Reflection coefficient impermeability

To calculate the osmotic pressure we used values of osmotic coefficients from ref. (lOj. Total organic carbon analysis (Beckman 914A] of samples from the water filled compartment verified that the membranes are impermeable to sucrose, so that the reflection coefficient a is equal to unity. 

A reflection coefficient characterizes some particular solute interacting with a specific membrane. In addition, oy depends on the solvent on either side of the membrane — water is the only solvent that we will consider. Two extreme conditions can describe the passage of solutes impermeability, which leads to the maximum value of 1 for the reflection coefficient, and nonselectivity, where ay is 0. A reflection coefficient of zero may describe the movement of a solute across a very coarse barrier (one with large pores) that cannot distinguish or select between solute and solvent molecules also, it may refer to the passage through a membrane of a molecule very similar in size and structure to water. Impermeability describes the limiting case in which water can cross some membrane but the solute cannot. 

As shown by the upper curve in Fig. 12.6, the traditional JARLAN-type caisson (OCS) has, at its optimal working point B/L 0.2), a much lower reflection coefficient (and thus a much larger energy dissipation) than a vertical impermeable wall. However, the response is very selective with respect to the incident wave periods i.e., it performs satisfactorily only within a very narrow range of the B/L-ratios. In order to overcome this drawback, a new Multi-Chamber System (MCS) was developed and tested in the Large Wave Flume of Hannover. As shown by the lower cmve in Fig. 12.6, the new MCS concept not only provides a lower reflection coefficient moreover this reflection coefficient is kept at its lowest level over the full range of practical B/L ratios (i.e., lov B/L > 0.25, where B is defined as the overall width of the Multi-Chamber System. 

When simulating the trajectories of dispersed phase particles, appropriate boundary conditions need to be specified. Inlet or outlet boundary conditions require no special attention. At impermeable walls, however, it is necessary to represent collisions between particles and wall. Particles can reflect from the wall via elastic or inelastic collisions. Suitable coefficients of restitution representing the fraction of momentum retained by a particle after a collision need to be specified at all the wall boundaries. In some cases, particles may stick to the wall or may remain very close to the wall after they collide with the wall. Special boundary conditions need to be developed to model these situations (see, for example, the schematic shown in Fig. 4.5). 

SBS Interphase. Since 20°C is below the 0-temperature for the polystyrene-cyclohexane systems, it was expected that the PBD phase would be permeable to cyclohexane, but the PS domains would be relatively impermeable. (It is known that PS swells almost fourfold in liquid cyclohexane and that SBS may be dissolved even in cyclohexane. However, the maximum uptake of cyclohexane vapor by SBS was approximately 40% of its original weight. Furthermore, a sample of pure PS did not absorb any vapor within the time scale of these experiments. It was concluded then that the pure PS domain was not penetrated by cyclohexane vapor in these experiments and that, except for the interface, the PS domains may be considered an impermeable phase dispersed within a permeable continuum.) Thus the diffusion coefficient would be expected to reflect the structure of the PBD phase and to be characteristic of diffusion in elastomers (i.e., Fickian diffusion). 

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