FLOW-THROUGH METALLIC FELD BODY HEATER FOR FLUID

COUSSIN METALLIQUE PERMEABLE ECHANGEUR DE CHALEUR POUR FLUIDES

English Abstract

ABSTRACT OF THE DISCLOSURE
An electrical heating device employs a metallic
felt body through which fluid to be heated is passed.
The felt may be of polycrystalline metal whiskers, or
non-metal whiskers or filements with metal coating applied.
The body is heated by contact with an element that is heated
electrically The fluid flows through the body in a
relatively long path compared with the distance through
which heat has to be conducted through the body from said
element. The body is conveniently a hollow cylinder, the
fluid flow being parallel to the axis and the heat being
applied from inner and outer tubes between which the felt
body is disposed.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An electric heating device for the heating or
vaporization of a liquid, comprising: at least one elongated
porous body having a small dimension perpendicular to its
longitudinal extension, said porous body consisting of a felted
mass of polycrystalline metal whiskers of metal-coated-non-metal
whiskers metallically interconnected at their point of contact,
said porous body being enclosed between walls of heat-conducting
material along its longitudinal dimension, means for passing
the liquid through the porous body in its longitudinal direction,
an inlet connection for the liquid to be heated at one end
face of the porous body and an outlet connection at the other
end face, an electric heating element in direct contact with
at least one of said walls, the small dimension of the porous
body perpendicular to its longitudinal extension providing a
thin cross section to facilitate an essentially uniform heating
of the porous body by heat radiation from said heated wall and
by heat conduction through the whiskers adjacent said wall to
the whiskers more remote from said wall.
2. A device as claimed in claim 1, in which said body
is of hollow cylindrical form and is arranged to be traversed
by the fluid to be heated in the direction of its axis and two
said walls are provided in the form of an inner tube and an outer
tube bounding said hollow cylinder.
3. A device in accordance with claim 2, wherein an
electric heating coil is arranged t least on the outer tube.
4. A device in accordance with claim 3, wherein an
electric heating coil is arranged within the inner tube.
5. A device in accordance with claim 2, wherein a
waste gas pipe communication with the inner tube and waste gases
in said pipe thereby heating said inner tube.

6. A device in accordance with claim 2, wherein
said cylinder and tube form a unit, a lagged housing encloses
said unit and said housing has at one end an inlet for the fluid
to be heated and at the other end an outlet for the evaporated
fluid,
7. A device in accordance with claim 4, in combination
with a pipe carrying combustion air, wherein said unit is
centrally mounted in said pipe.
8. A device in accordance with claim 5, wherein a
cover normally closes an opening in the side of said pipe and
said unit is arranged detachably thereon.
9. A device in accordance with claim 4, wherein a
valve is provided to govern said outlet.
10. An electric heating device for the heating or
vaporization of a liquid, comprising: at least one elongated
porous body having a msall dimension perpendicular to its
longitudinal extension, said porous body consisting of a felted
mass of polycrystalline metal whiskers or metal-coated non-metal
whiskers metallically interconnected at their point of contact,
said porous body being enclosed between walls of heat-conducting
material along its longitudinal dimension, means for passing
the liquid through the porous body in its longitudinal direction,
an inlet connection for the liquid to be heated at one end face
of the porous body and an outlet connection at the other end
face, an electric heating element in direct contact with at least
one of said walls, the small dimension of the porous body
perpendicular to its longitudinal extension providing a thin
cross section to facilitate an essentially uniform heating of
the porous body by heat radiation from said heated wall and by
heat conduction through the whiskers adjacent said wall to the
whiskers more remote from said walls, and said body being
a plate-like member.

11. A device in accordance with claim 10, wherein
a housing encloses a plurality of said plate-like members, each
with an electrically heated casing, arranged parallel to, but
spaced from, one another, and the intervening spaces between
neighboring plates form ducts for the passage of combustion air.
12. An electric heating device for the heating or
vaporization of a liquid, comprising: at least one elongated
porous body having a small dimension perpendicular to its
longitudinal extension, said porous body consisting of a felted
mass of polycrystalline metal whiskers or metal-coated-non-metal
whiskers metallically interconnected at their point of contact,
said porous body being enclosed between walls of heat conducting
material along its longitudinal dimension, means for passing
the liquid through the porous body in its longitudinal direction,
an inlet connection for the liquid to be heated at one end face
of the porous body and an outlet connection at the other end
face, an electric heating element in direct contact with at
least one of said walls, the small dimension of the porous body
perpendicular to its longitudinal extension providing a thin
cross section to facilitate an essentially uniform heating of
the porous body by heat radiation from said heated wall and
by heat conduction through the whiskers adjacent said wall to
the whiskers more remote from said wall, the device including an
elongated casing composed of two shells which are connected to
each other at their edges, the porous body comprising a flat hull
filled with the felted mass, and the hull being formed from a
pipe having been pressed flat to a minimum predetermined width.
13. A device in accordance with claim 12, wherein
electric heating elements are in the shape of flat plates each
comprising an electrical heating lead respectively lying on the
side faces of the hull.
14. An electric heating device for the heating or
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vaporization of a liquid, comprising: at least one elongated
porous body having a small dimension perpendicular to its
longitudinal extension, said porous body consisting of a felted
mass of polycrystalline metal whiskers or metal-coated-non-metal
whiskers metallically interconnected at their point of contact,
said porous body being enclosed between walls of heat-conducting
material along its longitudinal dimension, means for passing the
liquid through the porous body in its longitudinal direction,
an inlet connection for the liquid to be heated at one end face
of the porous body and an outlet connection at the other end
face, an electric heating element in direct contact with at
least one of said walls, the small dimension of the porous body
perpendicular to its longitudinal extension providing a thin
cross section to facilitate an essentially uniform heating of
the porous body by heat radiation from said heated wall and by
heat conduction through the whiskers adjacent said wall to the
whiskers more remote from said wall, the porous body comprising
an outer hull of good heat-conductive material having the
configuration of a flattened pipe so as to form a flat plate,
the flat plate being traversed in longitudinal direction by
bores which intersect each other to form an internal space
surrounded by corrugated walls, and the internal space being
filled with the felted mass.
15. An electric heating device for the heating or
vaporization of a liquid, comprising: at least one elongated
porous body having a small dimension perpendicular to its
longitudinal extension, said porous body consisting of a felted
mass of polycrystalline metal whiskers or metal-coated-non-metal
whiskers metallically interconnected at their point of contact,
said porous body being enclosed between walls of heat-conducting
material along its longitudinal dimension, means for passing
the liquid through the porous body in its longitudinal direction,
12

an inlet connection for the liquid to be heated at one end face
of the porous body and an outlet connection at the other end
face, an electric heating element in direct contact with at
least one of said walls, the small dimension of the porous body
perpendicular to its longitudinal extension providing a thin
cross section to facilitate an essentially uniform heating of
the porous body by heat radiation from said heated wall and
by heat conduction through the whiskers adjacent said wall to
the whiskers more remote from said wall, the porous body
including a casing formed of a number of pipes of rectangular
cross section filed with the felted mass, the pipes being stacked
upon each other so that the external shape of the porous body
assumes the configuration of a flattened pipe.
16. An electric heating device for the heating or
vaporization of a liquid, comprising: at least one elongated
porous body having a small dimension perpendicular to its
longitudinal extension, said porous body consisting of a felted
mass of polycrystalline metal whiskers or metal-coated non-metal
whiskers metallically interconnected at their point of contact,
said porous body being enclosed between walls of heat-conducting
material along its longitudinal dimension, means for passing
the liquid through the porous body in its longitudinal direction,
an inlet connection for the liquid to be heated at one end face
of the porous body and an outlet connection at the other end
face, an electric heating element in direct contact with at
least one of said walls, the small dimension of the porous
body perpendicular to its longitudinal extension providing a
thin cross section to facilitate an essentially uniform heating
of the porous body by heat radiation from said heated wall
and by heat conduction through the whiskers adjacent said wall
to the whiskers more remote from said wall, the porous body
having an outer hull with a configuration like that of a flattened
13

pipe so as to form a flat plate, the hull being taversed by
individual separated bores so that the sidewalls of the hull
are interconnected by webs between adjacenb bores, and the
bores being filled with the felted mass.
17. An electric heating device for the heating or
vaporization of a liquid, comprising: at least one elongated
porous body having a small dimension perpendicular to its
longitudinal extension, said porous body consisting of a felted
mass of polycrystalline metal whiskers or metal-coated non-
metal whiskers metallically interconnected at their point of
contact, said porous body being enclosed between walls of heat-
conducting material along its longitudinal dimension, means for
passing the liquid through the porous body in its longitudinal
direction, an inlet connection for the liquid to be heated at
one end face of the porous body and an outlet connection at the
other end face, an electric heating element in direct contact
with at least one of said walls, the small dimension of the
porous body perpendicular to its longitudinal extension providing
a thin cross section to facilitate an essentially uniform heating
of the porous body by heat radiation from said heated wall and
by heat conduction through the whiskers adjacent said wall
to the whiskers more remote from said wall, said body is of
hollow cylindrical form and is arranged to be traversed by the
fluid to be heated in the direction of its axis and two said walls
are provided in the form of an inner tube and an outer tube
bounding said hollow cylinder, and said wall forming an electrical
heating element.
18. An electric heating device for the heating or
vaporization of a liquid, comprising: at least one elongated
porous body having a small dimension perpendicular to its
longitudinal extension, said porous body consisting of a felted
mass of polycrystalline metal whiskers or metal-coated non-metal
14

whiskers metallically interconnected at their point of contact,
said porous body being enclosed between walls of heat-conducting
material along its longitudinal dimension, means for passing
the liquid through the porous body in its longitudinal direction,
an inlet connection for the liquid to be heated at one end of
the porous body and an, outlet connection at the other end face,
an electric heating element in direct contact with at least
one of said walls, the small dimension of the porous body
perpendicular to its longitudinal extension providing a thin
cross section to facilitate an essentially uniform heating of the
porous body by heat radiation from said heated wall and by heat
conduction through the whiskers adjacent said wall to the
whiskers more remote from said wall, and said body being a plate-
like member, and said wall forming an electrical heating element.
19. An electric heating device for the heating
or vaporization of a liquid, comprising: at least one elongated
porous body having a small dimension perpendicular to its
longitudinal extension, said porous body consisting of a felted
mass of polycrystalline metal whiskers or metal-coated non-
metal whiskers metallically interconnected at their point of
contact, said porous body being enclosed between walls of heat-
conducting material along its longitudinal dimension, means for
passing the liquid through the porous body in its longitudinal
direction, an inlet connection for the liquid to be heated at
one end face of the porous body and an outlet connection at the
other end face, an electric heating element in direct contact
with at least one of said walls, the small dimension of the
porous body perpendicular to its longitudinal extension providing
a thin cross section to facilitate an essentially uniform heating
of the porous body by heat radiation from said heated wall and
by heat conduction through the whiskers adjacent said wall to the
whiskers more remote from said wall, said body is of hollow

cylindrical form and is arranged to be traversed by the fluid
to be heated in the direction of its axis and two said walls
are provided in the form of an inner tube and an outer tube
bounding said hollow cylinder, and the porous body having a
thickness of between approximately 2 and 5 mm.
20. An electric heating device for the heating or
vaporization of a liquid, comprising: at least one elongated
porous body having a msall dimension perpendicular to its
longitudinal extension, said porous body consisting of a felted
mass of polycrystalline metal whiskers or metal-coated non-metal
whiskers metallically interconnected at their point of contact,
said porous body being enclosed between walls of heat-conducting
meaterial along its longitudinal dimension, means for passing
the liquid through the porous body in its longitudinal direction,
an inlet connection for the liquid to be heated at one end face
of the porous body and an outlet connection at the other end
face, an electric heating element in direct contact with at least
one of said walls, the small dimension of the porous body
perpendicular to its longitudinal extension providing a thin
cross section to facilitate an essentially uniform heating of
the porous body by heat radiation from said heated wall and
by heat conduction through the whiskers adjacent said wall to
the whiskers more remote from said wall and said body being
a plate-like member, and the porous body having a thickness
of between approximately 2 and 5 mm.
21. An electric heating device for the heating or
vaporization of a liquid, comprising: at least one elongated
porous body having a msall dimension perpendicular to its
longitudinal extension, said porous body consisting of a felted
mass of polycrystalline metal whiskers or metal-coated non-metal
whiskers metallically interconnected at their point of contact,
said porous body being enclosed between walls of heat-conducting
16

material along its longitudinal dimension, means for passing
the liquid through the porous body in its longitudinal direction,
an inlet connection for the liquid to be heated at one end face
of the porous body and an outlet connection at the other end
face, an electric heating element in direct contact with at
least one of said walls, the samll dimension of the porous body
perpendicular to its longitudinal extension providing a thin
cross section to facilitate an essentially uniform heating
of the porous body by heat radiation from said heated wall and
by heat conduction through the whiskers adjacent said wall to
the whiskers more remote from said wall, and said wall forming
an electrical heating element.
17

Description

~q)3E~ )6
The invention relates to electrical heating devices for
the heating or vaporisation of fluid. It is concerned with such
devices having at least one porous body of inter felted poly-
crystalline whiskers or metallised non-metallic whiskers or
filaments, joined together metallically at their points of con-
tact. The body is traversed by the medium to be heated and is
itself heated by being in contact with a~wal~ of good heat-
conducting material. This may itself be an electrical heating
element or be arranged to be heated by one.
Porous bodies which consist of interconnected poly-
crystalline metal whiskers or metallised non-metallic whiskers
or filaments, such as A12O3 whiskers, car~on, quartz or rock
fibres, can be produced with an extremely large inner surface
area for the volume of ~he envelope oE the body. They have been
used successfully as electrical heating resistance elements for
the vaporisation or atomising of liquid fuels. Since direct
heating by electric current in many cases causes trouble owing to
the good electrical conductivity of such a porous body, it has
been proposed to heat the body indirectly by electricity. The
porous body is then arranged to be in heat-conductive contact with
another element heated by electric current. It has been found
that this indirect electric heating does indeed have considerable
advantages from the point of view of the source of energy avail~
able, but by comparison with a whiskers skeleton heated by the~
direct passage of electric current it takes rather a long time to
heat the fluid to a desired temperature, particularly when a
cylindrical porous body oE rather large diameter is used. This
is because the central ~one of such a body is warmed very much
less strongly than the external zone, which is in the immediate
vicinity of the heated wall surrounding the cylinder. A body with
alternately arranged heating plates and whisker plates can pro-
duce more uniform heating of the whisker portions, but they are
'' ~
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3~0~6
traversed radially from inside to outside and only a short dwell
time is possible for the fluid to be heated. Such plates cannot
be made with an unduly large diameter for constructional reasons.
Therefore, in order to heat a determined volume of liquid in a
given time to a desired temperature or even to vaporise it, the
whisker plates must be heated to relatively high temperatures
which, when heating or vaporising hydrocarbons, intensifies their
tendency to crack and therefore to form pore-choking residues.
It is an object of this invention to provide an ele-
ctr.ic heating device using inter-felted whiskers of filaments
which is simple in construction and allows rapid and uniform
heating of the fluid.
According ko the present invention there is provided an
electrical heating device for the heating or vaporisation of
fluid, comprising at least one elongated porous body consisting of
inter-felted polycrystalline metal whiskers or metallised non-
metal whiskers or. filaments connected metallically together at
their points of contact, and arranged to be traversed in the
longitudinal direction by the fluid to be heated, and at least
one wall of heat conductive material bounding said bod~ and being
in conductive relationship therewith, said wall forming or having
associated therewith an electric heating element..
In a preferred embodiment, the body is of hollow
cylindrical form and is arranged to be traversed by the fluid in
the direc-tion of its axis. The two walls are conveniently inner
and outer tubes bounding the cylinder.
In this embodiment, compared with a porous solid cylin-
der, there is no central zone which is at a considerable distance
from a heat~emitting wall, and which therefore contributes only
slightly to the heating of the fluid. There is therefore a con-
siderable saving of whiskers and a more rapid and uniform heating
of the fluid. With a solid cylinder, the outermost zone has to
-- 3 --

be excessively heated to compensate for the poor heating of the
central zone, in order to attain the desired median temperature.
In particular, for vaporisation of liquid fuels, for instance
~uel oil, diesel oil or petrol, difficulties occur with solid
cylinders. It is not practical to heat such hydrocarbons beyond
a given temperature since there is otherwise the risk of the
formation of residues and cracking, and the excesslvely heated
outer zone can promote this.
In a preferred form there is arranged on the outer tube
at least, an electric heating coil. The cylinder and tubes
conveniently form a unit in a lagged housing having at one end
an inlet for the 1uid to be heated and at the other end an out-
let for the heated or evaporaked fluid. Such an electric heating
device can be used very satisfactorily for heating liquld ~uels,
and in particular for the evaporation of fuel oil. For this
purpose the unit may be centrally mounted in a pipe for carrying
the combustion air, and it can be arranged detachably on a cover
which normally closed an aperture in the wall of said pipe. The
outlet is preferably governed by a valve. In the event of a
breakdown, the unit, or even the housing with the unit, can be
removed and discarded and replaced by a new device.
The outer tube is conveniently electrically heated.
The inner pipe may be too, or alternatively it may communicate
with a waste gas pipe, so that the hot waste gases heat the
inner tube.
Instead of a hollow cylinder, a thin oblong plate-like
member may be adopted for the porous body. With this embodiment,
it is desirable for the heating of liquid fuels, and in particular
for the evaporation of fuel oil, for several such porous bodies
with an electrically heated jacket to be arranged parallel to,
but spaced from, one another, but at some distance apart, the
intervening spaces between neighbouring plates acting as ducts
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~)3~0~6
for the passage of the combustion air.
For a better understanding of the invention some con-
structional forms thereof will now be described, by way of
example, with reference to the accompanying drawing, in which:
Figure 1 is an axial section of part of an oil burner
with a heating device according to the invention, for vaporizing
the fuel oil, and
Figure 2 is a perpsective view, longitudinally sectioned,
of a modified electrical heating device which could be used in
the oil burner shown in Figure 1.
The oil burner of Figure 1 has a pipe 1 for carrying
the air for combustion capped at its combustion ch~mber end by a
perforated plate 2. Arranged centrally in the pipe 1 is a cylin-
drical electrical heating device 3, which serveq to evaporate the
fuel oil to be mi~ed with the combustion air. The electric
heating device 3 consists of a porous body 4 in the form of a
hollow cylinder, which is bounded by an inner tube 5 and an outer
tube 6. The porous body 4 is made of inter-felted polycrystalline
metal whiskers or metallised non-metallic whiskers or filaments
which are metallically bonded at their points of contact. The
body 4 is arranged to have good heat communication with both tubes
5 and 6, this being achieved for instance by sintering on or by
deposition of metal1for preference by thermal decomposition of a
metal compound, in particular a metal carbonyl. The inner tube
5 is provided on its inner surface and the outer tube 6 on it~
outer surface with respective electrical heating colls 7 and 8,
which can be connected with a source of electric current (not
shown). The space within the inner tube 5 and the intervening
annular space 9 between the tubes 5 and 6 containing the porous
body 4 are capped at their ends by covers 10 and 11.
An oil supply pipe 12 delivers through the cover 11
into the end of space 9 remote from plate 2. The cover 10 pro-
_ 5 _

~3~ 36
vides a number of outlet apertures 13 from the other end of
space 9, opening into a shallow cylindrical chamber 14 which is
bounded by the cover 10, an extended end portion of the outer tube
6 and an end plate 15 for the outer tube 6. The chamber 14 has
a central outlet aperture 16 in plate 15 with a valve seat 17
which acts in conjunction with a valve body 18 in a manner to be
described below. The outer tube 6 is surrounded by a heat-
insulating housing 19 at least in the zone of the electric heating
coil 8.
The valve body 18 is attached to a rod 20 which passes
through a guide tube 21 in the heating device 3 to rest against
a pivotable rod 22 spanning the pipe 1. ~rhis rod 22 protrucles
through an aperture 23 in the pipe 1 and is linked to the armature
of an electromaynet 24. A spring 26 acting between the cover 11
of the heating device 3 and a collar 26 on the rod 20 urges the
valve body 18 onto the valve seat 17. When the electromagnet 24
is excited, the rod 22 is pivoted into the position shown in
which the rod 20 has moved to the left and the valve body 18 has
been lifted from the valve seat 17.
The pipe 1 also contains, at the downstream end, a
freely rotatable auxiliary blower wheel 27 with blades or vanes
28. This is driven by the current of air flowing as indicated
by the arrows 29. The purpose of the blower wheel 27 with its
vanes 28 is to mix the oil vapour emergi.ng from the aperture 16,
when the valve 17, 18 is opened, intensively with the combustion
air, To prevent any small drops of oil present from being hurled
outward against the wall of the pipe 1, and from exerting an
unfavourable influence on combustion in the marginal zone of the
perforated plate 2, the blower wheel 27 .is surrounded by a casing
30 which tapers towards the perforated plate 2 and ensures that
non-vaporised drops of fuel oil are guided into the cen-tral region
of ~he pipe 1. To adjust the volume of air-fuel mixture admltted
- 6 -

to the co~bustion chamber, it is possible to arrange outside the
perforated plate 2 a second perforated plate 31 which can be
twisted or moved so that its perforations are brought more or
less into coincidence with the per~orations of the plate 2, as
required.
In operation, the combustion air is supplied through
the pipe 1 by means of a blower ~not shown), and the auxiliary
blower wheel 27 is caused to rotate. At the same time fuel oil
is supplied through the pipe 12 and the porous body 4 is heated
by connecting the heating coils 7 and 8 to a source of electrical
current. The fuel oil Elowing through the porous body ~ is then
vaporised and the oil vapour passes through the ou~Lct apertures
13 into the chamber 14. On switching on the burner, the electro-
magnet 29 is also excited, whereby the valve body 18 is liEted
from its seat 17. The oil vapour can now emerge from the chamber
14 through the aperture 16 and mix with the combustion air. The
oil vapour/air mixture passes through the apertures of the per-
~orated plates 2, 31 and enters the combustion chamber, where it
is ignited in the usual way. A blue, non-luminous flame is
produced by a short distance from the outer perforated plate 31.
In the event of breakdowns, and in order to allow the
rapid replacement of the electrical heating device 3, the latter
can be arranged detachably on a cover 33, which closes an aperture
34 in the wall o~ the pipe 1. When the cover 33 is removed, the
electrical heating device 3 can be removed as a complete unit,
including the valve body 18. To allow this, the supply pipe 12
can be made flexible.
In an alternative arrangement, the auxiliary blower
wheel 27 can also be driven by its own motor. The inner heating
coil 7 can be omitted, particularly if the inner tube 5 is
connected with a waste gap pipe tnot shown). It can then be
traversed by hot waste gases and heated by them. These hot waste
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- 1~3~0~
gases can then be returned, if required, to the combustion chamber.
Alternatively, either or both tubes can be heated directly by
electric current flowing through them.
Figure 2 shows an electrical heating device which can
be used instead of the heating device 3 in Figure 1. This device
contains a porous body 4' in the form of a thin oblong plate,
which is surrounded b~ a jacket 35 of good heat-conducting
material carrying an outer heating coil 36. The whole is sur-
rounded by a lagged housing 37. 12' denotes the oil supply pipe,
21' the valve .rod guide and 16' the continuation of the jacket
35 containing the valve seat and the outElow aperture, corres-
ponding to the parts o:E Figure 1 with the same re:~e.rences but
uprimed.
Common to the ~wo electrica:L heatincJ devices shown :Ln
Figures 1 and 2 is the fact that in both cases the.components of
the porous bodies which are only warmed by heat conduction are
at a slight distance from the electrically heated wall, so that
rapid and uniform heating of the fluid flowing through them is
obtained.
Of course, if necessary, several electrically heated
porous bodies can be provided. For instance, several plate-
shaped porous bodies corresponding to that of Fi~ure 2, with
electrically heated jackets, can be arranged parallel to one
another in a housing. The spaces between neighbouring plates
can form passages for the combustion air, for example when the
electrical heating device is to be used for vaporising fuel oil
inside an oil burner.