Mass resistances

Mass resistivity this is the resistance of a conductor of unit length and unit mass ... 

External mass transfer-limited reactions In the expression (5.191), km has to be known, but it is not necessaiy if the external mass transfer phenomena are very intense. Actually, if strong mass resistance exists, the knowledge of the rate law is not essential, because the rate can be written as... 

The heat and mass resistances within the baskets and the intraparticle resistances can be large unless a high degree of agitation is used. Baffles arc often used in the open volume in order to increase the degree of mixing. 

Shiraishi et al. [51] studied a process of oxidation of glucose to maltose in the presence of P-amylasc and debranching enzyme (pullulanase or isoamylase). Experiments were performed with glucose concentrations of 5-100 kg m" at 450°C and pH = 4.8. External mass resistance was found negligible. Again, stacked monolithic blocks were used. Production of maltose by this method was very efficient. 

Qi and Cussler [26] investigated the removal of ammonia by H2SO4. H2SO4 being a strong acid, the mass resistance offered by the membrane controlled the process. An industrial membrane gas absorption unit for ammonia recovery from an ammonia containing off-gas stream produced in a dyes intermediates production plant has been installed by TNO. The membrane plant is able to remove 99.9% of ammonia and produces aqueous solutions of 27% ammonia that can be reused in the dyes process [38]. 

Solvent transfer from the surface of the dried material can be treated in a manner analogous to Eq. (4) above for heat transfer. An expression for the convective mass resistance can be generated similar to that derived for the thermal resistance ... 

The three factors of inertia (mass), resistance and capacitance (the reciprocal of spring compliance) are collectively known as impedance as intuitively, the system impedes the motion in the system. 

Figure 21.3 Profiles of mass resistance in each stage.

In the transport of reactant gases from the gas flow channel through an electrode composed of a GDL and CL, there are a number of mass transfer resistances that influence the mass transport as shown in Figure 6.17. These resistances are (i) convective mass transfer resistance in the gas flow channel, l conv,mi (ii) diffusion mass resistance in the gas diffusion layer, Rdijf and (iii) diffusion and reaction resistance owing to reaction kinetics. Figure 6.17 shows a typical reactant gas concentration distribution across the gas channel, the gas diffusion layer, and the active CL. 

A precise column temperature control is now required for all commercial gas chromatographs. In practice, the GC ovens are designed to have low thermal mass. Resistance spirals situated inside the oven are proportionally heated, while the air circulation throughout the oven is provided by a fan. For adequate analytical work, the column temperature should be reproducible within at least... 

Minimization of mass-transfer resistances between liquid and solid catalyst particles was studied by varying the liquid/amonnt of catalyst ratio (Perego and Paratello, 1999). Experiments were conducted at two space velocities (0.33 and 1.5 h ) and two temperatures (360°C and 420°C). It was found that conversions did not change appreciably at LHSV = 1.5 h when lOOmL of catalyst was used. However, for LHSV = 0.33 h and for the same amount of catalyst, the conversions were not constant. This means that at high flow rates, interphase mass resistance is minimal but at low flow rates it is still present. To increase liquid flow rate, keeping constant the LHSV, it is... 

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