Membrane temperature field

To account for the much larger lateral extension of the membrane in comparison to its thickness, some approximations are made. The variation of the temperature field in the membrane along the z-axis is assumed to be small, i.e., the temperature is nearly constant. For further considerations, the temperature field within the membrane is... 

In the previous paragraph, the basic considerations of FEM modelling have been laid out. The outcome of a static thermal simulation based on this model is a 3-d temperature field T x,y,z). In this section it is discussed, how the characteristic figures, such as thermal resistance and thermal time constant of the membrane, can be deduced. 

The circular microhotplate was thermally characterized, and the results were compared with simulations carried out according to the approach discussed in Chap. 3. Applying FEM simulations as described in Sect. 3.3 generate a temperature field, and the temperature in the membrane center represents the overall membrane temperature according to Eq. (3.21). The values that have been used for the simulation are summarized in Table 4.2. 

Once the pore size and length I are given to the pore network, one can calculate the effective pressure field (by using iteration method), the temperature field through the network, and its effect on the vapor flux through the membrane. This model takes into account all molecular transport mechanisms based on the kinetic gas theory for a single cylindrical tube and could be applied to all forms of membrane distillation process [61]. 

The catalytic dehydrogenation of light alkanes is, potentially, an important process for the production of alkenes, which are valuable starting chemical materials for a variety of applications. This reaction is endothermic and is, therefore, performed at relatively high temperatures, to improve the yield to alkenes, which is limited, at lower temperatures, by the thermodynamic equilibrium. Operation at high temperatures, however, results in catalyst deactivation (thus, requiring frequent reactivation), and in the production of undesired by-products. For these reasons, this reaction has been from the beginning of the membrane reactor field the most obvious choice for the application of the catalytic membrane reactor concept, and one of the most commonly studied reaction systems. 

Examples of splitters are devices in which nonequilibrium separations are achieved by means of membranes, electrical fields, temperature changes, and others. The splitter can also be used to model any multistage chemical separator where stage details are not of interest. 

In the base case, the heat flux in the membrane is close to zero (Figure 3.5(a)). Due to its relatively low thermal conductivity, the membrane serves as a thermal insulator, which separates temperature fields on the anode and the cathode side. The heat flux from the CCL to the... 

Newer fabrics, not in common use but in development, test, and field trials, are described for higher temperature applications by Reference [50]. Application to 400°F—2100°F are potentially available using ceramic fibers Nextel 312 , laminated membrane of expanded PTFE on a substrate, polyimid fiber P-84, Ryton polyphenylene sulfide, and woven fiberglass. The heat and acid resistance of these new materials... 

In this chapter, we Hmit ourselves to the topic of zeolite membranes in catalysis. Many types of membranes exist and each membrane has its specific field where it can be appHed best. Comparing polymeric and inorganic membranes reveals that for harsher conditions and high-temperature applications, inorganic membranes outperform polymeric membranes. In the field of heterogeneous catalYsis, elevated temperatures are quite common and therefore this is a field in which inorganic membranes could find excellent applications. 

Recent developments in polymer chemistry have allowed for the synthesis of a remarkable range of well-defined block copolymers with a high degree of molecular, compositional, and structural homogeneity. These developments are mainly due to the improvement of known polymerization techniques and their combination. Parallel advancements in characterization methods have been critical for the identification of optimum conditions for the synthesis of such materials. The availability of these well-defined block copolymers will facilitate studies in many fields of polymer physics and will provide the opportunity to better explore structure-property relationships which are of fundamental importance for hi-tech applications, such as high temperature separation membranes, drug delivery systems, photonics, multifunctional sensors, nanoreactors, nanopatterning, memory devices etc. 

The design and implementation of a portable fiber-optic cholinesterase biosensor for the detection and determination of pesticides carbaryl and dichlorvos was presented by Andreou81. The sensing bioactive material was a three-layer sandwich. The enzyme cholinesterase was immobilized on the outer layer, consisting of hydrophilic modified polyvinylidenefluoride membrane. The membrane was in contact with an intermediate sol-gel layer that incorporated bromocresol purple, deposited on an inner disk. The sensor operated in a static mode at room temperature and the rate of the inhibited reaction served as an analytical signal. This method was successfully applied to the direct analysis of natural water samples (detection and determination of these pesticides), without sample pretreatment, and since the biosensor setup is fully portable (in a small case), it is suitable for in-field use. 

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