US2506535A - Gas analysis apparatus - Google Patents

Description

May 2, 1950 w. M. ZAIKOWSKY 3 GAS ,mwzsxs APPARATUS Original Filed March 1, 1943 2 Sheets-Sheet l Ha aii In an" a a. 21 I I a4) 1,, (2,3 11 My aqlfoinzy May 2, 1950 Original Filed March 1, 194;

w. M. ZAIKOWSKY 2,506,535

GAS mwzsxs APPARATUS 2 sheets-sheet 2 I M/LADIMIR M ZA/KUWSKY Patented May 2, 1950 UNITED STATES PATENT OFFICE GAS ANALYSIS APPARATUS Original application March 1, 1943, Serial No.

Divided and this application March 13, 1945, Serial No. 582,467

12 Claims. 1

This is a division of my copending application, Serial No. 477,675, filed March 1, 1943, and entitled Gas analyzer." The original application discloses complete systems for gas analysis by measurement of thermal-conductivity, whereas this application discloses and claims a specific cell block and associated apparatus that is particularly useful in connection with the systems and methods claimed in the original application but may also be useful in other systems.

An object of the present invention is'to provide apparatus that is particularly effective in making measurements of the thermal-conductivities of gases at pressures diflerent from the ambient pressure.

Another object is to provide a construction of thermal-conductivity cell that is simple and easy to construct.

Another object is to provide a thermal-conductivity cell assembly for measuring thermalconductivity of gases at sub-ambient pressures that does not require an elaborate sealing structure to prevent leakage of atmospheric air into the cells and can be repeatedly disassembled and reassembled without introducing leakage.

Another object is to facilitate the accurate mounting of the filaments in thermal-conductivity cells.

Another object is to provide a cell block construction for thermal-conductivity analysis that permits opening of the cell block without disconnecting the gas connections and the electrical connections.

Another object is to provide a cell capable of giving prompt and accurate response to a change in gas composition over a wide range of pressures.

Another object is to provide a construction that provides for the accurate mounting, and the inspection, of resistors in a cell of extremely small dimensions, to thereby facilitate manufacture of apparatus in which the stability of zero and the sensitivity is to a high degree unaffected by variations in the pressure of the'gas under test.

A feature of the invention is a cell structure in which one portion of the cell wall is incorporated in one member and the remaining portion of the cell wall is incorporated in a second member, the one member containing the gas connections to the cells and the other member containing the electrical connections to the cells, whereby the two members can be effectively produced as separate articles of manufacture.

Essentially the present invention comprises a cell structure consisting of two blocks that have registering recesses therein which define the cells when the blocks are bolted or otherwise clamped together. The cells are preferably circular in cross sectional shape and are defined by recesses of semi-circular cross section in the two blocks. The filaments are supported in only one of the blocks (which may be the front blocks) by insulated and hermetically sealed lead-ins that extend through the block to the exterior thereof. This permits ready assembly and adjustment of the filament while the two blocks are separated. The gas connections are preferably formed directly in the other block (which may be the rear block) so that the front block, carrying the filaments, can be removed for inspection, cleaning or repair without moving the rear block from its installed position and, hence, without breaking the gas connections to the rear blocks. The auxiliary electrical apparatus that is always used in conjunction with thermal-conductivity cells can be conveniently mounted directly on the front block.

To prevent leakage of atmospheric air into the cells, a seal is necessary between the abutting surfaces of the two blocks. In accordance with the present invention, I eliminate the necessity of a perfect seal between the blocks by surrounding the cell recess in one of thev blocks with a groove which is connected to the gas passage. With this arrangement the space defined by the groove is maintained at the same or a lower pressure than exists in the cells themselves, so that any air leaking between the blocks toward the cells will be trapped by the groove and drawn off before it can reach the cell.

A full understanding of the invention may be had from the detailed description to follow, read in connection with the drawing, in which:

Fig. 1 is a schematic diagram of a system with which the apparatus of the present invention can be employed;

Fig. 2 is a perspective view with parts broken away, showing one embodiment of the present invention;

Fig. 3 is a front elevational view of the apparatus shown in perspective in Fig. 2;

Fig. 4 is a front elevation of the rear block of the apparatus shown in Fig. 3; and

Fig. 5 is a vertical section taken along the line V-V of Fig. 4.

Referring to Fig. 1, there is shown a pipe II which contains a stream of gas to be analyzed. A portion of this gas in conveyed through a constriction II and conduit l2, thence through a valve l3 to a test passage ll, from which it is one diagonal point of the bridge.

exhausted through an exhaust conduit [3 by a suction pump it. The test passage i4 communicates through diffusion passages H with two test cells l8 and I9, respectively, which contain resistors connected in diagonally opposite arms of a bridge 29. The other arms of the bridge consist of-similar, resistors in test cells 2| and 22 which are connected by diffusion passages to a reference passage 23, similar to the test passage [4 but connected at its input end by a conduit 24 and a restrictor 25 to a source of reference gas in a pipe Illa, which gas in this instance is atmospheric air. The output end of the reference passage 23 communicates with the output end of the test passage I4 at thejunction 26.

The bridge 20 comprises, in addition to the resistors of the four test cells, a balancing potentiometer 21, the variable tap of which constitutes The energizing battery 28 is shown connected in one diagonal of the bridge through a variable resistor or rheostat 29 and an ammeter 39, whereby the amplitude of deflection of the galvanometer can be adjusted by varying the resistor 29 to vary the total current flowing through the bridge and the cells. The galvanometer 3| is connected in the other diagonal of the bridge.

It is to be understood that the resistors of either the cells l8 and 2| or the cells l9 and 22 could be replaced by fixed resistors, but the use of reference and test cells in all four arms of the bridge in the manner shown increases the sensitivity. 1 The valve I3 is provided to facilitate balancing of the bridge. Thus by rotating this valve slight- 1y counter-clockwise, the test passage l4 can be connected, by the valve passage l3a, to a branch passage 24a leading to the conduit 24 so that the reference gas is passed through both the reference passage 23 and the test passage l4, and the potentiometer 21 can be adjusted to give zero deflection on the galvanometer 3|. Thereafter the valve l3 can be restored to normal position ,to admit the gas being tested into the test passage l4. It will be observed that when the passage l3a shaft 39 extending forwardly and having a control knob 40 on its forward end.

The valve shaft 39 is extended rearwardly of the valve 38 and connected to a switch 4|, which is closed when the valve is in the normal position shown in Fig. 1, but is open when valve 38 is rotated counter-clockwise 90. The switch 4| may be the ignition switch of the engine or the power supply switch of an electric motor driving the suction pump, so that the shifting of the valve 33 occurs simultaneously with stoppage of the pump.

in the instrument panel 46. A removable insert 41 is preferably provided in this instrument panel 46 to facilitate disassembly of the instrument. The rear block 32 may be mounted by screws or bolts, one of which is indicated at 48, to a rear supporting panel 49 positioned back of the instrument panel 46. The front block 33 is secured to the rear block 32 in sealing engagement therewith by a plurality of bolts 59. The conduit 5| may consist of a piece of tubing extending is in registration with the inlet end of the passage H, the passagev l3b connects the constriction H and the passage l2 with the by-pass passage I4a, which extends to the exhaust conduit 15 connecting to the inlet of the pump Hi. Therefore, in each operative position of the valve l3, the pump I6 is fed with gas through both the constrictions H and 2.").v This insures that the same pressure will exist in the cells when balancing the bridge as when testing a gas.

Thermal-conductivity cells of the general type employed in the system so far described are well known, and many of the cells already in use can be adapted for operation in my system. However, I have developed a construction of cell that has special advantages, and which is disclosed in Figs. :2 through 5.

Referring first to Fig. 2, there is disclosed a rear block 32 and a front block 33, which together The meter 3| is These resistors 21 and 29 have their movable elements coupled by spur gears to control shafts 34 and 35, which extend forwardly alongside the meter 3! and terjminate in control knobs 36 and 31, respectively. A valve 38 in the suction line may have a control from the rear block 32 to the junction 26, which junction is formed by a single fitting 52 incorporating the valve 39 and adapted to be soldered or welded to the rear block 32.

Referring now to the face view of the rear block 32, shown in Fig. 4, and the sectional view of Fig. 5, it will be observed that the cell chambers for the gas are formed by registering depressions in the rear and front blocks. The passages l4 and 23 are formed completely within the rear block 32, both of these passages being of relatively large uniform diameter from the Y fitting 52 at the lower end of the block to a point adjacent the upper end of the block where they narrow gradually down to relatively small passages, passage extending directly outof the top of the rear block 32 and being connected to the conduit 24. Passage 23, after being tapered down to a small bore, communicates through the valve IS with the conduit l2. Both of these conduits 24 and I2 may consist of what is commonly referred to as thermometer tubing, which is a flexible metal tubing of substantially 1 mm. internal diameter and armored with a wrapping of .wire. By employing a small diameter conduit of this type, the block 32 may be mounted many feet from the sources It and Illa. This greatly facilitates the installation of the apparatus, since the source I9 would ordinarily be positioned closely adjacent the engine of an aeroplane some distance away from the cockpit or cabin where the instruments are located. If necessary to prevent condensation, the conduit can be heated, as by enclosing it in, or attaching it to a larger flexible tube through which hot gas such as exhaust gas is circulated.

The test chambers are formed between the rear and front blocks 32 and 33, as shown in Fig. 5. The recesses in the two blocks match in shape and dimensions, and, as shown in Fig. 4, there are two U-shaped recesses-the two arms of one of which constitute the chambers l8 and I9, respectively, and the two arms of the other of which constitute the chambers 2| and 22, respectively. The lower part of each U-shaped recess in the rear block is connected by a diffusionpassage with one of the passages l3 and 23. The diffusion passages are defined by a straight rearwardly extending cylindrical bore which, in this instance is shown to contain a plug 53 having four longitudinally extending grooves 54 in its surface. It is through the passages defined by these grooves .53 that the gases diffuse into the chambers l8 and I9, and 2| and 22.

As indicated in Fig. 1, there is a resistor positioned in each of the test chambers. These resistors are all identical, each consisting of a small helix of platinum wire 55 (Fig. 5) supported at opposite ends from lead-in wires 56, which extend through Kovar seals 51 having flanges 58 welded or soldered to the margins of bores 59 in which the Kovar seals are positionedthese bores extending from the front face of the front block 33 into the recesses in that block. The Kovar seals form gas-tight electrically insulating lead-' in structures for the filament-supporting pins 56. The construction described is highly desirable in practice because it permits accurate mounting and testing of the platinum filaments 55, while the front block 33 is removed from the rear block. Thereafter, the two blocks are assembled -and bolted solidly together with the bolts 56.

As is customary in apparatus of this type, it is desirable to maintain the apparatus at a uniform temperature. To this end, additional recesses are provided in the blocks 32 and 33, which together define cylindrical channels 60 and 6| for the positioning of a thermostatic switch 62 and an electric heater 63, respectively; these two devices being connected in series with each other and with an energizing battery 64 through a switch 65 (Fig. 4). These elements 62 and 63'are of standard construction and need not be specifically described herein. Suflice it to say that the thermostatic switch 62 opens the circuit to the heater 63 when the temperature of the apparatus exceeds a desired value, and closes the circuit from the battery to the resistor when the temperature falls below the desired value.

It is essential to prevent gas leakage into the test passages and chambers, and it is preferable to employ a construction utilizing materials that do not absorb water or other vapors, and that are not apt to form films of materials having low vapor pressure. Thus, although at atmospheric pressure a substance having a vapor pressure of 1 mm. Hg may not cause sensible error in ordinary apparatus operated at atmospheric pressure, the same substance may cause great error when the total gas pressure is only mm. Hg. This problem is relatively serious, because whereas apparatus adapted to operate at atmospheric pressure remains at its operating pressure continuously, the present apparatus working at reduced pressures will often be brought to the reduced pressure only for a. relatively short period of use. Hence, any material capable of giving off vapor has to be removed before accurate measurements at reduced pressure can be performed.

To eliminate substantially all possibility of leakage into the test cells, I surround the U- shaped recesses in one or both of the blocks 32 and 33 with guard grooves 66, each of which is connected by a bore 61 in the rear block to the associated passage M or 23 at points below the cells. Hence, the space defined by these guard grooves 66 is continuously maintained at a pressure at least as low, and possibly lower, than the pressure within the test cells themselves, so that any leakage of air between the blocks 32 and 33 will, upon reaching the guard rings 66, be drawn of! through the bores 61 before it can reach a test chamber and contaminate the gas therein. It is preferable to take similar precautions to prevent leakage of air along the sealing surfaces of the valve I3 to the valve passages by providing annular grooves 68 and 69 in the plug of the valve below and above the fluid passages therein, and connecting these grooves by a passage 16 in the rear block through a T fitting II to the conduit 5| leading to the pump. Longitudinal grooves 12 provided in the valve seat are in constant communication with the annular grooves 68 and 69. Since the space within the grooves 68, 69 and 12 is maintained at a pressure at least as low as the pressure within any of the valve passages, there can be no incentive for leakage of air along the sealing surfaces of the valve to the gas passages therein.

As best shown in Fig. 4, the marginal portions 14 of the meeting surfaces of the two blocks are slightly depressed to receive a compressible gasket 15 (Fig. 5), which can be compressed when the bolts 50 are tightened, without interfering with.

the close fit of the meeting surfaces immediately adjacent the cell chambers, which surfaces may be ground flat.

It is a relatively simple matter to test for the presence of extraneous substances within .the test passages and chambers by varying the pressure therewithin. Thus, variation of the pressure to which the gases are expanded will not materially affect the deflection of the indicating meter as long 'as extraneous vapors or fumeproducing materials are absent. Therefore, should the reading be found to vary in response to an increase in the pressure, and there is no leak into the cell, it is desirable to reduce the pressure to the lowest value obtainable for an interval of time to accelerate the evaporation and removal of the extraneous material, after which the pressure can be increased to a higher normal operating value. Variations in the pressure can be obtained by manipulating the valve 36 so as to reduce the rate of flow to the p mp l6 and thereby permit the exhaust gas passing the restriction ll (Fig. 1) to build up a higher pressure in the apparatus. The slight movement of valve 38 required to effect this can be had without opening the switch 4| As has been previously indicated, the apparatus so far described provides for transfer of the gas from passages I6 and 23 into the test chambers by diffusion through small openings provided, in this instance, by the grooves 54 in the plugs 53. It is old to transfer the gas to the test chambers in this fashion at normal pressures. An important feature of the present invention is the method of accelerating the migration of the gas between the passages i4 and 23 and the associated test chambers by greatly reducing the pressure. However, it is to be understood that the advantages of operating at reduced pressure are not limited to apparatus in which transfer of gas to and from the cells is effected by diffusion. In fact, the time lag may be reduced even further by positively circulating the gas through the cells at low pressure. The results are less accurate because the heat loss by convection is increased, but the convection losses are smaller relative to the thermal-conductivitylossesthan they would be at normal pressures.

It is desirable to make the blocks 32 and 33 of metal because of its good heat conducting characteristlcs. A metal should be chosen that is intrinsically corrosion-resistant or it should be plated with a coat of corrosion-resistant metal such as gold. It is also possible to employ glass in some instances.

- A very important feature of the construction 'within the cells. By virtue of the fact that the two blocks contact each other completely around the cells, there is no clearance to trap as or liquid. Thus the guard grooves are at the same or lower pressure than the cells and prevent leakage of air into the cells not only because of the pressure conditions that exist but because the composition of the gas in a guard groove is substantially identical with that in the cell it surrounds.

In my construction, all wiring and adjustment rheostats can be mounted on the front plate and be maintained at uniform desired temperature by the therm-oswitch and heater. This improves the stability of the instrument.

Manufacture of the blocks is facilitated by the fact that the front and rear blocks do not need to be made in individually matching pairs.

By virtue of the fact that the guard grooves are, interposed between the cells and the gaskets, the latter can be of any desired material since any gases that might be given off by the gasket would be trapped in the guard grooves.

In manufacture, the front blocks containing the filaments can be quickly tested in the factory immediately after their assembly by placing the blOCks against a fixed test block corresponding to the rear block of the instrument but permanently mounted in the factory for testing purposes only.

All parts can be readily cleaned and restored to proper operating condition, since by removing the front block containing the filaments and having all the electrical equipment mounted thereon, it can be checked without disturbing the rear block and the gas lines connected thereto. the front block removed, the recesses in the rear block are accessible for cleaning with the rear block in situ. By substituting a dummy front block, the passages in the rear block and in the gas lines can be cleaned by flushing them with a solvent, such as carbon tetrachloride. However, it is to be understood that cleaning is seldom necessary when operating at the low pressures I employ.

Heretofore, no attempt has been made to specifically describe'the constrictions employed to restrict the flow of gas and thereby expand it. Various types can be employed. Thus, it is possible to use a single very small orifice, but this is ordinarily objectionable because it must be so small that it is subject to clogging. I Another type that may be employed is a series of orifices, in which case they may be made larger and be less subject to clogging. Where a series of orifices is employed, the pressure drop across each orifice preferably should be at least half that across the preceding orifice to prevent back diffusion of the gas in the passage between successive orifices.

Still another constriction that may be employed is a length of capillary tubing, or a capillary tube with a wire in it to further reduce the flow space. This latter arrangement has the advantage that the wire can be moved to facilitate cleaning.

With

I cured together.

Referring to Figs. 4 and 5, the rear block 32 is provided with a pair of dowels projecting from the upper face at -diagonally opposite corners, which dowels are received in registering holes ill in .the outer block 33 when the t'wo'parts are se- The dowel pins" not only insure proper registration of the recesses defining the cell chambers, but prevent damage to the filamerits which might otherwise result from bringing the two parts together with the recesses out of registration with each other.

Although for the purpose of explaining the invention, one embodiment thereof has been described in great detail, numerous departures from the exact construction shown will be apparent to those skilled in the art, and the invention is to be limited only to the extent set forth in the appended claims.

I claim:

1. A cell construction for gas analysis by measurement of temperature change of a heated filament comprising: a pair of members having closely fitted surfaces and means for clamping them together, said members being so configured as to define a filament chamber bounded by said fitted surfaces, a filament and means supporting it in said chamber and making electrical connection thereto, one of said members containing a gas passage communicating with the filament chamber, means defining a gas channel connected to said passage for fiow of gas to be tested at sub-ambient pressure, at least one of said fitted surfaces having a groove surrounding said chamber, and means connecting said groove to said gas channel at a point therein on the downstream side of said gas passage.

2. In a gas analysis apparatus including a cell for measurement of the gas: a conduit leading gas to said cell; an operable valve in said conduit at a point on the upstream side of said cell, said valve having'relatively movable mating surfaces; a groove in said mating surfaces for intercepting leakage of gas from outside into said gas conduit; and a duct extending from said groove to a connection with said conduit at a point thereon on the downstream side of said gas measuring cell.

3. A cell construction for gas analysis by measurement of temperature change of a heated filament comprising: a pair of members so configured as to define a filament chamber, a filament and means supporting it in said chamber and making electrical connection thereto, one of said members containing 'a gas passage communicating with the filament chamber, means defining a gas channel connected to said passage for fiow of gas to be tested at sub-ambient pressure, a valve in said channel on the upstream side of said passage comprising a seating surface in one of said members, said seating surface and said valve formingcooperating sealing surfaces and fluid ports, one of said cooperating sealing surfaces containing annular grooves spaced from said fluid ports, and means connecting said grooves to said channel at a point therealong on the downstream side of said passage.

4. A cell construction of the type describe comprising: a pair of members having closely fitted surfaces and means for clamping them together, said members having complementary registering recesses in their fitted surfaces cooperating to define a filament chamber symmetrical with respect to a plane, the contacting portions of said fitted surfaces at'opposite ends of'said chamber lying in said plane; a filament-supportplane; a filament in said chamber; and means including said filament-supporting element for supporting said filament in said plane.

5. A cell' construction for gas analysis by measurement of temperature change of a. heated filament comprising: a pair of members having closely fitted surfaces and means for clamping them together, said membersdefining therebetween a filament chamber; gas-tight lead-.in wires extending through one of said members into said filament chamber; a filament supported by said lead-in wires; one 'of said members containing a gas passage communicating with said filament chamber, and one of said fitted surfaces containing a groove surrounding said chamber and spaced therefrom by a portion of the fitted surface; and means for applying suction to said groove.

6. An article of manufacture comprising: a member having a recess therein and having a smoothly finished face surrounding said recess. said face being adapted to fit against a complementary face on another member to form a thermal-conductive cell, said member having a groove in said finished face surrounding said recess, said member having a gas channel therein for the fiow of gas to be tested and having a passage extending from said gas channel to said recess, said member having a second gas passage extending from said gas channel at a point lying on the, downstream side of said first-mentioned gas passage to said groove.

7. As an articlev of manufacture, a section of a gas analysis cell comprising: a member having a smoothly finished face and having a recess in and completely surrounded by said face; a bare electrically conducting filament, and means supporting said bare filament in position extending across said recess in a position spaced from the wall of said member; said means consisting of lead-in wires extending through said member intosaid recess, said smoothly finished face containing a groove surrounding said recess.

8.'A cell construction for gasanalysis by measurement of temperature change of a heated filament comprising: a pair of members having closely fitted surfaces and means for clamping them together, said members being so configured as to define a filament chamber bounded by said \fitted surfaces, a filament and means supporting it in said chamber and making electrical convalve and connecting conduits for selectively in one position of said valve connecting one of said supply conduits to one comparison cell and the other supply conduit to the other comparison cell, and in the other position connecting said v one supply conduit to both comparison cells; said valve including means for connecting said other supply conduit to said suction means in bypassing relationship with said comparison cells in said other position of said valve.

10. Apparatus according to claim 9 in which said valve comprises two relatively movable members having mating-surfaces having cooperating ports therein, one of said members having a first port communicating with said one supply conduit, a second port communicating with said other supply conduit, a third port communicating with said one comparison cell, and a fourth port communicating with said suction means; the other memberhaving one set of ports for communicating only said first port with said third port in one position of said valve and communicating said first port only with said fourth port and communicating said second port only with said and a filament supported by said lead-in wires nection thereto, one of said members containing a gas passage communicating with the filament chamber, means defining a gas channel connected to said passage for flow of gas to be tested at sub-ambient pressure, at least one of said fitted surfaces having a groove surrounding said chamber, and means connecting said groove to said gas channel at a point therein below the point of connection of said gas passage to said gas channel.

9. In a gas analysis apparatus including a pair of comparison cells for analysis of a pair of gases: a pair of supply conduits adapted for connection to two different sources of gas and having constrictions therein for limiting fiow of gases therethrough: suction means for drawing gases through said supply conduits past um cells; a 10 of said member, said points lying on a straight face line that extends through portions of said at opposite ends of said recess.

wLAnmm M.ZA1KOWSK.Y. I

REFERENCES CITED The following references ares: record in the file of this patent:

v UNITED STATES PATENTS Date Number Name 1 1,436,084 .Hamlin Nov. 21. 1922 1,954,681 Oetjen Apr. 10, 1934 2,013,998 Goldsborough Sept. 10, 1936 2,211,627 Morgan et ai. Aug. 13. 1940 2,269,850 Hebler Jan. 13, 1942 FOREIGN PATENTS.

Number Country Date June 14, 1938

Claims (1)

1. A CELL CONSTRUCTION FOR GAS ANALYSIS BY MEASUREMENT OF TEMPERATURE CHANGE OF A HEATED FILAMENT COMPRISING: A PAIR OF MEMBERS HAVING CLOSELY FITTED SURFACES AND MEANS FOR CLAMPING THEM TOGETHER, SAID MEMBERS BEING SO CONFIGURED AS TO DEFINE A FILAMENT CHAMBER BOUNDED BY SAID FITTED SURFACES, A FILAMENT AND MEANS SUPPORTING IT IN SAID CHAMBER AND MAKING ELECTRICAL CONNECTION THERETO, ONE OF SAID MEMBERS CONTAINING

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