Gas and water transfer behaviors in gas permeable membranes.

摘要

Membrane gas transfer is a promising technology for stimulating in situ bioremediation of groundwater because it provides the ability to control the amount of gas delivered to the subsurface more effectively than alternative gas transfer technologies. This research addressed fundamental mass transfer behavior of membranes under conditions typical of groundwater flow.; Membrane gas transfer was studied using laboratory-scale glass columns operated at low flow velocities (0.086--130 m/d). H2 was supplied to the inside of the membrane fibers while water flowed on the outside and normal to the fibers (i.e. cross-flow). A dimensionless correlation was developed from the experimental results, expressing Sherwood number (Sh) as a function of Reynolds number (Re) and Schmidt number (Sc): Sh = 0.824Re 0.39Sc0.33 (0.0004 Re 0.6). This correlation is useful for predicting the rate of transfer of any gas from clean membranes to flowing water at low Re. This correlation provides a basis for estimating the membrane surface area requirements for groundwater remediation.; Change in gas composition in a flow-through membrane module was measured using a pilot-scale study and simulated with a computational model. The experiments were designed to deliver O2 into N2-saturated water via hollow-fiber membrane fabric. The predicted gas composition profiles from the model were in a good agreement with those from experimental measurements (≤10% difference), and both suggested that back diffusion of dissolved gases into the membrane had a significant effect on gas transfer. This model can be used to estimate gas transfer as a function of membrane module design and operating conditions.; Membrane gas transfer can be compromised by water condensation during operation. A mathematical model to simulate water transport was developed to predict conditions under which condensation may occur. Our study showed that in addition to a drop in temperature, the reduction in gas volume, which is inevitable when there is gas dissolution, could cause water condensation. In our experiments, no water nucleation was observed within membrane pores. Condensation occurred inside the membrane lumen, either in the gas phase or at the gas-membrane interface. While this condensation can not normally be avoided, module design can facilitate condensate removal.