US2595308A - Gas-to-gas heat exchanger - Google Patents

Description

May 6, 1952 c. s. SIMPELAAR 2,595,308

GAS-TO-GAS HEAT "'EXCHANGER Filed March 3, 1948 5 Sheets-Sheet 2 May 6, 1952 c. s. SIMPELAAR 2,595,308

GAS-To-GAS HEAT EXCHANEER Filed March 5, 1948 5 Sheets-Sheet 5 f2 ff ff-l May 6, 1952 c. s. s-IMPELAAR 2,595,308

GAS-TO-GAS HEAT EXCHANGER Filed March 5, 1948 '5 Sheets-Sheet 4 May 6, 1952 c. s. slMPELAAR 2,595,308

v GAS'TO-GAS HEAT EXCHANGER Filed March 5, 1948-.` 5 Sheets-Sheet 5 .6j A 45 fru/erzf.' 33 Qdi? jimelczcz gf v4@ @j satented May 6, 1952 GAS-TO-GAS HEAT EXCHANGER Clyde S. Simpelaar, Racine, Wis., assignor to Modine Manufacturing Company, Racine, Wis., a corporation of Wisconsin Application March 3, 1948., SerialNo. 12,865

1o claims. (c1. 257-245) A. This invention relates to gas to gas heat exchangers and is in the nature of an improvement on the heatexchanger disclosed in my pending application'Serial No. 780,251, -led October 16, 1947.

As in the heat exchanger of my said prior application, this heat exchanger is employed for heat exchange between two or more gases of different tern'peratu'res, and the principal object is to increase the efficiency in heat exchangers of this character.

Another object is to produce a heat exchanger suitable for high pressure operation and in which there is a true counterflow of gases and having a high heat transfer capacity and low pressure drop.

' Another object is to provide improved means to vent any vleakage of gas to the outer atmosphere.

Another object is `to provide improved means to urge the gas connections against the border frame members during the bonding operation.

`Another' object is to tie the gas connections to the side sheets of the heat exchanger by means which fallow for relative movement between the gas connections and side sheets during the bond ing operation.

Another object is to provide a novel and improvedmeans tosupport a heat exchanger unit n or several oi them arranged in a bank.

Anotherobject is to provide a simple mechanical assembly of Vrelatively few individual selflocating and supporting parts in which the baking of the assembled unit completes the fabrication thereof in a single bonding operation.

Another object is to yprovide a heat exchanger of which 'the component parts; except the inlet and voutlet gas connections and border frame members-are fabricated from relatively inexpensive metal sheet or strip stock. L`

Another object is to improve the construction of the border frame members as well as the method of assembling the border frame members withthe inlet and outlet gas connections.

Another object is to obtain a more efficient ow distribution through theheat exchanger unit. i

Another object is to` provide a heat exchanger assembly constructed of' a plurality of similar units capable of eiiicient usage in gasseparation plants such as oxygen and nitrogen plants.-

With these and other objects and advantages in view, this invention consists in thev several novel features of construction, arrangement and combination of parts hereinafter fully set forth andi-more definitely pointed out in the appended claims.

The invention is clearly illustrated in the drawings accompanying this specication, in which:

Fig. 1 is an end elevation of a bank of heat exchanger units;

Fig. 2 is a side elevation thereof partly broken away;

Fig. 3 is a view of one of the units partly in side elevation and partly in vertical section and with the middle portion thereof broken away and part of one of the side sheets broken away;

Fig. 4 is a View partly in end elevation and partly in vertical section of the unit seen in Fig. 3 taken substantially on the line 4--4 of Fig. 3;

Fig. 5 is a plan of the unit seen in Fig. 3;

Fig. 6 is a perspective view partly broken away of two border frame members of the unit;

Fig. 7 is a perspective view partly broken away of certain plenum` sections or filler and distribution strips and nn elements that comprise vone of the passes of the unit;

Fig. 8 is a side elevation of one of the side sheets oftheunit; l

Fig. 9 is a horizontal section through several of the separation sheets and several channel members of some of the border frame members taken substantially on the line'9-9 ofrFig. 3;

Fig. 10 is a detail fragmentalperspective view upon an enlarged scale of one `Aof the fin elements;

y Fig. 11 is a detail` fragmental view partly .in side elevation and partly in vertical section illustrating one of `the spring strips that are located between the gas connections and the border frame members;

Fig.12 is a detail fragmental plan ofthe spring l strip seen in Fig. 11;

Fig. 12a is an end view of the spring strip seen inFig.12; .l

Fig. 13 kis adetail fragmental side viewof a modified form of hanger connection;

Fig. '14 is a. detail fragmental side view of a second modified form of hanger connection;

Fig. 15 is a view of the hanger vconnection seen in Fig. 14looking in the direction of the arrow l 5 therein; J

Fig. 16 isa detailvertical section `through a third modified formof hanger connection; .f

, Fig. 17 is a diagrammatic view. in side elevation of a modified form of heat exchanger unit partly broken away; and

Fig. 18 is Van end elevation of two' nelements showing them in nested together-condition. Referring to said drawings and rst to Figs. 1 and 2,-the reference characterz designates several of the heat exchanger units with their broad sides placed side by side and provided at their ends with inlet and outlet manifolds as will hereinafter be described.

While the heat exchanger may be laid on its side, it is here shown as suspended vertically by hanger bars 2| secured to the upper and lower ends of the units by rods 22 which extend through the hanger bars and through lugs 23, 24 (see Figs. 3 and 6) formed on the border frame members. The upper holes in the hanger bars may be elongated vertically to allow for unequal expansion and contraction between the units and hanger bars.

The heat exchanger units are substantially identical in construction and each comprises a fabricated elongated unit composed of alternate and intermediate passes, each consisting of nested together iin elements 25 (see also Fig. l0) and plenum sections or filler and distribution sections 26, 26a. Gas of one temperature flows through alternate passes, and gas of a higher or lower temperature flows through the intermediate passes but in the opposite direction. The slabs of 1in elements extend lengthwise of the unit and are arranged in heat exchange relation with respect to each other and are spaced apart by separation sheets 2'1 (see Fig. 4). Side 'sheets 28 enclose two of the sides of the unit while arms 29 of the border frame members 33 (see Figs. 3, 2land 6) enclose the other two sides of the unit.

VThe border frame members 3G are similar in construction-l and a description of vone will suince for all of them. YEach border frame member contains two similar L-shaped bars 3l, each of which comprises the relatively long arm 29 and a relatively short arm 33, the long arms 2S extend the full'length of the unit, but the short arms stop short of the opposite long arms to Aleave gaps which serve as ports to the interior ofthe pass bounded by the border frame member.

The long arms of the L-shaped, bars in the main are composed of channel shaped members 29a, each temporarily fastened at one end to 'a right angle extension 46 of the short 'arm of the `Ls"hapedlb`ar as by screws 4l (see Fig. 6), and temporarily fastened at its other end to an 'extension 42 as by screws 4l. The ends of the extensions 40, 42 arerlet into the channels of the 'channel bars so that their side faces may be flush.

The channel shaped members 29a of the border frame members are tied to the separation sheets 21 as by drive screws 10 to temporarily secure them 'together prior kto the bonding operation.

The adjacent border frame members are reversed, with respect to each other, so that the short arm 33 of each L-s'haped bar extends along the gap at the end ofthe adjacent short arms. Thus, gas may 'enter and discharge from alternate "passes, but the 'intermediate passes are blocked off at these gaps so that gas 'cannot enter 'or discharge through the blocked off places.

Referring now to Fig. 3, it will be seen that 'a 'gap is left between therupper short arm 33 and the long arm at the left, and that a gap is left between theY lower short arm 53 and the long arm at the right. Gas enters Vthe pass shown and through the alternate passes from the gas inlet connection '32 and 'flows through the pass and discharges through the gas outlet connection 32a. The intermediate Vpasses are blocked off at the top and bottom (see Fig. 4), but. Vgas of a different temperature enters the intermediate passes 'through the gas inlet -c'o'nnection 34 and flows through the intermediate passes to the gas outlet connection 34a. Thus, it will be seen that a true counter-now for gases is provided.

The plenum sections are preferably composed of corrugated metal sheets of which the plenum sections 26a have perforations 35 in their side walls, whereby the gas may 'iiow laterally as well as longitudinally. The plenum .sections 26 extend at right angles to the plenum sections 26a and the top and bottom walls thereof have perforations 36 therein, through which gas may flow in a vertical direction as well as laterally of the unit.

The nn elements 25 extend longitudinally of `the unit between the plenum sections 26, and

the cross walls 38 of the iin elements are slit and offset to provide slots through which the gas may flow laterally therefrom and longitudinally thereof as in my prior application above referred to.

The fin elements are nested together as seen in Fig. 18 and may be constructed in accordance with the disclosure of my prior application above referred to. In Figs. 3 and 4, the major portion of the nn elements has been broken away and others omitted to permit the View to be made upon as large a scale as possible.

The gas connections extend between the side plates 23 at the top and bottom of the unit. Each gas connection is generally of rectangular form and has two solid side flanges 43 vby which it is secured to the L-shaped bars of the border frame members. At the gaps, the L-shaped bars 'are formed with ledges 44, against which the flanges 43 contact. Hooks 45 project outward from these ledges, and other hooks 46 are formed on the parts of the short arms 33 that block off the entrance to the interior of the unit. The hooks 46 are aligned with the hooks 45, so that the flanges '43 of the gas connections may enter the grooves between the hooks 45 and ledges 44, and between the hooks 46 and short arms 33 of the L-shaped bars.

For urging the gas connections against the ledges 44 and against adjacent parts of the short arms 33, prior to the bonding operation, spring strips 41 (see Figs. l1, 12 and 12a) are employed between the hooks 45, 46 and flanges 43 of the gas connections. These spring strips are struck up with vsuitable dies to provide groups of spring fingers 48 with the groups spaced apart the same distance, center to center, as are the hooks 45, 45, 'so that when the spring strips have been driven into place there will be a group of spring fingers between veach hook 45 and 45 and the flanges of the gas connections. When the spring strips have been 'driven into place, the spring fingers have been -placed under compression and function to urge the flanges 43 against the ledges 44 and the short arms 33, so as to hold them in intimate contact during the bonding operation to insure a perfect bond between the vgas connections and adjacent parts of the border frame members.

The ga's connections 'are respectively tied to the side sheets 28 by rivets 50 (see Fig. 4) which may have tapered lheads that extend through countersunk holes in the side sheets with their stems entering oversize sockets 5l in the gas connections. The walls of the sockets are lined with bonding material 52 so as to make 'the cavity in the sockets of the same Adiameter as that of the rivets, whereby the latter, when driven into the cavities, will be securely held therein. vThe purpose of lining the sockets with bonding material isto permit of any unequal expansion between the sidesheets and gas connections, and` to allow for movement of the gas connections toward the border frame members as the bonding material on the adjacent faces of the anges of the gas connections and the border frame members melts and as the spring iingers urge the gas connections toward the border frame members.'v As the bonding material around the rivets melts, the gas connections may move relative toV the rivets.

To prevent anypossibility of leakage between passes at the gasv connections, grooves 6| (see Fig. 6) are formed in the arms 33 of the border frame members at places adjacent the gaps. These grooves extend lengthwise of the arms and the separation sheets 27 extend past the grooves, thus providing ducts that open at their ends to the outeratmosphere. The grooves prevent the passage of gas from the gas connections to the blocked oi passes and likewise from the blocked off passes to thegas connections, any leakagein either direction is vented to the atmosphere.

When several units are used in a heat exchanger as shown in Figs. 1 and 2, gas inlet manifolds 62, 64 and gas outlet manifolds 63, E5 may be used in connection with the several units. The manifolds may be connected to the respective gas inlet and outlet connections by pipe connections 6 soldered or otherwise joined thereto.

...A heat exchange unit embodying the present invention `may be assembled as follows:

First, one of the side sheets 28 is laid upon a bench, table or other support with the rivets 55 projecting up through holes in the sheet. The gas inlet and outlet connections may then be set in-place on the side sheet, and two L-shaped bars of theborder frame member are laid in place upon the sheet, the flanges 43 of the connections serving as guides for the short arms of the L- shaped bars. Other suitable guides may also be provided for properly locating the border frame member on the side sheet. The plenum sections arethen laid on the side sheet and aslab of fin elements laid on the sheet in the space between the innermost plenum sections. A separation sheet 21 is then laid upon the assembled parts and another course or pass, similar to the first one, is laid upon the separation sheet exceptthat the borderframe member is reversed with respect to the oneV of the rst course or pass, so that the shorttop and bottom arms of the L-shaped bars block oi the entrance and exit to and from the next adjacent passes. In this manner, the several courses or passes are assembled, after which the springstrips are hammered into place withvv the springngers pressing .against the flanges` and urging them into intimate contact with the border frame members. f

The other side sheet is then laid on the assembled parts and rivets 50 are driven through the holes in the side sheet and into the lined sockets in the gas connection, after which the entire structure is placed in an oven and heated to the fusing temperature of the bonding material. It is to be understood that the surfaces of the contacting members of the unit are coatedwith a suitable bonding material or thin sheets of bonding material may be used between such members when that is more convenient or preferable.

In the modified form of hanger connection illustrated in Fig. 13, the upper short arms 33a ofthe border frame members are formed with L-shaped slots 53, extending down from their upper faces, and L-shaped bars 54 have .their lowenedge portions inserted Y.into saidslots with 6 their upper. edge portions bolted;i.to.l ahanger block 55 suspendedtonaibolt oriother :headed rod56. In the modified form ofV connectionshown'win Figs. 14 and 15, the upper intermediate lugs gbe.-

tween the lugs24a are omitted from ,the border frame members, and thelower ends of the hanger bars 51 are placedy between the llugs 24a andjsecured thereto as by a pin 58. i..; 'fIn the modif-led form of hangerJconnectionillustrated in Fig. 16,-the upper rod or,lziolt22aex-V tends through the hanger'bars, one of whichis seen at 2Ia and extends through oversizedfholes 24h in the Alugs' 24e, which 'lugs correspondjwith the lugs 24 inFig.` 3. A coiled spring; k (lfof hour glass form having coils that engagethe .wallsof the holes in the lugs, land othercoils-that' engage the rod or bolt 22a;permit;.unequal-expansion -between the unitsv and hanger-bars. The lower ends of the hanger bars may be connected to the units by a rodor bolt in the samefmannerfas is illustrated in Fig. 3. i

In the modified form of heat exchanger, unit illustrated fragmentarily in Fig.f17, in addition to the inlet and outlet gas connectionsatthe ends of the unit, other inlet and outlet gas connections are provided at'gthe sides Of the unit; an inlet-gas connection 31a and an outlet gas connection 34o are illustrated at the upper end of the uniti similar gas connectionsy are provided at the vlower andas illustrated in vconnection with the pref ferred form of the invention., Another gas inlet connection 3Ib is shown at one side of the unit adjacent its upper c nd, and an outlet vccrinectioig 34h is shown at thejopposite side of the unit. Gas inlet and outletconnectionsfare also provided on the opposite sides of the unitadjxacentthe lower end thereof except that the gas inletpon; nection will be at Vthe right hand sideand the gas outlet connectionwill be at the left. hand side,

This modified construction provides for harr-V dling four di'iferent gases of different temperatures; the border frame members Sila are-constructed so as to block oif all of the passesexcept those ,communicatingv with a gas inlet connection anda corresponding outlet connection. As an example, thelborder frame member shown has a gap at the gas outlet connection 34h, conse7 quently, said border -frame member hasl agap at the corresponding inlet connection', l

The passes are constructed substantially-1 in'l the same man-nenas those-.of the preferred;tornil and those passes which handle the same gas opento one of thegas inlet connections and a correspending gas outlet connection., u j. y In the operation of the heat exchanger offline preferred form, gas of one temperature ws through the alternate passes and gas of a higher or'lower temperature flows through the intermediate passes in the opposite direction.. vThe .heat of the hotter gas is conducted to the gas of lower temperature by the separation sheetsrn eleg ments and plenum sections. n Having thus described my invention. itis vious that various immaterial modiiicationsmay be made in the same withoutv departing fromthe spirit of my invention;l hence, I do not wish'to be understood as limiting myself tothe exact form, construction, arrangement and combination of parts herein shown and described cryuses mentioned.

What I claim as new and desire Letters Patent is: 1. In a gasto gas heatexchanger, vthe combi? .nation of.. border .frame members .having inlet to sie-cureby 7 and outlet openings, inlet and outlet gas con nections secured to said border frame members at said inlet and outlet openings, separation sheets overlapping the side edges of the border frame members and providing narrow spaces, corrugated and perforated plenum sections in said spaces extending longitudinally from the ends of the border frame members, other corrugated and perforated plenum sections in said spaces extending from said longitudinal plenum sections, and crosswise of the spaces, and nested together slotted n elements in said spaces extending between thevhorizontal plenum sections, all ofthe contacting parts being bonded together, the size and number of perforations in vthere-- spective plenum sections being such that a desired distribution of [gas flow vis achieved between the respective .openings and the finned space between the horizontal plenum sections.

2. A gas to gas heat exchanger comprising in combination, border frame members each having gaps therein, said gaps providing 'ports between the exterior and interior of the border frame members, the ports ateach end comprising inlet and outlet ports, separating sheets between ad- Ajacent border frame members, inlet and outlet gas connections disposed at the inlet and outlet ports, Va-pertured plenum sections adjacent the endsof the border frame members, some `extending at right angles tothe others, and rin elements occupying the space between and extending between theplenum sections, all adjacent par-ts being bonded together, the size and number of apertures in the respective plenum sections being such that a desired distribution of gas ilow is achievedbetween the respective ports and the `finned space between the horizontal plenum sections, Y

3. A gas to gas 'heat-exchanger comprising in combination, border frame members each having gaps therein, said gaps providing ports between the exterior and interior of the border frame members, the lports at each end comprising inlet and outlet ports, separating sheets between adjacent border frame members. gas inlet and gas outlet connectionsdisposed at the inlet .and out- -let Yports, aperturedgplenum sectionsV adjacent the ends of the border frame members, some ex- 'tending at right angles to the others, and slotted fm elements occupying the space between and :extending between the plenum sections, all of the'. contacting par-ts being bonded together, `the v'sireand number of apertures in the respective plenum sections being such that a desired distribution of gas flow lisachieved between lthe re- V'spective ports and the ilnned space Ybetween the horizontal plenum sections.

4. In a gas to gas heat exchanger, the combination of side sheets, separation sheets therebetween, heat exchanger elements including `border 'frame members ldisposed between said sheets, Igas connections disposed at the ends of said heat exchange elements vand extending 'between said 'side sheets, certain of said border frame members Vhaving openings therein operatively connecting said `connections with :the heat lexchanger elements associated with such frame members locating rivets extending through said side sheets and into :oversized holes in the .gas connections to maintain the latter and said sheets in assembled relation, and fusible bonding mate- `rial ldisposedlbetween the vwalls of the .holes and the rivets, said fusible bonding material, when fused, .permitting v.limited .relative adjusting border frame members .during .the bondineoif eration. said rivets providing in the bonded strut ture interlocked connections between the side plates and the gas connections,

5. In a gas to gas heat exchanger. the combination of rside sheets, separating Sheets .therebetween, heat exchanger elements including border frame `members disposed between ,said sheets. ses connections disposed at the ends of said heat exe change elements and extending between said .side sheets, certain of said border frame members having openingstherein operatively connecting said connections with the heat exchanger ele. ments Vassociated with .such frame members. taper headed locati-ng rivets .extending through counter-sunk holes yin said side .sheets and into oversized holes in the gas connections 'to main,- tain the latter and said side sheets in assembled relation, the walls of said holes being lined with fusible bonding material disposed 4between lthe walls of the holes and the rivets, said fusible bonding material, when fused, permitting limited relative adjusting movement between the gas connections and border `frame members during the bonding operation, said rivets providing -in .the bonded structure interlocked Vconnections be.; tween the side plates and the gas connections.

6, In a heat exchanger, the combination .of a multipass yheat exchange structure, including a plurality of pairs of L-shaped vborder frame members, each .pair forming .the side walls of a respective pass, the pairs of border frame members of corresponding passes carrying the same fluid being similarly positioned with gaps 'bef tween the adjacent ends of each :pair of frame members to form inlet and outlet openings there-` in similarly located in the respective passes to form a group of inlet openings and a group of outlet openings, inlet and outlet .connections respectively located at and operatively enclos-1 ing the respective groups of inlet and outlet openings, with .the connections abutting :the end portions of border frame members adjacent said openings, said connections eachjhaving a pair .of oppositely disposed, parallel anges extending transversely across the adjacent lborder frame members, the ends ofthe latter -eachex.- tending `outwardly therefrom with hooks at opposite sides of each gap terminating in :opposed portions, cach overlying .an `adjacent ilange of the connection .thereat and resilient means lin! terposed between the overlying :portions ,of the hooks and such flanges .operative to urge .the abutting surfaces of such connection and members toward oneanother, said members andconf.- nections being bonded into a unitary .structure with said resilient means operative to maintain the connections and members in close engagee. ment during the bonding thereof.

7. In a heat exchanger, the combination of a multipass heat exchange structure, including ,a plurality of border frame members forming the side walls :of such passes, the border'frame memsbers lof `corresponding Vpasses carrying the same uid having openings therein similarly vlocated in the respective passes tovform .a group of ylopen ings, Va connection located at and operatively .enclosing the vgroup openings, with .the connection abutting the portions of border frame members adjacent said openings, said border frame members having pairs of hooks extending Koutwardly from .the frame Awith their free ends terminating on opposed portions .overlying peripheral spor tions of the connection, and resilient means ini- :movement :between :the `.gas .connections Yand .75 tcrposed between `the overlying Portions of 'the hooks and said connection operative to urge the abutting surfaces of said connection and members toward one another, said members and connection being bonded into a unitary structure with said resilient means operative to maintain the connection and members in close engagement during the bonding thereof.

8. In a heat exchanger, the combination of a multipass heat exchange structure,` including a plurality of border frame members forming the side walls of such passes, the border frame members of corresponding passes carrying the same fluid having inlet and outlet openings' therein similarly located in the respective passes to form a group of openings, a connection located at and operatively enclosing the group of openings, with the connection abutting the portions of border frame members adjacent such openings, said connection having oppositely disposed Hanges extending across the adjacent ends of the respective passes, said border frame members having grooves therein disposed in opposed relation on opposite sides of each of the respective openings, said grooves extending transversely to their respective frame members and aligned with corresponding grooves in the other frame members, the anges on said connection being positioned in respective opposed grooves, and resilient means positioned between the outer faces of the flanges and the adjacent side walls of the grooves operative to urge the abutting surfaces of said connection and members toward one another', said members and connection being bonded into a unitary structure with said resilient means operative to maintain the connection and members in close engagement during the bonding thereof.

9. In a heat exchanger, the combination of a multipass heat exchange structure, including a plurality of border frame members forming the side walls of such passes, the border frame members of corresponding passes carrying the same fluid having openings therein similarly located in the respective passes to form a group of openings, a connection located at and operatively enclosing the group of openings, with the connection abutting the portions of border frame members adjacent such openings, said connections having oppositely disposed flanges extending across the adjacent ends of the respective passes, said border frame members having portions integrally formed therewith overlying the opposed anges of the connection, and resilient means interposed between the overlying portions of the border frame members and said -anges operative to urge the abutting surfaces of said connection and members toward one another, said members and connection being bonded into a unitary structure with said resilient means operative to maintain the connection and members in close engagement during the bonding thereof.

spaced from the closure means at a pair of opposite edges of said sheets, said elements substantially filling the transverse space between the closure means at the other pair of opposite edges of said sheets, with said iin elements extending from one sheet to the other, respective plenum structures positioned between the respective ends of the fin elements and adjacent closure means, said structures each comprising a pair of corrugated sheets, with the height of the corrugations being substantially equal to the distance between said rst-mentioned spaced sheets, with the corrugations of one sheet of each pair extending at right angles to the corrugations of the other sheet of such pair, said structures providing reinforcing means between said spaced sheets, said pass having a pair of openings therein each located at and communicating with a respective plenum structure to form fluid ports for the pass, the transverse walls of the corrugated plenum structures having a plurality of spaced openings therein arranged to provide a desired distribution of fluid flow between each fluid port and the adjacent corresponding ends of the nned elements, all adjacent parts of said uid pass being bonded together into a unitary structure.

CLYDE S. SIMPELAAR.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 837,146 Theryc et al Nov. 27, 1906 1,409,967 Prat Mar. 21, 1922 1,852,841 Healy et al Apr. 5, 1932 1,879,519 Ruff Sept. 27, 1932 1,992,097 Seligman Feb. 19, 1935 2,031,425l Muhleisen Feb. 18, 1936 2,133,502 Emmons Oct. 18, 1938 2,428,880 Kintner Oct. 14, 1947 FOREIGN PATENTS Number Country Date 534,313 Great Britain Mar. 4, 1941 574,949 Great Britain Jan. 28, 1946 875,306 France Sept. 16, 1942

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