| 摘要 |
1. A method of removing dissolved solids from water which method includes feeding said water through a salt retention passage bounded by a reverse osmosis membrane and subjecting the membrane, the water in the salt retention passage and the water which has passed through the membrane to a fluctuating magnetic field, characterized in that a magnetic field is generated by two coils spaced apart along the length of said salt retention passage. 2. The method according to Claim 1, and including the step of feeding three phase AC current to three coils spaced apart along the length of said salt retention passage, each coil having a respective one of said phases fed thereto. 3. The method as claimed in Claim 1 or 2, wherein the magnetic fields generated by the coils overlap. 4. Apparatus of removing dissolved solids from water comprising an elongate salt retention passage bounded by a reverse osmosis membrane, and means for feeding water to said salt retention passage so that the water flows along said salt retention passage, and means for generating a fluctuating magnetic field, characterized in that the means for generating a fluctuating magnetic field comprises two coils spaced apart along the length of the salt retention passage and means for applying a voltage of varying magnitude to each of said coils to cause each coil to generate a fluctuating magnetic field. 5. Apparatus of removing dissolved solids from water comprising an elongate salt retention passage bounded by a reverse osmosis membrane, and means for feeding water to said salt retention passage so that the water flows along said salt retention passage, and means for generating a fluctuating magnetic field, characterized in that the means for generating a fluctuating magnetic field comprises three coils spaced apart along the length of the salt retention passage and means for supplying three phase AC current, each coil having a respective one of the phases connected to it whereby the fields generated by the three coils are out of phase with one another. 6. Apparatus according to Claim 4 or 5, characterized in that comprises a casing of elongate form, and a cartridge of elongate form in said casing, said cartridge including semi-permeable membranes bounding a multitude of salt retention passages, said coils being spaced apart along the length of the casing. 7. Apparatus according to Claim 6, characterized in that comprises said means for feeding water includes a pump driven by a three phase electric motor, said motor being connected to said three phase AC supply through the coils which act as chokes for the motor. 8. Apparatus according to Claim 7, characterized in that comprises an adjustable frequency AC drive between said coils and said motor. 9. Apparatus according to Claim 8, characterized in that comprises a pressure sensor for sensing the pressure at the pump pressure port and feeding a control signal to said drive whereby the drive controls said motor in such manner as to provide a constant pressure at said port. 10. Apparatus according to Claim 4 or 5, characterized in that comprises a plate with a plurality of holes in it between said means for feeding water and said cartridge, the holes in the plate dividing the water up into streams and directing said streams of water against the end of the cartridge whereby the water entering the salt retention passages has eddy currents in it and there is a pressure drop across said plate. 11. Apparatus according to Claim 4 or 5, characterized in that said casing has a cylindrical wall of fibre reinforced settable resin, said coils being embedded in said cylindrical wall. 12. Apparatus according to Claim 11, characterized in that comprises layers of gel radially inwardly and radially outwardly of each coil, for protecting and cushioning each coil. 13. Apparatus according to any one of Claims 4 to 12, characterized in those said coils are positioned so that their magnetic fields overlap. |
