U.S. patent number 3,833,791 [Application Number 05/023,090] was granted by the patent office on 1974-09-03 for resistance type fluid heating apparatus.
This patent grant is currently assigned to Schladitz-Whiskers A.G.. Invention is credited to Hermann J. Schladitz.
United States Patent |
3,833,791 |
Schladitz |
September 3, 1974 |
RESISTANCE TYPE FLUID HEATING APPARATUS
Abstract
A method and apparatus for rapidly heating gases, liquids,
vapors and aerosols to a desired temperature by electric resistance
heating. More particularly, the present disclosure is directed to a
method and apparatus for rapidly heating up a medium such as gases,
liquids, vapors, and aerosols to a desired temperature by means of
an electric resistance heater, comprising the steps of guiding the
medium to be treated through the electric resistance heater in such
a manner as to expose said medium to a structural surface of at
least about 800 square centimeters per cubic centimeter of medium
to be treated.
Inventors: |
Schladitz; Hermann J. (Munich,
DT) |
Assignee: |
Schladitz-Whiskers A.G. (Zug,
CH)
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Family
ID: |
27176329 |
Appl.
No.: |
05/023,090 |
Filed: |
April 6, 1970 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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474797 |
Jul 26, 1965 |
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Foreign Application Priority Data
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Jul 28, 1964 [CH] |
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9872/64 |
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Current U.S.
Class: |
392/485; 55/523;
338/223; 428/613; 75/229; 219/553; 428/594 |
Current CPC
Class: |
H05B
3/141 (20130101); F24H 1/101 (20130101); F24H
1/0045 (20130101); H05B 3/48 (20130101); Y10T
428/12347 (20150115); Y10T 428/12479 (20150115) |
Current International
Class: |
F24H
1/10 (20060101); H05B 3/42 (20060101); H05B
3/14 (20060101); H05B 3/48 (20060101); H05b
001/00 () |
Field of
Search: |
;219/306,307,381,426,427,544,382,374,553 ;29/182,419 ;55/267,523
;75/2F ;338/223-225 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Bartis; A.
Attorney, Agent or Firm: Craig & Antonelli
Parent Case Text
This application is a Streamlined Continuation of my copending
application Ser. No. 474,797, filed July 26, 1965.
Claims
I claim:
1. A resistance heating element for an electric resistance heater
for heating fluids, comprising: a porous mat of fine,
electrically-conductive, elongated elements connected together so
as to be electrically conductive, and power means for supplying
electrical energy to said mat, said elongated elements being
selected from the group consisting of metal-coated non-metal
whiskers and polycrystalline metal whiskers, wherein said elongated
elements are connected at the contact points thereof by
metallization from the gaseous phase.
2. A resistance heating element for an electric resistance heater
for heating fluids, comprising: a porous mat of fine,
electrically-conductive, elongated elements connected together so
as to be electrically conductive, and power means for supplying
electrical energy to said mat, said elongated elements being
selected from the group consisting of metal-coated non-metal
whiskers and polycrystalline metal whiskers, said elongated
elements being connected at the contact points thereof by electron
beam welding.
3. A resistance heating element according to claim 2, wherein said
elongated elements consist of metalized monocrystalline whiskers of
aluminum oxide.
4. A resistance heating element for an electric resistance heater
for heating fluids, comprising: a porous mat of fine,
electrically-conductive, elongated elements connected together so
as to be electrically conductive, and power means for supplying
electrical energy to said mat, said elongated elements being
selected from the group consisting of metal-coated non-metal
whiskers and polycrystalline metal whiskers, wherein said elongated
elements are provided with a layer of electrically-insulating
material selected from the group consisting of insulating lacquers,
plastics and oxides.
5. A resistance heating element for an electric resistance heater
for heating fluids, comprising: a porous mat of fine, electrically
conductive, elongated elements connected together so as to be
electrically conductive, and power means for supplying electrical
energy to said mat, said elongated elements being selected from the
group consisting of metal-coated non-metal whiskers.
6. A resistance heating element according to claim 5, wherein said
elongated elements consist of metalized monocrystalline whiskers of
aluminum oxide.
7. A resistance heating element for an electric resistance heater
for heating fluids, comprising: a porous mat of fine,
electrically-conductive, elongated elements connected together so
as to be electrically conductive, and power means for supplying
electrical energy to said mat, said elongated elements consisting
of metalized monocrystalline whiskers of aluminum oxide, said
elongated elements being connected at the contact points thereof by
electron beam welding.
Description
The present invention relates to a method and apparatus for rapidly
heating gases, liquids, vapors and aerosols to a desired
temperature by electric resistance heating.
Already known in the art is a large number of electric resistance
heaters, also referred to at times as heat exchangers, which give
off to gases or liquids joulean heat, produced by the electric
current, either directly by heat conduction or indirectly by
convection heat or heat radiation, or by a mixed heat transfer of
these different types. A portion of these known electric resistance
heaters is electrically insulated from the medium to be heated, for
example, the generally known immersion heaters. Other resistance
heaters are self-supporting and freely exposed and without
protection of their metallic surface, for example, asbestos heating
grills or self-supporting, exposed heating coils of electric
furnaces or ovens.
These known resistance heaters do not act directly on the entire
volume of the medium to be heated, but only upon the portion
thereof which is present in the immediate vicinity of the
resistance heater, whereas the medium in its entirety is then
heated by heat convection to the desired temperature within a
certain amount of time. In order to heat the medium to be heated to
the desired temperature in as short a time as possible and in order
to compensate for heat losses, the surface temperature of the
resistance heater must be higher than the temperature which the
medium to be heated is to adopt ultimately.
This known manner of heating gases or liquids has the disadvantage
that, in order to impart to each space portion of the medium to be
heated the required amount of heat within a short period of time,
excessively long paths and therewith excessively long periods of
time are necessitated. This is a direct consequence of the fact
that of the total volume of the medium to be heated only a
relatively small proportion thereof will come into direct contact
with the resistance heater.
The process and apparatus according to the present invention also
makes use of a heat exchanger in the form of a resistance heater
which, however, enables to heat the entire volume of the medium
almost simultaneously by virtue of the fact that an extremely large
surface is offered to the gaseous medium by the resistance heater.
The process and apparatus according to the present invention for
the rapid heating of gases, liquids, vapors and aerosols to a
desired temperature essentially consists in that the material to be
treated is passed through an electric resistance heater which
comprises as the structural elements thereof electrically
conductive, mutually interlocked hair-like elements, needles or
rodlets, preferably so-called whiskers, and whose structural
elements offer to the material to be treated per cubic centimeter
thereof a surface of at least 800 square centimeters.
The resistance heater thus consists of extremely thin metal wires
metal hair-like elements or needles, with which the ratio of
diameter to length is approximately between 1:10 to 1:10,000 and
which are matted with each other or mutually joined with each other
in any suitable known manner so that a skeleton with fine pores and
having an extremely large surface comes into existence. If the
skeleton consists, for example, of small rods having a diameter of
1 micron and if one assumes as an example a specific weight of the
filament skeleton of 0.8, then one cubic centimeter of the volume
of this skeleton has a total surface of 3,600 cm.sup.2.
Accordingly, there is offered to the medium to be heated which is
introduced into the pores of 1 ccm of the heat exchanger in
accordance with the present invention, a heat-emitting surface of
3,600 cm.sup.2 so that the medium to be heated can be heated almost
instantaneously--as compared to other ways of heating thereof. A
very large heat-emissive surface thus confronts or faces directly
each smallest volume portion of the liquid or gaseous medium which
is present in one of the pores of the heating element in accordance
with the present invention which surface is able to give off its
heat to the medium over the shortest path by radiation and heat
conduction. In order to point out more clearly the unusually rapid
heat transfer from the resistance heater according to the present
invention to the medium to be heated, several examples will be
described hereinafter which relate to the respective ratio of the
surface of the heat exchanger to the volume present in its pores of
the medium to be heated.
While in the known heat exchangers for heating liquids, i.e., for
example, in an immersion heater, in an electric pot or in a flow
heater pipe, a heat-emitting surface on the average of
approximately 0.02 to 0.5 cm.sup.2 is coordinated to each ccm of
liquid, the corresponding value for each ccm--according to the
method and apparatus according to the present invention--amounts to
130 cm.sup.2 with filaments of 20 .mu.m, 200 cm.sup.2 with
filaments of 5 .mu.m and 1,000 cm.sup.2 with filaments of 1 .mu.m
in diameter.
The increase of the surface, coordinated to each volume unit of the
resistance heater with the decreasing diameter of the metal
filaments or wires is a result of the fact that the total surface
of a wire-like body below a certain diameter will increase to an
extraordinary extent so that, with the same total wire weight, a
wire with a 10 .mu.m diameter already possesses the 40-fold surface
of a wire of 100 .mu.m diameter, with a 1 .mu.m diameter the
100-fold and with a 0.1 .mu.m diameter the 1,000-fold surface.
If the liquid or gaseous medium to be heated is intended to flow
through the resistance heater, then it is advantageous to keep the
rate of flow of the medium to be heated as high as possible. This
means that the size of the pores of the resistance heater must be
as large or coarse as possible so as to reduce the flow resistance.
For this reason, the present invention utilizes for the structure
of the resistance heater, preferably the finest hair-like elements,
needles or rodlets and preferably so-called whiskers. In contrast
to the construction of a resistance heater from grain-like
individual elements, such a porous skeleton made of hair-like
elements, needles or rodlets has, apart from the aforementioned
extremely large surface, also substantially larger pores and thus a
lower flow resistance. Nevertheless, one still has to reckon in
connection with a rate of flow of the liquid or gaseous medium
through the porous skeleton of the resistance heater with high flow
resistances so that, in the course of overcoming the same,
relatively large forces may act on the individual structural
element. For this reason, the structural elements of the resistance
heater according to the present invention consist preferably of a
material having a particularly great rigidity, preferably of
hair-like elements, needles or rodlets with a crystallite size that
is considerably smaller than the filament diameter itself, or of
so-called metal whiskers which are grown from the gaseous phase and
which have either a polycrystalline or a monocrystalline character,
whereby the latter--despite the monocrystalline character
thereof--obtain their high strength by a minimum of dislocations,
while the former do so with a maximum of dislocations. According to
the present invention, the structural elements of the resistance
heater may also be metallized non-conductors, for example,
metallized highly resistant and notch-free glass fibers, quartz
fibers or organic fibers, or also metallized, non-metallic whiskers
having an above-average rigidity, for example, monocrystal-whiskers
of aluminum oxide or the like. The individual structural elements
may also consist of alloys instead of metals, or of metals and
alloys, or of metallized non-conductors and metals, or of alloys
and metallized non-conductors.
The structural elements may also be blade- or band-shaped. With
particular advantage, the structural elements may also be hollow
for the purpose of increasing the surface. Such hollow structural
elements are obtained, for example, by metallizing the finest
hair-like elements, needles, rodlets, foils or bands consisting of
organic substances and by dissolving out the organic substance so
that the metal shell or skin is left. For heating conductive liquid
media, the structural elements of the resistance heater of the
present invention are provided with a very thin insulating coating
essentially consisting of lacquer, plastic material, oxide or
electrophoretically deposited insulators of very fine grain size.
When higher specific pressures act on the liquid or gaseous medium
flowing through the heat exchanger, such rresistance heaters are
used with particular advantage whose structural elements are
mutually grown together or coalesced, soldered, welded, or sintered
together. The bonding, cementing, soldering, welding, sintering or
growing together of the hair-like, needle-like, or rod-shaped
structural elements may be achieved by a number of known
conventional measures and is effected after the porosity has been
pre-established by a corresponding filling and compression of the
structural elements. As a non-limitative example of this mechanical
stabilization of the skeletons the following may be mentioned.
Joining or connections of the structural elements at the points of
contact thereof by metallization from the gaseous phase, welding by
brief local melting with the aid of coherently bunched light rays,
by electron beam welding, by ultrasonic welding, further by
galvanic separation of metals, by recombination heat of atoms, such
as, for example, hydrogen atoms, and by similar measures which are
applicable dependent on the shape and material of the structural
elements of the resistance heater.
In accordance with the present invention, the mechanical stability
of the resistance heater may be further increased in that the
structural elements thereof are grown together with, cemented,
soldered, welded, or sintered to the walls of the container or
casing receiving the resistance heater. This measure prevents, at
higher pressures of the medium flowing through the resistance
heater, the tearing open of a path of lower flow resistance along
the enclosing wall. A further step consists in that the resistance
heater is more or less conically tapered, and more particularly in
the direction of flow of the medium to be heated. Owing to this
measure, the pressure rigidity of the resistance heater is
increased with respect to the flowing medium. Furthermore, an
intentionally non-uniform heating of the resistance heater is
attained thereby in that the relatively wider part of the
resistance heater is heated less by reason of its smaller
resistance than the narrower part so that the medium to be heated,
during its travel toward the narrower part of the column, is heated
progressively more intensely. In this manner, the medium is
initially preheated in the wider part of the resistance heater in
order to be heated subsequently to the final temperature at the
apex, i.e., in the narrower part.
This is of significance for such media which, because of the danger
of the chemical decomposition, can withstand only a heating of an
extremely short duration, for example, for hydrocarbons with which
a cracking process would set in at higher temperatures within a
short period of time.
The conical configuration of the resistance heater may be varied in
many different ways in that, for example, one changes the angle of
the cone or in that the cone is constructed hollow, or in that one
uses a heat-conducting disk or plate through which the medium to be
heated flows from the outer edge toward the inside of the disk to
leave the same in the center thereof.
The resistance heater can be connected thereby directly with a
source of current in any known manner whereby it is of particular
advantage to construct the current connections also highly porous.
The resistance heater may, however, also be an induction heater,
which involves the particular advantage that the contact means may
be dispensed with so that, in the operation of the method and
apparatus of the present invention, there exists the possibility of
eliminating heat losses due to heat conduction by way of the
current supply which is essential particularly in the case when the
resistance heater is intended to assume high temperatures. The
application of the present invention is concerned with gaseous and
liquid media in general, but is also applicable with other states
of aggregation of matter or material which is capable of being
transported through the pores of the heat exchanger, for example,
vapors, mists, aerosols, gels, suspensions and suspended particles
in liquids. It is also within the scope of the present invention to
utilize the heating of the medium or media treated together in the
heat exchanger for the initiation and/or realization of other
physical or chemical reactions which are initiated or accelerated
by the heating operation, whereby a catalytic effectiveness of the
material of the heat exchanger is included either additionally or
exclusively.
Finally, it is also within the purview of the present invention to
use the heating of a medium by means of the heat exchanger
according to the present invention for the selective physical or
chemical reactions, for example, for the fractional distillation,
for initiating a chemical partial reaction between constituents of
the heated medium, for changing the diffusion velocity of gases, or
for the ionization of gases at high temperatures of the heat
conductor.
Accordingly, it is an object of the present invention to provide a
method and apparatus for rapidly heating fluids and the like which
obviate the aforementioned shortcomings and drawbacks encountered
with the prior art.
It is another object of the present invention to provide a method
and apparatus for rapidly heating liquid and gaseous media which
heats directly substantially the entire volume of the medium to be
heated.
Another object of the present invention resides in the provision of
a resistance heater of the type described above which minimizes
heating losses and permits heating of the medium to be heated in a
relatively short time.
Still a further object of the present invention resides in a
resistance heater in which the entire volume of the medium to be
heated is heated nearly uniformly and which presents a skeleton
structure having fine pores with an extraordinary large
surface.
Another object of the present invention resides in the provision of
a resistance heater which permits an almost instantaneous heating
of the medium to be heated.
A further object of the present invention resides in the provision
of a resistance heater offering a large heating surface, yet having
substantial rigidity sufficient to withstand all pressures that may
be expected to occur in the system.
These and further objects, features and advantages of the present
invention will become more obvious from the following description
when taken in connection with the accompanying drawing which shows
for purposes of illustration only several embodiments in accordance
with the present invention and wherein:
FIG. 1 is a cross sectional view through a first embodiment of a
resistance heater in accordance with the present invention;
FIG. 1a is a sectional view along line II--II of FIG. 1 according
to one embodiment, wherein the tubular element is of uniform
cylindrical cross section.
FIG. 1b is a sectional view again along line II--II of FIG. 1 but
according to a slightly modified embodiment of the present
invention, wherein the tubular element is of uniform relatively
flat tubular shape.
FIG. 2 is a cross sectional view through a modified embodiment of a
resistance heater in accordance with the present invention, in
which the resistance heater is of conical construction;
FIG. 2a is a cross-sectional view through a modified embodiment of
a resistance heater similar to that shown in FIG. 2 but wherein the
heater is inductively heated;
FIG. 3 is a cross sectional view through a still further modified
embodiment in accordance with the present invention illustrating an
annular resistance heater in which the medium to be heated flows
from the outside toward the inside; and
FIG. 4 is a cross sectional view through a multi-section resistance
heater in accordance with the present invention combining some of
the features of the other embodiments.
The most simple form of an apparatus for carrying out the method
according to the present invention is a cylindrical tubular member
or pipe within which is accommodated the resistance heater.
FIG. 1 illustrates this arrangement, in which reference character a
designates a pipe or tubular element made of non-conductive
material, reference character b represents the column of the porous
conductive heat-conductor, reference character c indicates the
medium flowing through the heat exchanger, and reference characters
d and e designate electrodes which are positioned with a secure
contact at the ends of the porous heat exchanger and which supply
and carry off the heating current. The arrows indicate the
direction of flow of the medium to be heated.
FIG. 2 shows another embodiment of an apparatus in accordance with
the present invention, in which the resistance heater has a conical
configuration. Enclosed within a conical insulating tube a' is the
porous heat exchanger b through which flows the medium c to be
heated. The electrodes d and e which are pervious or permeable to
the flow medium to be heated are secured with good contact to the
heat exchanger cone b at both ends thereof.
The medium to be heated generally flows through the porous heat
exchanger b, heated by resistance heating, from the wider to the
narrower part of the cone. The temperature attained with the
resistance heating in the porous heat exchanger depends on its
cross section, and therewith on the electric conductivity thereof
so that, depending upon the angle which the heat exchange cone
possesses, a more or less great temperature drop or gradient exists
between the base and the apex thereof. Accordingly, the medium
flowing through the heat exchanger cone is heated less at the base
and is heated more strongly at the apex thereof. Simultaneously,
also the flow velocity of the medium increases from the base to the
apex of the heat exchanger cone so that the medium flows more
rapidly through the heat exchanger cone in the place of higher
temperature.
A further embodiment of the present invention is illustrated in
FIG. 3 in which reference character a" designates a flat cylinder
which is larger in the diameter thereof than the disk-shaped porous
heat exchanger b to form a peripheral inlet channel g connected
with the supply conduit f so that the medium c flowing through the
heat exchanger b flows through the heat exchanger b from the outer
rim thereof toward the center and leaves the same through the
central discharge conduit h. The annular electrodes d and e, which
are permeable or pervious to the medium to be heated, are connected
with good electrical contact in any conventional manner with the
heat exchanger disk b. As with the embodiment of the conical heat
exchanger according to FIG. 2, the heat exchanger disk b according
to FIG. 3 is heated, under resistance-heating, to a lesser degree
at the periphery thereof than in the central part thereof so that
also in this arrangement the temperature of the heat exchanger disk
and therewith of the medium flowing therethrough, increases from
the outside toward the inside thereof.
The embodiments of installations according to FIGS. 1, 2 and 3 may
also be varied in that the same or different embodiments are
combined with one another. An embodiment, wherein several of the
heat exchanger according to FIG. 3 constructed in a disk-shaped
manner are provided for the purpose of achieving a greater quantity
of rate of flow, is shown, for example, in FIG. 4. Reference
characters b.sub.1, b.sub.2, b.sub.3 and b.sub.4 designate therein
the individual heat exchanger disks through which flows
simultaneously the medium supplied through inlet conduit f and
common annular feed chamber g to be again discharged simultaneously
in the central bore h of the individual disks. The porous
electrodes d and e are thereby common to all of the used heat
exchanger disks. The heat exchanger disks b.sub.1, b.sub.2, b.sub.3
and b.sub.4 are arranged between flat cylinders a'" having several
stages with interposed induction coils i to furnish additional
heat. However, it is understood that in this, as well as in the
other embodiments, induction heating may be used additionally to
resistance-heating caused by a direct connection with the current
supply or in lieu of such direct connection with the current
supply.
While I have shown and described several embodiments in accordance
with the present invention, it is understood that the same is not
limited thereto but is susceptible of numerous changes and
modifications as known to a person skilled in the art and I
therefore do not wish to be limited to the details shown and
described herein but intend to cover all such changes and
modifications as are encompassed by the scope of the appended
claims.
* * * * *