| Packed beds of lithium hydroxide (LiOH) have been used to remove carbon dioxide in closed environments where space and mass are design criteria. The space suit systems of the Apollo astronauts held a LiOH system; developmental rebreathers for the U.S. Navy Seals contained LiOH; and space suits of the Shuttle U.S. astronauts contained a packed bed of lithium hydroxide to chemically remove metabolic CO2. However, the system was never well-characterized, and empirical testing did not adequately predict flight performance. NASA eventually replaced the LiOH flight system for extravehicular operations on the International Space Station (ISS), and the Navy decided to operate with an alternate rebreather system. However, LiOH may be the sorbent of choice for brief returns to the moon, and it is still used as backup in submarine applications.; This thesis quantifies the performance of the lithium hydroxide CO 2 adsorption system under a defined set of operational parameters. Two numerical modeling constructs have been developed for the LiOH system and validated with experiment. The applicability and limitations of each are detailed. The first approach, based on heterogeneous reactor theory, incorporates convection, dispersion, intraparticle transport, chemical kinetics and structural evolution. The chemistry is modeled as multi-step, with reversible water adsorption; and the model tracks the evolving particle porous structure. Reaction rates are determined by experiment; mass transfer coefficients are modeled according to theory.; The second approach draws from the atmospheric sciences and is built upon the fundamentals of liquid phase chemistry. Equilibrium reactions occur in the soluble LiOH-Li2CO3 particle in the humid environment. Condensation and evaporation of water and transport of carbon dioxide molecules to the particle surface are the governing processes.; Results from the models using mission input parameters or with data from the literature are illustrative. Using the model, an explanation is offered for the varied performance results found with regard to input humidity levels, and for interrupted use. In addition, options for a reusable canister are explored, and a comparison is made to the current system. Modifications for improved modeling sophistication and directions for future investigation are discussed. |
