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Applications and case studies
Published in Roderic S. Lakes, Viscoelastic Solids, 2017
Determination of viscoelastic properties can be used as a probe into various microphysical phenomena in materials. For example, the true and effective diffusion coefficients can differ as a result of differences in the thermodynamic activity of the diffusing substance [10.21.1]; calculations based on measurement of concentration vs. distance give the effective diffusion coefficient. True diffusion coefficients in alloys have been determined indirectly by evaluation of relaxation times via measurement of damping over a wide range of temperature. As another example, it is possible to achieve a qualitative mapping of viscoelastic properties using the atomic force microscope [10.21.2]. Viscoelasticity, as evaluated via the out-of-phase component of an electrical signal at 2 kHz, appears qualitatively as image contrast.
A Study of the Emissions of Volatile Organic Compounds Found in Landfill Gas
Published in John M. Bell, Proceedings of the 43rd Industrial Waste Conference May 10, 11, 12, 1988, 1989
Teresa A. Herrera, Robert Lang, George Tchobanoglous
The maximum concentration of a trace gas that could be present immediately below the landfill cover is the saturation vapor concentration, Cs, of the trace gas (see Figure 2). In Equation 5, the concentration of trace gas is written in terms of the vapor pressure and the molecular mass of the compound (PAMA/RT). The effective diffusion coefficient takes into account the tortuosity of the path through which the gas molecules must move. Effective diffusion coefficients are calculated by dividing the apparent diffusion coefficients reported in Table II by τ, a tortuosity term which ranges between 2 and 6 with a typical value of 3.8 The term, W1 in Equation 5 is a scaling factor used to account for the actual trace gas concentrations observed beneath landfill covers.
Soil Pollution and Its Control
Published in Danny D. Reible, Fundamentals of Environmental Engineering, 2017
In a porous medium, the effective diffusion coefficient is the product of the diffusivity in the fluid filling the pore spaces, in this case, air, and a correction for the fraction of void space available to diffusion, ε or εa, and the effective length of the diffusion path, the tortuosity, τ. () Dsv=Daετ
Effect of modeling simplifications on behavior and computational cost for simulation of fixed bed wheat drying process
Published in Drying Technology, 2020
Rodolfo de Mattos, Jorge Martínez Garreiro, Gustavo Meghirditchian, Adrián Ferrari, Berta Zecchi
An Arrhenius-type equation was used to describe the temperature effect on the effective diffusion coefficient.[24] where is the activation energy (J mol−1) and is the effective diffusivity value at temperature, fixed at 298 K. Parameter estimation in Eq. (33) was carried out by fitting predictions of Model 1 with experimental data obtained by Woodforde and Lawton from drying runs of wheat grains on a fixed bed with six different air inlet temperatures (316.5, 322.0, 333.2, 338.7, 344.3, and 360.9 K).[20] Drying runs at 322.0, 333.2, and 344.3 K were used for parameter estimation and the others for validation. Experimental data of grain's average moisture content as a function of time were available for all drying runs. Outlet air temperature and humidity were only recorded for drying runs with air inlet temperatures of 316.5, 338.7, and 360.9 K.
Kinetics of drying inorganic spheres: Simultaneous modeling of moisture and temperature during the constant and falling rate periods
Published in Drying Technology, 2018
J. A. Siles, M. A. Martín, E. Molina, A. Martín
The influence of air temperature on the drying kinetics of the spheres was evaluated by fixing G and L at noncontrolling values specifically 9,300 kg/h m2 and 0.03 m, respectively. The results obtained are plotted in Fig. 2c that shows the variation in moisture content with drying time at different temperatures. As can be observed, the slopes of the straight lines in the constant drying rate period increased with an increase in temperature. This might be explained mainly by the proportionality between temperature and the effective diffusion coefficient. The drying rate of pepper seed particles was found to increase with operating temperature; however, it was not affected much by the superficial gas velocity and the operating pressure.[21] Nevertheless, the reduced pressure operation increases the degree of superheating, which was found to be the most important parameter of the process. It was concluded that a relatively lower temperature process can be achieved through a reduced-pressure superheated steam fluidized bed.
Amine-modified silica surface applied as adsorbent in the phenol adsorption assisted by ultrasound
Published in Chemical Engineering Communications, 2019
Marília R. Oliveira, Matheus M. Oliveira, Ronney J. Oliveira, Adriana Dervanoski, Elton Franceschi, Silvia M. Egues, Juliana F. De Conto
The effective diffusion coefficient (Def) depends on the particle porosity, pore diameter, tortuosity, temperature, and nature of the species that diffuse (Welty et al., 2009; Çengel, 2007). According to the values of diffusion coefficient obtained (Table 5), it is possible to verify that the diffusivity increased with the increasing concentration and temperature. Diffusion coefficient represents the inverse of resistance to mass transport. Thus, the higher the concentration of the solute, the lower the resistance and the greater the mass transfer of the solute into the pore (Çengel, 2007).