Effect Of Mass Transfer Resistance Research Articles

Transport of volatile chlorinated hydrocarbons in unsaturated aggregated media

Transport of volatile hydrocarbons in soils is largely controlled by interactions of vapours with the liquid and solid phase. Sorption on solids of gaseous or dissolved compounds may be important. Since the contact time between a chemical and a specific sorption site can be rather short, kinetic or mass-transfer resistance effects may be relevant. An existing mathematical model describing advection and diffusion in the gas phase and diffusional transport from the gaseous phase into an intra-aggregate water phase is modified to include linear kinetic sorption on gas-solid and water-solid interfaces. The model accounts for kinetic mass transfer between all three phases in a soil. The solution of the Laplace-transformed equations is inverted numerically. We performed transient column experiments with 1,1,2-Trichloroethane, Trichloroethylene, and Tetrachloroethylene using air-dry solid and water-saturated porous glass beads. The breakthrough curves were calculated based on independently estimated parameters. The model calculations agree well with experimental data. The different transport behaviour of the three compounds in our system primarily depends on Henry's constants.

Effects of Mass Transfer Resistances on Hydrogen Absorption in Yttrium Particle Bed

Click to increase image sizeClick to decrease image sizeKEYWORDS: absorptionD-T reactorsfuel cyclefixed bedhydrogen isotopesnumerical calculationsmass transferdiffusion yttrium

Effects of Mass Transfer Resistances in Fluid and Permeable Walls on Hydrogen Permeation in Tube-Type Metal Window

Effects of Mass Transfer Resistances in Fluid and Permeable Walls on Hydrogen Permeation in Tube-Type Metal Window

Effects of mass transfer resistances in fluid and permeable walls on hydrogen permeation in tube-type metal window.

Effects of mass transfer resistances in fluid and permeable walls on hydrogen permeation in tube-type metal window.

Effects of mass transfer resistances on hydrogen absorption in yttrium particle bed.

Effects of mass transfer resistances on hydrogen absorption in yttrium particle bed.

Modeling Mass Transfer in Biological Wastewater Treatment Processes

Parameters characterizing intrasolid, liquid/solid, and gas/liquid mass transport phenomena in biological treatment systems are required if mass transfer is to be included in process models. Estimates of such parameters are presented and discussed. Collective and individual effects of mass transfer resistances are illustrated by computer simulation of a high-rate trickling filter.

MASS TRANSFER EFFECTS IN LIQUEFACTION OF COAL BY SRC-II PROCESS PART II STUDY OF BUBBLE COLUMN REACTORS

The effects of hydrogen mass transfer resistance in large-scale SRC-II bubble column reactors (BCR), over large ranges of process variables, are studied. Due to the interactive effects of mass transfer resistance and gas hold up, the hydrogen consumption or liquid yield in a BCR has a maximum with respect to the specific mixing power. Under normal SRC-II process conditions a superficial gas velocity of about 0.01 m/s represents the optimum with respect to the hydrogen consumption or liquid yield. In general, the product quality requirement rather than the rate of hydrogen consumption determines the minimum specific mixing power requirement. Increase in hydrogen partial pressure can be used to reduce the level of mixing power required to maintain the desired product quality. Interrelations between mass transfer and gas hold effects and the variations in hydrogen concentration in slurry over large ranges of process conditions are also illustrated. This work provides some bases for the selection of reactor dimensions and process conditions for an SRC-II bubble column reactor (BCR).

Kinetics of methane formation by granular sludge at low substrate concentrations

Apparent K m values for methanogenesis from volatile fatty acids by various sludge granules were determined from progress curve experiments. The influence of mass transfer resistance on the kinetics of methane formation in biofilms was demonstrated with the apparent K m values thus obtained. It was shown that the effects of mass transfer resistance depend on the maximum specific activity of the biolayers and on their thickness. the data indicate that mass transfer resistance in methanogenic biolayers becomes only of significance at low substrate concentrations and in thick biolayers with high methanogenic activities.

High-temperature fuel cells for power generation

Hybrid systems consisting of series-connected high-temperature solid-electrolyte fuel cells (HTSEFCs) thermally coupled to coal gasifiers show great potential for overall efficiencies of nearly 60% for the production of electricity from coal. This paper describes a steady-state model for the prediction of HTSEFC voltage, current and power density. The HTSEFC model is essentially a distributed parameter electrical network that includes the effects of mass transfer resistance (concentration polarization), chemical kinetic resistance (activation polarization), as well as all relevant electrical resistances (ohmic losses). This electrical network representation leads to a finite-difference discretization which, in effect, divides the fuel cell into many simple current-flow sections. Furthermore, the model computes the fuel and oxidant stream compositions as functions of axial length from energy and mass balances performed on each fuel cell slice. The model yields results that compare favorably with the published experimental data from Westinhouse.

Estimation of the intrinsic kinetic constants in the immobilized enzyme system

Abstract The effect of mass transfer resistance on the reaction kinetics of immobilized glucose isomerase was studied, using a commercially available enzyme Swetase (Nagase Co., Japan). The effective diffusivity of glucose in the support matrix of Swetase was first determined experimentally with the Horowitz method. Using the concept of effectiveness factor encountered in reaction kinetics, a method for estimating the intrinsic kinetic parameters for immobilized glucose isomerase from reaction rates of the enzyme system was proposed. Knowing these intrinsic kinetic parameters along with the diffusivity of glucose within the enzyme particle, we can simulate Swetase's behavior in a CSTR, with a mathematical model. The simulated results compared very well with experimental values, indicating that the methods for determining enzyme kinetic parameters and substate diffusivity within the enzyme system were quite reliable.

Diffusional falsification of kinetic constants on Lineweaver-Burk plots

The effect of mass transfer resistances on the Lineweaver-Burk plots in immobilized enzyme systems has been investigated numerically and with analytical approximate solutions. While Hamilton, Gardner & Colton (1974) studied the effect of internal diffusion resistances in planar geometry, our study was extended to the combined effect of internal and external diffusion in cylindrical and spherical geometries as well. The variation of Lineweaver-Burk plots with respect to the geometries was minimized by modifying the Thiele modulus and the Biot number with the shape factor. Especially for a small Biot number all the three Lineweaver-Burk plots fell on a single line. As was discussed by Hamilton, et al (1974), the curvature of the line for large external diffusion resistances was small enough to be assumed linear, which was confirmed from the two approximate solutions for large and small substrate concentrations. Two methods for obtaining intrinsic kinetic constants were proposed: First, we obtained both maximum reaction rate and Michaelis constant by fitting experimental data to a straight line where external diffusion resistance was relatively large, and second, we obtained Michaelis constant from apparent Michaelis constant from the figure in case we knew maximum reaction rate a priori.

Effects of mass‐transfer resistance on apparent stability and performance of fixed‐bed immobilized enzyme reactors: Theory and experiments with immobilized invertase

Taking the hydrolysis of sucrose by invertase immobilized on anion-exchange resin as an example, the effects of mass-transfer resistance on the apparent stability of immobilized enzyme (IME) and the optimal policy for an IME reaction in a fixed-bed reactor have been studied theoretically and experimentally. The following results were obtained: (1) The effect of mass-transfer resistance on the effective deactivation rate of IME is summarized in two parameters concerning the intraparticle diffusion alpha(p) and the interparticle alpha(f). (2) At a constant processed amount of raw materials, there exists an optimal flow rate of reaction fluid to enhance the reactor performance while the mass-transfer resistance shifts the optimal point. (3) The intrinsic deactivation rate of IME has been estimated from the relationship between the fractional conversion at the reactor outlet and the operation time.

Approximate relations for calculation of enhancement factor in gas absorption with chemical reaction

Based on the film theory of mass transport, new approximate relations for reaction factor are developed for gas absorption accompanied by irreversible chemical reaction A (g) + zB (l) → products. The relations are compared with exact numerical solutions obtained by the commonly used method of linearization (suggested by Van Krevelen and Hoftijzer and applied by Hikita and Asai) for several nonlinear reaction rate cases. The effect of mass transfer resistance in the gas phase is also considered and simple criteria for estimation of magnitude of the effect of chemical reaction on mass transport are given. It is shown, that the error of the new approximate method is several percent even in cases, where the error of the linearization method is high.

The effects of mass transfer resistances on encapsulated enzymatic reaction systems

The effectiveness factor for an encapsulated enzyme particle is investigated in the present work by considering complete internal and external mass tra

Effect of mass transfer resistance on the Lineweaver-Burk plots for flocculating microorganisms.

It is shown that the mass transfer resistance can significantly distort the linearity of the Lineweaver-Burk plot of the kinetic data for a microbial culture which forms aggregates. For small flocs, the linearity of the Lineweaver-Burk plot is largely retained, but a different slope and intercept will be obtained compared with flocs free from mass transfer resistance. For large flocs, the Lineweaver-Burk plot shows pronounced curvature at high limiting substrate concentrations. Hence, if the true intrinsic kinetic parameters are to be extracted from a highly flocculating microbial culture, sufficient agitation has to be provided to remove the effect of mass transfer resistance. If the behavior of the flocculating microbial culture is to be explored, additional values for some physical parameters, such as the effective diffusion coefficient of the substrate in floc, the floc density, and the mean floc radius, are needed.

Relationship between pellet size and performance of catalysts

AbstractThe effect of mass transfer resistance in reducing the effectiveness of porous catalysts has been known since the publication of Thiele's classical paper in 1939. The variation in temperature caused by resistance to heat transfer may bring about equally significant changes in effectiveness in some cases. An extension of Thiele's treatment to take exact account of heat transfer resistance leads to a set of nonlinear differential equations that can only be solved numerically.This paper presents an approximate treatment of the simulataneous effects of resistances to mass and heat transfer. With the limitations imposed by linearizing the equations the formulas derived give the activity and selectivity for any combination of reactions. The use of the results is illustrated by three examples. It is shown that the principal effects are associated with the variation of concentration within the pellet of catalyst and with the difference in temperature between the surface of the pellet and the bulk fluid.