A water-evaporation conduit for a humidifier

Abstract: The present invention provides a water-evaporation conduit 1 for use in humidifying equipment that is not adversely affected by contact with oils, detergents, and other liquids used in the manufacture and maintenance of the equipment.

Description: The present invention concerns a water-evaporation conduit for use in a humidifier, which conduit makes use of a porous hydrophobic polymeric material. Humidifying equipment having porous hydrophobic water channels or conduits, and fans or other means to blow air across the porous surfaces of the conduits are known in the art. The water conduits may be made of porous hydrophobic tubing or, in the other cases, laminated constructions of porous hydrophobic sheet. The porous hydrophobic materials used as humidifier water conduits resist passage of liquid water through them, but permit passage of water vapour through them, thus humidifying the air stream passing over the porous surfaces. Polymeric materials used for the hydrophobic tubing or sheet include polyethylene, polypropylene, polystyrene, poly (vinyl chloride), polyvinylidene chloride, polycarbonate, polyester, or fluoropolymers. Porous hydrophobic tubing or sheet of the above materials, although having good initial water repellency and resistance to passage of liquid water through their pores, can lose their water repelling ability due to contamination or degradation caused by oily materials, surfactants, detergents, and the like, with which they come into contact in the course of their manufacture or use. When this occurs, water begins leaking from the conduits, leading to failure of the humidifiers. An additional problem with such humidifying equipment is that during the initial charging of water into the conduits or during subsequent normal usage, air pockets form in the conduits which resist displacement by the water. This results in lower evaporation rates and reduces the efficiency of the humidifiers. An object of the present invention is to provide an improved water-evaporation conduit in humidifying equipment and the like by preventing contamination of porous hydrophobic water-vapour-permeable conduits used in such equipment by materials commonly encountered by them, for example, oils, surfactants, cleaning fluids and detergents, etc., which cause loss of hydrophobicity of the conduit materials and permit liquid water to pass through them, thus leading to leakage of water from the conduits and failure of the equipment. A further object of the present invention is to provide a means for enabling a complete displacement of air from the inside of the conduit as the conduit is filled with water, and which also, during operation, prevents development of air pockets inside the conduit which lower the humidifying performance of the conduit. According to the present invention there is provided a water-evaporation conduit for a humidifier or the like, said conduit comprising (a) water evaporation tubing of a porous hydrophobic polymeric material said porous hydrophobic tubing having on its inner surface (b) a continuous non-porous coating of hydrophilic water-vapor permeable material. Preferably, the water evaporation conduit tubing has a second porous hydrophobic tube for air removal inserted axially along the length of the water-evaporation tube; the air-removal tube having its distal end closed to prevent entry of liquid water, its proximal end open to permit displaced air to exhaust. Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawing in which:- Figure 1 is a schematic drawing of a simple humidifier; Figure 2 is an axial cross-sectional view of a water-evaporation conduit for use in the humidifier of Figure 1; Figure 3 is a schematic drawing of an air removal tube inserted in a water-evaporation conduit assembly; and Figure 4 is a schematic drawing illustrating an alternative configuration of water-evaporation conduit. A simple humidifier device 10 is shown schematically in Figure 1. The humidifying equipment comprises a water-evaporation conduit 1 connected to a water-supply reservoir 2 above it. A fan 11 blows air over the surface of the water-evaporation conduit which entrains the water vapor emanating from the water-evaporation conduit. The air and entrained water vapor are blown out of the humidifier equipment into the surrounding environment, thus humidifying the environment around the humidifier. Referring to Figure 2, the water-evaporation conduit 1 is formed from a porous hydrophobic tube 3 which is coated on its inner surface with a continuous non-porous hydrophilic water-vapor-permeable coating 4. Suitable polymeric materials for the porous hydrophobic tube 3 include polyolefin, polycarbonate, polyester, polystyrene, poly(vinyl chloride), polyvinylidene chloride, and the like. Preferred materials are fluoropolymers such as polyvinylfluoride, fluorinated ethylene/propylene (FEP), tetrafluoroethylene/perfluoroalkyl perfluorovinylether copolymer (PFA), polytetrafluoroethylene (PTFE), and the like. Most preferably, the porous hydrophobic tube is porous expanded polytetrafluoroethylene tube having the structure of interconnected nodes and fibrils described in U.S. Patent No. 3,953,566 (Gore) and U.S. Patent No. 4,187,390 (Gore). The non-porous hydrophilic water-vapor-permeable coating 4 on the inner surface of the porous hyrophobic tube can be a polyurethane resin containing oxyethylene groups in a weight ratio of 30% or more, or a prepolymer thereof; a polyester resin containing oxyethylene in a weight ratio of 30% or more, or a prepolymer thereof; or a resin containing a sulfonic acid group, an amino group, a hydroxyl group, or a carboxyl group in a terminal group or a pendant group. The thickness if the continuous non-porous coating can be from 3 to 400 micrometers thick, and is preferably in the range 5 to 30 micrometers thick. The water-vapor-permeability of the water-evaporation conduit should be at least 1,000 g/m 2 /day, and is preferably in the range 5,000 to 90,000 g/m 2 /day. Although having good water-vapor-permeability the continuous non-porous coating forming the inner surface of the water-evaporation conduit substantially prevents passage of air or liquids through its walls. Consequently, air pockets formed within the conduit, for example, as it is filled with water, are difficult to remove. Figure 3 depicts the water-evaporation conduit 1 and water-supply reservoir 2 with an air-removal tube 5 inserted. The air-removal tube 5 is disposed axially within the water-evaporation conduit 1; its distal end closed and located near the closed end of the water-evaporation conduit, and its proximal end open and extended above the liquid level of the water-reservoir 2. The air-removal tube is porous over its full length, permits air flow through its walls, and is made of porous hydrophobic polymeric materials for resistance to penetration of liquid water though its walls. Water entry pressure (WEP) of the porous hydrophobic air-removal tube should be at least 400 mm water pressure and, preferably is 500 mm water pressure or more in order to prevent leakage of water into the tube. The inner diameter of the air-removal tube can be 1 to 20 mm, preferably in the range 4 to 8 mm diameter. Suitable material for the air-removal tube can include the porous hydrophobic polymeric materials used for the water-evaporation tube and is preferably porous expanded polytetrafluoroethylene. Figure 4 shows the water-evaporation conduit 1, water-reservoir 2, and air-removal tube 5 arranged in a cyclic waveform configuration. The coil and waveform configurations shown in the drawings illustrate only two of many ways in which the coils can be configured and are not meant to be limiting. TEST DESCRIPTIONS WATER VAPOR TRANSMISSION RATE (WVTR) [Potassium Acetate Method] A description of the test employed to measure water vapor transmission rate (WVTR) is given below. The procedure has been found to be suitable for testing films, coatings, and coated products. In the procedure, approximately 70 ml of a solution consisting of 35 parts by weight of potassium acetate and 15 parts by weight of distilled water was placed into a 133 ml polypropylene cup, having an inside diameter of 6.5 cm at its mouth. An expanded polytetrafluorethylene (PTFE) membrane having a minimum WVTR of approximately 85,000 g/m 2 /24hrs as tested by the method described in U.S. Patent No. 4,862,730 to Crosby and available from W.L. Gore & Associates, Inc. of Newark, Delaware, was heat sealed to the lip of the cup to create a taut, leakproof, microporous barrier containing the solution. A similar water expanded PTFE membrane was mounted to the surface of a water bath. The water bath assembly was controlled at 23°C plus 0.2°C, utilizing a temperature controlled room and a water circulating bath. The sample to be tested was allowed to condition at a temperature of 23°C and a relative humidity of 50% prior to performing the test procedure. Samples were placed so the microporous polymeric membrane was in contact with the expanded polytetrafluoroethylene membrane mounted to the surface of the water bath and allowed to equilibrate for at least 15 minutes prior to the introduction of the cup assembly. The cup assembly was weighed to the nearest 1/1000g. and was placed in an inverted manner onto the center of the test sample. Water transport was provided by the driving force between the water in the water bath and the saturated salt solution providing water flux by diffusion in that direction. The sample was tested for 15 minutes and the cup assembly was then removed, weighed again within 1/1000g. The WVTR of the sample was calculated from the weight gain of the cup assembly and was expressed in grams of water per square metre of sample surface area per 24 hours. WATER ENTRY PRESSURE (WEP) Water entry pressure (WEP) of the air-removal tube is measured by filling the tube with water, connecting it to a metered pressure source, and increasing the pressure at a rate of 200 mm water pressure per minute. The pressure at which drops of water first appear on the outside of the tube is taken as the water entry pressure.

Claims: A water-evaporation conduit (1) for a humidifier, said conduit comprising water evaporation tubing (3) of a porous hydrophobic polymeric material, characterised in that said porous hydrophobic tubing has on its inner surface a continuous non-porous coating (4) of hydrophilic water-vapour-permeable material. A water-evaporation conduit as claimed in claim 1, wherein the porous hydrophobic polymeric material is polyolefin, polycarbonate, polyester, polystyrene, polyvinyl chloride, polyvinylidene chloride, or fluoropolymer. A water-evaporation conduit as claimed in claim 1 or 2, wherein the water-evaporation tubing (3) is porous expanded polytetrafluoroethylene tubing. A water-evaporation conduit as claimed in any of claims 1 to 3, comprising a second porous hydrophobic tube (5) for air removal inserted axially within the water-evaporation tubing along the length of the tubing, said air removal tube having a water entry pressure in excess of 400mm of water-pressure and said air removal tube (5) having its distal end closed and its proximal end open. A water-evaporation conduit as claimed in claim 4, wherein the material of the porous hydrophobic tube (5) for air removal is of polyolefin, polycarbonate, polyester, polystyrene, polyvinyl chloride, polyvinylidene chloride, or fluoropolymer. A water-evaporation conduit as claimed in claim 5, wherein the material of the porous hydrophobic tube (5) for air removal is porous expanded polytetrafluoroethylene. A humidifier (10) incorporating a water-evaporation conduit (1) as claimed in any preceding claim.

Inventors: HAMASAKI SADAKATU, HAMASAKI, SADAKATU
Applicants: JAPAN GORE TEX INC, JAPAN GORE-TEX, INC.
Application year: 1992
Main classification: B01D69
IPC codes: F24F6, B01D67, B32B1, B01D69, B32B5