EXPERIMENTAL AND ANALYTICAL STUDIES OF FULL-SCALE AMBERLITE WATER DE-IONIZING BED STRUCTURE FOR SPACE APPLICATION

Abstract eng:
A critical component in the oxygen generation assembly for long term human habitation system in space is the de-ionizing (DI) bed - a packed bed of ion-exchange resin beads - that purifies water by removing ions (dissolved salts and organic impurities) from reclaimed water. The DI bed shrinks during the course of its operation. For the bed to work satisfactorily in microgravity environment, it is required that the bed is kept compressed and this is done with the aid of a compressed spring mechanism placed at one end. The objective of this current research work is to study the behavior of the full-scale DI bed experimentally in order to gain an understanding of how a force applied at one end is transmitted along the length of the bed and to determine an analytical model that fits experimentally obtained data. A series of experimental investigations was carried out in several lengths of full-scale DI bed made of Amberlite IRN78 ion exchange resin to determine load-deflection characteristics of the bed, including the friction force characteristics between the resin bed and the inner wall of the housing cylinder. Stress behaviors (creep and stress relaxation), possibly through particle re-arrangement, were observed in the DI bed. It was also observed that the friction between the DI medium and the wall of housing cylinder plays crucial role in the transmission of load from one end of the DI bed to the other. An analytical model similar to that used for determining stresses in silos, incorporating deformation effects and density changes, was developed and found to fit experimental data reasonably well. An equation normally used for stress relaxation in soils was found to fit the stress relaxation curves that were obtained experimentally.

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