US2543201A - Circular radiator air heating furnace with spiral air baffles - Google Patents

Description

Feb. 27, 1951 R. w. RIFLEY CIRCULAR RADIATOR AIR HEATING FURNACE WITH SPIRAL AIR BAFFLES 3 Sheets-Sheet 1 Filed April 12 1948 JNVEN TOR. Ray W. EAif/ey ATTORNEYS Feb. 27, 1951 w R|FLEY 2,543,201

CIRCULAR RADIATOR AIR HEATING FURNACE WITH SPIRAL AIR BAFFLES Filed April 12, 1948 3 Sheets-Sheet 2 INVEN TOR. Ray W Rif/ey aw c/ W ATTORNEYS Feb. 27 R. w RlFLEY I CIRCULAR RADIATOR AIR HEATING FURNACE WITH SPIRAL AIR BAFFLES Filed April 12, 1948 3 Sheets-Sheet 3 INVENTOR. y W Rl'fley ATTORNEYS Patented Feb. 27, 1951 CIRCULAR RADIATOR AIR HEATING FUR- NACE WITH SPIRAL A'IR'BAFFLES Ray W. Riiley, Denver, (1010.; Florence Ross Rifley, administratrix of said Ray W. Rifley, deceased, assignor, by mesne assignments, to Florence Ross Rifley, Denver, Colo.

Application April 12, 1948, Serial No. 20,391

13 Claims. (Cl. 126-110) This invention relates to furnace constructions, and more particularly to a warm or hot air furnace.

Because of its quick response to changing weather conditions, and the normally w first cost and cost of installation of auxiliary equipment, such as .air ducts and radiators, the warm or hot air furnace has .achieved wide popularity in many sections of the United States, particularly for use in smaller homes and buildings of one or two stories in height. In a conventional construction, such a furnace includes a central combustion chamber, usually disposed vertically, in which the fuel is burned. This fuel may be natural or artificial gas, fuel oil or similar petroleum product, or .coal. When coal is utilized as the fuel, an automatically controlled stoker arrangement is usually found to be more satisfactory than hand firing. In such a furnace con struction, the upper end of the combustion chamber is closed, with the hot gases passing laterally through a flue connected to the .combustion chamber at a point adjacent the upper end. ,An air heating space is formed around the combustion chamber by a shell which encloses the combustion chamber and is spaced laterally therefrom and also at the top, the space between the top of the combustion chamber and the top of the shell forming a plenum or an air mixing and distributing space, the ducts for carrying the heated air to the desired points of distribution being connected to the plenum. The combustion chamber and shell may, of course, be round, square or rectangular, and with each a plenum or distributing space at the top. Cool or cold air :to be heated is supplied at one or more points about the periphery of the air heating space, adjacent the bottom thereof.

Certain improvements have been made in the construction of warm or hot air furnaces, but these improvements have been directed primarily to increasing the efliciency of combustion, or improving the path of travel of combustion gases. One such improvement is that of the Lennox furnace, wherein a radiation unit or annular enclosure for the combustion gases is disposed concentrically and in spaced relation to a cylin- .drical, vertical combustion chamber. The combustion gases, resulting from the combustion of either gas or oil, pass upwardly in the combustion chamber, then through a short connecting flue at one side to-the annular enclosure, thence around both sides of the annular enclosure, for

exhaust through a flue leading outwardly from the annular enclosure at the opposite side from the connecting flue. In such construction, the connecting flue between the combustion cham-- her and the annular enclosure is trapezoidal in cross section, with the narrow end at the top, to proportion more equally the amount of gases flowing through the annular enclosure. Despite such improvements, there is still room for improvementin warm and hot air furnaces, occasioned primarily by the tendency toward uneven heating .of the air, and the resulting differences in temperature between various parts of the plenum space. As a result .of such temperature diiferences, one duct may receive a greater amount of air at a considerable different temperature than the air received by other .ducts. Also, when the average temperature of the flue gases is raised, in order that a minimum temperatureof hot air passing'to the ducts may be produced, the maximum temperature of the air passing to other ducts may approach a danger point, While the higher temperature of the .flue gases alsomay approach the danger point. In addition, the higher the temperature of the flue gases, the less the amount of heat transferred to the air, and

' the lower the efficiency of operation of the furnace.

Among'the objectsof the present invention are toprovide an improved furnace of the hot or Warm air type; 'to provide sucha furnace in which a more even distribution of air to be heated in :the heating spaces is obtained; to provide such a furnace in which the temperature of various portions of the air being heated are more nearly the same; to provide such a furnace in which a more uniform temperature of the heated air in the plenum or distributing space is obtained; toprovidesuch a furnace wherein theflue gas temperature may be reduced without a reduction in the minimum temperature of the heated air supplied to any single duct; to provide such a furnace which will be more efiicient in operation. and particularly more efficient in the transfer of heat to the air being heated; and to provide such a furnace wherein the improvements are relatively simple and inexpensive.

Other objects and the novel features of this invention will become apparent from the description which follows, taken in connection with the accompanying drawings, in which:

Fig. 1 is a perspective View, with certain parts broken away to show the interior construction, of a hot air furnace constructed in accordance with this invention;

Fig. ,2 is a vertical .cross section through the heating portion of the furnace of Fig. 1;

Fig. 3 is a partial vertical section taken along line 3-3 of Fig. 2;

Fig. 4; is a partial vertical section taken along line 4- of Fig. 2;

Fig. 5 is a horizontal cross section taken along line EI-5 of Fig. 2; and

Fig. 6 is a vertical section similar to Fig. 2, but illustrating an alternative embodiment of this invention.

As illustrated in Fig. 1, the principles of this invention may be applied to a hot air furnace of a type which may operate on either oil or gas as fuel and which includes an outer shell or casing S, into the top of which an air intake duct or ducts (not shown) delivers air for passage through a pair of angularly disposed filters ill. The air passes downwardly to the intake of a blower B, driven in a suitable manner, as by a motor H, the air passing from an air space A within shell S, provided by a partition I2, to casing i3 of the blower B. Rotor i l of the blower B forces the air into a heating space H on the opposite side of the partition l2. Disposed centrally in the heating space H is a combustion chamber 15, in the lower end of which is installed a burner unit U to which fuel, such as gas, may be supplied through a gas pipe [3. The burner unit U is conventional in construction, the hot gases of combustion passing upwardly in the combustion chamber 15, and, as in Fig. 2, then at one side to an annular enclosure 11, having vertical inner and outer walls I8 and I8, respectively. The hot gases pass around both sides of the annular enclosure I1 to a flue 19 on the opposite side thereof, from which the hot gases are exhausted to the stack or chimney.

The heating space H may be substantially rectangular at its lower end, with the upper end formed by a cylindrical shell 20, disposed concentrically and in spaced relation to the annular enclosure [1. A transverse partition 21 may extend from the lower end of shell across to the outer shell S and the partition l2, so as to force the air delivered by blower B to flow within the confines of shell 20, and upwardly through a space 23 between combustion chamber [5 and annular enclosure [1, and also through a space 24 between annular enclosure l1 and the shell 28. The outlet of the blower B may open directly into the heating space H, as in Fig. l,

or the blower may be connected by a duct 25, as in Fig. 2, with the heating space H.

In accordance with this invention, in order to force the air flowing upwardly around the combustion chamber to follow a circuitous path through the spaces 23 and 24, and preferably such a path that each portion of the air passes entirely around the combustion chamber, i. e. approximately 360, a plurality of baffles 26, 21, 2 3, 29 and 30, respectively, extend spirally between the exterior of combustion chamber I5 and the inner wall I8 of annular enclosure 11. Similarly, a series of baflles 3|, 32, 33, 34 and 35, respectively, extend spirally in space 24, between shell 20 and the outer wall [8 of annular enclosure I,1. As in Figs. 2 and 5, the lower ends of the baflies 25 to inclusive, and also the baffles 3| to 35, inclusive, are spaced equidistantly, and each bafile preferably extends for about 360, i. e. makes one complete revolution between the lower end of annular enclosure l1 and the upper end thereof. The baffles 26 to 30, inclusive, and 31 to 35, inclusive, may extend spirally upwardly in the same direction, although the direction of the battles in space 26 may be the 4 reverse of that of the bafiles in space 23, such as shown in Fig. 6, described in detail later.

In further accordance with this invention, the combustion chamber l5 and the annular enclosure H are connected by a pair of flues 36 and 31, respectively, flue 33 being a smaller flue disposed in an upper position, and flue 31 being a larger flue disposed in a lower position. The difference in the size of the flues 36 and 31 tends to equalize the flow of hot gases from combustion chamber [5 to the interior of enclosure [1, since the hot gases naturally tend to rise and pass through the upper flue, but the lower flue 31 being larger, causes a more nearly equal proportion of the hot gases to flow to the lower portion of the annular enclosure l1. As in Fig. 5, the hot gases flow from flues 33 and 31 around each side of the annular enclosure l1, as indicated by arrows 38, and thence to stack flue 19.

In further accordance with this invention, the baffles 26 to 30, inclusive, and 31 to 35, inclusive, are so disposed and spaced that one of the baffles intersects each of the flues I9, 36 and 31, respectively, so that the flues provide a minimum of resistance to flow of air being heated along the spiral paths provided between the baffles. Thus, as in Figs. 2 and 3, the lower end of bafile 28 is disposed beneath lower flue 31, while the next baffle 21 intersects flue 31, preferably substantially centrally thereof so that one half of the flue 31 will be in the spiral passageway beneath baffle 21 and the other half in the spiral passageway above baffle 21. Bafiles 28 and 29 are so disposed that they intersect neither flue 36 nor flue 31, while baffle 33 intersects upper flue 36, preferably centrally. Also, the upper end of baffle 26, after completing a complete revolution, is disposed above flue 3B. As in Figs. 2 and 4, flue I9 is intersected centrally by bafiie 34, with baffle 33 passing below and baflie 35 passing above flue l9. Preferably flues I9, 36 and 31 are cylindrical or tubular, for ease in construction, although oval, elliptical or other cross-sectional shapes may be utilized. As is evident from Figs. 2 to 5, inclusive,

each set of baffles is shown as being five in number, but any other desired number may be used.

The air passing through the spiral passageway defined by each bafiie and the next adjacent baffle, preferably passes completely around the combustion chamber 15 or the annular enclosure l1, so that heat will be transferred on all sides to each portion of the air. This feature is of importance in equalizing the transfer of heat to the air, and in maintaining a more uniform temperature of each portion of the air being heated, as well as a more uniform temperature of the flue gases. As in Fig. 2, each portion of the air being heated, now at or about the same temperature, passes into the plenum chamber 39 at the top of the furnace, and thence into duct header 40, from which individual ducts 4| lead to the points of use of the heated air. As will be evident, the swirling movement imparted to the various portions of the air due to the movement thereof through spiral passageways, further tends to increase the mixing action in plenum chamber 39, thereby insuring a more uniform temperature of the heated air supplied to the duct header 40.

As indicated previously, sets of baflles may be any desired number, such as each set of bafiles being four in number, as in Fig. 6. Thus, baffles 52 to 45, inclusive, extend spirally in one direction between combus ion chamber [5 and annular enclosure [1, while baffles 46 to 49, inclusive, extend spirally in the opposite direction between the annular enclosure 1 l andshell 20. Each baflle again preferably extends for about 360, or one complete revolution. Also, the bafiles intersect the fiues i9, 35 and 3?, substantially centrally thereof, as before. Thus, batle 43 intersects lower flue 3i, baffle 05 intersects upper flue 36, and baflie 49 intersects stack flue l9 centrally. The positions of fines '36 and 31' may need to be adjusted slightly upwardly or downwardly, to insure central intersection by the respective bafile. The action of the bailies 2 to 35, inclusive, and d to '20, inclusive, of Fig. 6, is similar to that of the babies of the previous embodiment, except that the air passages may be slightly larger due to the lesser number of battles, and a more thorough mixing of the air in the plenum chamber 30 tends to be produced, due to the fact that the air discharged from the spaces between bailles 02 to 05, inclusive, tends to be moving in the opposite direction from the air discharged from the spaces between baffles 06 to 09, inclusive.

The spiral bafiles may be readily made of sheet metal or other suitable material, and may be brazed or otherwise suitably secured to the combustion chamber, the annular enclosure, or the shell. Since an air tight seal around the edge or each balile is unnecessary, it may in many instances be suitable to attach the baffles, as by brazing or the like, only to the inner and outer walls of the annular enclosure, for instance, so that the enclosure and baffles may, as a unit, be inserted in the furnace. The lines between the combustion chamber and the annular enclosure may be inserted later, or attached to the annular enclosure and baflies, and then attached to the combustion chamber upon assembly. Or, the entire unit may be assembled and the baffles brazed to the combustion chamber, annular enclosure and shell, in one operation. The exhaust flue may be inserted, after assembly, through the shell, or may be made in two sections, one section being attached to the respective bafile and the annular enclosure, and extending to the outer shell, with the other section fitting thereinto and. being attached to the first section upon assembly.

In controlling the operation of a furnace constructed in accordance with this invention, substantially conventional control mechanism may be used, but the control may be set so as to increase the effectiveness and efficiency of the furnace operation. In furnace control systems generally in use at the present time, .a thermostat which is responsive to the temperature in the room or space being heated, is adapted to close a control circuit whenever the room cools to a predetermined lower temperature, and to open the circuit whenever the temperature in the room reaches a predetermined higher temperature. Superimposed upon the room thermostat control is a circuit controlled by the temperature within the plenum, so that whenever the plenum temperature reaches a predetermined maximum, the burner will be shut oil, and cannot be turned on again until the plenum cools to a predetermined minimum temperature. The maximum temperature is controlled by the danger of wood or similar material adjacent the furnace or stack catching on fire if the flue gas temperatures are too high, so that a maximum temperature of the flue gases of below 700 F. is necessary, and desirably 500 F. or below.

With a gravity type furnace, i. e. wherein air circulation is by gravity, the controls are normally set higher, since a higher plenum temperature is necessary to start adequate circulation, so that a maximum of somewhat near 3.00 F. and .a minimum of 225 :F. or above may be utilized.

In nearly all modern installations, particularly of gas and oil fired furnaces, a fan or blower is utilized, and the plenum control .temperatures may be lower, while an additional control is usually provided for the fan. The blower control is normally a thermostatic control responsive to the temperature in the plenum, .and is set to turn the fan on whenever the .plenum temperature is sufiiciently high to warrant, such as 30 F. to 50 F. below the maximum plenum temperature, and toturn the fan off whenever the plenum temperature drops below a lower temperature, such as about 30 .F. below the fan starting temperature. With gravity type furnaces, the stack temperature is generally on the order of about twic the plenum temperature, so that when the plenum temperature .reaches a maximum of, say, 300 the stack temperature will probably be about 600 F., which is approaching the danger zone, so that it is usual to set the maximum at about 275 F., roughly equivalent to a stack ternperature of about 550 F., for shutting off the fuel.

When a fan or blower is used, the plenum control temperatures may be set somewhat lower, such as a maximum plenum temperature of 200 F or 210 F. and a minimum of F., with the type of furnace wherein there is a single heating passage surrounding the combustion chamber, which may be termed a single direct pass furnace. The stack temperature will generally again be roughly double the plenum temperature, or about 400 F. to 420 but sometimes higher, such as 450 F. to 500 F. The fan control thermostat may be set to turn the fan on at about 30 F. below the maximum plenum temperature, or 170 F. to 180 F., and to turn the fan 01f at F. to F. With a type of furnace having an annular enclosure spaced from the combustion chamber, through which the gases of combustion are also passed, which may be termed a double direct pass furnace, the controls may be set somewhat lower, such as for .a maximum plenum temperature of F. and a minimum of 130 F., with the fan starting temperature closer to the maximum, such as about 150 F. In this type of furnace, the stack temperatures will be lower, reaching the much safer temperature of about 350 F. or slightly less, when the plenum reaches the maximum temperature. However, there is one common characteristic of the direct pass furnace, through which the air is blown by a fan, and this is that when the fan is turned on, the plenum temperature is quickly reduced, so that the fan then turns on" but the burner stays on and the stack temperature continually rises, often to as high as 500 F. or more. Thus, when heat is called for by the room thermostat, the burner is turned on, the plenum heats up, then the fan is turned on, then the plenum cools and the fan turns off, and the later the plenum heats up again and the fan is turned on again, the cycle being repeated until the space to be heated reaches the desired temperature. Not only is such heating intermittent, but also the continual operation of the burner and the higher stack temperatures indicate a considerable loss of heat. The plenum temperature seldom reaches the maximum, but the stack temperature continues high.

In the case of a furnace constructed in accordance with this invention, as indicated by data obtained by tests thereof, a different condition prevails. The effectiveness and efiioiency of heat transfer to the air is sufficiently greater so that the stack temperature, with the fan running, is only slightly greater than the plenum temperature. For instance, when the plenum temperature of an experimental model was 225 F., the stack temperature was between 230 F. and 240 F. This means that the maximum plenum temperature can be set much higher, such as 225 F. to 250 F., without danger in the stack. Also, when the fan is turned on, the plenum temperature rises, due to the greater transfer of heat to the air, and as soon as the plenum temperature reaches the maximum, the burner shuts off. As soon as the plenum temperature drops to the minimum, the burner is turned on again. Thus, the fan will run continuously, rather than intermittently, thereby continuously supplying heated air to the space to be heated, and the burner will operate intermittently, the total period of operation thereby being considerably less, with a consequent saving in fuel. With a higher maximum plenum temperature, such as 225 F. to 250 F., the minimum plenum temperature is also preferably set higher, such as about 195 F. to 220 F., to provide a 30 F; differential and also to reduce the possibility of condensation in the stack. The fan control is also preferably set differently in relation to the plenum control than with a direct pass furnace, the fan being set to turn on at a much lower temperature relative to the maximum plenum temperature, such as 190 F., or even lower, and to turn off at a temperature about the same or lower than the temperature at which it turns on, but in any event lower than the minimum plenum temperature, thereby assuring that the fan will continuously supply heated air, which, of course, is the object of using the furnace, and the burner will be on a minimum of time.

From the foregoing, it will be apparent that the furnace of this invention fulfills to a marked degree the requirements and objects hereinbefore set forth. lhe spiral bafiies in the air heating spaces produce a more even distribution of air, render the temperature of various portions of the air more nearly the same, and provide a more uniform temperature of heated air in the plenum or distributing space. More effective heating of the air provides greater efficiency in operation, and a consequent saving in fuel. The fan will also operate more nearly continuously, and substantially continuous fan or blower operation, as long as heat is called for by the room thermostat, means that the space to be heated is heated more quickly and a greater degree of comfort is assured. Also, there is a possibility of a smaller furnace and burner requiring less fuel, with consequent obvious savings, for heating a space requiring a larger furnace of the direct pass type. It will be evident, of course, that the furnace of this invention may be constructed in any suitable manner, other than that described; that the spiral baffles of this invention may be applied generally to different sizes and shapes of air heating spaces; that the number and slope of bailies may be varied; that other flue arrangements may be used; and that the control system and its settings may be varied from that described. It will also be evident that various other changes may be made, and that embodiments other than those described may exist, all without departing from the spirit and scope of this invention.

What is claimed is:

1. In a furnace construction having a generally cylindrical combustion chamber disposed with its longitudinal axis in vertical position, spaced walls defining an annular enclosure including an inner wall of greater diameter and disposed substantially coaxially with and in spaced lateral relation to said combustion chamber, means for conveying hot gases from said combustion chamber to said annular enclosure, means for permitting said gases to exhaust from said annular enclosure, a shell surrounding said annular enclosure in spaced relation to the outer wall thereof, and means for effecting passage of air to be heated through the space between said combustion chamber and annular enclosure and also through the space between said annular enclosure and shell, the improvement which comprises a first plurality of spirally extending baffles between said combustion chamber and the inner wall of said annular enclosure; and a second plurality of spirally extending baffles between the outer wall of said annular enclosure and said shell, all of said bafiies being adapted to cause air to be heated to follow a plurality of circuitous paths in passing through said spaces.

2. In a furnace construction as defined in claim 1, wherein each baflle extends for about 360.

3. In a furnace construction as defined in claim 1, wherein each bafile has substantially the same slope and said first and second bafiles are axially spaced substantially equidistantly.

4. In a furnace construction as defined in claim 1, wherein said first plurality of bafiies slope in the opposite direction to said second plurality of baffles.

5. In a furnace construction as defined in claim 1, wherein said first plurality of baffles slope in the same direction as said second plurality of baffles.

6. In a furnace construction having a generally cylindrical combustion chamber disposed with its longitudinal axis in vertical position, spaced walls defining an annular enclosure including an inner wall of greater diameter and disposed substantially coaxially with and in spaced lateral relation to said combustion chamber, a shell surrounding said annular enclosure in spaced relation to the outer wall thereof, an exhaust flue leading from said annular enclosure outwardly through said shell, and means for effecting passage of air to be heated through the space between said combustion chamber and annular enclosure and also through the space between said annular enclosure and shell, the improvement which comprises at least two vertically aligned and spaced flues connecting said shell with said annular enclosure on the opposite side of said enclosure from said exhaust flue; a first plurality of spirally extending baffles between said combustion chamber and the inner wall of said annular enclosure, said bafi'les being spaced axially so that each said spaced flue will be intersected substantially centrally by a bafile; and a second plurality of spirally extending baffles between the outer wall of said annular enclosure and said shell, said bailles being axially spaced so that said exhaust flue will be intersected substantially centrally by a baffle.

7. In a furnace construction as defined in claim 6, wherein said upper flue is smaller than said lower flue.

8. In a furnace construction as defined in claim 7, wherein each said bafile extends for about 360.

9. In a furnace construction as defined in claim 8, wherein said first plurality of bafiles slope in the same direction as said second plurality of bafiles.

10. In a furnace construction as defined in claim 8, wherein said first plurality of baflles slope in the opposite direction to said second plurality of bailles.

11. In a furnace construction having a generally cylindrical combustion chamber disposed with its longitudinal axis in vertical position, spaced walls defining an annular enclosure including an inner wall of greater diameter and disposed substantially coaxially with and in spaced lateral relation to said combustion chamber, means for conveying hot gases from said combustion chamber to said annular enclosure, a tubular exhaust flue extending outwardly for leading said gases from the upper portion of said annular enclosure, a shell surrounding said annular enclosure in spaced relation to the outer wall thereof, and blower means for effecting passage of air to be heated through the space between said combustion chamber and annular enclosure and also through the space between said annular enclosure and shell, the improvement which comprises two vertically aligned tubular flues connecting said combustion chamber with said annular enclosure, said connecting flues being disposed opposite said exhaust flue and one of said connecting flues being smaller in diameter than the other said connecting flue with the 3 smaller flue connecting with the upper portion of said annular enclosure and the larger flue connecting with the lower portion of said annular enclosure; a first set of five equally spaced and equally inclined spirally extending baffles between of said annular enclosure and said shell, said secnd set of bafiles extending spirally in the same direction as said first set of bafiles and each of said second set of baiiles extending spirally for approximately 360 around said annular enclosure, and one of said second set of bailles intercepting said exhaust flue substantially centrally of said exhaust flue, all of said bafiles being adapted to cause air to be heated to follow a plurality of circuitous paths in passing through said spaces.

12. In a furnace construction having a generally cylindrical combustion chamber disposed with its longitudinal axis in vertical position, spaced walls defining an annular enclosure including an inner wall of greater diameter and disposed substantially coaxially with and in spaced lateral relation to said combustion chamber, means for conveying hot gases from said combustion chamber to said annular enclosure, a tubular exhaust flue extending outwardly for leading said gases from the upper portion of said annular enclosure, a shell surrounding said annular enclosure in spaced relation to the outer wall thereof, and blower means for effecting passage of air to be heated through the space between said combustion chamber and annular enclosure and also through the space between said annular enclosure and shell, the improvement which comprises two vertically aligned tubular flues connecting said combustion chamber with said annular enclosure, said connecting fiues being disposed opposite said exhaust flue and one of said connecting fiues being smaller in diameter than the other said connecting flue with the smaller flue connecting with the upper portion of said annular enclosure and the larger flue connecting with the lower portion of said annular enclosure; a first set of four equally spaced and equally inclined spirally extending baffles between said combustion cham her and the inner wall of said annular enclosure, each said bafile extending for approximately 360* around said annular enclosure, one of said first set of bafiles intercepting said upper flue centrally of said flue and another of said first set of bafiles intercepting said lower flue centrally of said flue; and a second set of four equall spaced and equally inclined spirally extending bafiies between the outer wall of said annular enclosure and said shell, said second set of bailles extend ing spirally in the opposite direction to said first set of baiiles and each of said second set of baliles extending spirally for approximately 360 around said annular enclosure, and one of said second set of baiiles intercepting said exhaust flue substantially centrally of said exhaust flue, all of said baffles being adapted to cause air to be heated to follow a plurality of circuitous paths in passing through said spaces.

13. In a furnace construction having a combustion chamber disposed with one axis thereof in generally vertical position, spaced walls defining an enclosure disposed in spaced relation to and surrounding said combustion chamber, and including an inner wall disposed in spaced lateral relation to said combustion chamber, means for conveying hot gases from said combustion chamber to said enclosure, means for permitting said gases to exhaust from said enclosure, a shell surrounding said enclosure in spaced relation to the outer wall thereof, said shell and outer wall defining an air passage and said combustion chamber and inner wall defining another air passage, and means for effecting movement of air to be heated through said passages, the improvement which comprises a first plurality of generally spirally extending battles between said combustion chamber and said enclosure inner wall; and a second plurality of generally spirally extending baflies between said shell and said enclosure outer wall.

RAY W. RIFLEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 11,278 Sweeney July 11, 1854 251,320 Towne Dec. 20, 1881 309,495 McCreary Dec. 16, 1884 446,222 Hoyt Feb. 10, 1891 563,240 McCowatt June 30, 1896 1,606,494 Barnhart Nov. 9, 1926 1,811,182 Neal June 23, 1931

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