U.S. patent application number 12/756780 was filed with the patent office on 2010-08-05 for helical formation for a conduit.
This patent application is currently assigned to TAYSIDE FLOW TECHNOLOGIES LTD.. Invention is credited to Robert Gordon Hood, John Graeme Houston, Peter Arno Stonebridge, Allan Thomson.
Application Number | 20100198337 12/756780 |
Document ID | / |
Family ID | 29725424 |
Filed Date | 2010-08-05 |
United States Patent
Application |
20100198337 |
Kind Code |
A1 |
Houston; John Graeme ; et
al. |
August 5, 2010 |
Helical Formation for a Conduit
Abstract
A helical formation within a conduit and a method of determining
the helix angle of the helical formation are disclosed. The method
includes specifying the internal dimensions of the conduit and an
intended fluid mass flow through the conduit. The helix angle is
determined from the pressure drop and the turbulent kinetic energy
for a conduit having the specified internal dimensions and intended
fluid mass flow.
Inventors: |
Houston; John Graeme;
(Perth, GB) ; Hood; Robert Gordon; (Longforgan,
GB) ; Stonebridge; Peter Arno; (Perth, GB) ;
Thomson; Allan; (Paisley, GB) |
Correspondence
Address: |
DeMont & Breyer, LLC
100 Commons Way, Ste. 250
Holmdel
NJ
07733
US
|
Assignee: |
TAYSIDE FLOW TECHNOLOGIES
LTD.
Dundee Tayside
GB
|
Family ID: |
29725424 |
Appl. No.: |
12/756780 |
Filed: |
April 8, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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|
10516875 |
Aug 4, 2005 |
7721767 |
|
|
PCT/GB02/05646 |
Dec 13, 2002 |
|
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|
12756780 |
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Current U.S.
Class: |
623/1.22 ;
138/39 |
Current CPC
Class: |
F15D 1/065 20130101;
A61F 2002/068 20130101; A61F 2/06 20130101 |
Class at
Publication: |
623/1.22 ;
138/39 |
International
Class: |
A61F 2/06 20060101
A61F002/06; F15D 1/04 20060101 F15D001/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 5, 2002 |
GB |
PCT/GB02/02580 |
Claims
1. A helical formation for a conduit, the helical formation
defining at least a portion of a helix, the helical formation being
made by a process comprising the steps of: (i) determining an angle
of the helix defined by the helical formation from the internal
dimensions of the conduit, the fluid mass flow of the conduit, the
pressure drop along the conduit and the turbulent kinetic energy
within the conduit; and (ii) producing the helical formation with
the helix angle as determined in step (i).
2. A helical formation according to claim 1, wherein the helix
angle is between 5.degree. and 50.degree..
3. A helical formation according to claim 1, wherein the helix
angle is between 5.degree. and 20.degree..
4. A helical formation according to claim 1, wherein the helix
angle is substantially 8.degree..
5. A helical formation according to claim 1, wherein the helical
formation is for effecting a rotational flow of fluid within the
conduit, in use.
6. A helical formation according to claim 1, wherein the helical
formation comprises an elongate member.
7. A helical formation according to claim 6, wherein the elongate
member comprises an inwardly extending portion.
8. A helical formation according to claim 1, wherein the helical
formation is in the form of an insert adapted to be mounted within
the conduit.
9. A helical formation according to claim 1, wherein the helical
formation is an integral part of the conduit.
10. A conduit comprising a helical formation according to claim
1.
11. A conduit according to claim 10, wherein the conduit is blood
flow tubing.
12. A conduit according to claim 11, wherein the blood flow tubing
comprises a graft.
13. A conduit according to claim 11, wherein the blood flow tubing
comprises a stent.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority of U.S. patent application
Ser. No. 10/516,875, with a U.S. filing date of Dec. 3, 2004. U.S.
application Ser. No. 10/516,875 is a 371 filing of PCT/GB02/05646,
filed on Dec. 13, 2002 which in turn claims priority of
PCT/GB02/02580, filed on Jun. 5, 2002.
[0002] Furthermore, the underlying concepts, but not necessarily
the language, of U.S. patent application Ser. No. 10/516,875 are
incorporated herein by reference. [0003] If there are any
contradictions or inconsistencies in language between this
application and the case that have been incorporated by reference
that might affect the interpretation of the claims in this case,
the claims in this case should be interpreted to be consistent with
the language in this case.
FIELD OF INVENTION
[0004] The invention relates to a method of determining the helix
angle of a helical formation for a conduit, and in particular, but
not solely, for blood flow tubing.
BACKGROUND OF THE INVENTION
[0005] A number of documents have proposed using helical formations
in conduits to encourage a desired flow pattern of a fluid within
the conduit. Such helical formations have been proposed for a wide
variety of applications, including pipelines and blood flow tubing.
The purpose of the helical formations is generally to generate
spiral flow of the fluid within the conduit to reduce turbulence
and dead spots within the conduit.
[0006] Although the use of helical formations has been proposed as
beneficial to fluid flow in conduits by helping to generate spiral
fluid flow patterns, there is little or no information on the
physical characteristics or design of the helical formation that is
required to create a suitable spiral flow pattern. Clearly, some
designs of helical formations will be ineffective at creating
spiral flow and others will not create a beneficial spiral flow.
For example, helical formations having a high helix angle may tend
to create turbulence rather than spiral flow due.
SUMMARY OF THE INVENTION
[0007] In accordance with a first aspect of the present invention,
there is provided a helical formation for a conduit, the helical
formation defining at least a portion of a helix, the angle of the
helix defined by the helical formation being determined from the
internal dimensions of the conduit, the fluid mass flow of the
conduit, the pressure drop along the conduit and the turbulent
kinetic energy within the conduit.
[0008] In accordance with a second aspect of the present invention,
there is provided a method of determining the helix angle of a
helical formation for a conduit, the method comprising specifying
the internal dimensions of the conduit and an intended fluid mass
flow through the conduit, and determining the helix angle from the
pressure drop and the turbulent kinetic energy for a conduit having
the specified internal dimensions and intended fluid mass flow.
[0009] The terms "helical", "helix" and "spiral" as used herein
cover the mathematical definition of helical and any combination of
the mathematical definitions of helical and spiral.
[0010] Typically, the pressure drop and the turbulent kinetic
energy are non-dimensionalised before the helix angle is
determined.
[0011] Preferably, the helix angle is determined as the helix angle
at which the non-dimensionalised pressure drop and the
non-dimensionalised turbulent kinetic energy are substantially
equal. However, the helix angle could be determined as a helix
angle at which the non-dimensionalised pressure drop and the
non-dimensionalised turbulent kinetic energy are not equal,
depending on the type of conduit, the fluid and/or the
application.
[0012] The helical formation may have a helix angle of between
5.degree. and 50.degree.. For example, the helical formation may
have a helix angle of about 8.degree., particularly but not
exclusively in relation to arterial flow in leg arterial
grafts.
[0013] Typically, the fluid to be carried by the conduit comprises
a liquid. The fluid may be solely a liquid, a liquid mixed with a
particulate solid, or a liquified solid. For example, where the
conduit is a blood vessel, the liquid is blood.
[0014] Typically, the helical formation may effect a rotational
flow of fluid within the conduit, in use. The rotational flow may
comprise a helical and/or spiral flow component.
[0015] Preferably, the helical formation may comprise an elongate
member. Typically, the elongate member comprises an inwardly
extending portion.
[0016] In one example of the invention, the helical formation may
be in the form of an insert adapted to be mounted permanently or
temporarily within the conduit.
[0017] In another example of the invention, the helical formation
may be an integral part of the conduit and may be formed, for
example, by a deformation of a side wall of the conduit.
[0018] The helical formation may effect helical and/or spiral flow
in such a fashion as to eliminate or reduce turbulence and/or
eliminate or reduce dead flow regions in the conduit. The helix
angle to achieve such flow will depend on such factors as diameter
of the conduit, longitudinal and rotational velocity of the fluid,
and the viscosity and other characteristics of the fluid.
[0019] The conduit may comprise tubing. For example, the conduit
may comprise artificial or natural blood flow tubing, such as a
vascular graft or a blood vessel, respectively. The tubing may be
used in blood treatment or delivery equipment, for example a
heart-lung machine, dialysis equipment or a giving set. The tubing
may also be used in industrial equipment, for example hoses, pipes
or fire hoses.
[0020] Alternatively, the conduit may comprise a stent. Stents, for
example made of mesh, expanded sheet or tube or wire spring type,
are inserted into blood vessels to provide mechanical support and
prevent collapse of the blood vessel. A structure according to the
present invention could be placed inside or outside the blood
vessel to impose, maintain and/or reinforce a flow guiding
formation through the blood vessel.
[0021] The invention may also be utilised for stent grafts. That
is, a combination of stent and graft.
[0022] Flow configuration through a conduit may, in general, be
measured using such techniques as magnetic resonance imaging (MRI)
and/or Doppler ultrasound, and the flow guiding formation may be
modified accordingly until a desired flow configuration is
achieved. Initial design of flow configuration may be by
mathematical modelling or by trial and error, with modification as
described above.
[0023] The conduit may be a flexible conduit, such as a tube or
hose, or a substantially rigid conduit, such as a metal pipe or a
pipeline.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] Examples of a method of determining the helix angle of a
helical formation will now be described with reference to the
accompanying drawings, in which:
[0025] FIG. 1 is a perspective view of an arterial graft having a
helical formation; and
[0026] FIG. 2 is a graph of helix angle versus pressure drop and
helix angle versus turbulent kinetic energy for the arterial
graft.
DETAILED DESCRIPTION
[0027] FIG. 1 is a perspective view of an arterial graft 1 for
implantation in the human or animal body. The graft 1 is fabricated
from a knitted or woven polyester material. However, any suitable
flexible material could be used, such as a spun polyurethane
multi-monofilament or a PTFE extrusion.
[0028] The graft 1 is in the form of a tube 2 that has a
deformation 3 in the side wall of the tube 2 so that the
deformation 3 extends inwardly generally towards the longitudinal
axis of the tube 2 to form a helical formation 4 on the internal
surface of the tube 2. The tube is also crimped to form
circumferential ridges 5 along the length of the tube 2. The
circumferential ridges help to provide radial strength to the tube
2 to minimise the risk of the graft collapsing during implantation
and subsequently during use.
[0029] The helical formation 4 is intended to promote a rotational
flow pattern to blood passing through the graft 1, in use. It is
believed that rotational flow has beneficial effects in reducing
the effect of and helping to prevent arterial diseases, by reducing
turbulent flow and reducing dead spots within the flow.
[0030] The inventors have found that the choice of the helix angle
of the helical formation 4 is important in minimising turbulent
flow and dead spots within the flow. The inventors have also found
that for a conduit having given internal dimensions and a
particular helical flow formation that is intended to carry a given
mass flow, the optimum helix angle can be determined from the
pressure drop along the conduit and the turbulent kinetic energy in
the conduit.
[0031] In addition, the inventors have found that, in order to
maintain a given mass flow in a given conduit, with a particular
helical flow formation, the pressure drop increases as the helix
angle increases and the turbulent kinetic energy decreases as the
helix angle increases. Hence, the choice of helix angle is a
compromise between minimising pressure drop and minimising
turbulent kinetic energy. If the pressure drop and turbulent
kinetic energy are non-dimensionalised using conventional
mathematical techniques, the curves of helix angle versus
non-dimensionalised pressure drop and helix angle versus turbulent
kinetic energy can be plotted on the same graph. A curve 50 of
helix angle versus non-dimensionalised pressure drop and a curve 51
of helix angle versus non-dimensionalised turbulent kinetic energy
for an arterial graft are shown in FIG. 2. These curves 50, 51 were
obtained from measuring pressure drop and turbulent kinetic energy
in the arterial graft 1 using conventional techniques. The curves
50, 51 show that at the region 52, the curves intersect and this
intersection occurs at a helix angle of approximately
8.degree..
[0032] By also analysing flow in the graft 1 using conventional
magnetic resonance imaging techniques it was found by trial and
error that the optimum helix angle for the graft 1 for the given
mass flow was also approximately 8.degree.. Hence, the optimum
helix angle for the graft 1 occurs at approximately when the
non-dimensionalised pressure drop is approximately equal to the
non-dimensionalised turbulent kinetic energy.
[0033] Although in the example described above the helix angle is
determined as the angle at which the non-dimensionalised pressure
drop and turbulent kinetic energy are substantially equal, there
may be situations in which the helix angle is selected so that the
non-dimensionalised pressure drop and turbulent kinetic energy are
not equal. This may situation may arise if, for example, a lower
turbulent kinetic energy is required and it is decided to tolerate
a higher pressure drop to obtain a lower turbulent kinetic energy.
Similarly, if a low pressure drop is more important than turbulent
kinetic energy, a higher turbulent kinetic energy may be tolerated
to obtain a lower pressure drop. Hence, the choice of the helix
angle can be chosen according to the particular application, and
different applications may have different requirements.
[0034] In the example described above, the helix angle of the
helical formation is determined for the graft 1. However, the same
technique can be used for other conduits where it is desired to use
a helical formation to alter the flow pattern of fluid the conduit.
For example, the same technique could also be used to determine the
helix angle for a helical formation for use in a stent, or indeed
any other medical application involving the flow of a fluid through
a tube.
[0035] The present invention is also suitable for industrial
applications. Helical formations may also be used in conduits such
as tubes to create improved efficiency through quicker transfer of
fluid and reduced energy use or a reduction in pressure gradient
along the tube allowing lower pressures within the tube to deliver
a specific end conduit pressure/flow rate. Helical formations could
be used to effect a reduction in turbulence, thereby reducing
vibration, noise, and/or fatigue in a conduit, which in pumps could
allow for reduced pump power consumption. Helical formations may
also be used to allow further penetration or more accurate
distribution patterns of fluid exiting a conduit, for example from
a hose pipe for domestic use or from a fire hose. The invention
will also be of benefit to industries where slurries or suspensions
are transported through conduits, for example food producers or
distributors involved with soups, sauces and like products.
[0036] As with the example above of the graft 1, the optimum helix
angle for these other types of conduits can be determined from the
pressure drop and the turbulent kinetic energy.
[0037] Therefore, the invention has the advantage of enabling the
helix angle of a helical flow formation in a given size of conduit
intended to carry a given fluid to be determined from the pressure
drop and the turbulent kinetic energy in the conduit.
* * * * *