Composite mass transport properties

Little is known about the mass transport properties of reinforced-composite materials. Certainly, there are no new relations or concepts that govern estimations of diffusiv-ities that have not already been discussed. In most polymer-matrix composites, the transport properties of the polymer play an important role in diffusion through the composite. For example, hydrophilic polymers such as epoxy readily absorb water from the atmosphere. Thermoplastic polymers absorb relatively little moisture since they are more hydrophobic, but are more susceptible to uptake of organic solvents. 

Results and Discussion. Figure 14 demonstrates the principal of separation through Ion-exchange membranes, where the counter-lon/permeate Interactions determine the mass transport properties of the system. In this set of experiments, the feed mixture was an azeotropic composition of 2-propanol and water (88.5/11.5 wt.X). A Naflon hollow fiber permeator was used In pervaporatlon mode. The... 

Since the rate of all electrocatalytic reactions is strictly related to the active surface area, besides the surface chemistry, the morphology of the electrocatalyst needs to be tailored. Morphology is not only related to the metal-phase area but also to the presence of micro- and macro pores in the electrocatalyst support that could facilitate or hinder the mass transport properties. All these characteristics determine the cell performance even if the relative influence of each parameter is still not known in detail. It is thus necessary to select appropriate procedures for the optimization of these characteristics, i.e. composition, structure, particle size, porosity, etc. Generally a combination of physico-chemical and electrochemical analyses carried out on different electrocatalysts indicates the system that best suits the scope of application in a DMFC. 

To prepare the FRP composite, the respective fiber is embedded in a polymer matrix mostly thermoset or thermoplastic resins. The role of the matrix is (i) to bind the fibers together, (ii) to transfer stresses between fibers, and (iii) to protect them against environmental attack and damage due to mechanical abrasion. The matrix also controls the processability, the maximum service temperatures, as well as the flammability and corrosion resistance of FRP. Most FRPs are made in order to improve mechanical performances such as elastic properties (modulus of elasticity) and ultimate properties (strength, toughness). To some extent and based on the choice of constituents, preparation of composites makes it also possible to tailor other physical properties, such as electrical conductivity, mass transport properties, heat conduction, etc. [49]. 

Mass transport inside the catalyst has been usually described by applying the Fick equation, by means of an effective diffusivity Deff a Based on properties of the interface and neglecting the composition effect, composite diffusivity of the multi-component gas mixture is calculated through the simplified Wilke model [13], The effect of pore-radius distribution on Knudsen diffusivity is taken into account. The effective diffusivity DeffA is given by... 

What is dear from this introduction is that the journey into the area of metal deposition from ionic liquids has tantalizing benefits. It is also dear that we have only just begun to scratch the surface of this topic. Our models for the physical properties of these novel fluids are only in an early state of devdopment and considerably more work is required to understand issues such as mass transport, spedation and double layer structure. Nudeation and growth mechanisms in ionic liquids will be considerably more complex than in their aqueous counterparts but the potential to adjust mass transport, composition and spedation independently for numerous metal ions opens the opportunity to deposit new metals, alloys and composite materials which have hitherto been outside the grasp of electroplaters. 

Park and Ortoleva (2003) have developed WRIS.TEQ, a comprehensive reaction-transport-mechanical simulator that includes kinetic and thermodynamic properties with mass transport (advection and diffusion). A unique property of this code is a dynamic compositional and textural model specifically designed for sediment alteration during diagenesis. 

The following discussion shows how the chemical composition, rate of formation, and heat of combustion of the pyrolysis products are affected by the variations in the composition of the substrate, the time and temperature profile, and the presence of inorganic additives or catalysts. The latter aspect, however, is discussed in more detail in Chapter 14. Combustion may be defined as complex interactions among fuel, energy, and the environment. Consequently, the combustion process is controlled not only by the above chemical factors, but also by the physical properties of the substrate and other prevailing conditions affecting the phenomena of heat and mass transport. Discussion of this phenomenon is beyond the scope of this chapter. 

The thermal conductivity k is a transport property whose value for a variety of gases, liquids, and solids is tabulated in Sec. 2. Section 2 also provides methods Tor predicting and correlating vapor and liquid thermal conductivities. The thermi conductivity is a function of temperature, but the use of constant or averaged values is frequently sufficient. Room temperature values for air, water, concrete, and copper are 0.026, 0.61, 1.4, and 400 W/(m K). Methods for estimating contact resistances and the thermal conductivities of composites and insulation are summarized by Gebhart, Heat Conduction and Mass Diffiision, McGraw-Hill, 1993, p. 399. 

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