the position of the bore is at most equal to the diameter of the orifice. The regenerator having such a nozzle connected to a pressurized oxygen cylinder is capable of sucking large amounts of air so that the voluminal yield expressed by the ratio of the volume of regenerated air to the volume of injected oxygen easily exceeds 37.

The present invention relates to air regenerators, individual or for 
collective premises, absorbing the carbon dioxide under the effect of a 
venturi drawing air through the cartridge by means of a nozzle placed in 
the axis of the venturi and connected to a pressurized oxygen supply. 
When it is a question of supplying a closed enclosure with regenerated air, 
such as premises or living spaces, the amount of air regenerated must 
correspond to a minimum providing for the personnel present a breathable 
amount of air allowing a certain expenditure of energy, for example for 
carrying out certain work in the closed space. It is admitted that such an 
activity, for example of the order of 100 watt, requires a minimum supply 
of 37 liters of regenerated air per minute and per person. 
Breathing apparatus of the above mentioned kind, operating without any 
addition of energy for drawing used air through the absorbant cartridge 
other than that of the expansion energy of oxygen compressed and injected 
into the venturi, consume 1 liter of oxygen at atmospheric pressure, which 
leads to a minimum voluminal yield: 
EQU Q.sub.2 /Q.sub.1 =37 
Q.sub.2 and Q.sub.1 being respectively the amount of regenerated air and 
the amount of injected oxygen in liters. 
To obtain such a voluminal yield, up to now two injectors have been used in 
series, operating with oxygen expanded by means of a two stage pressure 
reducer. Such a reducer is expensive and delicate in operation. 
Furthermore, the installation is cumbersome, for it also requires two 
venturi placed in series. Finally, the voluminal yield drops rapidly 
before the cylinder is exhausted, when the pressure in the cylinder 
reaches that of the upper pressure reducer, which reduces the volume of 
useful oxygen by about 10%. 
The present invention is based on the discovery of the extraordinarily high 
potential, for driving air by means of venturi, which an oxygen jet 
possesses whose molecules are reorientated and whose velocity distribution 
becomes anisotropic and does not follow the Maxwell distribution function. 
It should be recalled that the molecules forming a gas in equilibrium are 
propelled at all times by disordered movements which form what is called 
thermal agitation. 
To describe the microscopic state of a gas, we must be satisfied with 
statistic expressions which are called the velocity distribution functions 
and which are basic magnitudes of the kinetic theory of gases. The 
movement of the molecule is characterized by a vector of its position in 
space r and the vector of its velocity w. 
EQU dr=dx dy dz 
and 
EQU dw=dw.sub.x dw.sub.y dw.sub.z 
the function f (rwt) being the simple velocity distribution function. A 
velocity distribution function is anisotropic if it only depends on the 
modulus of w and not on its orientation. 
In the conventional calculation of injectors, the gas is considered as a 
perfect gas, that is to say a gas whose molecules have an isotropic 
distribution in direction and a Maxwellian distribution of the velocities. 
These conditions are approximately fulfilled when the duct of the nozzle 
is cylindrical, of a long length with respect to its diameter. The 
pressure drop in the duct is then great with respect to that at the outlet 
end or mouth piece and the expansion energy is mainly used for heating the 
oxygen cooled by its expansion. 
On the other hand, if the expansion takes place through a thin wall 
orifice, all the expansion energy is used for reorientating the molecules 
whose velocity distribution becomes anisotropic. This is the case of 
unstationary (the distribution depends on t), inhomogeneous (the 
distribution depends on r) and anisotropic (distribution depends on w and 
on r) distribution. 
The notion of temperature disappears and is replaced by a tensorial field 
of kinetic temperatures. This kinetic temperature in the axis of the jet 
may descend to less than a degree from absolute zero. Similarly, the 
discontinuity of the functions, when going over to supersonic speeds, 
disappears, the speed of sound itself becoming a function of the 
orientation with respect to the axis of the jet. 
For such orientated molecules, the voluminal yield easily exceeds the yield 
of 37, which provides a minimum volume of regenerated air for the 
personnel working in a closed enclosure. This increased potential for 
driving large amounts of air through the venturi may be explained by the 
fact that, in an orientated molecule jet there are few lateral collisions 
between the oxygen molecules and that all the energy dissipated in lateral 
collisions will be dissipated in collisions with the driven air, thus 
giving a good voluminal yield of the venturi. 
The air regenerator with a cartridge absorbing the carbon dioxide 
comprising a venturi providing suction of air through the cartridge by 
means of a nozzle emerging axially upstream of the constricted section of 
the venturi and connected to a pressurized oxygen supply in accordance 
with the invention is characterized in that the mouthpiece of the nozzle 
is formed by a relatively thin wall in which is bored a calibrated orifice 
and whose thickness at a position of the bore is at most equal to the 
diameter of the orifice, so that at the outlet of the nozzle the molecules 
of the oxygen jet are reorientated and the distribution of their 
velocities becomes anisotropic different from the distribution according 
to Maxwell's function. 
An oxygen jet with reorientated molecules may be formed using a nozzle 
constituted by a relatively wide tube, for example 2 mm in diameter, and 
ending in a mouthpiece formed by a calibrated orifice with a net contour 
of a diameter of 0.15 to 0.25 mm bored in a relatively thin wall, for 
example of a thickness of 0.01 mm. Such an orifice pierced wall may be 
formed in a copper or aluminium metal foil which is pierced with the aid 
of an appropriate tool. 
Another way of forming the mouthpiece consists in crimping, at the end of 
the tube, a clock pivot bearing made from ruby, saphire or cupro-beryllium 
whose flat face is turned outwardly and which is pierced with a central 
orifice whose diameter varies between 0.15 and 0.25 mm. 
The venturi used may have various forms. They may be symmetrical with inlet 
and outlet horns of the same length or asymmetrical, the outlet horn being 
longer than the inlet horn. The oxygen supply pressure does not 
consititute a critical element, very acceptable voluminal yields being 
obtained in the pressure range from 0.5 to 2 bars. 
Tests have shown that there exists a critical relationship between the 
diameter of the constricted section of the venturi and the distance at 
which the mouthpiece of the nozzle is placed upstream of the constricted 
section of the venturi, for a given oxygen pressure. Preferably, this 
distance is such that the diameter of the section of the oxygen jet, 
measured in free air, at the position of the constricted section of the 
venturi is substantially equal to the diameter of this section. 
For checking the shape of the jet and in particular for measuring its 
diameter at a given distance, the jet is directed perpendicularly against 
a target formed by a surface of water covering a white screen immersed 
under a few centimeters of water. The depression of the surface under the 
oxygen jet is observed and its diameter is measured, when a light beam is 
sent parallel to the screen through the liquid. The depression creates a 
circle of shadow on the screen whose diameter varies with the flow rate of 
the nozzle and the distance therefrom to the water surface. 
With this system of testing, the distance of the mouth piece of the nozzle 
from the constricted section may be determined as a function of the 
pressure of the oxygen flow so that the diameter of the section of the jet 
thus measured in the free air is substantially equal at the position of 
the constricted section of the venturi to the diameter of the section.

The air regenerator shown comprises a cylindrical duct 4 closed at the 
bottom, in which is placed a venturi 1 whose outlet horn 1a is welded to 
duct 4 and is connected to a regenerated air output tube 3. The opposite 
wall of duct 4 is in the form of a disc pierced with a central opening for 
passing therethrough a nozzle 2 connected through a duct 8 to the pressure 
reducer of a compressed oxygen cylinder. The end of the inlet horn 1b is 
open and opens freely inside the cylindrical duct 4. This duct 
communicates with two filtering cartridges 5 for absorbing the carbon 
dioxide, disposed on each side of the cylindrical duct 4. The cartridges 5 
are removably fixed by application under pressure against the plastic 
material seal. Nozzle 2 has a mouthpiece shown in FIG. 2. An end piece 10, 
having a circular shoulder 11 intended to bear against a support 12, ends 
in a constricted section at the end of which is crimped a ruby 13. This 
clockmaker's ruby is cut so as to have a flat face 14 in which opens a 
calibrated orifice 15 of a diameter of 0.20 mm. The inner face of the ruby 
is cut so as to have a hollow 16, which reduces its thickness at the 
position of the bore to 0.20 mm. The venturi used is asymetrical in shape. 
Its inlet horn, of a very bell mouthed shape, measures 20 mm, while its 
outlet horn of a conical shape of a length of 60 mm ends in a widened 
portion 30 mm in diameter. The diameter of the constricted section of the 
venturi is 12 mm. 
The inner diameter of the nozzle at the position of the narrowing of the 
section is 2 mm. The thickness of the ruby at the position of the bore is 
0.2 mm. The expansion of oxygen at the narrowed portion of the venturi 
causes upstream a depression which results in drawing the polluted air 
through the cartridges, causes it to pass inside the venturi where it is 
mixed with oxygen and causes a mixture of purified air and pure oxygen to 
leave through tube 3. 
By varying the oxygen pressure between 0.5 and 2 bars, its influence on the 
voluminal yield Q.sub.2 /Q.sub.1 has been shown in FIG. 3 for two venturi 
of different forms, having the same diameter of the narrowed portion. It 
can be seen that the voluminal yields remain substantially above the 
standard which has been fixed, namely 37 liters of regnerated air per 
liter of oxygen injected. The yields for a pressure of 1 bar differ 
between a venturi with a symmetrical shape (curve 1) and a venturi with an 
asymmetric shape (curve 2) and vary by only 6%, which proves that the 
shape of the venturi does not constitute an important criterion of choice. 
According to tests, the pressure loss caused by fitting an abscrbant 
cartridge lowers the voluminal yield by 10%, the end piece intended for 
the other cartridge being closed. The yield only drops by 5% when two 
cartridges are mounted. 
From tests, the results of which are shown in the graph of FIG. 4, the 
variation of the voluminal yield with the variation of the diameter of the 
constricted section of the venturi may be determined for a venturi of 
given shape (outlet diameter of 30 mm) and for a given oxygen pressure (1 
bar). It will be noted that the yield is of the order of 90 for a diameter 
of the section between 10 and 15 mm, when the measurements are effected 
with optimum distances between the mouthpiece of the nozzle and the 
constricted section of the venturi for each diameter. 
The results of measurements made concerning the distance between the 
mouthpiece of the nozzle and the constricted section of the venturi are 
shown in FIG. 5. The two curves 1 and 2 show the variation in the flow of 
regenerated air Q.sub.2 with the distance of the mouthpiece from the 
constricted section of the venturi for a venturi whose constricted section 
has a diameter of 12 mm and for oxygen flows of 1 bar (curve 1) and 2 bars 
(curve 2). In the case considered, the optimum flow is between 20 and 40 
mm of distance. These distances correspond to forms of jets such that the 
diameter of their section, measured in the free air, is substantially 
equal at the position of the constricted section to the diameter thereof. 
Similar curves may be plotted for each diameter and each pressure. 
Generally it is found that for an oxygen pressure varying from 1 to 2 
bars, and with the mouthpiece of the nozzle situated at a distance of 20 
to 40 mm upstream of the constricted section of the venturi whose diameter 
varies between 8 and 12 mm, the voluminal yields obtained were optimum of 
the order of 90. 
The device of the invention forms an undeniable progress in the field of 
regenerated air supply in a closed enclosure, for it allows an increased 
supply to be obtained and largely sufficient for the breathing comfort of 
persons who are present therein by means of a compact apparatus and 
without any external energy supply other than that provided by the 
expansion of the compressed air from a cylinder. 
The invention is not limited to the embodiments described but extends to 
all the variants which may occur to a man skilled in the art.