Note: Descriptions are shown in the official language in which they were submitted.
1~342~18
This is a divisional application of application serial No. 038383
filed on December 27, 1968.
The efficient transfer of lleat as well as the efficient and economi-
cal conversion of the~nal energy between flowing fluids and media to be heated
or cooled is highly desirous in the present day art The areas of interest
reside in the home, for example, in cooking and heating, and in industry in
numerous industrial processes such as condensation~ distillation and heating.
In the heat transfer art the completeness of extraction of thermal energy
between a heated flowing fluid and another medium ;s the parameter of primary
concern. In normal fuel burners, for example, with limited heat transfer
area the exhaust temperatures which may be a few hundred degrees indicate
that a considerable amount of available heat in the fuel is not utilized and
is transported through the chimney flue. Efficiencies of between 50 percent
to 60 percent are, therefore, quite conventional in present day thermal energy
conversion devices.
Increasing the transfer area between the flowing fluid medium to be
heated in applicable devices through baffles, plates, tinsel or other obstruc-
tions has not met with marked success in improvement of heat transfer efficien-
cies. An expression often utilized in the art to describe the heat transfer
characteristics is "power density" which denotes the thermal energy per unit
of time flowing through a unit of area of a body to be heated. Prior art
devices have normally observed power densities in the order of 100 watts per
square inch of transfer area. This indicates that with the numerous high
thermal energy sources available such as, for example, a direck flame having
a 7 kilowatt output capabillty higher efficiencies will be realized if the
power density characteristic of the transfer structure can be suitably en-
hanced. New and novel structures to achieve much higher efficiencies with
power densities 10 to 100 times that normally achieved in the transfer of
~hermal energy will be described in accordance with the teachings of the
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present invention.
A compact structure for rapid transfer of thermal energy and vast
improvement in the power density factor is provided by the arrangement of a
plurality of thermal conducting bodies in a bonded porous barrier matrix. The
interstices between the contiguous surfaces of the bodies in the matrix define
a tortuous path for a fluid heating or cooling medium. A heat transfer inter-
face surface arranged adjacent to the barrier matrix provides for the passage
of a second medium at a higher or lower temperature differential relative to
the fluid medium within the barrier matrix structure. The porosity and dens-
ity of the barrier matrix composed of individual thermally conductive membersis of a predetermined design parameter to provide f'or efficient heat transfer
betweenthe media. In accordance with this invention, an optimum requirement
for the depth and porosity of the barrier matrix is that the average size of
the thermal conducting bodies be substantially the size which will produce an
optically dense path in substantially the shortest distance along a passageway
or restricted path for a flowing fluid. For the purposes of the description
of the invention the term "optically dense" is defined as relating to the
packing of the individual thermal conductive bodies in such a manner that a
beam of light directed through the resultant structure will not be directly
visible but small traces of light~ay be noted in the interstices between the
individual bodies because of internal reflections and light scatter. The heat
transfer barrier matrix may be provided by joining together the thermally
conductive members through conventional brazing, sintering or soldering tech-
niques by coating the individual members with suitable materials having
characteristics for such metallurgical processes.
Another term useful in the understanding of the present invention
and description of the parameters of the individual thermal conducting bodies
and maximum heat flow paths is the"characteristic dimension." This term shall
be interpreted to denote the distance between adjacent transfer interface
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boundaries of a passageway occupied by the optically dense barrier matrix
throllgh which one of the fluid media flows. ~n a circular configuration with
an internally contained matrix st mcture the characteristic dimension will be
the diameter of the passageway containing the fluid medium means. In the flat
or planar configuration having spaced parallel thermally conductive interface
boundaries ~rith the barrier matrix structure disposed therebetween the term
shall denote the distance between the parallel boundary means. In configura-
tions providing fluid medium circulating means embedded in an external barrier
matrix configuration the term shall define the distance between adJacent inter-
face conduit means. If circular conduits are involved then the distance maybe derived by averaging the separation dimensions at preselected points.
Numerous embodiments of the present invention will be described in-
cluding coiled fluid passage means embedded within an optically dense barrier
matrix. Such a structure will provide an efficient domestic hot water source
and may be advantageously disposed at any desired utilization point. Another
embodiment of the invention incorporates the disposition of thermal conductive
bodies within as well as surrounding the medium conducting path to accommodate
heat power densities as high as lOgOOO watts per square inch for applications
such as, for example, boilers for furnaces. The high efficiencies realized
with the disclosed embodiments will result in substantial reductions in space
and cost of heat transfer modules.
Thus, in accordance with the invention, there is provided a heat
exchange system, comprising a thermally conductive structure in structural and
heat exchange association with a conduit for a first fluid and a plurality of
passages for directing the flow of a second and hotter fluid through the
thermally conductive structure, thereby to heat said first fluid, the therm-
ally conductive structure surrounding a central plenum, the conduit comprising
a plurality of elongated conduit portions spaced around the central plenum and
the thermally conductive structure rigidly interconnecting at least some of
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the conduit portions~ the length ot` said passages being less than twice the
average spacing be-tween said conduit portions, a burner supported outside
said plen~ for producing combustion within said plenum, a blower connected
to the burner and arranged for supplying a mixture of fuel and air thereto,
and a pressure regulator for supplying said fuel in gaseous form to the input
of said blower.
The invention, as well as the specific illustrative embodiments,
will now be described, reference being directed to the accompanying drawings
in which:
Figure 1 is a vertical cross-sectional view of an illustrative
embodiment of the invention for heating of a circulating liquid by an external
matrix structure;
Figure 2 is an enlarged fragmentary view of a portion of the exter-
nal matrix included within the line 2-2 in Figure l;
Figure 3 is a sectional view taken along the line 3-3 in Figure 1
viewed in the direction of the arrows;
Figure 4 is a diagrammatic representation cf the principal optimum
parameters of the illustrative embodiment;
Figure 5 is a diagrammatic representation of a flat planar heat
transfer configuration;
Figure 6 is a diagrammatic representation of the embedded external
barrier matrix structure illustrative of one of the conceptual configurations
of the present invention;
Figure 7 is a schematic representation of a complete system utilizing
the illustrative heat transfer module illustrated in Figures 1 through 3
inclu~ive;
Figure 8 is a vertical sectional view of an alternative embodiment
of the present invention;
Figure 9 is a horizontal sectional view taken along the line 9-9 in
-- 4 --
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Fi~lre 8)
~ lgnre 10 is a vertical sectional view of another alternative
embodiment of the invention to provide high power density parameters;
Figure 11 is a vertical sectional view along the line 11-11
in Figure 10; and
Figure 12 is an exploded fragmentary partially sectioned view
illustrative of an alternative embodiment of the invention.
In the drawings, Figures 1, 2, and 3 illustrate a preferred
embodiment of the invention. Before proceeding to the detailed
description, however, it will be of assistace to refer to
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~L~)4~418
Figurcs 4, 5 and 6 and a dcscription of the important conceptual
aspec~s of the invention.
A heat transfer arrangement which provides for a high
thermal transfer rate utili~ing a structure to provide optimum
power density along a heat flow path is illustrated in Figure 4.
Thermally conductive bodies are metallurgically bonded along
contiguous surfaces to define an optically dense barrier matrix 11
along a fluid flow path. The interstices between the bodies de~ine
a tortuous heat transfer path. Spherical members, such as shot or
ball bearingsJ have been shown although similar results are attainable
with other similaTly oriented members th~ configuration and
dimensions of whlch meet the critical parameters required by the
~n~ention. Suitable thermally conductive materials include copper,
brass, stainless steol, carbon steel, aluminum, as well as any of
the plastic materials embedded with metallic particles. Each of
the ferTous or copper body members may be coated with a copper-
silver eutectic solder and the uverall matrix structure may be
- conglomerated by any of the well known processes including brazing,
sintering or welding. A dip brazing technique is required for
aluminum conductive members.
Ach~evement of the maximum average size for the body
members to secure an optically dense matrix in the shortest distancs
possible along the direction cf fluid flow is one of the design
criteria to be followed in the practice of the invention. A flowing
fluid along a path indicated by arrow 13 will encounter the optically
dense structure which is joined to a surface of a conducting boundary
interface 12. Through the provision of a number of body members 10
arranged to provide tortuousheat transfer paths in the optically
dense barrier matrix the total overall efficiency of th~ heat trans-
fer device is enhanced. The pa~h of the thermal energy flow from the
,
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'.: . : ,
:3L04~
flowlng fluid through thc matrix 11 and interface surface 12 is indicated by
th~ arrow 14 to result in transfer to the media contacting the opposing sur-
face 15.
Another criteria required for the provision of an ef~icient heat
transfer structure in the shortest distance possible along the heat flow path
conce~ns the number of bonded joints or junctions in any direction from the
point of thermal contact along a heat path to the nearest adjacent conducting
interface. Referring to Figure 5, a matrix structure 16 is shown disposed
between spaced interface boundary surfaces 17 and 18. Such surfaces may be
provided between the walls within a conduit or between the outer walls of
spaced conduits as will hereinafter be described. The fluid flow path is
indicated by the arrow l9. It has been discovered that optimu~ results will
be obtained ~ith an optically dense arrangement when the number of contiguous
bonded joints in a desired heat path direction from the point of contact to
th~ nearest adjacent interface surface is in the order of two such brazed
joints. The barrier matrix structure disclosed herein is of the internally
mounted configuration and may be practicedin circular or rectangular conduits
as well as between flat planar plates.
The Temaining criteria hereinbefore defined is the characteristic
transrerse dimension shown in Figure 5, and designated by the arrow C.D. as
the dlstance between the parallel boundary surfaces 17 and 18. To achieve
t~e hi~hest heat transfer rates with an optically dense barrier structure
the heat path to the nearest boundary interface surface for aflowing fluid
directed along path 19 may be depicted by perpendicularly directed arrows
20 and 21. The maximum length of the heat path through the matrix ~rom the
~luid to the nearest boundary interface then may be defined as one-half of
the characteristic transverse dimension of the device. For barrier struFtures
employing discrete bodies the present invention discloses that the average
size of each of the
,.;.; . - . . ,., . . . :
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:lV~ 8
bodies shall preferably bo ~pproximatcly o~e-third of the character~s-
tic dimension of the device. Bodies of subs~antially lar~er dimen-
sions, for example, above on~-half of the characteristic dimension,
would not collectively define a sufficiently optically dense arrange-
~ent. In fact, such a device would ble highly inefficicnt in the
transfer of incremental quanta of thermal energy. At the other
oxtreme of the range, thermally conductive bodies of smaller diameters
b~low one_sixth of the characteristic dimension violate the number of
brazed joints requirement and thereby lower the thermal conductivity
eficiency of the heat transfer tevice.
Figure 6 illustrates an embodiment of the invention wherein
the spaced conduit means for directing the flow of a ~luid are
embedded in the barrier matrix and a seeond flowing fluid is directed
~n the region between ~he conduit means as indicated by arrow 22.
This confi~uration is referred ~o as the external type and again
*he design criteria of the number of bonded joints as well as
optical density of the ~atrix are applicable. A circular conduit
23 which may comp~ise a linea~ array of parallel members or a
~elical coil is encased in the barrier matrix 24 of thermally
conductive bodies fabricated in accordance with the invention.
The characteris.tic dimension of this configuration is calculated
between the conduit wall surfaces and is derived by averaging
the dimension A as well as the dimension B which represents ~he
furthermost spacing between the conduit means. Thermal energy
directed along path 22 will ~raverse heat paths indicated by
- ~rrows 25 and 26 to the adjacent conduit ;~alls. Again, as in
the example shown in Figure 5, the heat path maximum is desirably
one-half the characteristic dimension or average distance between
the spaced conduit walls. The number of brazed joints are in the
order of two from point of impact and the average size of ~he
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bodies will ~c bctwc~ll on~-halr to onc sixth of the ch~rackeristic d~.nlcnsion
for thc reguisit~ opt~c~1 density. In such cascs with the one-hRlf body
dimension an average Or one brazed ~oint will inh~rently result and in tho
case of the one-sixth dim~nsion an a~era~e or a~out three brazed joints will
lnherently result.
The hi~h heat transfer rate or increased pOWer density achi~ved by
the invention is believed to be attributable to the large number of surfaces
provided by the conducti~e area o~ each of the matrix body members, turbulent
~luid ~low and the ~ery short heat flow path through the matri~ from the fluid
to the interface surface. Relatively high power densities are attainable in
embodiments o~ the invention to be hereinafter described and may be as high
~s 10,000 watts per square inch of the area of the face of the m~trix body
initially im~inged by the flame. Compared with embodiments of conventional
prior art structures capable of handling power densities of only 100 watts
per area per unit o~ time it ~s apparent that an improvement of several
orders of magnitude have resulted. A use~ul equation in th~ determination
of the design criteria incorporating the teachings of the invention are as
~ollo-~s:
(1) Heat path (L) = (t~ dr~(condUcti~ity of ~ater~a~
~0 Ihe term "heat flux" referq to input thermal energy and may be expressed in
terms o~ British thermal units per hour per square feet o~ ~all area of ~he
~nterface boundary through ~Jhich the heat is trans~erred. Since the power
dens~ty on the face o~ the matrix is trans~erred to the wall area, the heat
flux ~riIl be approxi~ately one-tenth of the above 10,000 watts or 1,00~ watts.
$he~mal conducti~ity of the material is a constant value and is readily
determined from tables for that purpose. This term indicates the quantity
Or heat that 1ill flow aFross a unit area of the body heated if the temper-
ature ~radient is unity. As stated previously, the heat path then re-
presents one-half Or the characteristic dimension. The m.atrix body member
3D dimensions can then be rea~;ly computed from this value Or characteristic
:~0~43L~3
dimcnsion. Tho a~plication of this equation will be de~ans~rated
hereinafter in relation to one of the described embodiments.
In Figures 1, 2 and 3 a highly efficient and practical
embodiment of the present invention is illustrated and will now
be described. ~elical conduit 30 is embedded in and surrounded by
an external sintered barrier matrix 31. Ihe matrix 31 is composed
of discrete thermally conductive bodies to provide for the optical
density in accordance with the teachings of thc i~vention as have
hereinbefore been enumerated. The thermal conductivity, pressure
drop limits and power density will determine the piteh, diame~er
snd overall Iength of the conduit to arrive at the maximum allow-
~ble heat path and this in turn will determine the charactesistic
dimensions. The matrix design criteria a~e then determined from
the characteristic dimension value. An inlet 32 and outlet 33
are, respectively, connected to the water source and egress means
for the util~ization cf the fluid ~edium. The embedding of the
~ondui~ in the barrier matrix can be achieved by positioning the
helical conduit 30 within a cylindrical space defined by two con-
centrically disposed tubular jig ~embers of a material which will
not bond to the body members whose dimensions are related to the
cha~acteristic, dimension Yalue. The jig members have differen~ -
diameters and the circular spa~e between these members may be
filled ~ith the individual body members. Shaking and ~ibrating
of the over-all assembly will provide for the desired array of the
bodies around each of the conduit turns. The entire assembly is
then metal-~rgically treated at the requisite temperature and the
jig members may be separated. The combined externa~ barrier
matrix structure and conduit is then assembled in the embodiment
and a central combustion chamber 38 is defined by the disclosed
hea~ transfer ma~rix.
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Typically, a b-lrner platc member 34 may be provided with
a plurality of passagew~ys 35 for the admittance of an air-gas
~ixture under pressure from a source coupled to conduit 36 and
fitting 37 into the combustion chamber 38. Angularly and laterally
disposed within the burner plate mem'ber 34 is an ignition means 40
of any well known construction such ias a spark plug to provide the
~ecessary ignition of ~he gaseous fuel mixture, Outer wall member
41 s~rTounds the heat transfer structure and a flue 4Z for the
passage of the exhaust gases extends to a conventional chimney
tnot shohn~. Top plate member 43 is suitably secured to the heat
transfer structure and conduit such as by nut and bolt means 44J
part of which may also be embedded in the matrix.
In an ex~mplary working embodiment a heat transfer unit as
- described in Figures 1 ~hrough 3 inclusive having dimensions of
about ive inches in diameter and about five inches in leng~h was
utilized to provide a:continuous ho~"water ~low'of approximately
three gallons per minute. The burner driving'the heat transfer ',
unit and all the electrical controls including a thermostat~ air
filter and safety regulating devices were incorporated into a
stsucture having a hsight of about six inches, a width of about
twelve inches~and an overall len~h of about eighte~n inches.
Such a haat transfer module can replace conventional present day
hot water heaters of the storage tank variety having diameters
of approximately two feet and heights of approximately six feetO
TSe new improved structure can be very conveniently mounted
adjacent to the final utilization point. In view of the exceeding-
ly low cost many such devices can also be incorporated with resul-
, tant savings in cost of piping and plumbing necessary with present
J' day centralized domestic hot water heating systems.
' 30 Referring now to Figure 7, the embodiment of the invention
.
~a 11 ~
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Z4~8
shown in Figurcs 1-3 inclusivo together with the appurtenant
structures, is collectively referred to as a heat transfer ~odule
tesignated by tlle numeral 50. An air blower Sl is coupled through
the fitting 37 IO feed the air and gas mixture into combustion
chamber 38, A gas from source 53 which may be any commercially
available natural or tank type, is fed through a solenoid control
Yalve 54 and regulator 55 to the inlet 52 in blower 51~ Any small
si~e blower of the inexpensive varie~y should suffice for most
applications. The ven~ 42 extending laterally from ~he hea~
transfer module S0 will provide for the egress of the combustion
gases to a convenient outlet. Due to the efficiency of the heat
transfer and the fact ~hat the exhaust temperature is exceedingly
low a small vent opening in a wall may be used similar ~o ~he type
employed in home clothes dryers. No natural draft type chimney is
required, which also results in savings in construction costs. The
: ~ water supply is indicated by numeral 56 and the heated water medium
is fed through line 57 to the outlet tap 58 for instant usage. A
temperature and pressure relief valve 59 may be disposed in line
57. It is thus noted that large storage tanks or boilers utilized
in present day hot water generation sources are completely elimina-
ted. A compact and unique cource is thus disclosed which may be
- seadily installed directly in the area where the use is intended,
for example, the bathroom or kitchen.
Associated wiring for the control of the blower as well as
the thermosta~ and ignition controls toge~her with the main solenoid
~alve for the gas source have not been specifically described since
they are readily commercially available and normal techniques incor
porating such means will be fo11Owed.
In Figures 8 and 9 a linear array of fluid conduits 61 is
embedded within barrier matrix 62 composed of thermally conductive
.
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bodies as havc hcreinbcforc been dcscribcd. Upper plat~ ~cmber 63
supports fluid inlet passagc means 64 and is secured by fastening
means 65 to screws 66 embedded in collar member 67. The optically
densc matrix structure 62 surrounds the linear conduits 61 which
are embedded therein, ~he ends of these conduits and the inlet 64
all communicating with a channel 68 in the inner side of collar
member 67. A similar end arrangement is disposed at the opp~site
end of the matrix structure including a lower pl~te member 71 and
adjacent coilar member 70 and communicates with an inner channel
68a in collar member 70 with which the adjacent ends of conduits
61 also communicate. A fluid outlet means ?2 is supported by ~he
low~r collar member 70. Plate member 71 further defines a plurality
~f passages 73 for a gas-air mixture fed into the device through ~ -
- conduit 74. The ignition means for the combustible fuel within the
chamber 75 is furnished by spark plug member 76 supported by upper
:: plate member 63.~
Figures lO and ll are directed to an embodiment for very high
~ower density applica~ions. In 5uch embodiments conduits 77 and 7g
are disposed about a common axis. Outer conduit 77 is closed by
conductive pla~e means 79 and 80 at opposing ends. Inlet member
81 proYides f~r the ingress of a fluid medium and ou~let member 82
- provides for the egress of the medium in the Yaporized or heated
state. The inner conduit 78 is open at the ends for the flow of
a heated medium such as the gases from a direct oxygen-gas flame
along the inner passage B3 of this conduit, with the direction of
, flow being ~ndicated by the arrow 84. An optically dense barrier~atrix structure 85 comprises a plurality of thermally conductive
spherical members joined ~ogether to define the thermal transfer
paths in accordance with the teachings of the invention. The
barri~r struc~ure 85 occupies a major portion of the cross-sectional
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arca of the conduit 78 and the characteristic dimension of this
member will be the inner diameter of the circ~lar conduit as
designated by the arrow 86 and symbol C.D.
A similar barrier matrix 87 occupies the cross-sectional
area of the outer conduit 77. With the internal barrier ma~rix
structure 85 occupying only a portion of the overall length of the
passage 83 for concentration of the heated medium, the heat trans-
fer a~ea between the medium in the respective conduits will occur
substantially in the region indicated by the bracket 88. This
configura~ion ~hen provides for high power density applications.
An example of the application of the previously enumerated
equation ~1) in ~he transfer of heat from an intense heat source
~ay be ~oted in the high power density embodiment of Figures 10 and
11. Utili~ing a direct flame source we assume that a power density
of 10,000 watts per square inch of flame area is obtained and yet
silver brazed copper members may be employed. Addi~ionally, it is
assumed that a desired temperature drop of 100 degrees Fahrenheit
- is specified. Copper has a thermal conductivity value of about
200 BTU/hour/ft/F. In the final structure we assume that a lower
conductiYity will be realized due to the brazed joints and optical
tensity of th thermal paths. A conductiYity factor of 50 percent
then will provide a reliable design factor. Utilizing the other
known values the heat path (L3 is calculated as follows:
L = 100 X lO0 = 2 X lo-2 feet = 1/4 inch
,5 X lO6
Tha characteristic dimension will then be twice the hea~ pa~h value
or 1/2 inch. A thermally conductiYe bo~y 2verage size of between
; one-quarter and one-twel~th of an inch therefore is indicated for
the required optimum optical density. A one-third value or one-
sixth of an inch for thermal body size is preferred in most applica-
tions,
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Xn FlGure 12 anothcr embo(liment iB illu3tratcd. A hclical conduit
hnvin~ a plurallty Or turns 50 is c~bedded within ~ matrix 91 Or thc externa]
type. Ir we ~rovide the proper desi~n critcria for the matrix membcrs surround-
lne the conduit thc interior pa~sa~es thereor ~y be ~illed with other conduc-
tive member~ which need not meet these 52me critical requirements. Hence7 in
appl~cations where ~te~m is ~ener~tcd and in condcnsation devices particles
such as mesh, wires, shavings, cuttings and the like can be ~mployed, as indi-
cated collectively by numeral ~2. Such a confieuration for the obstructions
within the conduit will provide ror even wider application of the invention
in industry
As can be seen ~rom any fieure o~ the drawings, e.g. ~ig. 1, the
gas passage length through the sintered matrix of spheres 31 pre~erably does
not substan~ially exceed seven layers of balls, or approximately 15 times the
- aYerage radius o~ curvature of the passage surfaces, and the average radius oL
curvature of the spheres 31 is substantially less than the radius of curvature
o~ the in+.erior sur~ace of conduit 30.
~he advantages of compactness and efficiency of the disclosed.
thermal trans~er device in the provision o~ vastly improved power dens~ties
through the optically dense ~atrix structure will now be apparent to those
skilled in the art from this description. The deslgn criteria of the number
of bonded ~oints alon~ the heat path and the average size of the thermally
conductive bodies in relation to th_ characteristic dimension to provide the
desired optical density have been carefully enumerated. The foregoin~ dis-
cussion and exe~plary application o~ the equation will also assist in the
practice of the invention. In addition to the exe~plary embodiments n~nerous
other con~i~urations will be evident ~or othcr applications. For example, the
thcrmally conductive body members in contact with the outermost wall surfaces
o~ circular conduits sh~rn in Figs. 1 and ô may be eliminated, thereb~ exposing
thi6 portion o~ th~ boundary interrace conduit walls. The heat trans~er paths
w~thin thc ~trix bet~/cen ~he s~aced conduit rnembers would still be defincd in
~ccordance ~ h this invention by the thermally conducti~re bodies in the ~luid
flow path.
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