Mechanical Behavior of Water Deionizing Granular Material Bed for Space Life Support Systems

Abstract

One of the most critical components in the oxygen-generation and water-processing assemblies for human habitation in space is the deionizing (DI) bed—a packed bed of ion-exchange resin beads—that purifies water. The DI bed shrinks during the course of its operation, and therefore, for the bed to work satisfactorily, it must be kept properly compressed. To understand the force-transferring mechanism along the bed, sets of experimental programs were developed and conducted on the individual particles and bed samples of a DI granular material, Amberlite IRN-78. The presence of water reduced the load-bearing capacity of the individual particles, because most of the wet (water submerged) particles tested failed under relatively small crushing force, whereas the dry particles withstood a much higher load. The particle crushing force was found to be closely represented by normal and Weibull distributions. The DI material bed has a relatively small internal friction angle (shear strength). The lateral pressure coefficient was found to be relatively high. The material exhibited time-dependent behavior, creep, and stress relaxation, possibly through particle deformation and rearrangement. The friction force between the DI medium and the wall of the housing cylinder was significant, and increased rapidly in a nonlinear fashion with increasing sample length. The effect of friction was more significant for more densely packed beds. The loading and unloading tests showed that the compacted material bed exhibited an anelastic type of hysteresis behavior. The uncompacted bed was seen to have nonlinear load-deformation behavior, with a rapid increase in displacement with load, whereas the compacted bed showed linear or near-linear, load-displacement behavior.