US3581494A

US3581494A - Exhaust gas manifold

Info

Publication number: US3581494A
Application number: US187A
Authority: US
Inventors: George E Scheitlin; Frank L Zagar
Original assignee: Arvin Industries Inc
Current assignee: Meritor Inc
Priority date: 1970-01-02
Filing date: 1970-01-02
Publication date: 1971-06-01
Anticipated expiration: 1988-06-01
Also published as: DE2033434A1; DE2033434B2; JPS5014284B1; GB1301377A; FR2074857A5

Abstract

An exhaust gas manifold for an internal combustion engine in which there is provided an outer shell having a plurality of port runners for connection to said engine and an outlet for connection to an exhaust pipe. An inner shell is carried within the outer shell to receive the exhaust gases from the engine and increase their dwell time by providing adequate volume for oxidation to occur within the manifold prior to permitting said gases to discharge through the outer shell outlet. Said inner shell is formed from sheet metal and comprises a plurality of slidably interconnected chambers in open communication with each other and the outlet. Each of said chambers is provided with an inlet conduit carried within one of the port runners and disposed in sealing engagement therewith. A compressible insulation is interposed between said outer and inner shells for thermally insulating said outer shell from the exhaust gases passing through said inner shell, and for conserving the thermal energy of the exhaust gases.

Description

United States Patent [72] lnventors George E. Scheitlin;

Frank L. Zagar, Columbus, Ind. [21] Appl. No. 187 [22] Filed Jan. 2, 1970 [45] Patented June 1, 1971 [73] Assignee Arvin Industries, Inc.

Columbus, 1nd. Continuation-impart of application Ser. No. 785,650, Dec. 20, 1968, now abandoned.

[54] EXHAUST GAS MANIFOLD 12 Claims, 8 Drawing Figs. [52] U.S. Cl 60/29, 181/40 [51] Int.Cl F011! 3/00 [50] Field of Search 60/29, 30; 181/40, 57, 62, 64.1, 36.3, 56, 63, 59; 23/277 (C), 2 (C) [56] References Cited UNITED STATES PATENTS 2,078,754 4/1937 Day 60/29 2,611,238 9/1952 Fryer.. 60/29 2,886,945 5/ 1959 Hofer 60/29 3,177,649 4/1965 TI'OmCi 60/29 3,413,803 12/1968 ROSCniUIld 60/29 FOREIGN PATENTS 673,277 6/1952 GreatBritain 60/29 Primary Examiner-Douglas Hart Att0rney-Trask, Jenkins & l-lanley ABSTRACT: An exhaust gas manifold for an internal combustion engine in which there is provided an outer shell having a plurality of port runners for connection to said engine and an outlet for connection to an exhaust pipe. An inner shell is carried within the outer shell to receive the exhaust gases from the engine and increase their dwell time by providing adequate volume for oxidation to occur within the manifold prior to permitting said gases to discharge through the outer shell outlet. Said inner shell is formed from sheet metal and comprises a plurality of slidably interconnected chambers in open communication with each other and the outlet. Each of said chambers is provided with an inlet conduit carried within one of the port runners and disposed in sealing engagement therewith. A compressible insulation is interposed between said outer and inner shells for thermally insulating said outer shell from the exhaust gases passing through said inner shell, and for conserving the thermal energy of the exhaust gases.

PATENTEUJUR H971 3,581,494

SHEET 1 0F 4 0.. m co N In m l m 9 ID 3 l N .31 I y I o INVENTORS m GEORGE E. SCHEITLIN I I I BY FRANK L. ZAGER x ,V,..,,, A1/ 2 v J ATTORNEYS PATENTEUJUN H97! 3,5 1,494

sum 2 or a IN VENTORS GEORGE E. SCHEITLIN .FRANK L. ZAGER 'PATENTEDJUN 1191: V 3581.494

- I sum 3 or .4

GEORGE E. SCHEITLIN I YJATTORNEYS i v "EU M v l 1 -v INVENTORS EXHAUST GAS MANIFOLD This application is a continuation-in-part application of our copending application Ser. No. 785,650, filed Dec. 20, 1968, now abandoned.

BACKGROUND OF THE INVENTION Internal combustion engines, particularly the internal combustion engines in motor vehicles, contribute a substantial amount of exhaust products to the atmosphere including substantial amounts of the oxides of nitrogen, hydrocarbons and carbon monoxide which are discharged from such engines in the exhaust gases. These pollutants when introduced into the atmosphere in sufficient quantities produce an atmospheric condition referred to as air pollution.

Exhaust manifold gas temperatures will vary from 600 F. to over l,800 F. depending upon where temperatures are measured and engine-operating conditions. If the exhaust gases are permitted to be retained in the manifold at the higher temperatures for a relatively short period of time, and mixed homogeneously with air, the unburned hydrocarbons and carbon monoxide in the exhaust gases will be oxidized to thus reduce the amount of such pollutants that are discharged from the manifold. However, with the manifold designs heretofore employed, the exhaust gas temperature is reduced rapidly by radiation to the cold walls of the exhaust ports and manifold chamber.

The presentinvention provides a means of retaining the higher sensible exhaust gas temperatures and for increasing the dwell time of the gases in the manifold thereby providing homogeneous mixing of the exhaust and air while at the same time providing a lightweight manifold construction which will be able to withstand its inherent expansion and contraction due to the elevated temperatures caused by the oxidation of the smog-producing pollutants within the manifold.

SUMMARY OF THE INVENTION In accordance with one form of the invention, there is provided a manifold formed from sheet metal inner and outer shells; Said outer shell comprises an elongated casing having a pair of end caps at its opposite ends. One of said end caps is provided with an outlet duct adapted to be connected to an exhaust pipe. A plurality of port runners are secured to the outer shell casing along the length thereof and are adapted to be connected to the exhaust ports of an internal combustion engine.

The inner shell comprises aligned end chambers and a plurality of intermediate chambers carried within said outer shell and spaced therefrom. Each of said chambers has an inlet conduit carried within one of the port runners and disposed in sealing engagement therewith. Each of said chambers also has an outwardly projecting nipple, with the nipples on all but one of the end chambers being slidably fit into the next adjacent chamber and the nipple on that one end chamber being slidably carried in the outlet duct of said outer shell. In this manner, the chambers are in open communication with each other and with the outlet of the outer casing. This causes the flow of exhaust gases from the inlet conduits to the outlet to be disrupted and thereby increases the dwell time of said gases in the inner shell so that the noxious pollutants will be oxidized.

A compressible insulation is interposed between said chambers and between said chambers and the outer shell. Said insulation, the inlet conduits, and the nipple on said one end chamber suspend the inner shell within the outer shell so that said inner shell is free to expand and contract with respect to the outer shell, the sliding interfit between said chambers also permitting them to move with respect to each other during expansion and contraction.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings illustrate the invention. In such drawings:

FIG. 1 is a longitudinal section through a manifold embodying the invention;

FIG. 2 is a transverse section taken on the line 2-2 of FIG.

FIG. 3 is a longitudinal section showing a modified form of the invention;

FIG. 4 is a transverse section taken on the line 4-4 of FIG.

FIG. 5 is a longitudinal section showing another modified form of the invention;

FIG. 6 is a transverse section taken on the line 6-6 of FIG.

FIG. 7 is a longitudinal section showing another modified form of the invention; and

FIG. 8 is a transverse section taken on the line 8-8 of FIG. 7.

In the embodiment shown in FIG. 1, the manifold comprises an outer shell 10 and inner shell I2 formed from sheet metal. Said outer shell comprises an elongated casing 11 closed at its ends by a pair of

end caps

13 and 14 secured thereto, as by welds 15. Conveniently, if desired, said end caps can be connected to the casing by rolled lock seams. The end cap 14 is provided with an opening 16 to which an outwardly projecting outlet duct 17 is welded. The outer end of the duct I7 is connected, as by welding, to a flange 18 adapted to be connected to an exhaust pipe.

As shown, a plurality of longitudinally spaced port runners project outwardly from the casing 11. Each of said port runnets is identical in construction and comprises an inlet duct 20 welded to the casing, as at 21, and having its outer end welded, as at 22, to a flange 24 adapted to be rigidly connected to one of the exhaust ports of an internal combustion engine.

The inner shell 12 is spaced from the outer shell 10 and comprises a plurality of aligned chambers, desirably, one chamber for each port runner. Thus, in the embodiment shown in FIG. 1, there is provided a pair of

end chambers

26 and 27 interconnected by a pair of

intermediate chambers

28 and 29. Each of the chambers comprises an annular sidewall 30 formed in any desired manner and having a pair of

end caps

31 and 32 connected thereto, as by a rolled lock seam 33. As shown, the

end walls

31 and 32 are convex to prevent oilcanning" with the adjacent end walls on adjacent chambers being disposed in longitudinally spaced relation to each other. The end cap 32 on each of the chambers has an opening 35 formed therein, and a longitudinally extending nipple 36 bindingly staked to the end cap 32 around said opening projects outwardly therefrom. The end caps 31 of chambers 27- 29 are provided with openings 38 for the reception of the nipple 36 on the next adjacent chamber, said nipples being slidably received in said openings to thus permit the chambers to be longitudinally movable with respect to each other. As shown in FIG. I, the nipple 36 on chamber 27 which forms the outlet for the inner shell projects outwardly through the outlet duct 17 and is slidably received in the flange 13. Thus, the chambers 2627 are in open communication with each other and are slidably interconnected to each other.

As shown in FIG. 2, each of the chamber sidewalls 30 is provided with a longitudinally centered opening 42 to which the inner end of an inlet conduit 43 is bindingly staked, as at 45. Each of the inlet conduits 43 projects outwardly through an opening 46 in the outer shell casing 10 and through one of the inlet ducts 20. The inlet conduits'43 are in spaced relation to the ducts 20 throughout the major portion of their lengths but are disposed in fixed sealing engagement with the port runner flanges 24 adjacent their outer ends.

A compressible thermal insulating material 48 is interposed between the inner and outer shells It) and 12 and between the adjacent chambers 2629. Said insulating material is also interposed between the inlet ducts 20 and their associated inlet conduits 43 but the sealing engagement between said ducts and runners prevents any of the gas from contacting the insulation. In this manner, the temperature within the inner shell may reach a range of l,200 F.2,000 F., a temperature sufficient to oxidize the smog-producing pollutants, while the outer shell is maintained at a temperature in the range of 700 F. l ,000" F.

In operation, the exhaust gases along with the air introduced near the exhaust valves (not shown) enter the inner shell chambers 26-29 through the inlet conduits 43. Because of the chambered construction of the inner shell, the turbulence of the exhaust gases and the air introduced at the exhaust valves will be increased providing further mixing. Further, the chambered configuration of the inner shell increases the dwell time of the exhaust gases and air in the inner shell. This homogeneous mixing and increased dwell time results in the unburned pollutants being subjected to elevated temperatures for a longer time allowing the oxidation reaction to more nearly approach completion prior to their discharge from the manifold. During such oxidation, the temperature of the exhaust gas will increase because of the conservation of heat by the insulation causing the inner sheet metal shell to expand. However, the inlet conduits 43, the nipple 36 on the chamber 27, and the insulation 48 suspend the inner shell within the outer, and with the sliding interfit between the chambers, the inner shell can expand and contract without any distortion of the manifold.

The embodiment shown in FIGS. 3 and 4 differs from the embodiment shown in FIGS. 1 and 2 in that the outer shell is formed as a metal casting. As shown, said outer shell comprises an elongated casing 11 closed at one of its ends at 13' and at its opposite ends at 14. An outlet duct 17' projects outwardly from an opening 16 in the end wall 14 and is connected at its outer end to a flange 18 adapted to serve as a connector to an exhaust pipe. A plurality of port runners in the form of outwardly projecting inlet ducts 20' are longitudinally spaced along the shell 10' with the outer end of each of said ducts being connected to a flange 24' adapted to be secured to the exhaust port of an engine.

The chambers 26'--29 of the inner shell 12' are constructed in the same manner as the chambers 26-29, with the nipples 36' on chambers 26, 28', and 29' providing a sliding interfit between the various chambers and the nipple 36' on chamber 27 providing a sliding interfit with the outlet duct 17'. As with the embodiment shown in FIGS. 1 and 2, each of the inner shell chambers is provided with an inlet conduit 43' which is carried in one of the inlet ducts 20'. In the embodiment shown in FIG. 4, each of the inlet conduits 43 is provided with a series of axially spaced corrugations 52 bindingly retained against the inner wall of the associated inlet duct 20'. Said corrugations form seals between the inlet ducts and conduits to prevent the exhaust gases from coming in contact with the compressible insulation 48' interposed between the inner and outer shells 10 and 12'.

The embodiment shown in FIGS. 5 and 6 differs from the embodiment shown in FIGS. 14 in that the inner shell 112 is formed from a plurality of aligned sections defining chambers which are not separated by any partitioning walls. While this embodiment is shown as employing a sheet metal outer shell like the embodiment shown in FIGS. 1 and 2, it is to be understood, of course, that the outer shell can be formed as a metal casting like the embodiment shown in FIGS. 3 and 4.

As shown in FIGS. 5 and 6, the outer shell 110 comprises an elongated casing 111 closed at its ends by a pair of

end caps

113 and 114 fixedly secured thereto, as by welding or rolled locked seams. The end cap 114 is provided with an opening 116 to which an outwardly projecting outlet duct 117 is connected. The outer end of the duct 117 is connected to a flange 118 adapted to be connected to an exhaust pipe.

A plurality of longitudinally spaced port runners project outwardly from the casing. As shown in FIGS. 6, each of said runners is identical in construction and comprises an inlet duct 120 welded, as at 121, to the casing 111 and having its outer end welded, as at 122, to a flange 124 adapted to be rigidly connected to one of the exhaust ports of an internal combustion engine.

The inner shell 112 is spaced from the outer shell 110 and comprises a plurality of aligned sections forming chambers associated with each of the port runners. Thus, in the embodiment shown in FIG. 5, where four port runners are provided, there is provided a pair of

end chambers

126 and 127 interconnected by a pair of

intermediate chambers

128 and 129. Each of said chambers or sections comprises an annular sidewall 130 formed in any desired manner. As shown, the sidewalls of the

chambers

126 and 127 have

end walls

131 and 132 connected thereto, as by a rolled lock seam 133. The

end walls

131 and 132 enclose the ends of the inner shell 112, and are convex to prevent oil-canning."

The sleeve 130 of chamber 126 has its end remote from the end cap 131 deformed slightly inwardly, as at 134. An annular flange 135 is secured around the outer face of the sleeve 130 within the axial extent of the deformation 134. As shown, said deformation and flange define an annular channel 136 in which the adjacent end of the sleeve 130 for chamber 128 is slidably supported. In a like manner, one end of the sleeves for each of

chambers

128 and 129 is deformed inwardly, as at 134 and 134", and

flanges

135 and 135" are mounted on said sleeves within the axial extents of said deformations to define annular channels 136' and 136". In this manner, the channel 136' slidably receives the sleeve 130 for chamber 129, and the channel 136" slidably receives the sleeves 130 for chamber 127. Thus, the chambers are longitudinally movable with respect to each other and with respect to the outer shell to permit the inner shell to expand and contract as it is heated and cooled. As shown, the ends of

flanges

134, 134, and 134" may be bent slightly inwardly to prevent any pinching between the sliding interfits between the chambers.

The end cap 132 has an opening 138, and a nipple 139 is mounted on said end cap at said opening to project outwardly therefrom and define an outlet for the inner shell. The nipple 139 projects outwardly through the outlet duct 117 is spaced relation thereto and is slidably received in the flange 118.

As shown in FIG. 6, each of the chamber sidewalls 130 is provided with a longitudinally centered opening 142 to which the inner end of an inlet conduit 143 is rigidly staked, as at 145. Each of the conduits 143projects outwardly through an opening 146 in the outer shell casing and through one of the inlet ducts 120. The conduits 143 are in spaced relation to the ducts throughout the major portions of their lengths, but are disposed in fixed sealing engagement with the port runner flanges 124 adjacent their outer ends.

A compressible thermal insulating material 148 is interposed between the

shells

110 and 112 and between the inlet duct 120 and their associated inlet conduits 143. By being compressible, the insulation supports the inner shell within the outer shell in a manner such that it is free to expand and contract while still providing an insulating barrier between the two shells.

In the embodiment shown in FIGS. 5 and 6, the exhaust gases, and any air mixed therewith, will be introduced into the inner shell 112 as a turbulent mass. Upon entering the inner shell, the exhaust gases will be oxidized under the high-temperature conditions previously described with the insulation 148 conserving the heat within the inner shell. As the inner shell becomes heated due to the hot exhaust gases, it will expand with the chamber sidewalls sliding in their

respective channels

136, 136' and 136". The inlet conduits 143, nipple 139 and insulation 148 suspend the inner shell within the outer shell so that the inner shell is free to expand and contract at the sliding interconnections of several chambers without distorting the outer shell 110.

In the embodiment shown in FIGS. 7 and 8, the inner shell 212 is formed from a plurality of aligned sections defining chambers which are not separated by any partitioning walls. The outer shell 210, like the outer shell 10, is formed as a metal casting. As shown, said outer shell comprises an elongated casing 211 closed at its ends, as at 213 and 214. In this embodiment, the outlet duct 217 projects outwardly from an opening 216 in the casing 211 intermediate the length of said casing. The outer end of the duct 217 is connected to a flange 218 adapted to serve as a connector to an exhaust pipe. A plurality of port runners in the form of outwardly projecting inlet ducts 220 are longitudinally spaced along the shell 210 with the outer end of each of said ducts being connected to a flange v 224 adapted to be secured to the exhaust port of an engine. As

shown, one of the inlet ducts 220 is disposed in transverse alignment with the outlet duct 2l7.

The inner shell 212, which as in the case of the other embodiments, is formed from sheet metal, is spaced from the outer shell 210 and comprises a plurality of aligned sections forming chambers associated with each of the port runners. Thus, as shown in FIG. 7, where four port runners are provided, there is provided a pair of

end chambers

226 and 227 interconnected by a pair of

intermediate chambers

228 and 229. Each of said chambers comprises an annular sidewall or sleeve 230 formed in any desired manner. The sidewalls of

chambers

226 and 227 have

convex end walls

231 and 232 mounted thereon, as by a rolled lock seam 233.

As shown, one end of each of the sleeves 230 of

chambers

226, 228 and 229 is deformed slightly outwardly, as at 234, and the adjacent end of the next adjacent sleeve is slidably carried in the offset 234 to thus permit the chambers to be longitudinally movable with respect to each other and with respect to the outer shell 210, thereby permitting the inner shell to expand and contract as it is heated and cooled. Conversely, one end of one of the sleeves 230 in each interfitting pair could be offset inwardly to provide a sliding interfit between adjacent members.

As shown in FIG. 8, an outlet conduit 239 extends outwardly from an opening 238 in the sidewall 230 for chamber 229. Conveniently, the inner end of the outlet duct 239 is staked, as at 240, around the opening 238 with the outer portion of said outlet duct being disposed in slidable sealing engagement with the outlet duct 217, as by corrugations 241 formed in said duct.

As shown in FIG. 8, each of the sidewalls 230 is provided with a longitudinally centered opening 242 to which the inner end of an inlet conduit 243 is rigidly staked, as at 245. Each of the conduits 243 projects outwardly through one of the inlet ducts 220 and is disposed in sealing engagement therewith as by the corrugations 252.

As shown, the inner and

outer shells

212 and 210 are disposed in spaced relation to each other throughout substantially their entire extent. Thus, the space between said shells defines an insulating barrier of air and further permits the inner shell to freely expand and contract with respect to the outer shell. As with the other embodiments of the invention, the sliding fit between the adjacent chambers of the inner shell permits said inner shell to freely expand and contract due to temperature changes.

While the invention has been described as employing a manifold having a single outlet and four inlets, it is to be understood, of course, that any number of such inlets or outlets can be employed without departing from the spirit and scope of the invention with such inlets and outlets being disposed in any desired location on the manifold. However, in each embodiment of the invention, there is provided means between adjacent pairs of base inlets to permit the inner shell to expand and contract with respect to the outer shell. It should also be noted that while rolled lock seams have been shown as being employed in the hot areas of the inner shell, this is merely a preferred construction. Weld joints may be substituted for such seams, but such weld joints are subjected to oxidation by reason of the high-temperature environment.

We claim:

1. An exhaust manifold for an internal combustion engine, comprising an outer shell having an outwardly projecting outlet, a plurality of outwardly projecting port runners fixedly connected to said outer shell and adapted to be fixedly connected to said engine, and inner shell comprising a plurality of aligned chambers carried in said outer shell, each of said chambers being slidably interconnected to the next adjacent chamber and in open communication with each other, one of said chambers having an outwardly projecting outlet carried in the outer shell outlet and slidable with respect to said outer shell outlet, and a plurality of inlet conduits carried in said port runners and operatively connected to said chambers in open communication therewith,

2. The invention as set forth in claim I in which said chambers are spaced from the inner face of the outer shell and said inlet conduits are in sealing engagement with said port runners, and an insulating barrier is interposed between said inner and outer shells.

3. An exhaust gas manifold for an internal combustion engine, comprising an outer shell having an outlet, a plurality of port runners fixedly connected to said outer shell and adapted to be fixedly connected to said engine, an inner shell carried in said outer shell comprising aligned first and second end chambers and at least one intermediate chamber, each chamber having a sidewall and a pair of end walls, an outwardly projecting nipple fixedly mounted on said chambers, said first and intermediate chambers having openings formed therein for slidably receiving the nipple on the next adjacent chamber, the nipple on said first chamber being slidably carried in the outer shell outlet, and a plurality of inlet conduits carried in said port runners and operatively connected to said chambers in open communication therewith.

4. The inventionas set forth in claim 3 in which said end walls are convex.

5. The invention as set forth in claim 3 in which said chambers are spaced from the inner face of the outer shell, the end walls on adjacent chambers are spaced from each other, the inlet conduits are in sealing engagement with the port runners, and an insulating barrier is interposed between adjacent chambers and between said chambers and outer shell.

6. The invention as set forth in claim 3 in which said chambers are formed from sheet metal with said end walls and inlet conduits being bindingly connected to the chamber sidewalls and said nipples being bindingly connected to one of said end walls on said chambers.

7. The invention as set forth in claim 1 in which said chambers are formed from sheet metal and the outer end walls of the outermost ones of said chambers are convex.

8. The invention as set forth in claim 1 in which said inner and outer shells are formed from sheet metal and said outer shell comprises a casing, a pair of end caps are connected to the ends of said casing with one of said end caps having an o ening formed therein, an outlet conduit is connected to said one end cap at said opening, said casing having a plurality of openings formed therein, and a plurality of conduits are connected to said casing at said plurality of openings to form said port runners.

9. The invention as set forth in claim 1 in which said chambers are formed from sheet metal and said outer shell is formed from a metal casting, said casting having a plurality of ducts projecting outwardly therefrom to form said port runners, and insulating barrier is interposed between said inner and outer shells, and said inlet conduits are carried in said ducts in sealing engagement therewith.

10. An exhaust manifold for an internal combustion engine, comprising an outer shell having an outwardly projecting outlet and a plurality of outwardly projecting inlets, and inner shell carried within said outer shell and having an outwardly projecting outlet carried in and slidable with respect to said outer shell outlet and having a plurality of outwardly projecting inlets carried within said outer shell inlets, said inner shell being spaced from said outer shell throughout substantially their entire extents whereby said inner shell is expandable and contractable with respect to said outer shell, and means in said inner shell for disrupting the flow of gas from its inlets to its outlet.

11. The invention as set forth in claim 10 in which said means for disrupting the flow of gas are disposed along said inner shell on opposite sides of each of said inlets in said inner shell.

12. The invention as set forth in claim 10 in which said inlets on said inner and outer shells are in sealing engagement with each other at their ends remote from said shells, and a layer of insulation is interposed between said inner and outer shells including their inlets.

gg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,581,494 Dated June 1, 1971 Inventor) George E. Scheitlin and Frank L. Zagar It is certified that error appears in the aboveidentified patent and that said Letters Patent are hereby corrected as shown below:

Col. 4, line 31 "is" change to ---in--.

C01. 5, line 55, "base" change to --gas--.

Line 61, "high-temperature" change to -high temperature Signed and sealed this 28th day of December 1 971 (SEAL) Attest:

EDWARD M-FLETCHER, JR. ROBERT GOTTSCHALK Attesting Officer Acting Commissioner of Patents

Claims

1. An exhaust manifold for an internal combustion engine, comprising an outer shell having an outwardly projecting outlet, a plurality of outwardly projecting port runners fixedly connected to said outer shell and adapted to be fixedly connected to said engine, and inner shell comprising a plurality of aligned chambers carried in said outer shell, each of said chambers being slidably interconnected to the next adjacent chamber and in open communication with each other, one of said chambers having an outwardly projecting outlet carried in the outer shell outlet and slidable with respect to said outer shell outlet, and a plurality of inlet conduits carried in said port runners and operatively connected to said chambers in open communication therewith.

2. The invention as set forth in claim 1 in which said chambers are spaced from the inner face of the outer shell and said inlet conduits are in sealing engagement with said port runners, and an insulating barrier is interposed between said inner and outer shells.

4. The invention as set forth in claim 3 in which said end walls are convex.

8. The invention as set forth in claim 1 in which said inner and outer shells are formed from sheet metal and said outer shell comprises a casing, a pair of end caps are connected to the ends of said casing with one of said end caps having an opening formed therein, an outlet conduit is connected to said one end cap at said opening, said casing having a plurality of openings formed therein, and a plurality of conduits are connected to said casing at said plurality of openings to form said port runners.