Development of moisture absorber based on hydrophilic nonporous membrane mass exchanger and alkoxylated siloxane liquid desiccant

In order to deal with corrosion, crossover and desiccant utilization issues encountered in commercially available liquid desiccant systems, we develop and characterize the performance of a hydrophilic nonporous membrane-based liquid desiccant absorber. The liquid desiccant is an alkoxylated siloxane mixture, a modified silicone oil for enhanced moisture absorption. Performance is characterized for a shell and tube configuration by measuring air temperature and relative humidity at the inlet and outlet of the absorber. We determine the characteristics of counter and parallel flow configurations, various air and liquid desiccant flow rates and several contact lengths within the membrane absorber. The absorption was weakly increased by liquid desiccant flow rate. Results for counterflow configuration show that the humidity ratio of the air entering the membrane system can be reduced by up to 15.7 g/kg at maximum air flow Re number and longest contact length. Desiccant utilization in the system ranged up to 0.012 g of water per gram of desiccant. The highest desiccant utilization does not correspond to the highest mass flux rate, suggesting that the most effective system does not depend on on the quantity of removal, but rather the rate. Bulk diffusion of moisture into the desiccant is the rate limiting step for moisture absorption, with with five times faster absorption in the first 10 cm of contact length, guiding us toward future system design.