CA1044695A - Heat exchanger structure for a compact boiler and the like - Google Patents

Abstract

ABSTRACT OF THE INVENTION
Covers a boiler system which includes a heat exchan-ger comprising a plurality of substantially parallel conduits positioned between two substantially uniformly spaced bound-aries, and a plurality of matrices each composed of a plurality of conductive bodies interposed between said spaced boundaries so that only one matrix is positioned between two adjacent par-allel conduits. A first fluid, for example, heated gas, may impinge directly against each of the conduits and, at the same time, directly impinge against each of the matrices, while a second fluid, for example, water will pass through the parallel conduits and exchange heat with the first mentioned fluid.

Description

The present invention relates generally to heat ex-changers and, more particularly, to heat exchangers for boilers, water coolers, air conditioners, and other equipments for the transmission or reception of heat.
As is well known, a heat exchanger generally includes means whereby two fluids separated by a wall and having differ-ent temperatures are caused to transfer heat from one of thefluids to the other. A typical or conventional heat exchanger includes one or more pipes, tubes, or other conduits through which a fluid, such as water, flows and is intended to give up to or receive heat from a second fluid. Each such conduit may have, affixed to its outer surface, a plurality of fins, ribs, pins or other hardware usually provided on or near the outer surface thereof, so as to improve and increase the heat trans-fer capability of the conduit and thereby improve the relative efficiency of the heat transmission to or from the fluid flow-ing through the conduit. ~b1e~
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f `''`','.`',''' .''"~,.''.',' '"" " ` ~ ; ;'': ' ' ' ' 1(~4~95 -Heat exchangers usually include, in additiion to the conduit or conduits which carry a fluid, such as water to be ~
heated or to give up heat, a second or gaseous medium which may ;
be derived from an adjacent burner or from a refrigerator or .
from any other source supplying the gaseous medium which is to flow around the conduit or conduits, so as to change the temp-erature of the fluid flowing through the conduits. A prior typical boiler, for example, having such a heat exchanger for ;~
use in a residential or commercial building, even a small resi- ~ ~
dential building or an apartment of a large building, would be -. .: .
relatively so large-and bulky that it would require considerable j;
space to house and shelter the heat exchanger. The heat ex- ;
changer would also be so complex that it would usually require skilled manpower and considerable time to manufacture the struc~
ture and necessarily its costs would be relatively high. The efficiency of transmission of heat between a gaseous medium and a liquid medium in such a structure would be so poor that the cost of operation would be quite large. These are some of the adverse factors that suggest the serious problems facing indus- -`
try generally in meeting the needs for low cost residential and commercial buildings requiring heat exchangers for boilers and other heating or cooling structures.
In accordance with the present invention, a new form ;
of heat exchanger is provided, along with the necessary appur-tenances required for building, for example, a boiler, the heat exchanger being suitable for a miniature type of boiler system, that is, a boiler structure much smaller than conventional -boiler structures now made and sold for residential and commer-cial establishments. The heat exchanger structure, and the boiler systems of which it is a part, will be relatively easy

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446i~5 to manufacture, small in size, light in weight, relatively free of serious or costly maintenance problems, and easily incorpor-ated into small or mLniature boiler systems, and, if desired, into larger boiler systems, whether ~or use in small individu-alized city apartments or in large or small residential or commercial buildings. `~
In general, the heat exchanger of this invention may include, for example, a unitary cylindrical structure compris-ing a plurality of circumferentially arranged parallel conduits through which fluid, such as water, may flow and, between the :. ., conduits, there will be a matrix structure consisting of a plurality of separate and independent matrices each composed essentially of a plurality of pellets, preferably made of metal, integrally bonded to each other and to the side walls of the two adjacent conduits, so as to form the unitary substantially ,~
. . .
cylindrical structure. In the heat exchanger of this invention, no one of the matrices of pellets will be positioned-on the lower surface, nor on the upper surface, of the several parallel circumferential conduits. In other words, none of the pellets will~be positioned within the cylindrical tangential periphery i i . :
; defining the innermost points of the several parallel conduits, nor will any of the pellets of any matrix be positioned radial- ~ `
~ , . ': `.
ly beyond the cylindrical surface defining the outermost points of the several parallel conduits. Thus, all of the pellets of ,~;
all of the æeveral matrices will be positioned between the two designated tangential cylindrical peripheries defining the uppermost and lowermost points of the several conduits. Hence, the heat exchanger will comprisean hour-glass-shaped matrix ~ `;
structure in which each of the several matrices will be posi- -~
tioned between two adjacent parallel conduits. Such a composite

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4 4 ~i 9 5 r heat exchanger structure is easily and conveniently manufac-tured and assembled within a cylindrical casing for use in a boiler or other heat transfer apparatus.
In accordance with the present invention, a surface combustion burner, preferably a pressurized surface combustion ~;
burner, may be positioned within the central or axial space . . .
formed by the belt-shaped matrix structure above noted, which -i;-includes the several matrices and the corresponding interspersed .f. . ~ .
parallel conduits, so that heat generated by the surface com-bustion burner may deliver heated gases, at relatively high ' temperatures and suitable pressure, directly againæt the inner or under surfaces of the several conduits and also, simultane-ously, directly against the several matrices of pel1ets. Some ; of the gaseous heat from the burner, upon striking the under surfaces of the several parallel conduits, will deliver heat efficiently to the fluid within the conduits. Some of the gas-eous heat derived from the burner will, at the same time, be delivered to the under surfaces of the several matrices of pellets, 80 that the pellets will be heated and the heat trans- ';~
mitted to the pellets will be conducted to the sidewalls of the parallel conduits for simultaneously heating the fluid flowing r through the conduits. Moreover, the heated gases which are deflected from the under surfaces of the several parallel con-duits will necessarily traverse paths extending through the .~ , . . .
~ several matrices of pellets to further aid in raising the tem- -; .: -perature of the pellets and of the fluid within the conduits.
Thus, the heat of the gaseous combustion products from the l -~ burner will simultaneously and jointly attack the sides of the `-parallel conduits along several different fronts, all cooperat-ing to raise the temperature of the fluid flowing therethrough.
_4_ The gases, after traversing the paths of the several matrices, may be discharged through a chimney or any other convenient adjacent outlet which need not have, and need not produce, a substantiàl draft.
The matrix structure above referred to, which may be composed of a plurality of independent matrices as indicated, each embodying a plurality of pellets bound to each other and to the parallel adjacent conduits, will form what may be des-cribed as a circularly cylindrical belt. The spacings of the pellets of each matrix are randomly arranged and do not require any predetermined formation. The spacings between the pellets ~ill render each matrix porous with respect to the heated gases ~`
supplied by the surface ~ombustion burner, but notwithstanding `~
these inherent spacings, the pellets will freely conduct heat from one pellet to another and then to the walls of the adjacent ; conduits and, therefore, to the fluid transmitted through the conduits. Because of the random spacings of the pell~ts and their relative sizes, the combustion gases may rather freely and efficiently traverse the various matrices so that a good and predetermined rate of gaseous transmission f~om the burner will be maintained through the circularly cylindrical belt -structure. By means of this structure, a very high proportion of the heat within the generated combustion gases will be trans~
lated into heat in the fluid continuously flowing through the conduits to raise the temperature of the moving fluid to the ~;~
desired temperature. The pellets of the several matrices will be fairly large so that only a few, and not too many, pellets ;~
will necessarily be interposed between the adjacent parallel conduits. The random spacings of the pellets will allow the free and efficient flow of the combustion gases through the

-5-~, 1~44~i~95 matrix, thereby to dissipate heat to the several pellets which ,, . ,~ , will conduct the heat to the walls of the adjacent conduits.
The pellets are preferably constructed of the correct dimen-sions, that is, the correct range of diameters if the pellet#

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are spheres, so that their random spacings will provide the porous and optically transparent linkage between the several `~ ;
conduits for the conduction of heat to the fluid in the con-duits. No part of any matrix of pellets is positioned on the inner side of the inner cylindrical tangential surface of the parallel conduits. Nor is any part of any matrix of pellets positioned on the outerside of the outer cylindrical tangential surface defining the parallel conduits. This results in a considerable saving not only in the number of pellets used, but also in the cost of the pellets and in the cost of the matrix.
At the same time, the combustion gases make direct contact with the underside of the several parallel conduits so as to direct-ly raise the temperature of the fluid travelling through the conduits.

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Because of the spacings between the pellets of the , :, ., matrix, the matrix will be porous to the heated gases supplied by the burner and porous also to any other rays which are nec- ;
essar~ly generated by the gases burned by the pressurized bur-~ . ...
ner. In other words, the spacings of the pellets yield the correct fluid velocities in the form of heated gases through the several matrices. Some paths through each matrix will be ~ -straight-line or uninterrupted 80 as to yield a desired low pressure loss.
Thus, as already suggested, the heated and pressured gases supplied by the surface combustion burner will direc~ly and indirectly impinge upon the under surfaces of the several

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1~4~95 parallel conduits so that a high proportion of the heat of the gaseous products of combustion will be supplied against the walls of the conduits for rapidly heating the fluid flowing through the conduits. As already also suggested, the heated gases reflected by the conduits must necessarily impinge upon the matrix of pellets and hence the reflected gases will con-duct heat to the side walls of the conduits to contribute im-portantly to the heat supplied to the fluid within the conduit -walls. A good part of the heated gases will also directly strike the matrix of pellets independently of the reflected heat, to further increase the supply of heat to the fluid traversing the several parallel conduits. The several paths of the heated gases in supplying heat, directly or indirectly after reflection, ;
to the fluid of the conduits, join together to quickly and efficiently raise the temperature of the fluid. This process is carried out ~uickly and, therefore, in a rather limited space. ~ ~
~his invention, together with its o~her objects and ~ ~ ;
features, will be better and more clearly understood from the ,, .
more detailed description and explanation hereinafter following when read in connection with the accompanying drawing, in which Fig. 1 illustrates a cross-sectional view of an elemental seg-.
ment of a form of matrix structure according to this invention, this figure illustrating a single conduit and parts of the two adjacent matrices o~ pellets; Fig. 2 illustrates a fragmentary plan view of a portion of a matrix structure according to this ~--invention, this illustration including two conduits together with the contiguous matrices; Fig~ 3A shows a cross-sectional view of one form of pellet which may be used in the practice of this invention together with a coaring therefore; Fig. 3B shows a cross-sectional view of a cluster of three pellets adjacent to

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44~i,95 ~:
part of a wall ~f a conduit; Fig. 4 shows a perspective view , of a heat exchanger according to this invention, this figure illustrating a surface combustion burner partly remaved from the heat exchanger;Fig.5 shows another perspec~v~ ~ew of a heat exchanger according to this invention, illustrating the inter-connected piping; Fig. 6 shows a schematic diagram of a com--: .
posite boiler system, including its heat exchanger, which is suitable for providing heat to an apartment or to a building;
and Fig. 7 schematically shows a diagram illustrating one form , , of conduit interconnection ~ystem for use in the heat exchanger of this invention. ~`
Throughout the drawing, the same or similar reference characters will be employed to designate the same or similar -parts wherever they occur. ~ -Referring particularly to Figs. 4 and 5 of the draw- ,J,.
ing for a general description of the layout of the heat exchan-ger of this invention, there are shown two annular supports or ... . .
mounting plates designated MPl and MP2 which may be parallel to each other and spaced from each other. Both plates MPl and MP2 -;~
20~ have a plurality of openings for receiving and supporting a plurality of parallel conduits Tl to T24 which may be, for example, conventional pipes of the same general diameter and of the same general length. In the illustration furnished for explanation, all of the 24 substantially parallel conduits Tl to T24 are shown positioned be-tween, and perpendicular to, the two mounting plates MPl and MP2. The parallel conduits Tl to T24 may be grouped into four sets of 9iX conduits, Tl to T6, T7 to T12, T13 to T18, and Tl9 to T24 or in any other arrange- `
ments of æeries or parallel or series-parallel groups. All of ` ~, the conduits may or may not be encased within a common housing -

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HX as shown in Fig. 4. u-shaped couplers, to be presently described, may be employed to interconnect pairs of the con~
duits.
In Fig. 4, for example, cold water may be supplied ~o the two entrance conduits TCl and TC2 and the cold water, after it has been heated by the heat exchanger HX, will be dis-charged from two discharge conduits THl and TH2 (see Figs. 5 and 7). The water supplied to the entrance conduit TCl is fed simultaneously to two parallel conduits TCl and TC12, while the ~;
water supplied to the entrance conduit TC2 is supplied to two ~ .
other parallel conduits T13 and T24. conduit Tl is connected by a u-shaped coupler U12 to the next parallel adjacent conduit : T2, while a similar U-shaped coupler U23 interconnects parallel : :
conduits T2 and T3. Likewise, another u-shaped coupler U34 ; . ~.
interconnects parallel conduits T3 and T4. Similarly, coupler : :
U45 interconnects conduits T4 and T5, while another coupler U56 interconnects conduits T5 and T6. An elbow fitting L6 inter-connects conduit T6 to discharge conduit THl through which the .; .:~ .
heated water will be discharged. Thus, the conduits Tl to T6, ~ :
:,,~ . ... ..
representing a quadrant of the parallel donduits of the heat ~.r.::. :
exchanger HX, are interconnected to feed water received through .
the entrance conduit TCl to the discharge conduit THl, so that water flowing through the parallel conduits of this quandrant "~
: will receive heat furnished by the burning gases of the combus- ~ :
tion burner BU to raise the temperature of the water to a desired :~
thermal level to be discharged by the discharge conduit THl. .; .
Similarly, another quadrant of parallel conduits T12 to T7 will be interconnected with each other in the heat exchanger HX and ., .
these conduits will allow the water flowing therethrough to be ~`
raised in temperature by the combustion gases furnished by the _g_ -:

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combustion burner BU. Similarly, the other quadrants of parallel conduits T13 to T18 and Tl9 to T24 are interconnected and these other quadrants serve to raise the temperature of the water entering the entrance conduit TC2 to a desired tem-perature, the heated water then being discharged by the dis-charge conduit TH2.
Fig. 7 sch~ematically shows, in perspective, the four quadrants of parallel conduits interconnected between the two entrance conduits TCl and TC2 and the two discharge conduits THl and TH2 for the first fluid. The fluid discharged by the latter conduits THl and TH2 is, as already explained, the water raised considerably in temperature by the heated gases which constitute the second fluid. The second fluid, supplied by the burner BU, is impacted directly and indirectly against all of the quadrants of parallel conduits above referred to and this second fluid must traverse the matrices of pellets of the heat exchanger HX.
As,shown more clearly in Figs. 5 and 6, the heat ex-changer HX has an axial longitudinal cylindrical space for receiving a surface combustion burner BU. The burner may be partially or fully removed from the heat exchanger HX whenever desired by being slid axially out of the heat exchanger HX for repair or maintenance or replacement, and then returned to its normal position within the heat exchanger HX for normal opera-tion. The burner BU has an opening axially positioned therein for receiving the gas to be ignited and the air to be mixed therewith in predetermined proportions so as to be properly ignited and burned by the burner BU for producing gaseous prod- `
ucts at a relatively high temperature at the surface of the burner BU for heating the water circulated through the quadrants 4~ti95 of parallel conduits of the heat exchange HX. The efficient and predetermined mixture of air and gas, and the maintenance of the predetermined ratio of the two components are important in preventing the formation of noxious components, such as carbon monoxide, which, if produced in appreciable volume, may be dangerous to persons in the building. ~-Now coming to the matrix construction of this inven~
tion, Fig. ~A shows one form of an elemental pellet P which may be used in the practice of this invention. The pellet may ;
be coated by a layer of metal designated C. As shown more ~, , clearly in Figs. 1 and 2, each conduit, such as T, has two ma- ;~

trices affixed to its opposite side walls. As is more clearly ;.. ..
shown in the schematic drawing of Fig. 7, all of the conduits ;
Tl to T24 are arranged circumferentially about the axial center , of the heat exchanger HX and they are located between the two ~ concentric tangential cylindrical peripheries or boundaries, ~
:... . ~
namely, the inner tangential cylindrical periphery TGl and the outer tangential cylindrical periphery TG2, as shown in Fig. 1.
The overall matrix structure, which is composed of the plural- `~
... ~
ity of scparate and independent matrices M12, M23, M34, etc., is arranged so that each matrix, such as M23, is positioned ;~
between two adjacent conduits, such as T2 and T3. Thus, all of the matrices of pellets are positioned on what may be referred ` ~`
to as the sides or side walls of the parallel conduits Tl to T24 of the heat exchanger HX. No part of any matrix is posi-tioned on the underside of the tangential cylindrical periphery TGl (see Figs. 1 and 5) nor on the outer side of the tangential `~

cylindrical periphery TG2 which is further removed from the axis of the heat exchanger HX. No matrix of pellets completely sur- i ;

rounds any of the several parallel conduits in order that, in -11- ..... .

i95 accordance with this invention, there will be free access for the heated combustion gases to the underside of the various parallel conduits. There is, therefore, a considerable and important saving in material and labor and costs by omitting pellets both from the underside of the several parallel con-duits and from the outerside of the several conduits.
The surface combustion burner BU is supplied with sparks or with a pilot light and produces combustion gases at, say, 2,000 to 2,500F. and higher in the vicinity of the outer cylindrical surface of the combustion burner. The adiabatic flame temperature for n~tural gas burned with air is approxi-mately 3,600F. If natural gas i~ burned with oxygen, adia-batic flame temperatures approaching 6,000F. may be attained. :~
Under such conditions, higher heat fluxes can be obtained with-, out any increase in the size of the equipment.

The outer surface of the heat exchanger HX i9 shown . , , by a dotted line in the schematic drawing of Flg. 6. It may ~-take the form of a porous woven fabric of a heat resistant fiber .: :
which may be~cylindrical in shape~and through which the gases are transmitted and ignited upon reaching close to the inner , . .
circumferential p-riph-ry TGl. T e ignited gases are influ-enced by air pres-ure developed by appropriate blower equipment `~ .
80 that the flaming ga~es reach the under surfaces of the sev-ral parallel conduits Tl to T24 of the heat exchanger HX.
This direct contact with the under surfaces of the conduits is a factor in the increased efficiency of the equipment. The -`
...
~ burning gas also directly impinges upon, and necessarily i~ ~-:
passed through, the several matrices M12, M23, M34, etc. Very little, if any, of the combustion gases will impinge upon the outer walls of the parallel conduits Tl to T24 which are `' -12 - ~

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located on, or adjacent to, the outer cylindrical tangential -periphery TG2 (see Fig. 1). In accordance with this invention, no pellets are positioned beyond the outer periphery TG2 be-cause the combustion gases are relatively cooler in that region.
The savings and improvements due to this significant omission are considerable. ;~
By the proper choice of the size of the pellets with respect to the diameter of the conduits, a desirably tortuous -path for the flow of the combustion gases is achieved without any excessive pressure loss through the ~atrices. By omitting pellets from all but the sidewalls of the several conduits Tl -~
to T24, the small number of pellets employed will reduce the ~.i .,: .. .
weight of the structure, and the dimensions of the heat ex- ;
changer equipment will be relatively small.
In one embodiment of the heat exchanger HX of this invention, the various parallel conduits Tl to T24 were employed to transmit water to be heated. The conduits were made of steel and they had an outside diameter of 5/8". The parallel conduits `~
were spaced apart, having a spacing of about 1" between their ;
centers. The pellets were steel balls having an outside dia-meter of approximately 0.174 inches and each was coated with copper. Although they were randomly arranged between the side `
walls of the various parallel conduits, the combination of the pellets of the matrices and the adjoining conduits were brazed to each other so that there was gcod thermal contact not only between the steel balls, but also between the steel balls and the several conduits to provide a belt-connected heat exchanger , HX. The copper coating on each pellet was about l/lOOOth of an inch in thickness. It will be understood that any desired pressure drop..................................................

can be achieved in the heat exchanger merely by changing the diameter of the spherical pellet if a spherical pellet is used or by changing the spacing between the conduits, or both.
It will be apparent that the spaces between the pel- -lets allow the flue gases of the burner BU to be deflected in ;
their passage through the matrix. The spaces between the pel-lets, because of the size of the pellets, are sufficient to allow rays of light or luminous hot gaees to be observed through -the matrix. Lack of opacity is a feature of the matrix. Thus, linear openings permit the heated gases of the burner to move rather rapidly through the matrix to the chimney or to any other disposal point, thereby minimizing pressure loss commen-surate with efficient heat transfer.
By brazing the composite structure of each matrix with the adjacent parallel conduits, a unitary mass is estab-lished for the heat exchanger HX exhibiting a thermal conduc-tive property suitable for transferring heat efficiently from heated gases to the fluid carried through the parallel conduits.
As shown in Fig. 3B, the brazing operation will cause the partly molten copper to be accumulated or collected at the points of `~
contact of the several pellets and between the pellets and the adjacent conduits. The brazing operation can be performed in a container of dissociated ammonia, carbon dioxide or a vacuum or any other suitable atmosphere maintained at a suitable tem-perature for a sufficient time interval, after which the brazed product may be removed from the container.
Referring now to Fig. 6 of the drawing, there is shown a schematic diagram of the compact boiler system of this invention. Natural gas, for example, may be supplied through a conduit S which may be connected, through a solenoid valve 5V

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and a gas regulator RG, to a mixing chamber MC. The mixing chamber MC is also connected independently to a blower BL
which supplies air at a predetermined rate and at a predeter- ;
mined pressure into the mixing chamber MC. No venturi appara-tus is required in the s~stem. The gas supply pipe is equipped with a nozzle and pointed in the direction of the burner B~ so that the emitted gas will be mixed with the air supplied by the blower BL and the ratio of the volume of gas to the volume `
of air is maintained constant. The arrangement for mixing air and gas, and for maintaining their proportions substantially constant regardless of variations in the pressure of the air supplied by the blower B~, is shown and described in Canadian Patent Application ~o, 091,945 filed on August 19, 1970 in the name of American Standard Inc. ~-The output of the mixing chamber MC is fed through a ~ -conduit MP to the input of the burner BU. The burner BU may be, for example, any form of surface combustion burner but it is preferably one of the type shown and described in a united States Patent of W. J. Witten, No. 3,269,449, issued August 30, 1966 and assigned to the assignee of this application.
. .
The burner element of the surface combustion burner BU may, if desired, comprise a hollow cylindrical structure o a heat resistant porously woven fabric of heat resistant fibers, preferably of alumina ceramic and nichrome wire. This fabric may be about 1/8" thick and embody a weave density for dropping the pressure of the gas by about 1/2" or less of water for a ~ `
gas-air flow velocity of about 20 cubic feet per minute per square foot of the burner surface. A suitable fabric for the burner surface is that marketed ùnder the trademark "Fiber-Frax" by the Carborundum Co. Such a fabric can withstand a -`

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1~ 5 temperature of about 2,000F. continuously. Such a fabric is sufficient and appropriate even for the higher flame tempera-tures that may be produced, because o~ the cooling effect of the air supplied by the blower. The hollow cylinder of the fabric may be positioned within a corresponding cylinder of a wire mesh made, for example, of galvanized steel. The tubular -structure of the burner may be supported and held rigid by a steel wire or by any other appropriate or well known means.
As already noted, the burner BU is axially positioned -within the heat exchanger HX which embodies the parallel con-duits through which water flows, as already described. The inlet water received from a city water supply system, for example, a~nd flowing through a conduit W, travels through a fill valve FV. The fill valve FV may be opened whenever de- ~ ' sired in order to supply water to the boiler system initially or to supply water to replace water previously evaporated or leaked from the boiler system, as may be required. The boiler system includes a water loop which employs a pump circulator P, ;
the parallel conduits Tl to T24 of the heat exchanger HX, and a baseboard heater BH, only one of which is shown in Fig. 6 for illustation. Naturally, any number of baseboard heaters may be connected in series or in parallel with each other if so desired. The pu~p P raises the pressure of the water sup-plied to the water loop and maintains the pressure at a sub- -stantially constant level. The same water may be recirculated through the loop which, as already noted, would include both the heat exchanger HX and the baseboard heater BH and this recirculation of water may continue over and over again.
It will be also noted that the water loop of the boiler system may be connected to an expansion tank ET and to ,. . , . - ~ .:- `, . -16J 4~j9S ;~- ~
a conventional air eliminator AL. The expansion tank ET is intended to take up any change in the volume of the water nec-essarily resulting from changes in the temperature of the water.
The air eliminator AL will remove any surplus of air or oxygen that may be developed or entrapped in the water line. `~
A miniature boiler system of the kind described above may be fed water of a temperature of about 150F. and the water may be raised in temperature by the system to about 180F. or to a higher temperature. The size of the miniature boiler may, for example, require gas capable of yielding about 100,000 ;~
. .
B.T.U. per hour. A desirable air-fuel weight ratio may be about 20 to 1. The stack temperature of the exhaust gas may -be about 240F. The carbon dioxide content of the exhaust gas may be no more than about l~/o~ The carbon monoxide content is virtually zero due to the combustion efficiency of the system.
The matrix volume in the sample used was apprGximately 47 cubic inches and the weight of the pellets of each matrix was about eight pounds. The matrix and the burner assembly together weighed under about 20 lbs. and was, therefore, easily trans~
portable. The cylindrical heat exchanger sample had an approx-imate overall diameter of 8~i" and a length of 6". When pack-aged as a hydronic heating boiler, which included the heat --exchanger, the pump, the controls and the accessories, the overall dimensions were 19" in width, 17" in depth and 14" in height. Smaller packages are readily designed and constructed.
For example, the pellets need not be spherical; they may be ellipsoids or any other regular or irregular shaped bodies, preferably made of metal, but plastic materials, pre- ,~
ferably metallized, may also be employed, if desired. Further-more, t~e spherical pellets may be replaced by metallic scraps .~j , .- . .

or metallized plastic scraps or ~ ms of saddles, etc. It is important, however, to have the matrix exhibit good porosity `~
for the combustion gases and, in addition, some transparency to light and other rays that may be generated ~y the combu8- .
tion gases. Furthermore, although the pellets have been des- ` -cribed as made of steel and coated with copper, any other '~
materials may suffice for the pellets and their coatings, if any. For example, the pellets may be made of aluminum, and . : , .
the various pellets may be brazed to each other and to the adjacent conduits with a brazing material of copper, aluminum or any other metal so as to yield a unitary structure of rela- ;~
tively light weight. The term "pellet~', as used in the claims, i, is intended to include these variants and others.
Although twenty-four parallel conduits have been shown in the illustrated heat exchanger of this invention, it will be apparent that any number of parallel conduits may be employed in the heat exchanger, whether in a circularly cylin-drical assembly, or in a square or rectangular cylindrical assembly, or in any other form, but, in any case, a corres-, , ponding number of matrices of pellet~-of whatever shape may be brazed between the side walls of the various conduits to pro-vide a belt-shaped structure. The combustion burner should be designed to match and coordinate with the axial space, what-ever its shape, to provide a coordinated structure of minimal dimensions. A miniaturized assembly is one of the main features of this invention. Moreover, the conduits of the heat exchanger need not be arranged in quads. They may be interconnected to provide, if desired, a continuous unidirectional path for the fluid flowing through all of the various parallel conduits making up the heat exchanger, but any other circuital connec--18- `~

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`::
tions, whether parallel or series-parallel, may be employed.
The temperatures abovenoted which are developed by the structure in a typical installation and the fuel require-ments of the burner may be changed as desired. The geometry of the conduits, the nature of the pellets and their random ~ ~ -spacing, and the pressure of the combustion gases all contri-bute to determine the temperaturesand pressure losses developed in the apparatus, but they may be adjusted to meet any prede-termined or desired magnitudes.
It will be understood that, although the invention ~
has been described in connection with the production of hot ;~- -or heated water for illustrative purpose~ it is readily ad-justable for the production of steam, whether saturated or - -. . .
~upersaturated, or for heating or changing the state of any fluid, whether gaseous or liquid. The heat exchanger HX may ohviously be employed for cooling purposes, if so desired. , ~ ;
Furthermore, as will be apparent from a reading of this speci-fication, the fluids employed in the heat exchanger may, if `~ --desired, both be liquid or both be gaseous. ; ; -The dimensions of the several components above re- ~;
ferred to in connection with an example for the practice of -this invention were given merely for illustration and explana-tion and are not intended to be limitations upon the invention.
" " ' obviously, these values may be changed, as desired, to meet any `,t :' conditions and to achieve any desired heat transfer relations between fluids. Obviously, the conduits and their dimensions are readily changed, either increased or decreased, to meet the ~
exigencies of any p~rticular problem in the practice of this r' " ~ ' invention. `~
While this invention has been shown and described -19- , ~":

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in certain particular embodiments merely for illustration and explanation, it will be apparent that it may be organiz~d in many different arrangements within the scope of this invention.

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Claims (21)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A heat exchanger for transferring heat between a first fluid and a second fluid, comprising a plurality of spaced conduits through which the first fluid can be passed, each space between adjacent conduits being occupied by a heat-conductive, fluid pervious matrix through which the second fluid can be passed, each matrix being in thermally-conductive contact with only adjacent side surfaces of the conduits between which it lies leaving the front and rear surfaces of the conduits exposed, and each matrix being composed of a plurality of layers of particulate-bodies bonded together at their points of contact, with spaces between bodies in each matrix providing straight line paths along which light rays can pass from one side of the matrix to the other.

2. A heat exchanger according to claim 1, including means to discharge the second fluid at an elevated temperature so that the second fluid will be applied at the elevated tempera-ture directly, and indirectly through the spaces of the matrix, against said conduits.

3. A heat exchanger according to claim 1 in which the conduits comprise a plurality of interconnected longitudinal conduits through which a first fluid is transmitted.

4. A heat exchanger according to claim 1 in the form of a hollow annular structure, with said conduits being interconnected and substantially parallel to one another, and the matrices being interposed between and bonded to adjacent conduits.

5. A heat exchanger according to claim 4 in which the bodies are substantially spherical bodies and are made of steel and coated with copper and brazed to each other and to the ad-jacent conduits.

6. A heat exchanger according to claim 4, including means for radially transmitting the second fluid in the form of heated gases to said heat exchanger.

7. A boiler comprising heat exchanger according to claim 1, and a burner which discharges combustion gases constituting the second fluid at an elevated temperature to transfer heat to the first fluid, the burner applying the combustion gases substantially at the elevated temperature directly, and indirectly through the spacial paths of the matrices, against the conduits

8. A boiler comprising an annular heat exchanger according to claim 4 and a burner positioned to deliver the combustion gases radially within the cylindrical configuration.

9. A boiler according to claim 8 in which the burner located substantially coaxially within the inner wall of the annular structure, said burner feeding its combustion gases substantially along radial paths directly contacting the inner walls of said parallel conduits and said matrices.

10. A boiler according to claim 9, wherein the burner feeds combustion gases which directly impinge upon the walls of said con-duits and directly impinge upon all of said matrices, and including an exit port for discharging said gases after they have passed through the spaces between the bodies of said matrices.

11. A boiler according to claim 10 in which the exit port is exterior to and distant from the annular structure for trans-mitting to the external atmosphere the discharged gases after they have traversed the matrices.

12. A boiler comprising a heat exchanger according to claim 1 wherein said plurality of conduits comprise a plurality of interconnected longitudinal donduits through which the first fluid is transmitted, and a burner discharging combustion gases constituting the second fluid above a predetermined temperature against exposed segments of the conduits and against the matrices to transfer heat to the first fluid.

13. A boiler comprising a heat exchanger according to claim 1 having said conduits arranged substantially parallel to each other and positioned between two substantially uniformly paced coaxial boundaries contiguous to said conduits, a surface combustion burner emitting combustion gases constituting said second fluid for impinging directly against the exposed sections of each of said conduits and directly against each of said matrices for elevating the temperature of the first fluid to be heated as it is conveyed by said parallel conduits, whereby said matrices provide a medium of predetermined low pressure 1088 for the flow of the second fluid.

14. A boiler according to claim 13 in which the parallel conduits are connected in series with each other so that the fluid to be heated will be exposed to the combustion gases emitted by the burner for a large time interval.

15. A boiler according to claim 7 wherein said conduits are arranged substantially parallel to one another, and the bodies of each matrix are brazed to each other and to adjacent parts of the conduits, and wherein said burner is a surface combus-tion burner adjacent to the said parallel conduits and emitting combustion gases to be impinged directly against exposed parts of the conduits and also simultaneously directly against the front walls of said matrices, the gases emitted by the burner not impinging directly against the parts of the conduits to which the matrices are brazed.

16. A boiler according to claim 15 including a common portal for discharging the combustion gases after they have traversed the space between the particulate bodies of all of said matrices.

17. A boiler system comprising a surface combustion burner having a cylindrical porous surface member capable of continuously transmitting therethrough gases to be burned and transmitted in paths and capable of withstanding the heat generated by the continuously burning gases, and a heat exchanger according to claim 1 wherein said conduits are arranged parallel to one another and are positioned concentrically about said porous surface member, whereby gases burned by said burner will impinge against the exposed portions of said conduits exposed to said porous surface member and will impinge also against said matrices.

18. A boiler system according to claim 17, in which each matrix is composed of a plurality of copper coated spherical steel pellets.

19. A boiler system according to claim 17, including a blower, a source of combustible gas, and means for supplying to the combustion burner a mixture of air and gas in predeter-mined proportions at a predetermined pressure and for maintain-ing the proportions substantially constant.

20. A boiler system according to claim 19, including a utilization structure coupled to the parallel fluid-conveying conduits for receiving the heated fluids derived from the boiler system.

21. A boiler system according to claim 19, including means to maintain the proportions of air and gas substantially constant notwithstanding changes in the pressure developed by the blower.