Browsing by Author "ROSENBERGER, F"

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A GENERAL EXPRESSION FOR THE TOTAL RELEASE OF DIFFUSANT THROUGH HETEROGENEOUS MEMBRANES
(1992-02-19)
CHEN, JS
;
ROSENBERGER, F
;
應用化學系
;
Department of Applied Chemistry
An expression for the total amount of diffusant Q(t) released into a receiver by diffusion through a heterogeneous membrane is rigorously derived for time-dependent boundary conditions and a position-dependent initial condition. The heterogeneity of the membrane is characterized by a position-dependent diffusivity and partition coefficient. Two examples are given to demonstrate the utility of this general expression. It is shown that the expression for Q(t) proposed by Keister [ J. Membrane Sci., 29 (1986) 333-3441 is only valid when the asymptotic concentration of the diffusant within the membrane is zero.
CALCULATION OF LAG TIME FOR CONVECTIVE-REACTIVE DIFFUSION
(1991-11-28)
CHEN, JS
;
ROSENBERGER, F
;
應用化學系
;
Department of Applied Chemistry
Closed form solutions for the steady-state permeability P and the lag time L of a linear diffusion system with concurrent convection and reaction were obtained by two methods. In the first method, we identify the singularity at s = 0 of the Laplace transform of the total amount of diffusant, Q(s), released into the receiver as representation of the asymptotic diffusion behavior. P and L are then obtained from the time-independent coefficients of an expansion of Q(s) about s = 0. In the second method, we transform the convective-reactive diffusion equation into a form that contains only first and second derivatives of the concentration distribution function. By comparison of the resulting equation with that for a heterogeneous diffusion system, relationships of the convection velocity and rate constant with the position-dependent partition coefficient in heterogeneous diffusion is found. Taking advantage of the known solutions for permeabiliy and lag time in heterogeneous diffusion, the corresponding expressions for P and L in convective-reactive diffusion are then obtained by transcription. These methods have the advantage over earlier approaches in that solutions in an infinite form are avoided.
DIAPHRAGM DIFFUSION CELL - A CLOSED FORM SOLUTION TO THE TRANSPORT-EQUATION AND ITS APPLICATION TO THE DETERMINATION OF THE CONCENTRATION-DEPENDENCE OF THE HCL-H2O INTERDIFFUSION COEFFICIENT
(1992)
CHEN, JS
;
CLUNIE, JC
;
BAIRD, JK
;
ROSENBERGER, F
;
應用化學系
In a thermodynamically non-ideal solution, the interdiffusion coefficient D(c) of a two-component system is a function of the concentration c. Since the mean concentration cBAR in a diaphragm cell remains constant during interdiffusion, we have found it useful to expand D(c) in a Taylor series about cBAR. After truncating the series and substituting the result into the diaphragm cell transport equation, we obtain a Bernoulli ordinary differential equation, which we solve in closed form. This solution is experimentally tested by determining D(c) from diaphragm cell data which we accumulated on aqueous hydrochloric acid at 25-degrees-C. Our results are in qualitative agreement with those of R. H. Stokes, who obtained D(c) from diaphragm cell data by using a graphical method [J. Am. Chem. Soc. 72, 2243 (1950)].
DIFFUSION LAG TIME FOR MULTIPLE AND PERIODIC LAMINATES
(1991)
CHEN, JS
;
ROSENBERGER, F
;
應用化學系
;
Department of Applied Chemistry
RECIPROCITY OF LAG TIME FOR REACTIVE DIFFUSION THROUGH HETEROGENEOUS MEMBRANES - A GREEN-FUNCTION APPROACH
(1991)
CHEN, JS
;
ROSENBERGER, F
;
應用化學系
;
Department of Applied Chemistry