HYDROPHILIC MEMBRANE-BASED HUMIDITY CONTROL

A dehumidification system for low gravity plant growth experiments req uires the generation of no free-liquid condensate and the recovery of water for reuse. In the systems discussed in this paper, the membrane is a barrier between the humid air phase and a liquid-coolant water ph ase. The coolant water temperature combined with a transmembrane press ure differential establishes a water flux from the humid air into the coolant water. Building on the work of others, we directly compared di fferent hydrophilic membranes for humidity control. In a direct compar ison of the hydrophilic membranes, hollow fiber cellulose ester membra nes were superior to metal and ceramic membranes in the categories of condensation flux per surface area, ease of start-up, and stability. H owever, cellulose ester membranes were inferior to metal membranes in one significant category, durability. Dehumidification systems using m ixed cellulose ester membranes failed after operational times of only hours to days. We propose that the ratio of fluid surface area to memb rane material area (congruent to membrane porosity) controls the relat ive performances among membranes. In addition, we clarified design equ ations for operational parameters such as the transmembrane pressure d ifferential. This technology has several potential benefits related to earth environmental issues including the minimization of airborne pat hogen release and higher energy efficiency in air conditioning equipme nt. Utilizing these study results, we designed, constructed, and flew, on the space shuttle missions a membrane-based dehumidification syste m for a plant growth chamber. (C) 1998 Elsevier Science B.V. All right s reserved.