Swell-shrink operation

The membrane must be mechanically robust and also suitable for manufacture. One of the consequences of the need for a fully hydrated membrane is that the membrane will shrink and swell between operation and resting. This can have dire consequences for an FC stack that must be sealed if the membrane dimensions are radically changing between on and off conditions. So, ideally the membrane should not... 

The biopolymer CSPs are attractive owing to the ready availability of the chiral precursors. Offsetting this advantage is an innate complexity that more or less baffles one s ability to deduce the details of the operative chiral recognition processes. Moreover, one cannot easily alter or "fine tune" the structure of the CSP to enhance selectively. Finally, there may well be limitations as to the mobile phases which can be used owing to possible swelling, shrinking, denaturation, or dissolution. 

The most diffused actuating configuration, in which these materials are used, is represented by the so-called unimorph bilayer bender. This kind of actuator consists of a film of active material coupled to a passive supporting layer. The bilayer structure is operated within an electrochemical cell, having a liquid electrolyte in which the device is immersed. The active polymeric layer of the actuator works as one electrode of the cell, while a counter electrode and a third reference electrode are separately immersed in the electrolyte. One end of the bilayer is constrained, while the other is free. The potential difference applied between the electrodes causes red-ox reactions of the conducting polymer. Since the CP and the passive layers are mechanically interlocked, when the polymer swells/shrinks the passive layer, which can not modify its dimensions, transforms the CP linear displacement into a bending movement of the structure [238-242]. Very similar is the bimorph structure. In this case the passive layer is substituted by a second CP film and they work in opposition of phase. 

Influence parameters are especially the press temperature and the moisture content in the mat. Additional parameters are the wood density, the porosity, the swelling and shrinking behavior of the wood, the structure at the surface and the wetting behavior. During the press cycle several mechanisms are in operation ... 

Most SAW transducers are inadequate for operation in liquids because most types of surface acoustic waves are completely damped in this viscous environment. Therefore, QCM transducers are used instead. For successful operation of an MIP-QCM chemosensor in liquid, the MIP film should be sufficiently stable with respect to dissolution and peeling off from the resonator surface. Moreover, this film should be relatively rigid, neither shrinking nor swelling in the test solution. 

Alternatives to batch testing include the use of diffusion cells or flowthrough columns. Diffusion cells are easier to operate, but are less representative of field conditions where some advection may occur. However, operation of columns at very low flow rates is difficult and subject to artifacts. To minimize possible wall effects associated with shrink/swell behavior of low-permeability clay materials, several researchers have utilized column devices that provide a confining pressure, such as flexible wall permeameters (e.g., Acar and Haider, 1990 Smith and Jaffe, 1994 Shackelford and Redmond, 1995 Khandelwal et al., 1998 Khandelwal and Rabideau, 2000). 

This work presents the on-line level control of a batch reactor. The on-line strategy is required to accommodate the reaction rate disturbances which arise due to catalyst dosing uncertainties (catalyst mass and feeding time). It is concluded that the implemented shrinking horizon on-line optimization strategy is able to calculate the optimal temperature profile without causing swelling or sub-optimal operation. Additionally, it is concluded that, for this process, a closed-loop formulation of the model predictive controller is needed where an output feedback controller ensures the level is controlled within the discretization intervals. 

The wet-exchange capacity accounts for the fact that the resin will swell or shrink during operation. This quantity will vary with moisture content. It is usually reported as equivalents per liter of resin (eq/L). Units of kilograms of CaCOs per cubic foot (kg/ft ) are also used. It is this term that is typically reported. 

Stability is directly related to the lifetime of the resin. This, in turn, directly affects the cost of the process. Physical stresses can occur through swelling and shrinking cycles due to osmotic pressure changes. Mechanical forces, such as static pressure load, and abrasion can cause breakage. Operation outside the normal temperature range will also add to particle degradation. 

During the first operation hydrogel elements often shows a poor repeatability and a drift of the parameters. This is caused by changes in the microscopic structure of the polymer network. By swelling and shrinking the too short polymer chains have to be cracked and the chains in general have to find their optimal moving way and position. 

---