Force-Displacement Behavior of Activated Alumina Packed Beds for Water Processing Application in Space Life Support Systems

Granular hard bed materials like activated alumina and magchem packed in cylindrical containers are used for removing volatile organic components from wastewater aboard the International Space Station. For proper packing in the microgravity environment and to keep the bed material in place, a spring mechanism is used at one end of the bed. Spring force is a critical factor in providing appropriate compaction to the entire length of the bed media throughout the course of operation. This paper presents results from an experimental study of a full-scale, 38.1 cm (15 inches) long and 3.7 cm (1.44 inches) diameter, activated alumina bed enclosed in a cylinder to determine its force-displacement (loading-unloading) behavior, friction mobilizing force, and normal stress distribution under various axial loads and levels of packing. It is observed that force-displacement behavior becomes more linear with decrease in void ratio (increase in compaction) of the bed media. Friction mobilizing force between the bed media and the wall of the encasing cylinder is found to be significant. Axial normal stress distribution along the length of the bed media is determined using a load sensor. It is seen that the axial stress decreased exponentially with increase in depth from the loading end of the granular media.