Migration water transport

Fissure Elution Experiments. The migration characteristics of americium by water transport in fissures fabricated from gray hornblende schist were determined. Fissures not used in the previous sorption experiments were used for these elution experiments. A diagram of the experimental apparatus is shown in Figure 4. Solution reservoirs were attached above the fissures and the small bore tubes affixed to the bottom of the fissures were connected to solution metering pumps. 

In the same ED cell pair, the overall water transport through the electromembranes from the dilute stream to the concentrate one can be expressed by accounting for electroosmosis (i.e., the migration of water molecules associated with ions, this being proportional to j) and osmosis phenomena ... 

One of the more recent technologies in pollution treatment and remediation is based on the electrokinetic decontamination of soils [126-128], in which a dc potential (a few volts per centimeter) is applied across two inert electrodes embedded in a soil mass. This applied potential causes decomposition of the soil water to occur at the two electrodes. The migration of contaminants in the electric field, water transport, and reactions at the electrodes, as well as reactions caused by the induced pH gradient, can effectively clean soils. Acar et al. [127] reviewed electrokinetic remediation for the removal of metals and other inorganic contaminants from soil as well as its use in the extraction of organics from contaminated soils. 

Moving air can only transport sand and dust, and does not erode solid rock very effectively. Its characteristic landforms, sand dunes, occur in many sizes and shapes. Most have a gentle slope on the windward side, where sand is being eroded away, and a steeper leeward side, where sand is deposited. Movement of sand from one side to the other may result in the migration of the sand dnne in the direction the wind is blowing. As with water, transport capability varies with velocity, so sand dunes often develop where the wind slows down. This is the case at Great Sand Dunes National Monument, Colorado, and Death Valley National Park, California, where spectacular, but localized, dune fields occur. 

The co-transport of water with protons (the so-called electro-osmotic drag) is to some extent unavoidable, at least in aqueous media, due to the fact that protons do not migrate through the membrane as such but as part of protonated clusters I D, 110, (see below). Water transport should, however, be reduced as much as possible for several reasons ... 

After release into the near field, the radionuclides can only migrate via a water transport path (Figure 22.10). Migration in the far field may occur for radionuclides with long lifetimes, high solubility in ground water, and low sorption along the transport pathway. In repositories where the water is confined to interstitial fracture and pore areas, the... 

Operation mode of fuel cell is strongly determined by water balance. Water production by electrochemical process and also water transport due to proton migration and diffusion were measured with use of special complex. For MEA based on MF-4SK proton exchange membrane with hydrophobic catalytic layer an effective water drag coefficient =0.28 for air and =0.53 for pure oxygen, water diffusion coefficient trough membrane T) , =l.55x10 mVs. 

Mass transport assumes the flow of all dissolved components together with water, underground gas or oil in the direction of their flow. That is why the path and rate of mass transport depend first of all on the nature and rate of fluid migration. Mass transport by water is subject to the laws of hydrodynamics and are defined by gradients of hydrostatic head. Rates of the mass transport cannot exceed average real velocity of migration of the transporter itself Exactly mass transport is responsible for mass exchange within boxmdaries of the lithosphere and for the formation of most deposits of economic minerals. 

Latex compounds have been typically used in paper, textile and construction. One of the most popular applications is their use in self-sealing envelopes. This application is based on the fact that when NR dries, some soluble non-rubber compounds migrate to the surface by water transport, leaving a thin film when drying is completed. This film reduces the surface tack on the rubber, and when pressed against a similar film, the non-rubber layer is displaced, allowing the two rubber surfaces to create a bond. 

In the presence of an electric field, the sodium ions surrounded with free water molecules can move to the cathode. Selective ionic and water transport across the polymer under an electric field results in volumetric changes, which in turn lead to bending. When a DC electric field was applied, the cellulose EAPap actuator was bent to the positive electrode, which confirmed the above explanation. The ambient humidity effect on the EAPap actuator performance is further evidence, where ion transport is facilitated when humidity intake is higher. Thus, the actuation principle of cellulose EAPap might be a combination of piezoelectric and ionic migration effects associated with the dipole moment of cellulose material. 

In the near-field of the contaminant source, the actinides may be at saturation with respect to primary or secondary solid phases, depending on the water infiltration rate. When actinides will be released and migrate in lower concentrations (by dilution) along water transport paths they will come into contact with hundreds of chemically active compounds and minerals. The intimate contact between contaminant and geologic medium provides a dominant reaction path for its retention... 

As we have discussed in Chapter 7, the water transport in the electrol5he is governed primarily by diffusion owing to concentration difference and migration owing to pressure difference. The governing equation is given as... 

All three major components of an ME A, membrane, catalyst, and diffusion medium, can be contaminated by foreign species during PEMFC operation. Contamination of the diffusion medium usually lowers its hydrophobicity, which leads to water transport problems and can potentially create a continuous liquid path from the membrane to the gas flow channel. Foreign ionic contaminants can directly migrate to the membrane via this liquid path. Consequently, faster contamination may occur under this condition. Since diffusion medium contamination does not directly cause more severe membrane degradation, the discussion of the contamination issue will focus on two aspects membrane contamination and catalyst contamination. 

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