US2886295A - Heat exchanger for warm air furnaces - Google Patents

Description

y 12, 59 L. BETZER 2,886,295

HEAT EXCHANGER FOR WARM AIR FURNACES Filed me 11, 1956 2 Sheets-Sheet 1 i E a F/ 2 INVENTOR. g C/oyd L. Befzer His Attorney May 12, 1959 c. BETZER HEAT EXCHANGER FOR WARM AIR FURNACES Filed June 11, 1956 2 Sheets-Sheet 2 INVENTOR. C/oyd L. Be/zer .2. C. 5% His Attorney United States Patent 2,886,295 HEAT EXCHANGER FOR WARM AIR FURNACES 'Cloyd L. Betzer, Rochester, N.Y., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application June 11, 1956, Serial No. 590,725

2 Claims. (Cl. 257-139) This invention pertains to heat exchangers, and particularly to heat exchangers for warm air furnaces.

Heretofore, heat exchangers for warm air furnaces have been made with externally finned surfaces which increase the area of metal exposed to the air to be heated, thereby increasing the rate of heat transfer between the hot flue gases and the air to be heated. The present invention relates to an improved heat exchanger having integral internal and external fins so as to further increase the rate of heat transfer between the hot flue gases and the air to be heated. With the improved heat exchanger, the overall size of the heat exchanger for a furnace of predetermined capacity can be materially reduced. Accordingly, among my objects are the provision of a heat exchanger having duplex fin surfaces; the further provision of a heat exchanger comprising a plurality of metal stampings, each stamping having integral internal and external fins; and the still further provision of a heat transfer stamping having spaced, oppositely directed portions adapted to constitute integral internal and external fins in an assembled heat exchanger.

The aforementioned and other objects are accomplished in the present invention by constructing the side, top, and bottom walls of a heat exchanger from a plurality of sheet metal stampings having oppositely directed leg portions interconnected by a web portion. Specifically, each heat transfer stamping is formed from a flat strip, opposite edge portions of which are bent in opposite directions and the interconnecting web portion of which is bent to have a stepped configuration. Thereafter, the deformed strip is bent into a U-shaped section.

In assembling the heat exchanger, the side, bottom and top walls are constituted by the U-shaped sheet metal sections. The interconnecting web portion of each section is telescopically received by the web portion of an adjacent section by reason of the stepped configuration of the web portions. Thereafter, the several sections are rigidly united by seam welding or furnace brazing. One sidewall, half of the top wall and half of the bottom wall of the heat exchanger are formed by one set of U-shaped sheet metal sections, and the other sidewall, half of the top wall and half of the bottom wall are formed by another set of U-shaped sections. The two subassemblies may then be rigidly connected to form an integral unit by seam welding.

The front and rear walls of the heat exchanger comprise dished sheet metal stampings, the peripheral edges of which are seam welded to the top, bottom, and sidewall unit. Preferably, the front and rear wall stampings have sheet metal fins welded to their exterior surfaces to further increase the heat exchange area. In addition, the front wall stamping has one or more openings adjacent its top and a lower opening arranged to accommodate a fuel burner.

The heat exchanger of this invention also constitutes the combustion shell of a warm air furnace. In a furnace installation, the combined heat exchanger and combustion shell is enclosed by an outer casing within which a suitable 2,886,295 Patented May 12, 1959 blower is mounted. The blower discharges air to be heated across the outer surface of the heat exchanger, and hot flue gases are circulated through the interior of the heat exchanger.

Further objects and advantages of the present invention will be apparent from the following description, reference being bad to the accompanying drawings wherein a preferred embodiment of the present invention is clearly shown.

In the drawings:

Fig. 1 is a view, partly in section and partly in elevavation, taken along line 1--1 of Fig. 2 of a warm air furnace having a heat exchanger constructed according to this invention.

Fig. 2 is a fragmentary sectional view, taken along line 2-2 of Fig. 1.

Fig. 3 is a fragmentary perspective view, depicting the duplex fin arrangement of the heat exchanger of this invention.

Fig. 4 is a fragmentary perspective view, of one of the duplex fin heat exchange sections.

With particular reference to Figs. 1 and 2, a warm air furnace is shown including an outer sheet metal casing 10, a centrifugal blower 12 being mounted in the lower portion of the casing 10 and a combined heat exchanger and combustion shell 14 being mounted in the upper portion of the casing. As seen in Fig. 2, the blower 12 discharges air through an opening 16 in contiguous relation with the exterior of the combined heat exchanger and combustion shell 14. The air discharged by the blower 12 flows upwardly across the exterior surface of the heat exchanger 14 and is discharged through an opening 18 in the top of the casing 10. Air is supplied to the blower through a suitable inlet opening, not shown.

The combined heat exchanger and combustion shell 14 includes a front wall 20, a rear wall 22, as well as top, bottom, and sidewalls, the construction of which will be described hereinafter. The front wall 20 has a lower 'opening at 24, into which a suitable gas burner 26 extends.

The gas burner 26 may be of any conventional design and is supported in the casing 10 by any suitable means, not shown. The front wall 20 is formed with a pair of openings 28 and 30 adjacent the upper end thereof to which flue gas pipes 32 and 34 are connected. The combustion chamber flues 32 and 34 discharge into the space 70 and is mixed with air aspirated through the opening 72 in the casing 10 and the mixture passes out to the stack through stack pipe 36. The action is the same as that of a drafthood well known in the art.

In addition, the front and rear walls 20 and 22 have welded thereto a plurality of sheet metal fins 38. The fins 38 increase the external heat transfer area of the heat exchanger 14 and thereby assist in facilitating the transfer of heat between the hot flue gases flowing upwardly through the interior of the heat exchanger and the air to be heated flowing across the exterior thereof.

With particular reference to Figs. 3 and 4, the novel duplex fin arrangement of the side, top and bottom walls of the heat exchanger 14 will be described. As seen in Fig. l, the top, bottom, and sidewalls of the heat exchanger are constituted by U-shaped sheet metal sections, such as indicated by numeral 40. Each intermediate U-shaped sheet metal section has an outwardly directed fin portion 42, an inwardly directed fin portion 44, and an interconnecting web 46 of stepped configuration. Thus, the web 46 includes a portion 48 and a portion 50, the inner surfaces of which are located in spaced parallel planes. The externally extending portion 42 and the internally extending portion 44 are located at substantially right angles to the interconnecting web 46. In addition, the ends 52 and 54 of the fin portions 42 and 44, respectively, are cut off at an angle, as shown more particularly in Fig. 1, to

essence facilitate seam welding of the sections into an integral unit.

As seen in Fig. 3, the end section 4% adjacent the front of the heat exchanger has its outwardly directed fin portion 42 located at an angle of substantially 45 to the web 46. This arrangement facilitates its inner connection with the front wall 20, which comprises a substantially cup-shaped member having edge portions 56 and bent outwardly at an angle of 45. The end section 4% adjacent the rear wall of the heat exchanger does not include an internally extending fin portion since it is connected to the rear wall member 22. in order to facilitate its conned tion with the rear wall member 52, the portion 44' is bent outwardly at an angle of 45 and cooperates with a similarly formed portion 53 on the rear wall member 22.

In assembling the extended surface heat exchanger of the present invention, a plurality of the U-shaped sections 40 are assembled in telescopic relation, as shown in Fig. 3. That is, the portion of the web 46 of one section is telescopcd over the portion 5% of the web 46 of the section in front thereof. in other words, the U-shaped sections 40 are assembled in stacked relation, alter which they are seam welded, as indicated at 6% Since one set of U-shaped members 4%, when so assembled, forms one sidewall and half of the top and bottom walls, a complementary set of sections is assembled to form the other sidewall and half of the top and bottom walls. The two subassemblies are then seam welded along the top and bottom, as indicated by numeral 62 in Fig. 1. Thereafter, the front wall member 20 and the rear wall member 22 are attached by seam welding, as indicated by numeral 64 to complete the heat exchanger assembly.

By reason of the fact the heat exchanger of the present invention has extended surface portions, or fins, on its interior and exterior surfaces, the overall size of the heat 0 exchanger can be materially reduced over that previously used for a given furnace capacity. Since in the assembled heat exchanger, the hot flue gases transfer heat directly to the internal fins, and since the internal fins are integral with the external fins, the heat transfer efiiciency of the heat exchanger is appreciably better than the prior heat exchangers wherein the fins were merely attached to a shell and it was, thus, necessary to transfer heat by conduction through the joint between the fin and the shell.

From the foregoing, it is apparent that the present invention results in the unique heat exchanger designed particularly for warm air furnaces having integrally finned interior and exterior surfaces. Moreover, by using a heat exchanger construction of the type set forth herein, the overall size of a heat exchanger for a given size furnace can be materially reduced over that required with a conventional type heat exchanger.

While the embodiment of the present invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted.

What is claimed is as follows:

1. A heat exchanger for warm air furnaces including,

a plurality of intermediate sheet metal sections constituting top, bottom and side walls of the heat exchanger, each intermediate section having integral internal and external extended surface portions and an interconnecting web portion, means uniting said intermediate sections to form the top, bottom and side walls of the heat exchanger, a rear sheet metal section attached to one of said intermediate sections having a pair of integral external extended surface portions and an interconnecting web, one of said ex ternal extended surface portions being arranged at an acute angle relative to said interconnecting web, a cupshaped rear wall having an edge portion complementary to the external extended surface portion of said rear section located at an acute angle to said interconnecting web and attached thereto, and a front wall connected to said intermediate sections, one of said walls having openings for the entrance and exit of hot flue gases.

2. A heat exchanger for warm air furnaces including, a plurality of intermediate sheet metal sections constituting top, bottom and side walls of the heat exchanger, each intermediate section having integral internal and external extended surface portions and an interconnecting web portion, means uniting said intermediate section to form the top, bottom and side walls of the heat exchanger, a front sheet metal section attached to one of said intermediate sections having integral internal and external extended surface portions and an interconnecting web, the external extended surface portion of said front section being arranged at an acute angle relative to its web, a rear sheet metal section attached to another of said intermediate sections having a pair of external extended surface portions and an interconnecting web, one of said external extended surface portions of said rear section being arranged at an acute angle relative to its web, and a pair of cup-shaped end walls having edge portions complementary to the external extended surface portions of said front and rear sections which are located at an acute angle relative to their respective Webs and secured thereto, one of said cup-shaped end walls having openings for the entrance and exit of hot flue gases.

References Cited in the file of this patent UNITED STATES PATENTS 501,109 Smead July 11, 1893 1,777,782 Bundy Oct. 7, 1930 1,913,019 Bluemel June 6, 1933 2,002,020 Nyborg May 21, 1935 2,028,298 Sucharski et a1 Jan. 21, 1936 2,045,657 Karmazin June 30, 1936 2,566,161 Brown Aug. 28, 1951 2,703,226 Simpelaar Mar. 1, 1955 FOREIGN PATENTS 324,654 France Sept. 22, 1902 999,598 France Oct. 3, 1951

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