US2432929A - Internal-combustion heater with spiral type heat exchanger - Google Patents

Description

-w. c. PARRlsl-l 2,432,929

F'iled June 9. 1945 4 snQets-shet 1 M .w ...,H..Hdhmnunuumnhwwwuwnuwuuhu-i Il-- :Q #MIT a. u lmwf/ UHVILRIU "m I Dec. 16, A1947.

INTERNAL-COMBUSTION HEATER WwITH SPIRAL TYPE HEAT EXCHANGER- 16, 1947. w. c. PARRlsH `INTERNAL-COIBUS'IION HEATER WITH SPIRAL TYPE HEAT EXCHANGER Filed Jne 9, 1943 4 Sheets-Sheet 2 w. c. PARRlsH ITERNAL-COIBUSTION HEATER WITH SPIRAL TYPE HEAT EXCHANGER Vl";.1"ed June 9, 1943 4 Sheets-Sheet 3 Dec. 16, 1947. w. c. PARRlsH ,v 2,432,929

INTERNTL-COMBUSTION HEATER WITH SPIRAL TYPE HEAT EXCHANGER Fi1ed June 9, 1943 4 Sheetsf-SheetA Y passageway.

VPaizentec'i Dec. 16, 1947 UNITED STATE s PATENT orric INTERNAL-conmusrron HEATER WITH SPIRAL TYPE HEAT EXCHANGER william c. Parrish, Park mage, nl., assigner u Stewart-Warner Corporation, Chicago. Ill., a corporation of Virginia I' Application June 9, 1943, Serial No. 490,162

. 4 Claims.

l My invention relates generally to heating apaparatus and more particularly to aircraft heaters and heat exchangers therefor.

exchanger in which the flow of one. of the fluids is lin a generally spiral direction.

A further object is to provide an yimproved heater embodying a heat exchanger in which one of the fluids flows in a generally spiral path defined by spaced spirally arranged walls, while the other iiuid ows transversely of the first fluid through the space between the external surfaces of said walls.

A further object is'to provide an improved heater construction in which the products of combustion flow through Ja 4generally spiral passageway and in which a combustion chamber is connected to a space at the central end of the spiral Other objects will appear from the following description, reference being had to the accompanying drawings, in which:

Fig. l lis a central longitudinal of the improved heater;

Fig. 2 is a transverse sectional view thereof sectional view Ytaken on the lineZ--Z of Fig. 1;

Fig. 3 is a longitudinal sectional view of a modi-f ed form of combustion chamber;

Fig, 4 is a sectional view taken on the line l-l of Fig. 3;

Fig.5 is a fragmentary perspective view illustrating the direction of flow of the products of 'combustion and Ventilating air through the heat exchanger;

Fig, 6 is a fragmentary sectional view showing a modified form of secondary air admission means;

Fig. 7 is a fragmentary sectional view showing a further modification of the means for admitting secondary air.

The rate at which heat may be transferred from a metal surface to alluid depends'ln part upon the direction of ilowof the fluid with respect to If the metal surface is fiat the metal surface.

fluid from the metal surface. 'This tendency to form such relatively stagnant layers of the fluid along the metal surface may be greatly reduced and the heat transfer rate substantially increased if the fluid is caused to impinge against the surface, that is, if the ow direction has a 'component perpendicular to the surface. Apparently such impinging flow of the fluid against the heat exchanger surface has a. scouring eect so that molecules of the iluid which would Aotherwise tend to adhere to or move slowly with respect to the surface. are forcibly carried away from the surface, thus increasing the opportunity of other molecules of the fluid to come into actual contact with the heated metal surface, with the ultimate result that the rate of heat'transfer is substantially increased.

In the heater of my invention. the heat exchanger surfaces with which the products of combustlon come in contact are arranged in a. spiral shape so that the products of combustion, due

l to the inertia. or centrifugal force, are repeatedly and fluid flows along thesurface in a direction parallel tothe surface, the rate of heat transfer from the surface 4to the fluid'is reduced considerably by the fact that the fluid tends to adhere to the metal surface and form a relatively stagnant 55 layer partially insulating ,the remainder of the of the heater for the projected against the heat exchanger surface,

with consequent vigorous scouring effect and resultant high rate of heat transfer. i

The invention is illustrated in Figs. 1 2, and 5 as comprising a single sheet 20 folded back upon itself as indicated at 2i to form spaced walls of generally spiral shape. These walls are held in spaced relation by a plurality of channels 24, to which the sheet 20 may be spot-welded at intervals. The sheet 20 thus defines a spiral passageway 30 of approximately three turns and a plurality of PB SSageways 32 extending longitudinally flow of Ventilating air. The ends of the sheet 20 are suitably secured in header plates 34 and 35, which close the sides of the passageway lll but provide spiral 4openings f or the flow of Ventilating air through the passageways 32. The headers 34 and 35 are preferably in the form of flanged stampings, to the flanges of which the edges of the sheet 20 may be welded or brazed.

An inlet duct 36 is suitably secured to the head 34 and may be connected to an air ram or scoop, or to any other suitable source of air under pressure. A combustion chamber 38 is s uitably secured to the head 34, as by cap screws 39. A combustible mixture of fuel and air is supplied by a carburetor 42 connected to the combustion chamber by a conduit 44 terminating in an arcuate induction tube 43 located within the com,

bustion chamber 38. An electrical igniter, shown assassin end of which faces against the direction of now of Ventilating air at the outlet ends oi the passageways Ventilating air outlet duct I2, which is suitably secured to the head 35.

The head 35 has a cup-shaped element I4 secured thereto, this cup being closed by a perforated plate I8. 'I'he cup 54 forms an acoustic damper and is preferably lled with an acoustic vibration-absorbing material B8. such as glass wool or the like. A pipe 80 projects into the central space 82 of the heat exchanger and extends through the cup Il and through the outlet duct 82. This pipe is preferably connected to an air ram or scoop. which may or may not be the same ram or scoop to which the inlet duct ll is connected. Air will thus flow into the space l2 through the pipe 80 to ymix-with the products of A combustion to assure completion of combustion and to retard rapid changes in pressure within the chamber 82. 'I'he tube 40 thus performs functions similar to those of the acoustic damper I4 in addition to supplying secondary air for combuston and temperature moderation to the space 82.

In utilizing the heater of Figs. 1, 2, and 5, assuming theigniter 48 has been energized and the supply of air under pressure permitted to flow into the inlet duct 38, the ventilating air will ilow through the passageways 82 and some of it will enter .the combustion air supply tube 50, be admixed with fuel in the carburetor 42, and ow into the combustion chamber through the induction tube 46. It will be noted that the iiow from the tube 48 is generally tangential with respect i2. 'I'he pipe I8 projects through a heater has an extremely large heat transfer surface compared with its overall dimensions. It will be noted that all of the surfaces of the sheet 28 are primary heat transfer surfaces, that is. the sheet has throughout its extent. Ventilating air on one side and hot products of combustion on the other sides. By making the sheet 20 very thin and of a metal having good thermal conductivity, the heat exchanger may be made very efficient. In the heater illustrated, the products of combustion may have a decidedly corrosive effect upon most metals, and it is preferred in this instance to make the sheet out of stainless steel even though its heat conductivity is not very high. The disadvantage of the use of stainless steel in this respect is more than compensated for by the fact that the sheet may be made very thin and will not b e destructively corroded throughout the useful life of the heater.

Although the induction tube 48 is illustrated as being curved in the same direction as the spiral passageway formed by the lsheet 20, the induction tube may, if desired, face in the opposite dlrection so as to make it necessary for the products of combustion to reverse their direction of rotational flow upon entering the passageway 30. W'hen constructed in the latter manner, there is greater turbulence within the space B2, .with consequent greater assurance of complete combustion of the fuel, but, on the other hand, the resistance to flow through the heater will be increased someto the generally cylindrical combustion chamber 38 so that the fuel mixture will flow through the combustion chamberin a generally helical path and enter the space 62 at the center of the heat exchanger.

As best shown by the arrows in Fig. 2, the flow,

will be in a counterclockwise direction and will continue in this direction through the spiral passageway 38, which terminates in the outlet channel 84, which, as best shown in Fig. 5, may be welded to the sheet 20 and may have a flanged outlet fitting 88 welded thereto.

In the flow of the products of combustion from the space 62 .to the outlet fitting 86, the direction of ilow is continuously changed so that a very advantageous scouring of the surfaces of the sheet 20 which deiine the passageway 30, takes place throughout the length of the passageway.

It will be noted that the cross-sectional area of the passageway 30 decreases from its inlet end towards its outlet end. As a result of this construction, the velocity of flow of the products of combustion through thispassageway increases as the products approach the outlet. Thus, as the products of combustion become cooler, the velocity of flow thereon increases to compensate for the reduced temperature, with the result .that the rate of heat exchange between the products of combustion and the sheet 20 is increased. The overall enect of this construction is that the temperature of the sheet 20 is substantially uniform what as compared with the construction shown in Figs. 1,2, and 5.

Any tendency toward acoustic vibration in the space 82 is effectively damped by virtue of the provision of the cup member 54 with its acoustic damping material communicating with the space 82 through the small apertures inthe plate 56. Since the tube 8U provides a somewhat restricted passageway leading to the space 62, it is also effective to damp acoustic vibrations. Although the tube 88 is provided primarily for the purpose of damping acoustic vibrations within the space 82, it also serves the function ofsupplying some air to assure complete combustion of the fuel within the chamber 62 and also to moderate the temperature of the gases within this space and thereby reduce the possibility of the sheet 20 being burned or melted.

In Figs. 3 and 4 is shown a modified form of combustion chamber comprising generally a cupshaped element 10 provided with a conical baille throughout its length. There is thus no tendency for damage or destruction to the heat exchangerV due to the localization of the heat transfer from r thev products of combustion to the sheet 20, and maximum efliciency of heat transfer from the products of combustion thereby assured.

Due to the spiral shape of the sheet 28. the

to the Ventilating air is wall 12, the latter being provided with louver openings 14. A nozzle supporting sleeve 18 is welded to the combustion chamber stamping 10 and has a fuel nozzle 18 detachably secured therein, as by a. spring clip 80. Fuel is supplied to the nozzle '18 through a conduit 82, in which the fuel may be maintained 'under pressure by a suitable fuel pump.

Air for combustion is supplied through a conduit 84, which leads into the space surrounding the conical baille 12. The conduit 84 may be sup -plied with air under pressure from an air ram means, shown as spark plug 86. It'will be noted that the type of combustion chamber shown in Figs. 3 and 4 may be substituted for the combustion chamber 38 of Figs. 1 and 2, and the necessity of utilizing a carburetor 42 thus avoided.

Instead of admitting air from the atmosphere to the tube 60, as shown in Figs. 1 and 2, this tube may be conformed, as shown, in Fig. 6, to have a bend portion 88 opening in a position to receive heated Ventilating air being discharged through the passageways 32. Since the pressure within the outlet duct 52 will always be higher than that within the space 62, there will be no danger of the escape of products of combustion tothe Ventilating air through this tube.

The tube B0 is normally so. effective las an acoustic vibration damper or muiller that it may be utilized as the sole means for damping such vibration, as indicated in Fig. 7, wherein, the tube 60 has a hook portion 90 for conducting Ventilating air, heated by its ilow through passageways 32, to the space 62.

From the foregoing, it will be apparent that the heat exchange surface of the heat exchanger is of great area compared with its overall dimen sions and that all of the heat exchange surfaces are primary surfaces. As a result, there is no substantial temperature drop across the metal walls forming the spiral passageway and the metal temperature throughout the heat exchanger is substantially uniform.

While I have shown and described particular embodiments of my invention, it will be apparent to those skilled in the art that numerous varia.. tions and modifications may be made therein without departing from the underlying principles of the invention. I therefore desire, by the following claims, to include Within the scope vof my invention all such variations and modications by which substantially the results of my invention may be obtained by the use of substantially the same or equivalent means.

I claim:

1. In a heater which includes a combustion chamber, and means to supply a combustible mixture of fuel and air to said chamber, a heat exchanger having a generally cylindrical space in the center thereof and a spiral passageway extending outwardly from said space, said passageway being formed by a pair of thin metal sheets held in spaced relation, the spaces between said pair of sheetsforming passageways for the ilow of Ventilating air, one end of said cylindrical space being in free communication with said combustion chamber, and means forming an acoustic vibration damper having restricted communication with the generally cylindrical space at the end thereof opposite said combustion chamber.

2. In a heating apparatus which includes a combustion chamber, a heat exchanger having a generally cylindrical space in free communication with said combustion chamber, means forming a passageway generally rectangular in transverse cross-section and extending spirally outwardly from and around said space, the cross sectional area of said passageway tapering substantially from its innermost end to its outermost end by decreasing the width of its rectangular cross sectional area, means forming Ventilating air pas- V sageways between successive convolutions of said spiral passageway, substantially the entire cross section of said Ventilating air passageways being open at both ends for the ilow of air therethrough in a direction parallel to the axis of said cylindrical space, conduits for conveying Ventilating air to and from said Ventilating air passageways, and means to `supply a, combustible mixture of fuel and air to the combustion chamber including a conduit arranged to deliver to the combustion chamber 'a small proportion of the ventitile of this patent:

said Ventilating air passageways.

3. In a heating apparatusuwhich includes a combustion chamber, a heat exchanger having a generally cylindrical space in free communication with said combustion chamber, means forming a passageway generally rectangular in` transverse cross section and extending spirally outwardly from and around said space, means forming Ventilating air passageways between successive convolutions of said spiral passageway, conduits for vconveying Ventilating air to and from said venti.-

lating air passageways, and meansto supply a combustible mixture of fuel and air for the apparatus including means furnishing air for combustion to the combustion chamber and means furnishing additional air to said cylindrical space of the heat exchanger, the air furnished by one of said means comprising a portion of the Ventilating air which has been heated by ilow through said Ventilating air passageways.

4. In a lightweight aircraft heater, the combination of means forming a combustion chamber, means for supplying fuel and air for combustion to said combustion chamber, a double walled spiral coil of sheet metal closed at the inner and outer ends of the spiral, the space between the convolutions of said double walled spiral coil forming a passageway generally rectangular in cross section and of relatively great thickness at the end of the inner convolution and tapering in thickness toward the outer end thereof the innermost convolution of said double walled spiral coil forming a generally cylindrical space in direct communication with said combustion chamber..

means forming an outlet for exhaust gases at the outer end of said passageway, said passageway between the convolutions being entirely unobstructed for the iiow of hot gases from said cylindrical space in a continuously outward spiral path to said exhaust outlet, spacers between the two walls of said coil at spaced intervals in the length of the spiral, and a pair of spirally shaped headers sealing thesides of said passageway and leaving open at both sides substantially the entire cross section of the space between the two walls of said spiral coil for the iiow of Ventilating air directly 4through vsaid space, together with conduit means REFERENCES CITED The following references are of record in the UNITED STATESy PATENTS Number Name Date 1,110,065 Linge. Sept. 8, 1914 1,746,982 Atwater Feb. 11, 1930 1,448,325 Alexander Mar. 13. 1923 1,613,615 Lippert Jan. 11, 1927.

1,594,074 Shuell, et al July 27, 1926 1,990,827 Iier Feb. 12, 1935 870,821 Hall Nov. 12, 1907 1,799,039 Conejos Mar. 31, 1931 1,357,598 Thompson Nov. A2, 1920 2,364,214 Hess et al Dec. 5, 1944 FOREIGN PATENTS Number Country Date 308,648 Germany Oct. l25, 1918

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