US3183895A

US3183895A - Apparatus for heating water and similar fluids

Info

Publication number: US3183895A
Application number: US223104A
Authority: US
Inventors: Haag Franz
Original assignee: Junkers and Co GmbH
Current assignee: Junkers and Co GmbH
Priority date: 1961-09-14
Filing date: 1962-09-12
Publication date: 1965-05-18
Anticipated expiration: 1982-05-18
Also published as: GB942246A; DE1238180B; CH411288A

Description

F. HAAG May 18, 1965' APPARATUS FOR HEATING WATER AND SIMILAR FLUIDS Filed Sept. 12, 1962 2 Sheets-Sheet 1 lw szvro/ FPA/VZ MAG ff/7%- b/S Arrow/5y May 18, 1965 F. HAAG 3,183,895

APPARATUS FOR HEATING WATER AND SIMILAR FLUIDS Filed Sept. 12, 1962 2 Sheets-Sheet 2 R /0a I y A9016 f0 f0 4 fi mas w m g #4 '66 904 I /J& l\ I I.

\ I wll Imam-0,? FRANZ 6 446 714214.! f {"3421- 6/5 ArmPA/Ey United States Patent APPARATUS FGR HEATING WATER AND SIMELAR FLUIDS Franz Haag, Plochingen, Germany, assignor to Junkers 8: Co. G.m.b.H., Wernau (Neckar), Germany Filed Sept. 12, 1962, Ser. No. 223,104 Claims priority, application Germany, Sept. 14, 1961,

17 Claims. (Cl. 122-24) The present invention relates to apparatus for heating water and similar fluids, and more particularly to a Water heater which comprises one or more pulse jet or resonance duct burners. Still more particularly, the invention relates to an apparatus which heats water or a similar fluid while the fluid circulates in a suitable conduit or the like so that fresh quantities of fluid are being heated in a continuous operation as long as the burner or burners produce thermal energy. 7

It is already known to utilize pulse jet burners for heating of water and similar fluids. As a rule, the combustion chamber and/or the resonance duct of such heating apparatus is completely surrounded by a water-filled jacket. A serious drawback of such apparatus is that, due to very unsatisfactory distribution of specific thermal stresses, there is considerable wear caused by premature and excessive corrosion and, furthermore, such heating apparatus are diflicult to build and are too expensive to warrant their manufacture on a large scale.

Accordingly, it is an important object of my invention to provide a very simple, reliable, inexpensive and corrosion-resistant apparatus for heating water and similar fluids.

Another object of the invention is to provide an apparatus of the just outlined characteristics which is constructed and assembled in such a way that the distribution of thermal stresses to all of its component parts i more uniform than in conventional heaters which utilize pulse jet burners and of which I am aware at this time.

A further object of the instant invention is to provide a heating apparatus of the above described character which is easy to assemble and wherein, owing to uniform distribution of thermal stresses, the likelihood of rapid and excessive corrosion is much less pronounced than in conventional heaters utilizing one or more pulse jet burners.

An additional object of my invention is to provide an improved heat exchanger for use in heating apparatus of the above outlined characteristics.

A concomitant object of the invention is to provide an improved pulse jet burner with a built-in heat exchanger for use in heating apparatus for flowing or circulating water and similar fluids.

With the above objects in view, the invention resides in the provision of an apparatus for heating water and similar fluids which comprises at least one pulse jet burner having combustion chamber means provided with an inlet through which a combustible mixture may enter into and with an outlet through which products developing during pulsating combustion of such mixture are evacuated from the combustion chamber means, and resonance duct means communicating with the outlet so as to receive products of combustion from the combustion chamber means. The apparatus further comprises a heat exchanger including heat accumulating elements provided in the combustion chamber means and/ or in the resonance duct means so as to be heated by products of combustion, and fluid-containing conduit means having at least one portion located in such close proximity of the heat accumulating elements that the elements transmit heat to the fluid.

In accordance with a feature of my invention, the heat tion 4a thereof extends through the mantle and traverses accumulating elements are provided in the region of the outlet and occupy the entire cross-sectional area of the combustion chamber means and/ or of the resonance duct means, and the side faces of such elements are preferably parallel with the direction in which the products of combustion pass from the combustion chamber means to the resonance duct means.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following detailed description of certain specific embodiments with reference to the accompanying drawings, in which:

FIG. 1 is an axial section through the pulse jet burner of an apparatus which is assumed to be utilized for heating of water and which embodies one form of my invention according to which the fluid-containing conduit passes transversely across and through the combustion chamber and wherein the heat accumulating elements are arranged in a single group and are located in the interior and close to the outlet of the combustion chamber;

FIG. 2 is a similar axial section through the pulse jet burner of a modified heating apparatus wherein the heat accumulating elements are again located in the combustion chamber but whose fluid-containing conduit merely surrounds the burner without, however, passing through the combustion chamber; and

FIG. 3 is an axial section through a different heating apparatus which comprises a plurality of pulse jet burners and wherein the heat accumulating elements are provided in the resonance duct near to the outlet of the combustion chamber.

Referring now in greater detail to the drawings, and first to FIG. 1, there is shown an apparatus for heating water or a similar fluid which comprises a single pulse jet burner and a heat exchanger. The pulse jet burner comprises a combustion chamber 1 having an inlet 1a for admission of a combustible mixture which is formed in a pipe 2. The pipe receives oxygen or an oxygen-containing gas in a direction as indicated by the arrow 2a, and this pipe communicates with a pipe 3 which admits a gaseous, liquid or pulverulent fuel, e.g., a heating gas (arrow 3a). The products developing on combustion of the mixture admitted through the inlet 1a are evacuated through an outlet 1b and pass through a resonance duct 7 (arrows 5). The manner in which the inflammable mixture is ignited in the interior of the combustion chamber 1 is well known in the art and need not be described here.

The heat exchanger comprises a plurality of thin platelike heat accumulating elements 6 which are located in the interior of the combustion chamber 1 and which are immediately adjacent to the outlet 1b. The end faces of the elements 6 are secured to the mantle of the chamber 1 and their side faces are parallel with the direction (arrows 5) in which the products of combustion advance from the chamber 1 into and through the resonance duct 7. The heat exchanger further comprises a water-containing conduit 4 whose intake end 4' is connected to a suitable source of water (for example, a tank and a pump which causes water to flow through the conduit 4). The discharge end 4" of the conduit 4 leads hot water to radiators or to another locale of use. As shown, the conduit forms one or more convolutions 4b about the mantle of the combustion chamber 1 and an elongated straight porthe heat receiving elements 6 so that the latter may transmit heat to water flowing toward the discharge end 4". The conduit portion 4a preferably makes right angles with the direction (arrows 5) in which the products of combustion pass from the interior of the chamber 1 to the resonance duct '7. If necessary, the conduit 4 may comprise two or more portions which extend through the combustion chamber, depending on the temperature of products of combustion, on the material of the heat exchanger, on the heat storing capacity of the elements 6, and on the desired temperature of hot water. Spent liquid may be returned to the tank to be recirculated through the conduit 4 if necessary. The elements 6 preferably assume the form of thin, corrosion-resistant metallic laminations which are welded to the mantle of the combustion chamber. It will be noted that these elements are disposed in planes which are perpendicular to the axis of the conduit portion 4a.

1 have found that, in order to improve the thermal efiiciency of the heating apparatus, the combined crosssectional area of spaces or passages 6a between the heat accumulating elements 6 should be considerably less than the cross-sectional area of the chamber 1. For example, the combined cross-sectional area of the spaces 60: may be between 0.5 and 5 times the cross-sectional area of the resonance duct '7. It will be noted that the spaces 6a are spaced from each other transversely of the combustion chamber 1, i.e., substantially at right angles to the direction indicated by the arrow 5.

The heating apparatus of FIG. 1 operates as follows: Once the combustion of mixture admitted through the inlet la is started, the combustion continues in pulsating fashion and new quantities of combustible mixture are sucked continuously into the chamber 1. Hot products of combustion developing in the chamber 1 are caused to pass into and through the outlet 1a and through the resonance duct 7 to thereby heat the elements 6 which in turn transmit heat to the conduit portion 4aand to the fluid contained therein. The fluid is preheated while flowing in the coiled portion 4b of the conduit. All parts of the heating apparatus preferably consist of corrosionresistant material.

FIG. 2 illustrates a slightly different heating apparatus wherein the interior of the combustion chamber 1 accommodates a series of radially arranged heat accumulating elements 8 here shown as laminations which are secured to the mantle of the combustion chamber and/or to a centrally located bafile plate 9 which deflects products of combustion into segmental spaces between the adjacent elements. It will be noted that the upper end faces of the elements 8 are located in the general plane of the baffle plate 9. If desired, a second baifie plate 9' may be provided at the opposite end faces of the heat accumulating elements, and such second bafile plate is indicated in FIG. 2 in broken lines. If the products of combustion contain comparatively large quantities of soot or other solids, deposition of such solids on the baflle plate 9 may be avoided or kept within permissible limits by forming the underside of the plate 9 (as viewed in FIG. 2) with a conical face along which the products of combustion stream while advancing through the outlet 1]) and into the resonance duct 7. I

In the apparatus of FIG. 2, the water-containing con duit 104 does not extend through the burner but merely forms several (e.g., six or seven) closely adjacent convolutions 194a surrounding that portion of the combustion chamber 1 which contains the elements 8 so that the latter may transmit heat to water flowing toward the discharge end 104". The conduit 1G4 preferably forms one or more convolutions 1%!) which surround the remaining part of the chamber 1, i.e., that part which extends between the inlet la and the elements 8. The manner in which a combustible mixture is formed in the pipe 2 is the same as described in connection with FIG. 1. The intake end Hi4 of the conduit 104 receives water from a suitable source which is not shown in FIG. 2.

' Referring finally to FIG. 3, there i shown a different heating apparatus which comprises two pulse jet burners each having a combustion chamber 10 provided with an inlet Ida and an outlet 1%, a pipe 11 which communicates with a fuel-admitting pipe 12 and which conveys a combustible mixture to the respective inlet 10a, and a composite resonance duct 13 having a smaller-diameter portion 13a which is spaced from the respective chamber 19 and a larger-diameter portion 1317 which communicates with the respective outlet 19b.

The heat exchanger of this modified apparatus comprises heat accumulating elements 14a, 1412 which are dis posed in two groups each of which comprises parallel laminations mounted in the larger-diameter portions 13b of the respective resonance ducts 13 It will be noted that, analogously to the position of heat accumulating elements 6 and 8 in the apparatus of FIGS. 1 and 2, the elements 14a, 14b are located in the region of the outlets 19b, i.e., in Zones which are located in the general area where hot products of combustion pass from the respective chambers 10 into the associated resonance ducts 13.

The conduit 204 comprises an intake end 204 and thereupon passes at least once but preferably more than once through the larger-diameter portions 13b (see the conduit portions 264a) as well as through the heat accumulating elements 14a, 14b so that these elements may transmit heat to water which thereupon passes through convolutions 2M!) surrounding the mantles of the combustion chambers 19 prior to advancing through the discharge end 204" and to the locale of actual use.

It will be readily understood that the

laminations

6, 8, 14a, 14b may consist of corrugated stock and/or that the thickness of all such laminations need not be the same.

Owing to the fact that the heat accumulating elements occupy the entire cross-sectional area of the burner or burners, thermal stresses upon the heating apparatus of my invention are more uniform and the likelihood of corrosion is remote. Furthermore, the construction of apparatus of the type shown in FIGS. 1 to 3 is very simple so that such apparatus may be manufactured at reasonable cost. v

I have found that it is of considerable advantage if the resonance duct or ducts by themselves do not constitute component parts of the heat exchanger because, by utilizing a heat exchanger other than the resonance duct, the latter may be made of a greater variety of available materials. This is due to the fact that the temperatures prevailing in the resonance duct may be readily selected and regulated with a view to insure that they do not exceed temperatures which the material utilized in making of the resonance duct can safely withstand.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic and specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be Letters Patent is:

1. In an apparatus for heating water and similar fluids, in combination, at least one pulse jet burner including combustion chamber means having an inlet through which a combustible mixture may enter into and an outlet through which products developing during pulsating combustion of such mixture are evacuated from said chamber means, and resonance duct means communicating with said outlet so as to receive products of combustion from said chamber means; and a heat exchanger including heat accumulating elements provided in at least one of said means in the region of said outlet so as to be heated by products of combustion, said heat accumulating elements defining between themselves a plurality of passages spaced from each other transversely of said means and having a combined cross-sectional area which at most equals five secured by times the mean cross-sectional area of said resonance duct means, and fluid-containing conduit means having at least one portion located in such close proximity of said elements that the elements transmit heat to the fluid.

2. In an apparatus for heating water and similar fluids, in combination, at least one pulse jet burner including combustion chamber means having an inlet through which a combustible mixture may enter and an outlet through which products developing during pulsating combustion of such mixture may be evacuated from said combustion chamber means, and resonance duct means communicating with said outlet so as to receive products of combustion from said chamber means; and a heat exchanger including heat accumulating elements provided in at least one of said means in the region of said outlet and occupying substantially the entire cross-sectional area of said one means so to be heated by products of combustion, said heat accumulating elements defining between themselves a plurality of passages spaced from each other transversely of said means and having a combined crosssectional area which at most equals five times the mean cross-sectional area of said resonance duct means, and fluid-containing conduit means having at least one portion located in such close proximity of said elements that the elements transmit heat to the fluid.

3. In an apparatus for heating water and similar fluids, in combination, at least one pulse jet burner including combustion chamber means having an inlet through which a combustible mixture may enter and an outlet through which products developing during pulsating combustion of such mixture may be evacuated from said combustion chamber means, and resonance duct means communicating with said outlet so as to receive products of combustion from said chamber means; and a heat exchanger including a plurality of heat accumulating elements provided in said burner in the region of said outlet so as to be heated by products of combustion and occupying substantially the entire cross-sectional area of the burner, said heat accumulating elements defining between themselves a plurality of passages spaced from each other transversely of said means and having a combined crosssectional area at most equal to five times the mean crosssectional area of said resonance duct means, and fluidcontaining conduit means located in such close proximity of said elements that the elements transmit heat to the fluid, said conduit means having a portion extending through said burner and traversing at least some of said elements.

4. In an apparatus for heating water and similar fluids, in combination, at least one pulse jet burner including a combustion chamber having inlet means through which a combustible mixture may enter and outlet means through which products developing during pulsating combustion of such mixture are evacuated from said chamber, and a resonance duct communicating with said outlet means so as to receive products of combustion from said chamber; and a heat exchanger including a plurality of heat accumulating elements provided in said chamber near to said outlet means so as to be heated by products of combustion and occupying substantially the entire cross-sectional area of said chamber, said heat accumulating elements defining between themselves a plurality of passages spaced from each other transversely of said chamber and having a combined cross-sectional area which at most equals five times the mean cross-sectional area of said resonance duct, and fluid-containing conduit means having at least one portion located in such close proximity of said heat accumulating elements that the elements transmit heat to the fluid.

5. In an apparatus for heating Water and similar fluids, in combination, at least one pulse jet burner including a combustion chamber having inlet means through which a combustible mixture may enter and outlet means through which products developing during pulsating combustion of such mixture are evacuated from said chamber, and

a resonance duct communicating with said outlet means so as to receive products of combustion from said chamber; and a heat exchanger including a plurality of heat accumulating elements provided in said duct near to said outlet means so as to be heated by products of combustion and occupying substantially the entire cross-sectional area of said duct, said heat accumulating elements defining between themselves a plurality of passages spaced from each other transversely of said duct, and fluid-containing conduit means having at least one portion located in such close proximity of said heat accumulating elements that the elements transmit heat to the fluid.

6. In an apparatus for heating water and similar fluids, in combination, at least one pulse jet burner including combustion chamber means having an inlet through which a combustible mixture may enter and an outlet thnough which products developing during pulsating combustion of such mixture are evacuated from said combustion chamber means, and resonance duct means communicating with said outlet to receive products of combustion from said chamber means; and a heat exchanger includ ing a plurality of heat accumulating elements provided in at least one of said means in the region of said outlet so as to be heated by products of combustion and occupying substantially the entire cross-sectional area in the interior of said one means, said elements defining between themselves a plurality of passages spaced from each other transversely of said burner and the combined cross-sec tional area of said passages being at most equal to five times the mean cross-sectional area of said resonance duct means, and fluid-containing conduit means having at least one convolution surrounding said burner in such close proximity of said elements that the elements transmit heat to the fluid.

7. In an apparatus for heating water and similar fluids, in combination, at least one pulse jet burner including combustion chamber means having an inlet through which a combustible mixture may enter and an outlet through which products developing during pulsating combustion of such mixture are evacuated from said combustion chamber means, and resonance duct means communicating with said outlet to receive products of combustion from said chamber means; and a heat exchanger including a plurality of heat accumulating elements provided in at least one of said means so as to be heated by products of combustion and occupying substantially the entire cross-sectional area in the interior of said one means and in the proximity of said outlet means, said elements defining between themselves a plurality of passages spaced from each other transversely of said burner and the combined cross-sectional area of said passages being at most equal to five times the mean cross-sectional area of said resonance duct means, and fluid-containing conduit means having a plurality of convolutions surrounding said burner in such close proximity of said elements that the elements transmit heat to the fluid.

8. In an apparatus for heating water and similar fluids, in combination, at least one pulse jet burner including combustion chamber means having an inlet through which a combustible mixture may enter into and an Outlet through which products developing during pulsating combustion of such mixture are evacuated from said chamber means, and resonance duct means communicating with said outlet so as to receive products of combustion from said chamber means; and a heat exchanger including a plurality of closely adjacent but spaced heat accumulating laminations provided in at least one of said means in the region of said outlet so as to be heated by products of combustion, said laminations defining between themselves a plu rality of passages spaced from each other transversely of said burner and the combined cross-sectional area of said passages being at most equal to five times the mean cross-sectional area of said resonance duct means, and fluid-containing conduit means having at least one portion located in such close proximity of said laminations that the laminations transmit heat to the fluid.

9. In an apparatus for heating Water and similar fluids, in combination, at least one pulse jet burner including combustion chamber means having an inlet through which a combustible mixture may enter into an outlet through which products developing during pulsating combustion of such mixture may be evacuated from said chamber means, and resonance duct means communicating with said outlet so' as to receive products of combustion from said chamber means; and a heat exchanger including a plurality of adjacent but spaced heat accumulating laminations provided in at least one of said means in the region of said outlet so as to be heated by products of combustion, said laminations defining between themselves a plurality of passages spaced from each other transversely of said burner and the combined cross-sectional area of said passages being at most equal to five times the mean cross-sectional area of said resonance duct means, and fluid-containing conduit means having at least one portion extending through said one means and traversing at least some of said laminations so that the laminations transmit heat to the fluid.

10. In an apparatus for heating water and similar fluids, in combination, at least one pulse jet burner including combustion chamber means having an inlet through which a combustible mixture may enter into and an outlet through which products developing during pulsating combustion of such mixture may be evacuated from said chamber means, and resonance duct means communicating with said outlet so as to receive products of combustion from said chamber means; and a heat exchanger including a plurality or" adjacent but spaced heat accumulating laminations provided in at least one of said means in the region of said outlet so as to be heated by products of combustion, said l-aminations being parallel with each other and with the direction in which the products of combustion pass from said chamber means into said duct means and said laminations defining between themselves a plurality of passages spaced from each other transversely of said burner and having a combined cross-sectional area which at most equals five times the mean cross-sectional area of said resonance duct means and fluid-containing conduit means having at least one portion extending through said one means and traversing said laminations so that the laminations transmit heat to the fluid.

11. In an apparatus for heating water and similar fluids, in combination, at least one pulse jet burner including combustion chamber means having an inlet through which a combustible mixture may enter into and an outlet through which products developing during pulsating combustion of such mixture may be evacuated from saidchamber means, and resonance duct means communicating with said outlet so as to receive products of combustion from said chamber means; and a heat exchanger including a plurality of radially arrange-d substantially plate-like heat accumulating laminations provided in at least one of said means in the region of said outlet so as to be heated by products of combustion, said laminations defining be tween themselves a plurality of passages spaced from each other transversely of said burner and the combined crosssectional area of said passages being at most equal to five times the mean cross-sectional area of said resonance duct means, and fluid-containing conduit means having at least one portion located in such close proximity of said laminations that the laminations transmit heat to the fluid.

12. In an apparatus for heating water and similar fluids, in combination, at least one pulse jet burner including combustion chamber means having an inlet through which a combustible mixture may enter into and an outlet through which products developing during pulsating combustion of such mixture may be evacuated from said chamber means, and resonance duct means communicating with said outlet so as to receive products of cornbustion from said chamber means; and a heat exchanger including a plurality of adjacent but spaced heat accumu- 3 lating laminations provided in at least one of said means in the region of said outlet so as to be heated by products of combustion, said laminations defining between themselves a plurality of passages spaced from each other transversely of said burner and the combined cross-sec tional area of said passages being at most equal to five times the mean cross-sectional area of said resonance duct means, and fluid-containing conduit means having at least one substantially straight elongated portion extending through said one means and traversing said laminations so that the laminations transmit heat to the fluid, said elongated portion being substantially perpendicular to the direction in which products of combustion pass from said chamber means into said duct means.

13. A combustion as set forth in claim 12, wherein said laminations are disposed in planes substantially perpendicular to the longitudinal extension of said elongated portion.

14. In an apparatus for heating water and similar fluids, in combination, at least one pulse jet burner including a combustion chamber having inlet means through which a combustible mixture may enter and outlet means through which products developing during pulsating combustion of such mixture are evacuated from said chamber, and a resonance duct comprising a larger-diameter portion communicating with said outlet means to receive products of combustion from said chamber and a smaller-diameter portion communicating with and receiving products of combustion from said larger-diameter portion; and a heat exchanger including a plurality of heat accumulating elements located in and occupying substantially the entire cross-sectional area of said larger-diameter por tion in the region of said outlet means so as to be heated by products of combustion passing from said outlet means to said smaller-diameter portion, said elements defining between themselves a plurality of passages spaced from each other transversely of said burner and the combined cross-sectional area of said passages being at most equal to five times the mean cross-sectional area of said resonance duct means, and fluid-containing conduit means having at least one portion located in such close proximity of said heat accumulating elements that the elements transmit heat to the fluid.

15. A combination as set forth in claim 1, wherein the combined cross-sectional area of said passages is between 0.5-5 times the mean cross-sectional area of said resonance duct means.

16. In an apparatus for heating water and similar fluids, in combination, a plurality of pulse jet burners each including combustion chamber means having an inlet through which a combustible mixture may enter into and an outlet through which products developing during pulsating combustion of such mixture are evacuated from the respective chamber means, and resonance duct means communicating with the respective outlet for receiving products of combustion from the respective chamber means; and a heat exchanger comprising a plurality of heat accumulating elements located in at least one of said means in each of said burners in the region of the respective outlet so as to be heated by products of combustion passing from said chamber means to the respective duct means, said elements defining between themselves a plurality of passages spaced from each other transversely of the respective burner and the combined cross-sectional area of said passages being at most equal to five times the mean cross-sectional area of the respective resonance duct means, and fluid-containing conduit means having portions located in such close proximity of said heat accumulating elements in each of said burners that said elements transmit heat to the fluid.

17. A combination as set forth in claim 16, wherein said portions of the conduit means extend through said burners and traverse the respective heat accumulating elements.

(References on following page) References Cited by the Examiner UNITED STATES PATENTS Mcllvaine 122-24 Miller 122-367 Paris et a1. 122-24 McIlv-aine 158-4 Russell et a1 122-367 10 FOREIGN PATENTS 885,247 12/ 61 Great Britain.

ROBERT A. OLEARY, Primary Examiner.

FREDERICK L. MATTESON, IR, KENNETH W.

SPRAGUE, Examiners.

Claims

1. IN AN APPARATUS FOR HEATING WATER AND SIMILAR FLUIDS, IN COMBINATION, AT LEAST ONE PULSE JET BURNER INCLUDING COMBUSTION CHAMBER MEANS HAVING AN INLET THROUGH WHICH A COMBUSTIBLE MIXTURE MAY ENTER INTO AND AN OUTLET THROUGH WHICH PRODUCTS DEVELOPING DURING PULSATING COMBUSTION OF SUCH MIXTURE ARE EVACUATED FROM SAID CHAMBER MEANS, AND RESONANCE DUCT MEANS COMMUNICATING WITH SAID OUTLET SO AS TO RECEIVE PRODUCTS OF COMBUSTION FROM SAID CHAMBER MEANS; AND A HEAT EXCHANGER INCLUDING HEAT ACCUMULATING ELEMENTS PROVIDED IN AT LEAST ONE OF SAID MEANS IN THE REGION OF SAID OUTLET SO AS TO BE HEATED BY PRODUCTS OF COMBUSTION, SAID HEAT ACCUMULATING ELEMENTS