Continuous SPLITT Fractionation

点击翻译按钮获取中文摘要

This proposal studies a flow based separation technique for fractionating particles. The separation is carried out in a rectangular flow chamber which is generally under 5 mm in thickness, and approximately 2 cm in width and 20 cm in length. At the entrance of the channel, a splitter plate which extends lengthwise a few millimeters down the tube, partitions the inlet region of the channel into two halves. A carrier fluid is pumped into the chamber on one side of the splitter, and the fluid containing the particles is introduced on the other side. As the fluids pass the splitter edge, a two phase adjacent Poiseuille flow is created with fluid near the wall boundaries moving slower than fluid in the center of the channel. As the particles are carried along the length of the channel, a field applied in a direction perpendicular to the flow axis forces the particles to migrate towards the carrier stream. Gravitational and electric forces are two examples of fields which can be used. The separation is effected by the fact that the magnitude of the force exerted by the field on the particles depends on a particular particle characteristic, and if that characteristic differs between particles then so does the magnitude of the force. Examples of such characteristics are size which would result in a different gravitational force and electric charge. Particles more strongly acted upon by the applied force migrate further into the carrier stream where they decelerate as they are entrained by slower moving fluid. After the particles have translated a certain distance downstream, particles which are not acted upon as strongly by the force are more centrally located and have moved further downstream than particles more strongly acted upon which are nearer the boundary and have not progressed as far downstream. During the last two and one-half decades, the PI developed the technique of collecting the particles by taking advantages of the developing separation distance between the particles along the flow direction. As the fluid leaves the channel, those travelling near the center elute first and can be collected, while those travelling near the boundary elute later and can be collected separately. The PI has termed this techniques FFF for field flow fractionation. In the development of FFF, scale-up proved difficult and the technique could only be used for analytical measurement since the quantities harvested were very small. In contrast to FFF, a different technique for harvesting the separation is to use a splitter at the downstream end to divide the stream into two exiting streams. One stream would contain the particles moving near the center, while the other would contain the particles moving closer to the channel cell boundary. The PI has termed this separation CSF for continuous SPLITT fractionation and has been working on CSF since 1985 (refs. 11-19 of the proposal). The research suggested in this proposal is concerned with scaleup of the cell, improving its performance, and examining different separation mechanisms.