US2586250A - Heat exchanger - Google Patents

Description

Feb. 19, 1952 Filed Sept. 12, 1949 L. PARKER HEAT EXCHANGER 2 SHEETS-SHEET l INVENTOR.

LEONPHRKEAL T TaRNE v.

L. PA R K E R HEAT EXCHANGER Feb. 19, 1952 Filed sept. 12, 1949 2 SHEETS-SHEET 2 INVENToR. Y LEON ,PARKER .TTaRNEY.

Patented Feb. 19, 1952 HEAT EXCHANGER Leon Parker, Burbank, Calif., assigner to The H. I. Thompson Company, Los Angeles, Calif., a corporation of California Application September 12, 1949, Serial No. 115,242

s claims.

This invention relates to regenerative heat exchange apparatus operable at high ambient temperatures and over large ranges of temperatures. It is particularly designed for use with jet or turbo-jet airplane engines wherein the ternpera-` tures may range from 900 F. to 1500 F.

In such units it is desired to devise a regenerah tive heat exchange structure of low pressure drop, high stability against thermal and mechanical shock and corrosion resistance, and of low bulk volume and weight.

I have devised a regenerative heat exchange medium which has the desirable properties speciiied above. It is formed of silica laments arranged to present unobstructed longitudinal pas- ,1

sageways, preferably by employing textiles, such las woven, knit, corded, braided material or any other interlaced or interwoven silica bers. The interwoven silica fibers are arranged in a chamber so as to present elongated unobstructed chan- ,ff

permeable to the gases passed through the heat exchange apparatus.

Silica has the useful properties for this purpose in that of all solid materials which soften or melt above the temperatures previously referred to, it has a relatively high specic heat and is not corroded or eroded by high temperatures, high velocity combustion gases, or by air at high temperatures moving at high velocity.

While fused quartz, in tubular or massive form, has a low -coeicient of expansion and is relatively weak tcthermal and mechanical shock, in lamentary form, as yarn, batt, woven, knitted, braided and corded iibers, and, in fact, in any interlaced textile form, the silica bers have a high degree of stability against thermal shock, and the ratio of exposed surface to total volume of the silica is extremely high. The textile material has a high degree of hull: exibility, but has 'ttle or no rigidity. The textile also may have a high porosity, depending upon the weave, knit or braid pattern employed.

I have found that if this textile is arranged so as to present longitudinal passageways, the textile acting as the separating wall of the passageways, a heat exchange apparatus of very low pressure drop and high eiiiciency, small volume and high heat capacity results which will be stable to thermal and mechanical shock.

In order to support the fabric to present the aforementioned small :pressure vdrop but to assure that it has a high ratio of wall surface to volume of the passageways, I have found it desirable that the passageways be channels of relatively small cross sectional area but of considerable longitudinal dimension in direction of ow so arranged as to introduce little or no obstruc- -tion to flow but insure adequate and rapid heat transfer from the gases to the walls. To obtain this effect I have found it desirable to form the heat exchange apparatus of a multiplicity of longitudinally parallel channels the cross sections of which are but a small fraction of their length, but to use a suciently large number of these parallel channels so that the free area of the channels is large. Since the walls of the channels are very thin, depending upon the `thickness 'of the yarn and the nature of the weave, the total cross sectional area of the vfree space may be made the majo-r part of the total cross sectional area and, in fact, the cross sectional area occupied by the textile walls forms but a small percentage of the total cross sectional area. The diculty in arranging such passagewy's'resides in the inherent lack of rigidity of the fabrics.

'I-have found it desirable to avoid employing a framework or skeleton to support the textile material-...whenx arranged in the manner described abov y si elit reduces the free area and increases .'theiressure drop and also adds weight to the heat. exchange apparatus.

Ihavjfound that I may construct such a siliceous-textile so that it has sufficient rigiditl7 toretainlitsfshape and resist deformation due to eitherithernial or mechanical shock or mechanical :deform'ation without using any framework 'or structur which will be positioned in the free space. I have accomplished this by using a silica textile formed of interwoven silica lament and metallic wire-lilaments. The metallic wire forms a skeleton which is much more rigid than the silica textile "and will support the silica fibers in any desired conformation. Since the'wires are positioned in the textile'as a component thereof, they occupy no portion of the free volume. By employing wire having a high tensile strength, rigidity, and corr-osion resistance, I may use relatively thin wires and thus reduce the bulk and weight of the non-siliceous portion of the textile.

It has been recently discovered that ordinary glass fibers usually employed in making glass fiber textures may be extracted to remove the glass making oxides, other than silica, and to leave a highly siliceousmaterial in which the silica, element may run from 90% to over 99|% of the oxide element of the extracted material. The extracted material is hydrated and in ring at high temperature the material is dehydrated and shrunk. Reference may be had to the Nordberg Patent No. 2,461,841 and to application Serial No. 669,098, filed May 11, 1946, now Patent No. 2,491,761, by Leon Parker and Alexander Cole, for details of this process.

This procedure results in a large impairment in the tensile strength of the glass fabric. While careful control of the extraction and the washing process will give silica fabrics of relatively high tensile strength, the resultant tensile strength is at best much lower than that of the original glass fiber material.

It is difficult to weave, knit, braid, or cord silica fibers thus produced because of its inherent low strength and therefore it has not been practicable to form the desired composite textile formed of metallic wireand silica fibers for the above use. In my co-pending application, Serial No. 114,998, led September 10, 1949, I have disclosed procedures whereby this may be accomplished. Instead of Weaving or knitting the composite textile using the extracted or extracted and fired silica bers in thread oryarn form, I first form the textile by weaving or knitting the textile using glass fibers and the other filamentary material to be incorporated in the composite textile. The composite fabric may then be leached to remove from the glass filaments the glass forming oxides other than silica in the usual manner. The composite ber may then be red if desired.

The fiber other than glass employed should preferably be immune to chemical or physical attack by the leaching solution in a degree to materially impair its physical or chemical properties.

Glass filaments are leachable either with water alone or by acids, depending upon the nature of the glass. The nature of theglasses and their relation to and method for leaching such glasses are described in the above mentioned-Norberg patent and the Parker-Cole application.

Thus, if the glass filament is leachable with water as, for example, the alkali boro-silicate glass having Va* high boron-oxide to alkali ratio, for example, not less than about 5: 1, I may employ almost any other filament in forming the original composite glass cloth, for example, any of the filaments referred to above, since-they will not be impaired by the water. In fact, most filamentary material, such as is used for-weaving, knitting, braiding, cording or other textile forming process, whether metallic or non-metallic, or yorganic or inorganic, such the glass, not leachable'by water, may be used, since what is desired is a fiber which will not be attacked by Water or attack by water will not be significant in reducing its strength to a relatively low value. I may extract the glass cloth by prolonged attack by water to remove the non-siliceous oxides and thus give a leached composite cloth of higher tensile strength than can be obtained by leaching a textile formed of the leachable glass fibers. When I employ a glass fiber which is leachable with water, I may form a composite fabric formed of water leachable glass and also of glass which is immune to attack by such water. Such glasses are the boro-silicate glasses having 70% or more of SiOz, and if containing'less than 70%, thosewhich are substantially free fromv alkali metal oxides but which contain substantial amounts of second group oxides and -alumina or any other type of stantially free from alkali and containing substantial amounts of second group oxides and alumina, for example, 56% or less of S-iOz, about 22% or less of second group oxides, about 12% or more of AlzOs, and about 5% or more of B203. Soda-lime glasses may also be leached with acid, i. e., those containing about 20% or more of alkali and about or less of SiOz and containing second group oxides.

I have found that for my purposes, because of their adaptability to forming glass filaments and textiles, the acid leachable boro-silicate glasses are to be preferred.

I, therefore incorporate as the added strengthimparting filament one which is resistant to such attack by acid and preferably by acid at the elevated leaching temperatures employed. Such laments are the acid resistant glass laments and acidresistant organic synthetic fibers such as polyvinylidene chloride, polyvinyl chloride, and the noncorrosive metallic Wires listed below. All of these materials form a natural group in that they can be formed into filaments which can be formed into textiles and resist chemical attack by HCl'at elevated temperatures above 100 F. and below 212 F., which temperatures are usually employed in the glass leaching operation.

However, if the textile is to be fired to dehydrate it, I must use as the iiber, other than the leachable glass fiber, a material `which will be stable at the elevated firing temperature of about '750 F. and preferably as high as l600 F. at which the textile is iired. In such circumstances I cannot use the organic fibers, natural or synthetic, since they will be destroyed by firing and glass filaments will lose their strength by devitriflcation or may actually melt if the higher temperatures are used. In such circumstance I preer to employ filaments of material which will be stable at the high temperatures used for dehydration and shrinkage of the leached fabrics.

I thus prefer to use the metallic filaments. Many metals are available in ne wire form and may be handled on conventional braiding, cording, weaving or knitting machines. These include copper, steel, nickel, chromium, nickel-molybdenum, and manyothers which will suggest themselves to those skilled in this art. However, if the leaching agent be acid, I must select those which are not corroded by acid, and thus I prefer to employ the acid resistant filaments made of I-Iastelloy B (whose composition is referred to below), platinum, tantalum, Phosphor bronze, aluminum-bronze, gold, silver, nickel-silver alloy, Everdur, which is a copper, silicon, manganese alloy, copper ranging from 94.9 to 98.2%, silicon 1.5 to 4%; manganese 0.25 to 1.1%, and also chromium-copper alloys. 'Ihe metallic wires which have a melting point at about 1500 F. or higher form a sub-group of the acid resistant metallic Wire group referred to above in that they are'not only acidV resistant, as described above,

' loops.

filaments as leachable glass filaments and nonleachable reinforcing filaments, meaning that under the conditions of leaching'wherein I extract the non-siliceous glass oxides of the leachable glass to produce silica fibers containing nonsiliceous oxides in the ratio of 9:1 or more of silica to non-metallic oxides, the non-leachable fibers will not be attacked in any substantial manner during such leaching, and I refer to the latter as a reinforcing filament in that the properties of the composite fabric, such as tensilev strength and abrasion resistance, are enhanced by their presence in the reinforced fabric above that formed of the siliceous material alone.

The properties of the resultant'leached fibers thus formed into a composite textile material-'include resistance to acid or water attack. The` V fired silica fibers are not attacked by alkali. The fusion and softening points are high above 1600 F., depending upon the amount of leaching and the melting and softening points may be as high..w

as 2000 F. or more.

The dried silica fibers (dried below about 385 F.) Vand unnred silica fibers have desiccant properties. The fibers are soft, and before and after firing are soft and silky and resemble silk even,

more than do the original glass fibers.

I prefer to employ the wires which belong te this sub-group since, as will be indicated below, I prefer to use the acid leachable glass filaments.

On firing the glass filament woven into a composite fabric, the silica shrinks while the metallic wires do not. This shrinkage causes a crinkling of the wires so as to cause them to protrude from the surface of the fabric in the form of hooksor Superposed fabric is thus interlaced and locked in position.

I have thus developed a heat exchange apparatus composed of a plurality of channels separated by walls formed of a composite textile material, which composite textile material is composed of interlaced silica and metallic wire filaments.

This invention will be further described in connection with the drawings, in which Fig. 1 is a showing somewhat schematic of aV vertical section of a regenerative heat 'exchanger-.

such as forms the subject matter of this tion;

Fig. 2 is a plan view somewhat schematic of a tubular woven fabric which may be used yinthe invenexchanger of Fig. 1; "J5

Fig. 3 is a section taken on line 3--3 of Fig.2; of an extracted tubular woven fabric before firing;

Fig. 4 is a section of Fig. 3 of the tubular material after firing;

' before itis fired; Y v Fig. 8 is a section similar to Fig. 7, showing the leached and fired fabric;

Fig. 9 shows the fabric of Fig. 6 corrugated;

Fig. 10 shows one method of stacking such corrugated fabric to give the longtudinal'passageways shown in Fig. 1;

6 Fig. 11 is a perspective of the fabric of'Fig. 9 corrugated for stacking as in Fig. 10.

The heat exchange unit of Fig. 1 is composed of a box 1 of any desired cross section, Whether circular, square or otherwise, having an inlet 2 and outlet 3 for gases. The heat exchange contact material, shown schematically at li, may be positioned between two retaining screens 5 and 6. The heat exchange material may be of the form shown in Figs. 4 and 5, that is, of tubular woven character. Fig. 6 shows schematically the nature of the Weave composed of the metalliclament 1 and leachable glass fiber filaments 8. These are woven in tubular fashion on a standard tubular braiding machine and results in a tubular fabric having pore spaces in the Walls between the fabric filaments and a composite Wall composed of the metallic filaments 9 and the glass filaments 8. The metallic fibers, even if the same number of threads of metallic fibers and glass fibers is employed, are such that the exposed area is a major part of the glass.

As examples of this type of reinforced silica ber cloth, the following may be taken as illustrative, but not as a limitation of the invention.

A tubular braid may be formed using .007" diameter dead soft Hastelloy B- wire having the following composition: C, 0.12%; Mo, 26-30%; Fe, 4-7%, and Ni on balance to make 100%.

This is braided with glass fiber yarn .01" in diameter (made of glass fibers each less than .001I in diameter) having the following composition:

The glass fiber had 2.09% organic matter, being the lubricant employed lin the weaving. The material was burned off and the loss in weight .(2.09%) is here reported as lubricant. 'I'he residual 97.91% had the following composition on a lubricant free basis:

Per cent SiOz 53.95 A1203 16.14 F8203 .56 CaO 15.96 MgO 4.10 B203 8.20 NazO .88

The braiding machine, for example, may have 24 carriers, using 12 carriers of wire and 12 carmaterial. The braiding may be leached yby any strong acid, preferably one whose salts of the non-siliceous metal oxides are soluble in water; for example, HNO3,HC1, chloroacetic acid. Thus, for example, the braiding can be leached with 12% hydrochloric acid solution for 2 hours at 170 F., then washed in water until chloride free,

Vwhen the Water has a pH of about 7-8. Ther wire is not attacked by the acid and no discoloration of the glass cloth results. The leachingoperavtion is conducted until the silica ratio to the remaining non-siliceous oxides is about 9:1 or more, preferably until the total silica content based on the fired dehydrated silica filament is 95 to about 99+%. The leached fibers have the conformation and arrangement of the original fibers of the composite textiles, as is illustrated in Figs. 2, 3, 6 and '7.

The resultant sleeving has the characteristic of look and feel as sleeving produced when only glass cloth is leached. The revealed wires appear uniformly spaced over 'the surfaceof the sleeving.

` shape and when so flexed Will hold its shape.

The sleeving is then iiredat an elevated "temperature to dehydrate the silica, for example, at l500 F. for 20 minutes. The silica shrinks and causes a crinkling of the wires. As a result the wires where they are revealed at the surface appear to be crimped, thus giving a series of hook-like projectionsSa. These tubes can then be stacked between the screens and i3 to give a plurality of longitudinal passageways with porous walls, through and around the stacked tubes. The hook-likel projections `9a interlock, holding the ends in place relative to each other, resulting in a compact stable structure. The natural bulk flexibility of the fabric tubes makes them resistant to mechanical and thermal shock. The weight of the tubular material perdnch was 4.3 104 pounds and about 2.9 pounds per square feet of cross-sectional area one inch thick in the heat exchanger I.

Instead of the fibers of .01 in diameter used in the previous example, a glass fiber of .0065" in diameter may be used which would result in a leached and fired sleeving of .1057 internal diameter. All of these sleevings will have the necessary rigidity to Vmaintain their shape and will be interlocked in the manner described above by the use of any framing other than the structure of the sleeve itself.

Instead of using sleeving, I may use tape which may be corrugated in the formy shown in Figs.

9, 10, and 11. For example, these figures illustrate the use of wires of vdiierent diameters-to be interwoven with the tape. Thus, in Figs. 9, 10, and 1l the wire of .007 diameter, of the type previously described illustrating the formation of the tubes, was employed as the Warp and a wire of .003 diameter was employed as fill, shown at I0, spacing the warp more closely than the lill. The glass fiber of .0065" diameter was interknit on a standard tape knitting machine. The tape was then leached in the manner as described for the tube and iired in the same way. The finished tape Was 3A" wide, and had a thickness of .029".

The tape was woven to 11/3" wide, 'and after' leaching and firing it iinished asl-5s wide and .019" thick anda weight of .009 pound per foot. This'tape was corrugated 'll" overall height and 1A," between corrugations, as illustrated in Fig.

11, the tapes being stacked side-by-side across' the width of the heat exchanger to give tubular passageways Il. The interlocking of the protruding metallic hooks positions these several layers of corrugated tape which tape holds its form after corrugation and is'retained'snugly in the modifications and adaptations thereof may Abel made within the spirit of the invention 'asset forth in the appended claims.

Iclaim: ,Y u l l. A heat exchange unit, comprisingahousing,

vafiuid inlet, a fluid outlet from saidhusing, a

plurality of elongated iiuid'passageways through said housing, the said passagewayshavinglwalls comprising textile material-formed of interlaced silica iilaments.

2. A heat exchange unit, comprising a housing, a iiuid inlet, a fluid outlet from said housing, a plurality of elongated iiuid passageways through said housing, the said passageways having walls comprising textile material formed of interlaced silica laments containing non-siliceous metallic oxides, the ratio of silica to non-siliceous metallic oxides being at least 9:1 said silica filaments having a fusion point in excess of 1600 F.

3. A heat exchange unit, comprising a housing' a iiuid inlet, a iiuid outlet from said housing, a

plurality of elongated fluid passageways through said housing, the said passageways having walls comprising textile material formed of interlaced metallic iilaments and silica filaments.

4. A heat exchange unit, comprising a housing, a fluid inlet, a iiuid outlet from said housing, a plurality of elongated iiuid passageways through said housing, the said passageways having walls comprising textile materials formed of interlaced metallic filaments and silica iilaments, said silica filaments containing non-siliceous metallic oxides, the ratio of silica to non-siliceous metallic oxides being at least 9:1 said silica filaments having a fusion point in excess of 1600 F.

5. A heat exchange unit, comprising a housing, a iiuid inlet, a iiuid outlet from said housing, a plurality of elongated fluid passageways through said housing, the said passageways having walls comprising tubular textile material formed of interlaced silica iilaments.

6. A heat exchange unit, comprising a housing, a fluid inlet, a fluid outlet from said housing, a. plurality of elongated fluid passageways through said housing, the said passageways having walls comprising tubular textile material formed of interlaced silica filaments containing non-siliceous metallic oxides, the ratio of silica to nonsiliceous metallic oxides being at least 9:1 said silica filaments having a, fusion point in excess of 1600 F.

7. A heat exchange unit, comprising a housing, a fluid inlet, a uid outlet from said housing, a plurality of elongated fluid passageways through said housing, the said passageways having walls comprising tubular textile material formed of interlaced metallic filaments and silica filaments.

8. A heat exchange unit, comprising a housing. a fluid inlet,`a iiuid outlet from said housing, a plurality of elongated fluid passageways through said housing, the said passageways havingwalls comprising tubular textile material formed of interlaced metallic iilaments and silica iilaments containing non-siliceous metallic oxides, the ratio of silica to non-siliceous metallic oxides being at least 9:1 said silica filaments having a fusion point in excess of 1600 F.

LEON PARKER.

REFERENCES CITED UNITED STATES PATENTS Number Name Date l 1,418,234 Cleary. l May 30, 1922 1,745,113 Odell 1 Jan. 28, 1930 1,879,056 Brassart 1-- Sept.Y 27,1932 Jacob Aug. 9, 2,385,577

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