ABSTRACT
Separation of atmospheric moisture from ambient air is termed as dehumidification, an important unit operation with widespread applications in buildings with high outdoor air facility, air conditioning, and spacecraft missions. Recent innovations in the development of porous hollow fibers for membrane contactor based air dehumidification have enabled energy efficiency, process safety, and environmental benignity. The hydrophobic porous membrane with high surface area per unit volume acts as an interface to separate the liquid desiccant from the air stream by effectively withdrawing water vapor from air. Performance of the contactor primarily depends on membrane selection, absorbent / desiccant type, module design, and real time working conditions such as temperature, flow rate, humidity and pressure of air, and liquid desiccant. An emphasis on the characterization of surface / cross-sectional morphology, pore diameter, pore size distribution, and hydrophobicity of the hollow fiber membrane is highly significant for prediction of separation performance. Basic concepts relevant to solute transport phenomena through non-wetted membranes with relevant mathematical correlations for determination of heat and mass transfer coefficients for design of dehumidifiers are discussed. Case studies pertaining to dehydration of natural gas and flue gas are presented. Future scope and recommendations for system design and scale-up of air dehumidification are discussed.
