BACKGROUND OF THE INVENTION
[0001] The present invention relates to immersion heaters for corrosive fluids and particularly
to a grounded gas purged immersion heater.
[0002] The invention relates further to the use of such an immersion heater. An immersion
heater according to the preamble of claim 1 is knowen from document EP-A-419 351.
[0003] Tubular electric heating elements are known in the art to consist of a resistance
wire coil or ribbon wound in such a way as to provide an exact electrical resistance
for a given length of coil. The coil is generally inserted in a sheath, usually a
tube made of metal, and filled with an electrically insulating material, such as magnesium
oxide. The assembly is then roll reduced or swaged to compact the fill material and
eliminate any voids with the assembly so as to facilitate heat transfer. The entire
structure is then annealed to eliminate stresses built up during roll reduction. The
finished heating element can then be formed into an unlimited variety of shapes or
configurations as needed for the process requiring heat.
[0004] It is also known in the art that watt densities or the amount of heat which can be
transferred from a given length of tubular heating element varies depending upon the
process for which the heater element is used. As an example, an oil based liquid transfers
heat much more slowly than does a water based liquid. Since the resistance wire must
stay well below its melting point to provide economical, useful life, the amount of
power (or watts) for a unit area must be varied. A common "watt density" known in
the art for heating an oil type liquid is 20 watts per square inch of heater sheath
area. For a water based liquid, watt densities can be as high as 90 watts per square
inch.
[0005] From the above, it is evident that for any given application, a certain amount of
material must be used to achieve the proper watt density. Therefore, it would be beneficial
if one could use less material to provide an equivalent amount of surface area. If
this were done, a cost saving would be achieved.
[0006] Many shapes have been used for tubular heater sheaths. It is common in the art to
use triangular, oval or even flat surfaces on the sheaths in order to increase heater
efficiencies. Protrusions along the heater sheath, such as fins, splines or pins,
have also been used and work very well for certain applications. Each of the shapes
described, however, has specific limitations. Flat and oval sheaths lack the ability
to maintain sufficient compacting of the fill material. This in turn can produce voids
within the heater element thus limiting heat transfer. Fins and other protrusions
increase the amount of surface area but also require additional manufacturing steps,
as well as additional material. Both of these increase costs. It would be desirable
to increase the surface area of a tubular heating element without adding material
or requiring additional shaping.
[0007] Electrical resistance heaters formed of a continuous flexible cable are particularly
suitable for immersion in corrosive chemical baths since the exterior of the flexible
cable may be jacketed with a suitable plastic material having satisfactory resistance
to the corrosive nature of the chemical bath being heated. An example of a flexible
cable resistance heater is shown and described in U. S. Patent No. 4,158,764.
[0008] It is known to provide such flexible cable heaters with an outer casing or jacket
formed of a polytetraflouroethylene (PTFE) material (see for example EP 0419351A).
PTFE has satisfactory resistance to chemical attack by corrosive media. However, it
has the disadvantage that when employed in a thin walled tube for desired flexibility,
the permeability of PTFE permits transmigration of heated chemical vapour into the
interior of the cable heater. To overcome this problem, US Patent No. 4,553,024 discloses
that the outer jacket of the cable-type immersion heater can be connected to a suitable
source of a dry gaseous medium for circulation from an inlet end of the heater cable
through the interior thereof, and over the heating element, to an exhaust at the other
end of the heater cable. This provides a continuous dry gas flow or purge over the
resistance heating element to scavenge any accumulated corrosive chemical vapors which
may have permeated through the outer plastic jacket of the heater cable.
[0009] One of the difficulties with the flexible cable heaters illustrated in US Patent
Nos. 4,158,764 and 4,553,024 is that the heaters are not grounded. Such grounding
is required by various regulatory authorities, such as Underwriters Laboratories (UL)
and the Canadian Standards Association (CSA) in order to be approved. It would also
be desirable to have a gas purge take place on such grounded flexible cable heaters
while maintaining good heat transfer through the PTFE jacket of the cable heater.
[0010] Accordingly, it has been considered desirable to develop a new and improved heater
sheath element which can be used in a purged grounded fluid heater to meet the above-stated
needs and overcome the foregoing difficulties and others while providing better and
more advantageous overall results.
[0011] Accordingly, the present invention provides an immersion heater for corrosive fluids,
comprising: an electrically resistive material strand operative upon connection to
a source of power to provide heat, and a thermally conductive electrically insulating
fill material disposed around said electrically resistive material strand; an electrically
conductive sheath disposed around said fill material; a tubular jacket of a flexible
chemically inert material encasing said electrically conductive sheath; a fluid flow
passage defined between said tubular jacket and said sheath for allowing a fluid to
flow therethrough; characterised by: a source of a pressurized purge fluid medium
connected to said fluid flow passage to enable the purge fluid to flow therethrough.
[0012] In one embodiment, a knurled pattern, comprising sets of first and second helically
extending channels which spiral in opposite directions, is provided on the outer surface
of the electrically conductive sheath to allow for a purge fluid to flow over the
outer surface of the sheath and between the sheath and the jacket in order to remove
any corrosive fluid which may have penetrated the jacket. In another embodiment, a
tubular jacket is provided with a series of spaced internally extending ribs which
contact the outer surface of the sheath. The valleys between the ribs cooperate with
the outer surface of the sheath to form channels through which a purge fluid can flow.
In yet another embodiment, a braid material is disposed between the sheath and the
tubular jacket in order to form fluid flow channels for the purge fluid.
[0013] The heater is preferably manufactured by providing an electrically resistive material
strand and a tubular sheath of electrically conductive material. The strand is inserted
into the sheath. A thermally conductive electrically insulating material is packed
between the strand and the sheath in order to isolate the strand from the sheath.
Any voids in the fill material located in the sheath are removed. A tubular jacket
of a chemically inert material is slipped over the sheath. A channel is formed between
an outer periphery of the sheath and an inner periphery of the jacket.
[0014] Accordingly, the present invention provides a heater element with an electrically
conductive sheath for grounding and a chemically inert outer covering or jacket wherein
flow channels are formed between the sheath and the covering to allow a purge fluid
to flow therebetween.
[0015] An embodiment of the present invention also provides a technique for increasing the
surface area of a tubular sheath without adding additional material or needing additional
manufacturing steps.
[0016] An embodiment of the present invention can also provide a heater element sheath which
is provided with integral flow channels while maintaining the structural integrity
of the sheath because no material is removed from the sheath.
[0017] The heater element can also provide a heater element sheath with an increased heating
efficiency but which sheath is capable of being readily compacted so as to eliminate
any voids in a fill material held within the sheath.
[0018] One embodiment of the present invention provides a heater element having a tubular
jacket provided with internally extending ribs. The ribs cooperate with an outer surface
of a heater element sheath to define fluid flow channels to allow a purge fluid to
flow therethrough.
[0019] Another aspect of the present invention provides a heater element including a heater
element sheath, a tubular jacket and a braided sleeve of material disposed between
the sheath and the jacket. The braided sleeve cooperates with the inner surface of
the jacket and the outer surface of the sheath to define flow channels for a purge
fluid to flow therethrough.
[0020] The preferred embodiments of the present invention also provide a heater element
which allows for monitoring the integrity of the outer chemically resistant tubular
jacket by measuring either loss of flow or loss of pressure, if no flow is desired.
[0021] Still other benefits and advantages of the invention will become apparent to those
skilled in the art upon a reading and understanding of the following detailed specification.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The invention may take physical form in certain parts and arrangement of parts preferred
embodiments of which will be described in detail in this specification and illustrated
in the accompanying drawings which form a part hereof and wherein:
Figure 1 is a cross-sectional view through a gas purged flexible cable type immersion
heater according to a first preferred embodiment of the present invention;
Figure 2 is a schematic view of a heater cable installation in a system for heating
liquid in an open vat;
Figure 3 is a side elevational view on a reduced scale of the heater sheath of Figure
1;
Figure 4 is a perspective view of a gas purged flexible cable type immersion heater
according to a second preferred embodiment of the present invention; and
Figure 5 is a perspective view through a gas purged flexible cable type immersion
heater according to a third preferred embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0023] Referring now to the drawings wherein the showings are for purposes of illustrating
preferred embodiments of the invention only and not for purposes of limiting same,
Figure 1 illustrates a heater cable A according to a first preferred embodiment of
the present invention. The cable comprises a heater element 10 which can be a conventional
cylindrical heater wire. The heater wire is surrounded by a fill material 20. The
fill material is an electrically insulating thermally conductive material. Preferably,
the material comprises magnesium oxide or another conventionally known such material.
[0024] Enclosing the fill material is a conductive, sheath 30, preferably made from a conventional
deformable metal. The sheath includes an inner periphery 32 which contacts the fill
material 20 and an outer periphery 34. Located in the outer periphery are a plurality
of grooves 36.
[0025] With reference now also to Figure 3, the grooves comprise a series of parallel helically
spiralling left hand grooves 38 and a series of parallel helically spiralling right
hand grooves 40. The two sets of grooves intersect at a number of locations around
the outer periphery 34 of the sheath 30 to form a plurality of diamond-shaped islands
42. In essence, a knurled pattern is provided on the outer periphery 34 of the sheath
30.
[0026] The knurled pattern can be manufactured by using a conventional set of dies during
final roll reduction of the sheath element 30 so as to compact the fill material 20
and remove any voids within the heater element. Such voids are undesirable since they
limit heat transfer. The method of producing this knurled pattern does not remove
any material from the sheath 30 and thereby maintains the structural integrity of
the tubular element. The knurled pattern can be produced by using conventional dies
and allows for increased cost savings. It has been found that the knurled pattern
provides an increase in surface area of the sheath of approximately 17%.
[0027] While a knurled pattern is illustrated in Figure 3, it should be appreciated that
a variety of other patterns can be produced on the outer periphery of the sheath by
using other types of conventional dies. All that is necessary is that the sheath be
so formed as to provide a plurality of longitudinally extending flow channels in the
outer surface of the sheath while maintaining a sufficient amount of sheath surface
area for conductive heat transfer to a casing 50.
[0028] After the knurled pattern has been formed in the sheath 30, the casing or jacket
50 can be slipped over the sheath 30. An inner periphery 52 of the casing 50 contacts
the several islands 42 of the sheath 30 in order to enhance heat transfer. An outer
periphery 54 of the casing 50 is in contact with the solution which is to be heated.
[0029] As is known, one end of the tubular casing 50 can be expanded mechanically and the
heater element can be forced into the casing. This method provides a tighter fit than
even directly extruding of the casing onto the sheath. The casing is preferably made
from a suitable chemically inert thermoplastic material, such as polytetrafluoroethylene
sold under the brand name Teflon.
[0030] Preferably the sheath 30 is made of a suitable conventional metal. When the heater
cable A is used to heat a corrosive type liquid, such as deionized water or another
type of liquid used in the manufacture of e.g., computer chips, the sheath 30 is preferably
made of a suitable corrosion resistant material, such as stainless steel, titanium,
incaloy or copper. For other types of applications, other types of metals such as
zirconium or columbium can be employed.
[0031] With reference now to Figure 4, a heater cable B according to a second preferred
embodiment of the present invention is there illustrated. The heater cable comprises
a heater element 80 which can be a conventional cylindrical heater wire that is surrounded
by a known fill material 84. Enclosing the fill material is a conductive sheath 90,
preferably made from a conventional metallic material. The sheath includes an inner
periphery 92 which contacts the fill material 84 and an outer periphery 94.
[0032] A casing or jacket 100 encloses the sheath 90. In this embodiment, the casing includes
an inner periphery 102 on which there are provided a plurality of spaced longitudinally
extending ribs 104. Defined between the ribs are respective valleys 106. Since the
ribs 104 contact the outer periphery 94 of the sheath 90, the valleys 106 can serve
as longitudinally extending flow channels for a purge fluid which flows through the
jacket 100. An outer periphery 108 of the jacket 100 is in contact with the solution
which is to be heated. As in the previous embodiment, the heater element sheath 90
can be forced into the jacket 100. Alternatively, the jacket 100 can simply be pulled
over the sheath 90. Also, if desired, the jacket 100 could be extruded over the sheath.
[0033] With reference now to Figure 5, a heater cable C according to a third preferred embodiment
of the present invention is there illustrated. In this embodiment, the cable comprises
a heater element 120, preferably in the form of a conventional wire which is surrounded
by a known fill material 124. Enclosing the fill material is a conductive sheath 126
made from a suitable known metal. The sheath has an outer periphery 128 which is contacted
by a braid layer 130. The braid layer can comprise one or more strands 132 of a suitable
conventional strand material. Enclosing the braid is a tubular jacket 134. The jacket
has an inner surface 136 which contacts an outer surface of the braid layer 130 while
the inner surface of the braid layer contacts the outer surface 128 of the sheath
126. Formed by a cooperation of the jacket 134, braid 130 and sheath 126 are a plurality
of flow channels 140 which allow a purge fluid to flow therethrough. As in the previous
embodiments, the jacket 134 can be pulled over the remaining elements of the heater.
Alternatively, the jacket can simply be extruded over such elements.
[0034] The braid layer can be made of any suitable conventional material, whether it is
thermoplastic or metallic strand material. The only requirement is that the material
be capable of accommodating and transmitting high temperatures. Another material which
may be suitable for this purpose would be an insulating glass or quartz material.
[0035] With reference now to Figure 2, the heater cable A can be employed in an open liquid
container 140. The heater cable is shown to be immersed in a liquid held in the container
140. The flexible heater cable A has its ends extending out of the liquid bath and
through a suitable mounting arrangement 144 provided on the rim of the container.
[0036] There is a conventional thermocouple which can extend into the heater cable A to
allow for sensing of an overheating condition to prevent the melting of the thermoplastic
casing 50. The thermocouple has a pair of leads 156, 158 which extend longitudinally
through the heater cable A and longitudinally outward of the casing 50. The casing
50 is connected to a tee 160 to make pressure tight connection. One branch of the
tee 160 is connected to a pressure fitting tubing 162 connected to the inlet of a
pressure relief valve 164. The other branch of the tee 160 is closed by a pressure
type fitting tubing 162 connected to the inlet of a pressure relief valve 164. The
other branch tee 160 is closed by a pressure tight fitting and resilient grommet 166
and has one power lead 168 of the heater cable extending therethrough and connected
via lead 170 to one side L1 of the power line. The thermocouple leads 156, 158 also
extend through grommet 166 and are connected via leads 172, 174 to the input terminals
of a temperature controller 176. The controller, in turn, is connected via a junction
178 to one side of power line L1 and via junction 180 to the other side L2 of the
power line through controller terminals 182 and 184.
[0037] The opposite end of the heater cable A is connected to a bracket 144 and has suitable
pressure type fittings connected to a conduit tee 186 which has one branch thereof
connected to a flexible tube 188 which is connected to a tee fitting 190. One branch
of tee 190 is connected to a fluid conduit 192 to the outlet of meter 194 which receives
a pressurized, gaseous medium from a reservoir 196. The remaining branch of tee 190
is connected to a fluid pressure fitting tube 198 which is in fluid contact with a
sensing cavity of a pressure switch 200.
[0038] The gaseous fluid supply 196 is connected to provide a supply of purged gas through
tee 190, tubing 188 and tee 186 through the cable heater 142 and thus, through relief
valve 164 to thereby provide a continuous gas purge between the inner periphery 52
of the casing and the outer periphery 34 of the sheath 30.
[0039] The pressure switch 200 is connected electrically in series via leads 202, 204 to
terminals 206, 208 of a relay indicated generally at 210. Terminal 206 of the relay
is connected to one signal output terminal 212 of the temperature controller 176.
Terminal 208 is connected through relay coil 214 to terminal 216 of the temperature
controller.
[0040] The relay coil 214 has an armature operably connected to a movable switch contact
member 218 connected to junction 220. The stationary contact 222 of relay 210 is connected
to terminal 224 and lead 226 to a heater power lead 228 out of tee 186.
[0041] In operation, the temperature controller 176 energizes the relay coil 214, and closes
contacts 218, 222. Coil 214 is thereby energized. In the event that a break or leak
in the casing 50 occurs permitting loss of the gaseous medium, the decrease in the
gas purge is sensed by a pressure -switch 200. This breaks the circuit in relay coil
214 thereby de-energizing the coil and opening switch contacts 218, 222 to turn off
power to the heater cable. In the event that there is a loss of liquid in the container
so that the level drops below the surface of the heater cable causing an overheat
condition, the increase in temperature of the heater cable jacket is sensed by the
thermocouple. This causes controller 176 to deenergize relay coil 214 and break the
power connection to the heater cable.
[0042] It should be evident that a pressure sensor could be used without benefit of purge
fluid flow. In this application, pressure alone would operate the pressure sensor
indicating a sound tubular heater jacket. In the event of pressure loss, the pressure
sensor would signal a failure of the tubular heater jacket alerting the user prior
to catastrophic failure.
[0043] As mentioned, the purpose for employing a metal sheath 30 is because the heater cable
A needs to be grounded in order to obtain Underwriters Laboratories (UL) or Canadian
Standards Association (CSA) approval.
[0044] In all of the embodiments illustrated, multiple parallel passages are provided between
the sheath and the jacket to allow the flow of a purge fluid between the grounded
heater sheath and the outer protective non-conductive tubular jacket.
[0045] The invention has been described with reference to several preferred embodiments.
Obviously, modifications and alterations will occur to others upon the reading and
understanding of this specification. It is intended to include all of such modifications
and alterations insofar as they fall within the scope of the appended claims.
1. An immersion heater for corrosive fluids, comprising:
an electrically resistive material strand (10, 80, 120) operative upon connection
to a source of power to provide heat, and
a thermally conductive electrically insulating fill material (20, 84, 124) disposed
around said electrically resistive material strand;
an electrically conductive sheath (30, 90, 126) disposed around said fill material;
a tubular jacket of a flexible chemically inert material (50, 100, 134) encasing said
electrically conductive sheath;
a fluid flow passage (38, 40, 106, 140) defined between said tubular jacket and said
sheath for allowing a fluid to flow therethrough; characterised by:
a source of a pressurized purge fluid medium connected to said fluid flow passage
to enable the purge fluid to flow therethrough.
2. The heater of claim 1 wherein said fluid flow passage comprises a first helically.extending
channel (38).
3. The heater of claim 2 wherein said fluid flow passage further comprise a second helically
extending channel (40) which intersects said first helically extending channel, wherein
said first and second channels spiral in opposite directions.
4. The heater of claim 3 wherein said first and second channels (38, 40) are located
on an outer periphery (34) of said electrically conductive heater element.
5. The heater of claim 1 wherein said fluid flow passage comprises at least one channel
located on a knurled outer periphery (34) of said electrically conductive sheath.
6. The heater of claim 1 further comprising a heat transfer means for transferring heat
between said sheath and said tubular jacket.
7. The heater of claim 6 wherein said passage comprises at least one channel (38, 40,
106).
8. The heater of claim 7 wherein said at least one channel comprises a groove (38, 40)
defined in an outer surface of said sheath.
9. The heater of claim 7 wherein said at least one channel comprises a valley (106) defined
in an inner surface of said jacket.
10. The heater of claim 7 wherein said at least one channel extends longitudinally along
a major portion of said sheath.
11. The heater of claim 10 wherein said at least one channel extends from a first end
of said sheath to a second end of said sheath.
12. The heater of claim 1 further comprising a conduit (192) for connecting said source
of purge fluid medium to said fluid flow passage.
13. The heater of claim 1 further comprising a braid layer (130) located between said
tubular jacket (134) and said electrically conductive sheath (126), wherein said braid
layer cooperates with said tubular jacket and said sheath to define said fluid flow
passage.
14. A method of using the immersion heater for corrosive fluid according to any one of
claims 1-13, the method comprising the step of:
flowing a purge fluid through the fluid flow passage (38, 40, 106, 140).
1. Tauchheizer für korrosive Fluide, aufweisend:
eine Litze (10, 80, 120) aus mit elektrischem Widerstand behafteten Material, die
in Betrieb in Verbindung mit einer Leistungsquelle steht, um Wärme bereitzustellen,
und
ein thermisch leitfähiges, elektrisch isolierendes Füllmaterial (20, 84, 124), das
angeordnet ist um die Litze aus elektrischem Widerstandsmaterial;
eine elektrisch leitende Umhüllung (30, 90, 126), die um das Füllmaterial angeordnet
ist;
einen röhrenförmigen Mantel eines flexiblen chemisch inerten Materials (50, 100, 134),
das die elektrisch leitende Umhüllung ummantelt;
eine Fluidflußpassage (38, 40, 106, 140), die definiert ist zwischen dem röhrenförmigen
Mantel und der Umhüllung, um es dem Fluid zu erlauben, durchzufließen; dadurch gekennzeichnet:
eine Quelle eines unter Druck stehenden Reinigungsfluidmediums, das verbunden ist
mit der Fluidflußpassage, um es dem Reinigungsfluid zu ermöglichen, hindurchzufließen.
2. Heizer nach Anspruch 1, wobei die Fluidflußpassage einen ersten sich helikal erstreckenden
Kanal (38) aufweist.
3. Heizer nach Anspruch 2, wobei die Fluidflußpassage weiterhin aufweist einen zweiten
sich helikal erstrekkenden Kanal (40), der den ersten sich helikal erstrekkenden Kanal
kreuzt, wobei die ersten und zweiten Kanäle in entgegengesetzte Richtungen spiralförmig
verlaufen.
4. Heizer nach Anspruch 3, wobei die ersten und zweiten Kanäle (38, 40) lokalisiert sind
an einer äußeren Peripherie (34) des elektrisch leitenden Heizelementes.
5. Heizer nach Anspruch 1, wobei die Fluidflußpassage wenigstens einen an einer gerändelten
äußeren Peripherie (34) der elektrisch leitenden Umhüllung lokalisierten Kanal aufweist.
6. Heizer nach Anspruch 1, weiterhin aufweisend ein Wärmeübertragungsmittel zum Übertragen
von Wärme zwischen der Umhüllung und dem röhrenförmigen Mantel.
7. Heizer nach Anspruch 6, wobei die Passage wenigstens einen Kanal (38, 40, 106) aufweist.
8. Heizer nach Anspruch 7, wobei der wenigstens eine Kanal eine Rille (38, 40), definiert
in einer äußeren Oberfläche der Umhüllung, aufweist.
9. Heizer nach Anspruch 7, wobei wenigstens ein Kanal eine Kehle (106), definiert an
einer inneren Oberfläche des Mantels, aufweist.
10. Heizer nach Anspruch 7, wobei der wenigstens eine Kanal sich longitudinal entlang
eines Hauptabschnittes der Umhüllung erstreckt.
11. Heizer nach.Anspruch 10, wobei der wenigstens eine Kanal sich von einem ersten Ende
der Umhüllung zu einem zweiten Ende der Umhüllung erstreckt.
12. Heizer nach Anspruch 1, weiterhin aufweisend einen Kanal (192) zum Verbinden der Quelle
des Reinigungsfluidmediums mit der Fluidflußpassage.
13. Heizer nach Anspruch 1, weiterhin ausweisend eine umflochtene Schicht (130), die lokalisiert
ist zwischen dem röhrenförmigen Mantel (134) und der elektrisch leitenden Umhüllung
(126), wobei die umflochtene Schicht zusammenwirkt mit dem röhrenförmigen Mantel und
der Umhüllung, um die Fluidflußpassage zu definieren.
14. Verfahren der Verwendung des Tauchheizers für korrosives Fluid nach einem der Ansprüche
1 bis 13, wobei das Verfahren den Schritt aufweist:
Fließen eines Reinigungsfluides durch die Fluidflußpassage (38, 40, 106, 140).
1. Thermoplongeur pour fluides corrosifs, comprenant :
un brin de matériau résistant électriquement (10,80,120) actionné lors de la connexion
à une source d'alimentation pour fournir de la chaleur, et
un matériau de charge isolant électriquement thermoconducteur (20,84,124) disposé
autour dudit brin de matériau résistant électriquement :
une gaine conductrice (30,90,126) disposée autour dudit matériau de charge ;
une chemise tubulaire d'un matériau inerte chimiquement flexible (50, 100, 134) englobant
ladite gaine conductrice ;
un passage de fluide (38,40,106,140) défini entre ladite chemise tubulaire et ladite
gaine pour permettre le passage d'un fluide à travers celui-ci ; characterisé par
:
une source d'un milieu fluide de purgé sous pression connectée audit passage de fluide
pour permettre le passage du fluide de purge à travers celui-ci.
2. Élément thermique selon la revendication 1, dans lequel ledit passage de fluide comprend
un premier canal s'étendant en hélice (38).
3. Élément thermique selon la revendication 2, dans lequel ledit passage de fluide comprend
en outre un second canal s' étendent en hélice (40) qui coupe ledit premier canal
s'étendant en hélice, dans lequel ledit premier canal et ledit second canal forment
des spirales dans des directions opposées.
4. Élément thermique selon la revendication 3, dans lequel ledit premier canal et ledit
second canal (38,40) sont situés sur une périphérie extérieure (34) dudit élément
de chauffage conducteur.
5. Élément thermique selon la revendication 1, dans lequel ledit passage de fluide comprend
au moins un canal situé sur une périphérie extérieure moletée (34) de ladite gaine
conductrice.
6. Élément thermique selon la revendication 1 comprenant en outre des moyens de transfert
de chaleur pour transférer de la chaleur entre ladite gaine et ladite chemise tubulaire.
7. Élément thermique selon la revendication 6, dans lequel ledit passage comprend au
moins un canal (38,40,106).
8. Élément thermique selon la revendication 7, dans lequel ledit au moins canal comprend
une rainure (38,40) définie dans une surface extérieure de ladite gaine.
9. Élément thermique selon la revendication 7, dans lequel ledit au moins un canal comprend
une vallée (106) définie dans une surface intérieure de ladite chemise.
10. Élément thermique selon la revendication 7, dans lequel ledit au moins un canal s'étend
longitudinalement le long d'une portion principale de ladite gaine.
11. Élément thermique selon la revendication 10 dans lequel ledit au moins un canal s'étend
d'une première extrémité de ladite gaine à une seconde extrémité de ladite gaine.
12. Élément thermique selon la revendication 1 comprenant en outre un conduit (192) pour
connecter ladite source de milieu fluide de purge audit passage de fluide.
13. Élément thermique selon la revendication 1 comprenant en outre une couche de tresse
(130) située entre ladite chemise tubulaire (134) et ladite gaine conductrice (126),
dans lequel ladite couche de tresse coopère avec ladite chemise tubulaire et avec
ladite gaine pour définir ledit passage de fluide.
14. Procédé utilisant le thermoplongeur pour fluide corrosif selon l'une quelconque des
revendications 1 à 13, le procédé comprenant l'étape consistant à :
faire couler un fluide de purge à travers le passage de fluide (38,40,106,140).