The Experts below are selected from a list of 294 Experts worldwide ranked by ideXlab platform

B Auclair - One of the best experts on this subject based on the ideXlab platform.

  • Correlation between ion-exchange Membranes characteristics for evaluation of the permselectivity and the diffusion coefficients
    Desalination, 2002
    Co-Authors: Salah Nouri, Lasâad Dammak, Christian Larchet, B Auclair
    Abstract:

    Abstract The quantity of absorbed electrolyte and the electrical Membrane Conductivity have been measured and correlated for three cation-exchange Membranes (CM2, CMx and MK-40), two electrolytes (KCl and LiCl), over a large concentration range of the solution (0.1 M ≤ C0 ≤ 3.0 M). The Membrane Conductivity has been measured according to a French standard. However, because of the lack of standards fixing all the operating conditions, we established an experimental protocol, validated by a statistical study. This method will be proposed to be standardized for this category of measurements. Relationships have been established between the two parameters allowing us to determine both the counter-ion and the co-ion diffusion coefficients in a cation-exchange Membrane, considered as homogeneous. The values of these coefficients for the counter-ions are in good agreement with those obtained from other methods. The variations of the computed diffusion coefficients of counter-ions and co-ions for the different studied systems are discussed in terms of internal interactions with the charged polymer matrix and the other diffusing species. The discussion also takes into account the free water content of the polymer.

  • determination of the diffusion coefficients of ions in cation exchange Membranes supposed to be homogeneous from the electrical Membrane Conductivity and the equilibrium quantity of absorbed electrolyte
    Electrochimica Acta, 2001
    Co-Authors: L Dammak, Roger Lteif, G Bulvestre, Gerald Pourcelly, B Auclair
    Abstract:

    Abstract Two ion-exchange Membrane characteristics, the quantity of absorbed electrolyte and the electrical Membrane Conductivity have been measured and correlated for three cation-exchange Membranes (CM2, CMx and MK-40), two electrolytes (KCl and LiCl), over a large concentration range of the solution (0.1 M≤ C 0 ≤3.0 M). The Membrane Conductivity has been measured according to a French standard. However, because of the lack of standards fixing all the operating conditions for good determination of the second parameter, we established an experimental protocol, validated by a statistical study and made a comparison with the theoretical Glueckauf's equation. This method will be proposed to be standardized for this category of measurements. Relationships have been established between the two parameters allowing us to determine both the counter-ion and the co-ion diffusion coefficients in a cation-exchange Membrane, considered as homogeneous. The values of these coefficients for the counter-ions are in good agreement with those obtained from other methods. The variations of the computed diffusion coefficients of counter-ions and co-ions for the different studied systems are discussed in terms of internal interactions with the charged polymer matrix and the other diffusing species. The discussion also takes into account the free water content of the polymer.

Peter Urban - One of the best experts on this subject based on the ideXlab platform.

Damijan Miklavčič - One of the best experts on this subject based on the ideXlab platform.

  • A Time-Dependent Numerical Model of TransMembrane Voltage Inducement and Electroporation of Irregularly Shaped Cells
    IEEE transactions on bio-medical engineering, 2009
    Co-Authors: Gorazd Pucihar, Damijan Miklavčič, Tadej Kotnik
    Abstract:

    We describe a finite-element model of a realistic irregularly shaped biological cell in an external electric field that allows the calculation of time-dependent changes of the induced transMembrane voltage ( DeltaPsi) and simulation of cell Membrane electroporation. The model was first tested by comparing its results to the time-dependent analytical solution for DeltaPsi on a nonporated spherical cell, and a good agreement was obtained. To simulate electroporation, the model was extended by introducing a variable Membrane Conductivity. In the regions exposed to a sufficiently high DeltaPsi, the Membrane Conductivity rapidly increased with time, leading to a modified spatial distribution of DeltaPsi. We show that steady-state models are insufficient for accurate description of DeltaPsi, as well as determination of electroporated regions of the Membrane, and time-dependent models should be used instead. Our modeling approach also allows direct comparison of calculations and experiments. As an example, we show that calculated regions of electroporation correspond to the regions of molecular transport observed experimentally on the same cell from which the model was constructed. Both the time-dependent model of DeltaPsi and the model of electroporation can be exploited further to study the behavior of more complicated cell systems, including those with cell-to-cell interactions.

  • effective Conductivity of a suspension of permeabilized cells a theoretical analysis
    Biophysical Journal, 2003
    Co-Authors: Mojca Pavlin, Damijan Miklavčič
    Abstract:

    During the electroporation cell Membrane undergoes structural changes, which increase the Membrane Conductivity and consequently lead to a change in effective Conductivity of a cell suspension. To correlate microscopic Membrane changes to macroscopic changes in Conductivity of a suspension, we analyzed the effective Conductivity theoretically, using two different approaches: numerically, using the finite elements method; and analytically, by using the equivalence principle. We derived the equation, which connects Membrane Conductivity with effective Conductivity of the cell suspension. The changes in effective Conductivity were analyzed for different parameters: cell volume fraction, Membrane and medium Conductivity, critical transMembrane potential, and cell orientation. In our analysis we used a tensor form of the effective Conductivity, thus taking into account the anisotropic nature of the cell electropermeabilization and rotation of the cells. To determine the effect of cell rotation, as questioned by some authors, the difference between Conductivity of a cell suspension with normally distributed orientations and parallel orientation was also calculated, and determined to be <10%. The presented theory provides a theoretical basis for the analysis of measurements of the effective Conductivity during electroporation.

  • Effective Conductivity of a Suspension of Permeabilized Cells: A Theoretical Analysis
    Biophysical Journal, 2003
    Co-Authors: Mojca Pavlin, Damijan Miklavčič
    Abstract:

    During the electroporation cell Membrane undergoes structural changes, which increase the Membrane Conductivity and consequently lead to a change in effective Conductivity of a cell suspension. To correlate microscopic Membrane changes to macroscopic changes in Conductivity of a suspension, we analyzed the effective Conductivity theoretically, using two different approaches: numerically, using the finite elements method; and analytically, by using the equivalence principle. We derived the equation, which connects Membrane Conductivity with effective Conductivity of the cell suspension. The changes in effective Conductivity were analyzed for different parameters: cell volume fraction, Membrane and medium Conductivity, critical transMembrane potential, and cell orientation. In our analysis we used a tensor form of the effective Conductivity, thus taking into account the anisotropic nature of the cell electropermeabilization and rotation of the cells. To determine the effect of cell rotation, as questioned by some authors, the difference between Conductivity of a cell suspension with normally distributed orientations and parallel orientation was also calculated, and determined to be

Hossein Salehfar - One of the best experts on this subject based on the ideXlab platform.

  • semiempirical model based on thermodynamic principles for determining 6 kw proton exchange Membrane electrolyzer stack characteristics
    Journal of Power Sources, 2008
    Co-Authors: Nilesh Dale, Michael D Mann, Hossein Salehfar
    Abstract:

    Abstract The performance of a 6 kW proton exchange Membrane (PEM) electrolyzer was modeled using a semiempirical equation. Total cell voltage was represented as a sum of the Nernst voltage, activation overpotential and ohmic overpotential. A temperature and pressure dependent Nernst potential, derived from thermodynamic principles, was used to model the 20 cell PEM electrolyzer stack. The importance of including the temperature dependence of various model components is clearly demonstrated. The reversible potential without the pressure effect decreases with increasing temperature in a linear fashion. The exchange current densities at both the electrodes and the Membrane Conductivity were the coefficients of the semiempirical equation. An experimental system designed around a 6 kW PEM electrolyzer was used to obtain the current–voltage characteristics at different stack temperatures. A nonlinear curve fitting method was employed to determine the equation coefficients from the experimental current–voltage characteristics. The modeling results showed an increase in the anode and cathode exchange current densities with increasing electrolyzer stack temperature. The Membrane Conductivity was also increased with increasing temperature and was modeled as a function of temperature. The electrolyzer energy efficiencies at different temperatures were evaluated using temperature dependent higher heating value voltages instead of a fixed value of 1.48 V.

  • Semiempirical Model for Determining PEM Electrolyzer Stack Characteristics
    Journal of Fuel Cell Science and Technology, 2005
    Co-Authors: Kevin W. Harrison, Eduardo Hernández-pacheco, Michael D Mann, Hossein Salehfar
    Abstract:

    A semiempirical equation was used to represent the performance characteristics of a 20-cell proton exchange Membrane electrolyzer stack. The coefficients of the equation are the exchange current densities and Membrane Conductivity. These coefficients were determined using experimental data and a nonlinear curve fitting method. The anode exchange current density was found to be 1.65× 10 -8 A cm -2 , the cathode exchange current density 0.09 A cm -2 , and the Membrane Conductivity 0.075 S cm -1 . External programmable power supplies were used to obtain the (I-V) characteristic curve of a commercial proton exchange Membrane electrolyzer. Stack current, voltage, and system temperature were monitored while 1 A current steps were applied to the electrolyzer stack.

Ricard Garcia-valls - One of the best experts on this subject based on the ideXlab platform.

  • Porous lignosulfonate Membranes for direct methanol fuel cells
    Journal of Membrane Science, 2006
    Co-Authors: Xiao Zhang, Andreas Glüsen, Ricard Garcia-valls
    Abstract:

    Abstract Porous lignosulfonate (LS) Membranes were prepared and considered for their potential application in direct methanol fuel cells (DMFC). Membranes were characterized by impedance spectrometry and water uptake measurement. Both their ion exchange capacity (IEC) and water uptake capacity affected porous Membrane Conductivity. Membrane conductivities were in the range 5–12 mS/cm at 80 °C. Membrane electrode assemblies (MEAs) based on lignosulfonate Membranes were also prepared and characterized in a single cell in order to determine whether they can be used in a DMFC. The current density at 300 mV was of 42 mA/cm 2 at 80 °C.