LIQUID TRANSFER DEVICE, AND USE OF THE DEVICE FOR IRRIGATION

Abstract: The present invention relates to a liquid transport device comprising a reservoir and a liquid conduit comprising an inlet and an outlet, wherein the inlet is connected to the reservoir, wherein the device further 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. The invention further relates to the use of the liquid transport device for the irrigation of plants.

Description: LIQUID TRANSFER DEVICE. AND USE OF THE DEVICE FOR IRRIGATION 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 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 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 liquid transported is water, optionally with fertiliser, plant nutrients, insecticide and/or weedkiller. DE-A-26 55 656, published on June 16 th , 1977 discloses a device 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 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, 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. WO-A-86 04 212, published on July 31 st , 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 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 pumps, and without the need to provide gravity driven or pump driven flow. SUMMARY OF THE INVENTION 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 1mm. 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 distribution system". By "closed distribution system" it is meant herein that a 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 pressure. In particular the seal between membrane and the liquid conduit prevents the device frdrn 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 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 Ts permeable for liquid, gas or a suspension of particles in a liquid or 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 (e.g. air) will essentially not pass through the membrane if the driving pressure is 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. 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. 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 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. The membrane has an average thickness of less than 1mm, 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. 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 will be impermeable to gas. However, once wetted and the poly(vinyl)alcohol film 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 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 is at least 1 x 10 "7 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 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. 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 siphon effect is maintained. The driving pressure to move liquid along the siphon 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 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, 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 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. 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 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 weedkiller. 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 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 (membrane) 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 Parafilm 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. 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 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 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. 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 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/s 2 ). 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 when the first air bubbles "break through". Determination of Pore Size 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 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 low enough to allow a clear cross-section image under the microscope. Typical sample calipers are below 200μm. 2) A microscopic image is obtained via a video microscope using the appropriate magnification. Best results are obtained if about 10 to 100 pores are visible on 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 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/π) 1/2 . 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 Flow 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-1200AEXI, such as 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 caliper 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 " (about 2.86 cm), exerting a pressure of 0.2 psi (about 1.4 kPa) on the sample, unless otherwise desired. Determination of permeability and conductivity Permeability and conductivity are conveniently measured on commercially available test equipment. For example, equipment is commercially available as a Permeameter such 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, 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 th June 1998 (attorney docket no. CM1841 FQ). Examples 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 connection with the internal cavity. The flange and the adapter were made from 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 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 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 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 Haver & Boeker of Oelde Westfalen, Germany under the trade name HIFO 20. Example 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 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 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 tube is submerged in a water reservoir. The test apparatus ensures that all water 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. The membrane is a polyamide membrane having an average pore size of 20 micrometers, an open area of 14%, and a caliper of 55 micrometers, manufactured by Sefar Inc., of Ruschlikon, Switzerland, number 03-20/14. 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 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 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.

Claims: CLAIMS 1. A liquid transport device comprising a reservoir and a liquid conduit comprising an inlet and an outlet, wherein the inlet is connected to the reservoir, characterised in that the device further 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. 2. A liquid transport device according to claim 1 wherein the device is for transporting an aqueous liquid and the membrane is hydrophilic and has a contact angle with distilled water which is less than 70°. 3. A liquid transport device according to claim 2 wherein the membrane has a bubble point pressure of at least 1 kPa, when measured at ambient temperature and pressure with distilled water. 4. A liquid transport device according to claim 3 wherein the membrane has a bubble point pressure of from 8 to 50 kPa, when measured at ambient temperature and pressure with distilled water. 5. A liquid transfer device according to any of the previous claims wherein the membrane has a membrane conductivity (k/d) of at least 1 x 10 9 m. 6. A liquid transfer device according to claim 5 wherein the membrane has a membrane conductivity (k/d) of from 1 x 10 9 to 300 x 10 ~9 m, preferably at least 10 7 , and more preferably at least 10 5 m. 7. A liquid transfer device according to any of the previous claims wherein the device further comprises a second membrane hermetically sealed to the conduit in the region of the inlet, the second membrane being liquid permeable and having an average pore size not greater than 100 micrometers and a thickness of less than 1mm. 8. Use of a liquid transfer device according to any of the previous claims for irrigation of plants. 9. Use of a liquid transfer device according to claim 8 wherein the outlet is at a higher level than the level of liquid in the reservoir so that negative hydrostatic suction is created between the reservoir and the outlet. 10. Use of a liquid transfer device according to any of claims 1 to 7 for the drainage of agricultural fields, sports fields, and the like. 11. Use of a liquid transfer device according to any of claims 8 to 10 wherein the liquid flow through the liquid conduit can take place in both directions.

Inventors: DIRKSING ROBERT STANLEY, EHRNSPERGER BRUNO JOHANNES, SCHMIDT MATTIAS, DIRKSING, ROBERT, STANLEY, EHRNSPERGER, BRUNO, JOHANNES, SCHMIDT, MATTIAS
Applicants: DIRKSING ROBERT STANLEY, EHRNSPERGER BRUNO JOHANNES, PROCTER & GAMBLE, SCHMIDT MATTIAS, DIRKSING, ROBERT, STANLEY, EHRNSPERGER, BRUNO, JOHANNES, SCHMIDT, MATTIAS, THE PROCTER & GAMBLE COMPANY
Application year: 1999
Main classification: A01G27
IPC codes: A01G7, A01G25, A01G27, A61F5, A61F13, B01D17, B01D61, B01J20, B32B5, B65D47, C02F1, E02B15