Gerry B. Andeen

Effects of acceleration on particulate fouling in reverse osmosis

Abstract Experimental data show that acceleration, as in a centrifuge, is effective in reducing the amount of particulate fouling in reverse osmosis. The effects of acceleration on particulate fouling were determined by testing hollow-fiber elements under accelerations of up to 500 G. The fouling agent was 40 ppm of iron hydroxide suspended in a solution of 0.5 percent sodium chloride. The data indicate that steady-state operating conditions of a fouled membrane are approached asymptotically. 500 G of acceleration allows a fouled membrane, in a steady-state, to realize over 90 percent of its unfouled capacity; the same membrane in a nonaccelerated state produced as little as 62 percent of its unfouled desalinate flow.

Effects of acceleration on reverse osmosis desalination

Abstract Hollow fine-fiber reverse osmosis elements were run in a continuous-flow centrifuge at accelerations up to 1000 G. Under acceleration, the elements produced more desalted water and passed less salt, showing a reduction of concentration polarization. Reduced data showed that the mass transfer co-efficient of salt from the membrane surface to the bulk of the brine increased with acceleration to the 0.3 power. Acceleration also improved flow distribution by eliminating regions of high-density stagnant brine. Use of a centrifuge will allow utilization of higher transport membranes.

Dynamics of a Flexible Passive Space Array

A passive space communicator in synchronous orbit will consist of small aluminum beads chained together and aligned vertically by the Earths gravity gradient. The analysis for small deviations from vertical uses a continuous-chain model, and pitch and roll frequencies and mode shapes are described with and without the attachment of substantial end masses. An end mass with appreciable moment of inertia can provide effective damping of the lowest-order, otherwise rigid and undamped, modes. The distortion of the chain by solar radiation pressure is estimated, assuming undesirable variations in the mass-to-area ratio of beads and end masses.

Effects of acceleration on spiral-wound membrane performance in reverse osmosis

Abstract Experimental data show that acceleration, applied to spiral-wound reverse osmosis membranes by centrifugation, increases membrane performance. The effects of acceleration on concentration polarization were determined by testing spiral-wound membranes under accelerations up to 500 × g with 0.5% sodium chloride. The data indicate a reduction in salt concentration at the membrane surface from 2.2 to 1.0% from a nonaccelerated state when 500 × g acceleration is applied to a properly oriented membrane. This reduces the osmotic pressure at the membrane and increases permeate recovery by 21%.

A Flexible Passive Space Array with Springs (II)

A passive space communicator in synchronous orbit will consist of small aluminum beads chained together and aligned vertically by the Earth’s gravity-gradient. The analysis for small deviations from vertical uses a continuous chain model, and pitch and roll frequencies and mode-shapes are described. Damping of the lowest-order, otherwise rigid and undamped, modes can be obtained by inserting springs between the end portions and the main portion of the chain. The roll damping depends on tuning the springs so that energy is transferred out of roll. The effect of detuning on roll damping time is investigated.