Note: Descriptions are shown in the official language in which they were submitted.
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LIQUID TRANSFER DEVICE. AND USE OF THE DEVICE FOR IRRIGATION
10
FIELD OF THE INVENTION
The invention relates to liquid transport device primarily intended to deliver
controlled volumes of liquid at a preferred rate to a particular end-use.
The need to transport liquids from one location to another is a well-known
2o problem. Generally, the transport will happen from a liquid source through
a
liquid transport member to a liquid sink, for example from a reservoir through
a
pipe to another reservoir. There can be differences in potential energy
between
the reservoirs (such as hydrostatic height) and there can be frictional energy
losses within the transport system, such as within the transport member, in
particular if the transport member is of significant length relative to the
diameter
thereof. For this general problem of liquid transport, there exist many
approaches
to create a pressure differential to overcome such energy differences or
losses
so as to cause the liquids to flow. A widely used principle is the use of
mechanical energy such as pumps. Often, however, it will be desirable to
overcome such energy losses or differences without the use of pumps, such as
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by exploiting hydrostatic head differential (gravity driven flow}, or via
capillary
effects (often referred to as wicking).
In many of such applications it is desirable to transport the liquids at high
rates, i.e. high flow rate (volume per time), or high flux rate (volume per
time per
unit area of cross-section).
Whilst many different end-uses of many different liquids fall within the scope
of the present invention, irrigation systems in particular are foreseen, for
example
for agricultural or domestic purposes. In such irrigation systems the liauid
transported is water, optionally with fertiliser, plant nutrients, insecticide
andlor
weedkiller.
DE-A-26 55 656, published on June 16'", 1977 discloses a device
~5 comprising a porous, water permeable lower section which is inserted in the
soil
of the flower pot; and an upper section which is impermeable to air. A tube
leads
from the upper section to a reserve supply of water.
One of the disadvantages of many prior art devices has been the low flow
2o rate through the porous element, which has typically been made from a clay-
based material. Subsequent attempts to address this problem have included
devices wherein the irrigating water no longer flows through the porous
element,
but instead the porous element is part of a moisture measuring device, often
referred to -as a tensiometer, which acts upon a valve either mechanically,
25 electronically or hydraulically, in order to open or close an irrigation
conduit. In
this case the irrigating water does not flow through the porous element.
Another
disadvantage of such systems is that an external driving force such as
provided
by a pump or a positive hydrostatic head is needed for water supply.
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WO-A-86 04 212, published on July 31St, 1987 discloses a device for
regulating the watering of plants by a watering hose comprising a porous
element. The device has an inner sealed air-tight space connected to a closing
valve responsive to soil moisture. The closing valve controls the flow through
an
s irrigating conduit.
It is an object of the present invention to provide a liquid transport device
for
delivering liquid from a reservoir through a liquid conduit to a point of end-
use at
a relatively high flow rates, without the need for moving parts, such as
valves or
o pumps, and without the need to provide gravity driven or pump driven flow.
SUMMARY OF THE INVENTION
~5 The device comprises a membrane hermetically sealed to the conduit in the
region of the outlet, the membrane being liquid permeable and having an
average pore size not greater than 100 micrometers and a thickness of less
than
1 mm.
2o In a preferred embodiment, the liquid transport device is for transporting
an
aqueous liquid and the membrane is hydrophilic. Preferably the membrane has a
bubble point pressure of at least 1 kPa, more preferably from 2 kPa to 100
kPa,
and most preferably from 8 kPa to 50 kPa, when measured at ambient
temperature and pressure with distilled water.
DETAILED DESCRIPTION OF THE INVENTION
The device of the present invention works on the principle of a "closed
3o distribution system". By "closed distribution system" it is meant herein
that a
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membrane is saturated with a wetting liquid (e.g. with water or an aqueous
solution) and that air is prevented from entering the system even under
vacuum,
provided the vacuum pressure does not exceed the bubble point pressure of the
membrane. Liquid can then be drawn from the reservoir, rapidly transported
along the liquid conduit to the outlet and across the membrane out of the
closed
distribution system, for example by capillary forces. The effect of the vacuum
is
that the liquid can be transported to and delivered across the membrane much
faster than in prior art processes.
The term "hermetically sealed" as used herein means that a gas (especially
air) can neither pass from the outside environment to the inside of the
reservoir
or liquid conduit; nor from the inside of the reservoir or liquid conduit to
the
outside environment, when the membrane is saturated with liquid as long as the
pressure differential across the membrane does not exceed the bubble point
~5 pressure. In particular the seal between membrane and the liquid conduit
prevents the device frdm leakage of gas across the sealed region.
The term "hydrophilic" as used herein refers to materials having a receding
contact angle for distilled water of less than 90 degrees, preferably less
than 70
2o degrees, more preferably less than 50 degrees, even more preferably less
than
20 degrees, and most preferably less than 10 degrees.
The term "membrane" as used herein is generally defined as a material or
region that is permeable for liquid, gas or a suspension of particles in a
liquid or
25 gas. The membrane may for example comprise a microporous region to provide
liquid permeability through the capilliaries. In an alternative embodiment,
the
membrane may comprise a monolithic region comprising a block-polymer
through which the liquid is transported via diffusion. Hydrophilic microporous
membranes will transport water based liquids. Once wetted, however, gases
30 (e.g. air) will essentially not pass through the membrane if the driving
pressure is
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below a threshold pressure commonly referred to as "bubble point pressure".
Hydrophilic monolithic films will typically allow water vapour to permeate,
while
gas will not be transported rapidly through the membrane.
5 Membranes are often produced as thin sheets, and they can be used alone
or in combination with a support layer (e.g. a nonwoven) or in a support
element
(e.g. a spiral holder). Other forms of membranes include but are not limited
to
polymeric thin layers directly coated onto another material, bags corrugated
sheets.
o
The membrane has an average pore size of no more than 100 micrometers,
preferably no more than 50 micrometers, more preferably no more than 10
micrometers, and most preferably of no more than 5 micrometers. It is also
preferred that the membrane has a pore size of at least 1 micrometer,
preferably
~5 at least 3 micrometers. It is further preferred that the pore size
distribution is such
that 95% of the pores have a size of no more than 100 micrometers, preferably
no more than 50 micrometers, more preferably no more than 10 micrometers,
and most preferably of no more than 5 micrometers.
2o The membrane has an average thickness of less than 1 mm, preferably less
than 100 micrometers, more preferably less than 30 micrometers, and even more
preferably the membrane has an average thickness of no more than 10
micrometers, and most preferably of no more than 5 micrometers.
25 Further known membranes are "activatable" or "switchable" membranes
that can change their properties after activation or in response to a
stimulus. This
change in properties might be permanent or reversible depending on the
specific
use. For example, a hydrophobic microporous layer may be coated with a thin
dissolvable layer e.g. made from poly(vinyl)alcohol. Such a double layer
system
3o will be impermeable to gas. However, once wetted and the poly(vinyl)alcohol
film
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has been dissolved, the system will be permeable for gas but still impermeable
for liquid.
Another useful membrane parameter is the permeability to thickness ratio,
which in the context of the present invention is referred to as "membrane
conductivity". This reflects the fact that, for a given driving force, the
amount of
liquid penetrating through a material such as a membrane is on one side
proportional to the permeability of the material, I.e. the higher the
permeability,
the more liquid will penetrate, and on the other side inversely proportional
to the
o thickness of the material. Hence, a material having a lower permeability
compared to the same material having a decrease in thickness, shows that
thickness can compensate for this permeability deficiency (when regarding high
rates as being desirable). Typical k/d for an irrigation device according to
the
present invention is from about 1 x 10'9 to about 300 x 10-9 m. Preferably the
k/d
~ 5 is at least 1 x 10-' and more preferably at least 1 x 10-5 m.
For a porous membrane to be functional once wetted (permeable for liquid,
not-permeable for air), at least a continuous layer of pores of the membrane
always need to be filled with liquid and not with gas or air. Therefore
evaporation
20 of the liquid from the membrane pores must be minimized, either by a
decrease
of the vapour pressure in the liquid or by an increase in the vapour pressure
of
the air. However evaporation does not need to be minimised if the membrane is
in constant contact with the liquid from at least one side.
25 In a particular aspect of the present invention, a siphon effect is used to
transport liquid to the point of end-use. The liquid conduit is kept
substantially full
of liquid, and the membrane is saturated. Liquid can pass through the
membrane, either into or out of the device, but air is prevented from entering
the
siphon because air cannot pass across the saturated membrane. In this way the
3o siphon effect is maintained. The driving pressure to move liquid along the
siphon
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can be obtained via a variety of mechanisms. For example, if the inlet is at a
higher position than the outlet, gravity will generate a hydrostatic pressure
difference generating liquid flow through the system. Alternatively, if the
outlet
port is higher than the inlet port, and the liquid has to be transported
against
gravity, the liquid will flow through this siphon only if an external pressure
difference larger than the hydrostatic pressure difference is applied. For
example,
a pump could generate enough suction or pressure to move liquid through this
siphon. Thus, liquid flow through a siphon or pipe is caused by an overall
pressure difference between its inlet and outlet port region. This can be
described by well known models, such as expressed in the Bernoulli equation.
In one particular embodiment of the present invention an additional
membrane may be provided. The additional membrane being hermetically sealed
to the conduit in the region of the inlet, the membrane being liquid permeable
~5 and having properties similar to the outlet membrane described herein.
The direct suction is maintained by ensuring that substantially no air or gas
enters the liquid transport member during transport. This means that the
membrane should be substantially air impermeable up to a certain pressure,
2o namely the bubble point pressure. it also typically means that the inlet
should
preferably be connected to the liquid in the reservoir during use.
The term "liquid conduit" as used herein refers to any suitable pipe or tube
or any other geometric structure acting as means for liquid transport. The
liquid
25 conduit may have flexible walls (e.g. polypropylene tube), or may have
inflexible
walls (e.g. glass tube). In a particular embodiment the material of the liquid
conduit and/or the membrane is selected to be biodegradable. In another
particular embodiment of the present invention the liquid conduit may contain
a
porous material, for example to provide stability for the walls.
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Preferably, the device of the present invention is used by burying the wetted
membrane amongst the plants roots. The device provides "water on demand", for
example when the capillary action of the dry soil overcomes the resistance of
the
membrane, and water is "sucked" through the membrane from a reservoir via a
liquid conduit. In addition, the device also provides for moisture control by
removing water when it is present in excess.
One specific application can be seen in self-regulating irrigation systems for
plants. Thereby the inlet can be immersed into a reservoir, and the liquid
conduit
1o can be immersed into a reservoir, and the transport member can be in the
form
of a long tube.
Additives may be added to the liquid reservoir such as fertiliser, plant
nutrients, insecticides and/or weedkiiler.
In use, the liquid transfer device may enable liquid to flow in both
directions
through the liquid conduit. This is particularly useful for irrigating
agricultural
fields, sports fields, and the like and contributes to the avoidance of
flooding by
means of the removal of water from soaked earth through the membrane and
2o back to the reservoir.
The present invention may also comprise a multiplicity of the systems
described above. For example one reservoir might be connected via a number of
conduits to ~a number of separate outlets. This may, for example, be chosen to
supply a number of plants in culture pots.
Test method: Bubble Point Pressure (membrangy
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The following procedure applies when it is desired to asses the bubble point
pressure of a membrane.
First, the membrane material is connected with a plastic funnel (available
from Fischer Scientific in Nidderau, Germany, catalog number 625 617 20) and a
length of tube. The funnel and the tube are connected in an air tight way.
Sealing
can be made with Parafiim M (available from Fischer Scientific in Nidderau,
Germany, catalog number 617 800 02). A circular piece of membrane material,
slightly larger than the open area of the funnel, is sealed in an air tight
way with
the funnel. Sealing is made with suitable adhesive, e.g. Pattex from Henkel
KGA,
Germany). The lower end of the tube is left open i.e. not covered by a
membrane
material. The tube should be of sufficient length, i.e. up to 10m length may
be
required.
~5 In case the test material is very thin, or fragile, it can be appropriate
to
support it by a very open support structure (as e.g. a layer of open pore non-
woven material) before connecting it with the funnel and the tube. In case the
test specimen is not of sufficient size, the funnel may be replaced by a
smaller
one (e.g. Catalog # 625 616 02 from Fisher Scientific in Nidderau). If the
test
2o specimen is too large size, a representative piece can be cut out so as to
fit the
funnel.
The test device is filled with distilled water by immersing it in a reservoir
of
sufficient size filled with the distilled water and by removing the remaining
air with
25 a vacuum pump. Whilst keeping the lower (open) end of the funnel within the
liquid in the reservoir, the part of the funnel with the membrane is taken out
of the
liquid. If appropriate, but not necessarily, the funnel with the membrane
material
should remain horizontally aligned.
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Whilst slowly continuing to raise the membrane above the reservoir, the
height is monitored, and it is carefully observed through the funnel or
through the
membrane itself (optionally aided by appropriate lighting) if air bubbles
start to
enter through the material into the inner of the funnel. At this point, the
height
5 above the reservoir is registered to be the bubble point height.
From this height H the Bubble point pressure BPP is calculated as:
BPP = p ~ g ~ H with the liquid density p, gravity constant g ( g ~ 9.81
m/s2).
0 In particular for bubble point pressures exceeding about 50 kPa, an
alternative determination can be used, such as commonly used for assessing
bubble point pressures for membranes used in filtration systems. Therein, the
membrane is separating two liquid filled chambers, when one is set under an
increased gas pressure (such as an air pressure), and the point is registered
~5 when the first air bubbles "break through".
Determination of Pore Size
2o Optical determination of pore size is especially used for thin layers of
porous system by using standard image analysis procedures know to the skilled
person.
The principle of the method consists of the following steps: 1 ) A thin layer
of
2s the sample material is prepared by either slicing a thick sample into
thinner
sheets or if the sample itself is thin by using it directly. The term "thin"
refers to
achieving a sample caliper fow enough to allow a clear cross-section image
under the microscope. Typical sample calipers are below 200um. 2) A
microscopic image is obtained via a video microscope using the appropriate
3o magnification. Best results are obtained if about 10 to 100 pores are
visible on
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said image. The image is then digitized by a standard image analysis package
such as OPTIMAS by BioScan Corp. which runs under Windows 95 on a typical
IBM compatible PC. Frame grabber of sufficient pixel resolution (preferred at
least 1024 x 1024 pixels) should be used to obtain good results. 3) The image
is
converted to a binary image using an appropriate threshold level such that the
pores visible on the image are marked as object areas in white and the rest
remains black. Automatic threshold setting procedures such as available under
OPTIMAS can be used. 4) The areas of the individual pores (objects) are
determined. OPTIMAS offers fully automatic determination of the areas. 5) The
1o equivalent radius for each pore is determined by a circle that would have
the
same area as the pore. If A is the area of the pore, then the equivalent
radius is
given by r=(A/n)"2. The average pore size can then be determined from the pore
size distribution using standard statistical rules. For materials that have a
not
very uniform pore size it is recommended to use at least 3 samples for the
determination.
Optionally commercially available test equipment such as a Capillary Fiow
Porometer with a pressure range of 0-1380 kPa (0-200psi), such as supplied by
Porous Materials, inc, Ithaca, New York, US model no. CFP-1200AEX1, such as
2o further described in respective user manual of 2/97, can also be used to
determine bubble point pressure, pore size and pore size distribution.
Determination of caliber
The caliper of the wet sample is measured (if necessary after a stabilization
time of 30 seconds) under the desired compression pressure for which the
experiment will be'run by using a conventional caliper gauge (such as supplied
by AMES, Waltham, MASS, US) having a pressure foot diameter of 1 1/8 "
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(about 2.86 cm), exerting a pressure of 0.2 psi (about 1.4 kPa) on the sample,
unless otherwise desired.
Determination of laermeability and conductivity
Permeability and conductivity are conveniently measured on commercially
available test equipment.
For example, equipment is commercially available as a Permeameter such
0 as supplied by Porous Materials, Inc, Ithaca, New York, US under the
designation PMI Liquid Permeameter. This equipment includes two Stainless
Steel Frits as porous screens, also specified in said brochure. The equipment
consists of the sample cell, inlet reservoir, outlet reservoir, and waste
reservoir
and respective filling and emptying valves and connections, an electronic
scale,
~5 and a computerized monitoring and valve control unit. A detailed
explanation of a
suitable test method using this equipment is also given in the applicants co-
pending application PCT/US98/13497, filed on 29'" June 1998 (attorney docket
no. CM1841 FQ).
~m~les
Example 1
A test apparatus comprises a cylindrical pot having an internal diameter of
150 mm and a height of 130mm, and a flange at one end of the pot. The flange
was detachably connected to an adapter which internally has a cylindrical
cavity
with a diameter of 150 mm and a depth of 25 mm. The adapter also had a hole
drilled radially inwards from one side, with a diameter of 10 mm which is in
fluid
3o connection with the internal cavity. The flange and the adapter were made
from
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plexiglass and are detachably connected so that the internal diameter of the
pot
is located directly above the cylindrical cavity of the adapter. An O-ring
prevented
leakage from between the cylindrical pot and the adapter. A membrane having a
diameter of about 300 mm was held between the flange and the adapter, and
was hermetically sealed by the O-ring. The membrane was supported by a
structural grid on each side of the membrane. The structural grids were both
made from polyester, having a 900 micrometer pore size, a thickness of 1.5 mm
and were supplied by Peter Villforth GmbH & Co of Reutlingen, Germany. A
plastic tube with a diameter of 10 mm, and a length of about 50 cm, was
1o connected to the radially drilled hole of the adapter.
In a first example, the membrane was made from polyamide, having an
average pore size of 20 micrometers and an open area of 14%, and was
manufactured by Verseidag Techfab GmbH of Geldern Waldeck, Germany under
the trade name Monodur PA20.
Example 2
2o The previous example was repeated with the membrane being replaced by
a polyamide membrane having an average pore size of 20 micrometers, an open
area of 14%, and a caliper of 55 micrometers. The membrane was manufactured
by Sefar Inc., of Ruschlikon, Switzerland, number 03-20/14.
Example 3
The previous example was repeated with the membrane being replaced by
a polyamide membrane having an average pore size of 5 micrometers, an open
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area of 1 %, and a caliper of 75 micrometers. The membrane was manufactured
by Sefar Inc., of Ruschlikon, Switzerland, number 03-5/1.
Example 4
The previous example was repeated with the membrane being replaced by
a steel membrane having an average pore size of 20 micrometers, an open area
of 61 %, and a caliper of 90 micrometers. The membrane was manufactured by
o Haver & Boeker of Oelde Westfalen, Germany under the trade name HIFO 20.
Example 5
~5 A cylindrical piece of open-celled polyurethane foam, manufactured by
Reticel of Wetteren, Belgium under the trade name Bulpren S10, having 10 pores
per inch has a diameter of 40 mm and a length of 100 mm. One end of the foam
cylinder is placed in the middle of a membrane having a diameter of 350 mm.
The membrane is then folded so as to cover the sides of the foam cylinder, and
2o the free part of the membrane, i.e. the region around the circumference of
the
membrane is hermetically sealed around the outside of an adapter. The adapter
is an internally hollow bottle cap number 19/26 supplied by Merck Eurolab GmbH
of Frankfurt, Germany, and the sealing is achieved by a rubber seal, Gukos
EPDM, 24 & 43 OD, supplied by Merck Eurolab GmbH. A plastic tube, Tygon
25 Vacuum R-3603 supplied by Norton Performance Plastic Corp. of Akron, Ohio,
USA, having an internal diameter of 7 mm, and a length of about 50 cm, is held
inside the internal hole of the adapter. The tube and the polyurethane foam
are
filled with water and the membrane is completely wetted. The foam/membrane
assembly is buried in the earth in proximity to the plant roots, and free end
of the
3o tube is submerged in a water reservoir. The test apparatus ensures that all
water
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passing from the reservoir, through the tube, into the foam cylinder and
finally out
of the apparatus, must pass through the membrane which is held around the
outside of the foam cylinder.
5 The membrane is a polyamide membrane having an average pore size of
micrometers, an open area of 14%, and a caliper of 55 micrometers,
manufactured by Sefar Inc., of Ruschlikon, Switzerland, number 03-20114.
1o Example 6
A tube has a polyamide membrane hermetically sealed over each end using
glue (Quicktal Art No. 300.43). The membrane has an average pore size of 15
micrometers, an open area of 1 %, and a caliper of 60 micrometers. The
15 membrane is manufactured by Sefar Inc., of Ruschlikon, Switzerland, number
03-15/10. The tube is available as Tygon Vacuum R-3603 from Norton
Performance Plastic Corp. of Akron, Ohio., has an internal diameter of 7 mm
and
a length of about 1 m. The tube is completely filled with water, and both
membranes are completely wetted. One end of the tube is buried in the earth in
2o proximity to the plant roots, and free end of the tube is submerged in a
water
reservoir.
In all of the examples 1 to 6, the device is used as an irrigation system to
provide water for cress plants. Cress plants were successfully cultivated for
a
period of four weeks during which the water withdrawn from the reservoir was
observed to be about 1 ml per day per square centimeter of cultivated area.
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