U.S. patent number 4,038,519 [Application Number 05/524,210] was granted by the patent office on 1977-07-26 for electrically heated flexible tube having temperature measuring probe.
This patent grant is currently assigned to Rhone-Poulenc S.A.. Invention is credited to Jacques Foucras.
United States Patent |
4,038,519 |
Foucras |
July 26, 1977 |
Electrically heated flexible tube having temperature measuring
probe
Abstract
A flexible heating tube especially for medical use, e.g. for
taking blood away from and returning it to the body, in which a
flexible pipe of transparent plastics material is provided with at
least one electrical helical resistance heating conductor and at
least one helical filiform temperature measuring resistance probe.
The two elements are wound on the same axis and are embedded in the
wall of the pipe and are in surrounding relation to the bore in the
pipe. The helical turns of the at least one electrical resistance
conductor and of the at least one temperature measuring probe are
of the same pitch and are coextensive along the length of the pipe.
Electrical connection terminals at at least one end of said pipe
are connected to said at least one heating conductor and said at
least one temperature measuring probe.
Inventors: |
Foucras; Jacques (Bron,
FR) |
Assignee: |
Rhone-Poulenc S.A. (Paris,
FR)
|
Family
ID: |
26218026 |
Appl.
No.: |
05/524,210 |
Filed: |
November 15, 1974 |
Foreign Application Priority Data
|
|
|
|
|
Nov 15, 1973 [FR] |
|
|
73.40688 |
Oct 7, 1974 [FR] |
|
|
74.33694 |
|
Current U.S.
Class: |
392/472; 138/33;
174/47; 219/505; 338/23; 392/495; 138/133; 219/522; 392/480;
604/114 |
Current CPC
Class: |
A61M
5/44 (20130101); B29C 48/09 (20190201); A61M
1/369 (20130101); B29C 61/025 (20130101); F16L
53/38 (20180101); F16L 11/127 (20130101); H05B
3/58 (20130101); F16L 59/10 (20130101); A61M
2205/3653 (20130101); A61M 2205/3368 (20130101); B29C
48/15 (20190201); B29L 2031/779 (20130101); A61M
25/0012 (20130101) |
Current International
Class: |
A61M
1/36 (20060101); A61M 25/00 (20060101); B29C
61/00 (20060101); B29C 61/02 (20060101); F16L
11/127 (20060101); A61M 5/44 (20060101); F16L
59/10 (20060101); F16L 11/12 (20060101); H05B
3/58 (20060101); H05B 3/54 (20060101); H05B
003/58 (); A61M 005/14 (); F16L 011/12 (); F24H
001/10 () |
Field of
Search: |
;219/301,535,504,505,522
;174/47 ;128/214A ;138/33,133 ;338/22R,23 ;222/146HE,146R
;137/341 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Bartis; A.
Attorney, Agent or Firm: Stevens, Davis, Miller &
Mosher
Claims
I claim:
1. A flexible heating tube, especially for medical use, comprising
a flexible pipe of transparent plastics material, at least one
electrical helical resistance heating conductor and at least one
helical filiform temperature measuring resistance probe being wound
on the same axis and being embedded in the wall of the said pipe,
and in surrounding relation to the bore in the pipe, the helical
turns of the at least one electrical resistance conductor and of
the at least one temperature measuring probe being of the same
pitch, and being coextensive along the length of the pipe and
electrical connection terminals at at least one end of said pipe
connected to said at least one heating conductor and said at least
one temperature measuring probe.
2. A flexible heating tube as claimed in claim 1, wherein the
flexible pipe includes an inner pipe around which said at least one
electrical resistance heating conductor and at least one
temperature measuring probe are helically arranged and an outer
insulating covering is firmly fixed to said inner pipe.
3. A flexible heating tube as claimed in claim 2, wherein the
insulating covering consists of a heat-shrinkable sheet.
4. A flexible heating tube as claimed in claim 2, wherein the inner
flexible pipe and the insulating covering are made of silicone
elastomer.
5. A flexible heating tube as claimed in claim 1, wherein the
electrical turns of the at least one electrical resistance heating
conductor and of the at least one temperature measuring probe are
substantially of the same diameter, and are staggered by half a
pitch.
6. A flexible heating tube as claimed in claim 1, wherein the pitch
of the coils of the helices is between 0.2 and 20 times the coil
diameter of said at least one electrical resistance leading
conductor.
7. A flexible heating tube as claimed in claim 1, wherein a
plurality of electrical resistance heating conductors are provided
and are grouped in webs adapted to be connected to one and the same
source of potential.
8. A flexible heating tube as claimed in claim 1, wherein a
plurality of said electrical resistance heating conductors are
provided.
9. A flexible heating tube as claimed in claim 1 wherein there are
a plurality of said resistance heating conductors, at least one of
said conductors being connected separately whereby it may be used
as an earthing element.
10. A flexible heating tube as claimed in claim 1, wherein the at
least one electrical resistance heating conductor comprises a metal
tape.
11. A flexible heating tube as claimed in claim 1, and further
comprising lacquering on at least one of the inside and outside
surfaces of the pipe.
12. A flexible heating tube, especially for medical use, comprising
two flexible pipes of transparent plastics material, at least one
helical electrical resistance heating conductor and at least one
helical filiform temperature measuring resistance probe being wound
on the same axis and being embedded in the wall of each of said
pipes and in surrounding relation to the bore in the pipe, the
helical turns of the at least one electrical resistance conductor
and of the at least one temperature measuring probe of each pipe
being of the same pitch, the electrical resistance conductor and
the temperature measuring probe of each pipe being coextensive
along the length of the pipe, at least one electrical connection
terminal at at least one end of said tube connected to said at
least one heating conductor and said at least one temperature
measuring probe and an outer insulating covering extending over
both of said pipes simultaneously.
Description
The present invention relates to a flexible heating tube which is
suitable especially for medical use, and to a process for its
manufacture.
A heat exchanger is usually employed for keeping the temperature of
a fluid constant, particularly is cases of extracorporeal
circulation; this possesses the disadvantage of requiring a larger
amount of fluid and of increasing the overall size of the
apparatus. It is also possible to lag the tubes or to surround them
with heating elements, but these devices are not easy to use around
flexible tubes; furthermore, the lagging makes it impossible to
follow the flow of the fluid visually in the case of a transparent
tube.
According to the present invention, there is provided a flexible
heating tube, especially for medical use, comprising a flexible
pipe, at least one electrical resistance conductor and at least one
filiform temperature measuring probe each arranged helically in the
wall of said pipe.
Such a flexible heating tube is simple to manufacture and easy to
employ.
The invention also provides a process for the manufacture of a
flexible heating tube comprising forming a flexible pipe on a
thermoplastic mandrel which does not adhere to the pipe, winding at
least one electrical resistance conductor and at least one filiform
temperature measuring probe in a helix on the exterior surface of
the flexible pipe, forming an insulating covering on the
combination thus produced, heating the tube to a temperature such
that it is possible to free the mandrel by exerting a translational
movement relative to the tube and withdrawing the mandrel.
In order that the invention will be better understood, the
following description is given, merely by way of example, reference
being made to the accompanying drawings, in which:
FIG. 1 is a perspective view of a first embodiment of transparent
tube according to the invention;
FIG. 2 is an enlarged cross-section taken along the line II--II of
FIG. 1.
FIG. 3 is a perspective view of a second embodiment of the tube
according to the invention;
FIG. 4 is an enlarged cross-sectional view taken along the line
IV--IV of FIG. 3;
FIG. 5 is a cross-sectional view through a plane perpendicular to
the axis of a tube according to FIG. 3, in the course of
manufacture.
FIG. 6 is a perspective view of a third embodiment;
FIG. 7 is an enlarged section on the line VII--VII of FIG. 6;
and
FIG. 8 is a view similar to FIG. 1 of a still further
embodiment.
The tube represented in FIGS. 1 and 2 comprises a flexible pipe 1
around which eight electrical resistance conductors 2 are arranged
in a helix, and the whole is equipped externally with an insulating
covering 3 firmly fixed to the flexible pipe.
The pitch of the coiling helix of the electrical conductor is
advantageously between 0.2 and 20 times, and preferably between 1
and 10 times, the coil diameter of this conductor.
When using electrical conducting wires, they can be between 1 and
50, and preferably between 3 and 30 in number. The ends of the
wires are connected at each end to connection terminals 8 which can
be placed either at the opposite ends of the tube or at one and the
same end (the electrical conductor then going to the end of the
tube and back as shown in FIG. 1). In the case where the connection
terminals are grouped at the same end of the tube, the current can
return via a single wire of suitable resistance (for example, the
wires which provide the heating effect can be made of nickel, and
the current can then return via a copper wire which is a better
conductor). The electrical conductors can optionally be grouped in
webs brought to the same potential.
At least one of the electrical conductors can be connected to a
measuring probe which is generally a temperature measuring probe.
Optionally, at least one of the conductors can be used
simultaneously for heating and for measuring the temperature after
having been connected to a suitable device which makes it possible
to provide alternately the heating effect and the switch-over to a
measuring bridge.
One of the electrical conductors 5' can also be used as an earthing
element.
The length and the external and internal diameters of the tube
according to the invention are not critical. Advantageously, the
wall thickness of the inner pipe is such that it allows the heat
given off by the electrical resistance conductor to be transmitted
to the fluid conveyed through the tube.
The insulating covering 3 is of such a thickness that it provides
good heat insulation between the combination consisting of the
conveyed fluid, the flexible pipe and the electrical conductors on
the one hand and the surrounding atmosphere on the other hand.
Another embodiment of the flexible heating tube is represented in
FIGS. 3 and 4. It comprises a flexible pipe 1 and an insulating
covering 3 firmly fixed to this pipe. The combination of the
flexible pipe and the insulating covering forms the wall of the
flexible heating tube. An electrical resistance conductor 4, in the
general form of a tape, and a filiform temperature measuring probe
5 are wound in a helix inside the wall of the flexible heating
tube.
The electrical resistance conductor in the general form of a tape
can be a shaped unit with any flattened cross-section whatsoever,
and especially a rectangular cross-section, and it can also consist
of a bundle of fine wires joined in webs (see FIG. 8) or braided.
The characteristics of the coiling helix are of course the same as
those defined above, and the helices are advantageously of the same
pitch and of similar diameter and are staggered by half a
pitch.
Variants lying within the ability of those skilled in the art form
part of the present invention. The variants mentioned below are in
no way limiting. They can optionally be combined with one
another.
The outer insulating covering can consist of a heat-shrinkable
sheath.
The electrical resistance conductors can be arranged in a helix
inside the wall of the flexible tube when the latter is being
extruded.
The electrical conductors can be enamelled or covered with
materials such as polytetrafluoroethylene which provide electrical
insulation, and the coiling helices can then touch one another.
The flexible pipe can be made of any flexible or semi-rigid
material which may or may not be opaque, which is electrically
insulating and preferably withstands rather high temperatures, and
which is generally used for this type of article. Natural or
synthetic rubbers, polyvinyl chloride or polyurethanes are usually
employed as the material. It is, however, preferred to use
elastomers such as silicone elastomers. The high heat conductivity
of silicone elastomers promotes the dissipation of heat (compare
MacGregor -- Silicones and Their Uses -- 1955 edition). It is
advantageously possible to lacquer the inside of the flexible pipe
by depositing a thin layer of silicone elastomer 9 at its surface
in accordance with the technique described especially in the French
Patent published under the Number 2,126,573.
The electrical resistance conductor can be made of any known type
of electrical resistance conducting material and can, for example,
consist of a metallic material or carbon.
The outer insulating covering can be made of any material similar
to those used to produce the flexible pipe. It is possible
optionally to lacquer it on the outside.
The flexible heating tube which is the subject of the invention can
be produced, for example, in accordance with the process described
below, with reference more particularly to a flexible heating tube
as represented in FIGS. 3 and 4. FIG. 5 represents an intermediate
stage of the process.
The flexible pipe 1 is formed, for example by extruding silicone
elastomer, on a mandrel made of a heat-shrinkable material 6, the
external diameter of which is substantially equal to the internal
diameter desired for the heating tube. The electrical resistance
conductor in the general form of a tape is wound in a helix on the
non-vulcanised flexible pipe under a tension, such that the tape is
in perfect contact over its entire surface with the extruded
silicone elastomer forming the flexible pipe. Because of its
bearing surface and because of the low mechanical tension exerted
on the tape in order to maintain contact between the tape and the
flexible pipe, the electrical resistance conductor remains in
position on the surface of the flexible pipe whilst embedding
itself slightly in the wall of the latter. Advantageously, the
filiform temperature measuring probe is wound in a helix
simultaneously; because of its low bearing surface and because of
the mechanical tension applied, the probe becomes deeply embedded
in the wall of the flexible pipe and is thus near the inner surface
7. The insulating covering 3 is formed, for example by extrusion,
on the combination made up as above. The insulating covering can
also be produced by the technique of immersion in a polymer
solution, for example in accordance with the technique described in
the examples of French Pat. No. 1,499,305.
The flexible heating tube is then heated in order to vulcanise the
silicone elastomer. During the heating process, the diameter of the
mandrel 6 made of a heat-shrinkable material decreases and the
mandrel becomes detached from the inner surface 7 of the flexible
pipe. The flexible heating tube is cut to the desired length and it
is then easy to withdraw the mandrel by means of a simple
translational movement. It is then possible, advantageously, to
lacquer the inside and/or the outside of the flexible pipe by
depositing a thin layer of silicone elastomer at its surface, in
accordance with the technique described especially in the French
Patent published under No. 2,126,573.
Mandrels made of materials which have a shrinkage temperature close
to the vulcanisation temperature of the material forming the wall
of the flexible heating tube are advantageously used as the
heat-shrinkable mandrel. A mandrel made of a polyolefine, for
example heat-shrinkable polyethylene, is preferably used in the
case of a flexible heating tube made of silicone elastomer.
Variants of the way in which the manufacturing process is carried
out, which lie within the ability of those skilled in the art, form
part of the present invention. The variants mentioned below are in
no way limiting.
It is possible, for example, to use a mandrel made of a
thermoplastic material which is not heat-shrinkable and which does
not have a sharp melting point, such that longitudinal traction
exerted on this mandrel when hot makes it possible to reduce its
diameter and the mandrel then detaches itself from the inner
surface of the heating tube and can be withdrawn easily. Polymers
such as polyolefines or halogenated vinyl polymers, or mixture of
polymers can be used to produce this mandrel; in the case of a
heating tube made of silicone elastomer, it will be preferred to
use a mandrel made of polyvinyl chloride.
The electrical resistance conductor can be a round wire, like the
temperature measuring probe, both embedding themselves in the wall
of the flexible pipe. Because it has a larger diameter and because
of its lower tension during the winding process, the electrical
resistance conductor becomes only slightly embedded in the wall of
the flexible pipe.
The process which is the subject of the invention is in no way
limited to the manufacture of a flexible heating tube comprising
only one electrical conductor and only one temperature measuring
probe, but covers the manufacture of heating tubes comprising
several electrical conductors and several temperature measuring
probes.
The process which is the subject of the invention can optionally be
carried out by using a mandrel, the length of which is limited to
the length desired for the flexible heating tube.
As shown in FIGS. 6 and 7, it is possible to group at least two
flexible heating tubes 1 inside a single insulating covering 3, it
being possible for the flexible tubes optionally to be of different
diameters. To do this, after having extruded two flexible pipes 1
and after having formed the coils 2 of electrical resistance
conductors and temperture measuring probes on the latter in
accordance with the technique described above, the tubes are placed
side by side and the insulating covering 3 is extruded on the
combination thus formed. The insulating covering can advantageously
consist of an elastomer with a cellular structure. It is also
possible to mould an insulating covering from a cold-curable
organopolysiloxane elastomer. The insulating covering can also
consist of a heat-shrinkable material. The heating resistances of
such flexible heating tubes are preferably connected in series;
this has the advantage of positioning the electrical connection at
the same end of the tube. The heating tubes with a double flexible
pipe are particularly valuable in the medical field for circuits
for extracorporeal circulation; in effect, by making it possible
both for the blood to flow out and to return, they reduce both the
number of tubes and the number of electrical conductor connections
necessary.
It is thus possible to produce great lengths of such tubes and to
do so in all the diameters usually employed. These tubes can be cut
to the required length, the electrical conductors being sheared by
the usual means. It is then easy to free the ends of the electrical
conductors and to connect them to a source of electric current,
generally at a very low voltage. Of course, it is advantageous to
equip these tubes with nozzles and/or suitable connections of any
known types. The flexible heating tube is connected in a leakproof
manner in accordance with the usual techniques to an apparatus
which can accept such tubes. The ends of the electrical conductors
are connected to a suitable source of current. It is thus possible
to connect -- hydraulically and/or electrically -- several of these
tubes in series and/or in parallel. A fluid -- a liquid or a gas --
can flow inside each flexible tube. When an electric current is
passed through the electrical resistance conductors 2, heat is
given off by the Joule effect. This heat is transmitted through the
wall of the inner flexible pipe to the fluid contained inside.
The flexible heating tube which is the subject of the invention
possesses numerous advantages.
The materials used for manufacturing the flexible heating tube
provide it with complete leakproofness to fluids, which is
necessary for conveying biological fluids. The materials used are
moreover compatible with biological fluids and the lacquer finish
of the inner pipe is particularly advantageous for conveying blood.
The flexible heating tubes can be sterilised by radiation, and the
tubes made of silicone elastomer are advantageously sterilised by
means of dry heat.
It is preferable for the tube to be transparent in order to make it
possible visually to follow the flow of the biological liquids
conveyed.
The flexible heating tube which is the subject of the invention
makes it possible to keep a fluid at a particular temperature above
ambient temperature. The uniform distribution of the electrical
conductors makes it possible to transmit a moderate amount of heat
which is well distributed throughout a section and over the entire
length of the heating tube, avoiding local overheating effects. By
connecting the electrical conductors of the heating tube to a
suitable control device it is possible to keep the temperature of
the conveyed fluid constant despite variations in flow rate.
The process for manufacturing the flexible heating tube possesses
numerous advantages.
Thus this process is easy to carry out because, due to the fact
that the electrical conductors become embedded, their relative
positions are fixed and sideways movements, for example due to
slipping, are not possible.
Another great advantage connected with the use of this process is
that the information relating to temperature provided by the
measuring probe is more representative of the temperature of the
fluid conveyed; in fact, the measuring probe is placed as close as
possible to the inner surface of the flexible heating tube, that is
to say as close as possible to the fluid, the temperature of which
it is desired to control.
The manufacturing process which is the subject of the present
invention possesses the advantage of requiring only a flexible pipe
of low thickness in order to be able to produce the helical coils
of the electrical resistance conductor and of the temperature
probe, the flexible pipe being held by the heat-shrinkable mandrel
during the winding operation. It is consequently easier to transmit
heat from the electrical resistance conductor to the fluid
conveyed. At the same time, in order to provide the heating tube
with sufficient rigidity, the thickness of the outer insulating
covering can be greater, and consequently heat losses to the
surrounding atmosphere can be reduced.
The manufacturing process also possesses the advantage of requiring
only one vulcanisation operation.
The use of a flexible heating tube according to the invention is
particularly valuable in extracorporeal blood circulation because
it makes it possible to dispense with heat exchangers, avoiding
heat losses in the lines for conveying the blood between the
patient and the extracorporeal circulation apparatus. It also makes
it possible to reheat the blood after an operation carried out
under conditions of hypothermia. Its use in the artificial lung
apparatus makes it possible to prevent condensation when conveying
moist air. The tube according to the invention can also find
numerous laboratory applications.
The characteristics and the capabilities of such a heating tube are
illustrated by the following example:
EXAMPLE
A flexible heating tube made of silicone elastomer, of length 2.5
m, is manufactured. The flexible pipe having an internal diameter
of 10 mm and a wall thickness of 1.3 mm, and has wound around the
latter in a helix 24 electrical resistance conductors (12 on the
outward and 12 on the return path) made of nickel of diameter 0.20
mm, the pitch of the helin being 72 mm. The electrical conductors
are distributed uniformly over the wall of the flexible pipe in a
cross-section of the tube. The outer insulating covering consists
of a 1.5 mm layer of silicone elastomer.
The tube according to the above embodiment is placed at ambient
temperature, and the lowering of the temperature of water (.DELTA.
T) between the inlet and the outlet of the tube when no current is
passed through the electrical conductors was measured for various
water flow rates. The power which it sufficies to apply in order to
keep the temperature of the water constant while passing from one
end to the other of the tube was measured.
The table below gives the results of the experiments for water flow
rates of 1, 2, 3 and 4 l/minute, the electrical conductors being
supplied with direct current from a 12 volt battery during the
heating process.
__________________________________________________________________________
F Power required to 1/min- T.sub.A T.sub.I T.sub.O .DELTA.T
compensate for .DELTA.T ute .degree. C. .degree. C. .degree. C.
.degree. C. V I W
__________________________________________________________________________
1 23.6 39.2 38.92 0.28 7.6 7 53 2 23.8 39.2 39.01 0.19 8.8 8 70.4 3
23.8 39 38.83 0.17 9 10 90 4 24 39 38.855 0.145 9.9 10.8 107
__________________________________________________________________________
F : Flow rate of water through the tube in 1/minute T.sub.A :
Ambient temperature, in .degree. C. T.sub.I : Temperature of the
water at the inlet of the tube, in .degree. C. T.sub.O :
Temperature of the water at the outlet of the tube, in C., C, with
no current passing through the electrical conductors .DELTA.T :
Lowering of the temperature of the water between the inlet and the
outlet of the tube (T.sub.I - T.sub.O = .DELTA. T) W : Power
dissipated in the electrical conductors, sufficient to compensate
.DELTA.T, in watts. V : Voltage applied to the electrical
conductors, in volts I : Current passing through the electrical
conductors, in amperes.
* * * * *