Liquid purification or separation – Casing divided by membrane into sections having inlet – Energy recovery from treated liquid
Patent
1984-06-29
1987-01-13
Spear, Frank
Liquid purification or separation
Casing divided by membrane into sections having inlet
Energy recovery from treated liquid
210356, B01D 1300
Patent
active
046363092
DESCRIPTION:
BRIEF SUMMARY
The invention relates to apparatus for effecting transfer of heat or mass between two fluids, of which at least one is usually a liquid, through a transfer membrane. Such apparatus is used in blood oxygenators and dialysers, in which case one fluid is blood and the other is oxygen or dialysate. In practice the efficiency of the transfer across the membrane is limited by the extent to which the total volume of fluid can be brought into close proximity with the membrane.
GB-A-No. 1,442,754 describes an apparatus wherein the membrane surface exposed to the fluid in one of the conduits is provided with a regularly repeating array of hollows, and there is superimposed on the mean flow of fluid through the conduit a pulsatile component which promotes vortex mixing of the fluid in the hollows.
It has been proposed to provide the conduit, in which the vortex mixing occurs, between two closely spaced generally planar sheets of transfer membrane material, in at least one of which the hollows are formed. The hollows proposed were then furrows extending transversely to the pulsatile component in the fluid flow. The furrows may be preformed in the membrane or produced by initial stretching of the membrane by fluid in the conduit whilst the membrane is supported externally against a profiled support plate. In that case a conduit for the second fluid is provided between the membrane and the support plate. These are advantages however in providing the conduits, in which the vortex mixing is promoted, in the form of axisymmetric tubular conduits having a series of larger cross-sectional bulbous portions connected by smaller cross-sectional neck portions. However, such tubular conduits are difficult to mount in the apparatus. GB-A-No. 2,042,926 discloses a technique for making an integral array of tubular conduits by sealing together two sheets, of which at least one is transfer membrane material, along a series of sinuous lines extending generally in the same direction alongside one another, with the undulations of adjacent lines out of phase with one another. This provides a generally planar compact nesting array of conduits. Each bulbous portion of each conduit is positioned between neck portions of adjacent conduits. However problems arise in sealing, e.g. by means of heat, the delicate transfer membrane material. Also, narrow crevices tend to be formed along the sides of the conduit adjacent to the seal lines and these provide possible locations for blood to collect and clot.
In accordance with the present invention, a membrane assembly for use in mass or heat transfer or filter apparatus, comprises a pair of generally parallel plates spaced apart with a profiled surface of one plate facing a similarly profiled surface of the other plate; and a pair of sheets of transfer membrane material closely spaced face to face between the plates with each sheet supported by and partially nesting in the profiled surface of the adjacent plate, to provide between the membranes a conduit for one fluid and, between each sheet and the adjacent plate a conduit for the second fluid; whereby in use each sheet presents in its surface facing the other sheet a regular array of close packed depressions. Preferably, each of the depressions faces a similar depression in the other sheet.
Surprisingly this geometry provides extremely good fluid dynamics in the conduit between the two membrane sheets. Specifically, since the membrane sheets are spaced, at least slightly, throughout the majority of their areas, hydraulic resistance is low, and yet adequate vortex mixing can be promoted in the depressions with a small pulsatile component of flow superimposed upon the mean flow of fluid through the conduit. Even compared with apparatus in which the liquid flow rate is already turbulent, ie. with Reynold's numbers of say greater than 15,000, with the apparatus of the invention there is an effective trebling of the mass transfer rate. When the fluid is blood, the positive spacing of the membrane sheets, substantially throughout their whole area, minimi
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WO80/01042, Bellhouse et al., 5-1980.
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