Zoran ILIĆ., Avital BEN-YOSEF., Yaccov PARTZELAN., Sharon ALKALAI-TUVIA and Elazar FALLIK
Eiran Kochavi, Yoram Oren, Abraham Tamir, Tuvia Kravchik BEN-GURION UNIVERSITY OF THE NEGEV, FACULTY...
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Transcript of Eiran Kochavi, Yoram Oren, Abraham Tamir, Tuvia Kravchik BEN-GURION UNIVERSITY OF THE NEGEV, FACULTY...
Eiran Kochavi, Yoram Oren,
Abraham Tamir, Tuvia Kravchik
BEN-GURION UNIVERSITY OF THE
NEGEV, FACULTY OF
ENGINEERING SCIENCES, DEPARTMENT
OF CHEMICAL ENGINEERING,
BEER-SHEVA, ISRAEL
MASS TRANSFER TO MASS TRANSFER TO SPHERE AND HEMISPHERE SPHERE AND HEMISPHERE ELCTRODES BY IMPINGING ELCTRODES BY IMPINGING
JETJET
The goals of this work:
• Characterization of mass transfer rates
to sphere and hemisphere electrodes,
under impinging jet of solution.
• Characterization of mass transfer with
both electrodes in two systems:
submerged in the electrolyte solution
and unsubmerged.
• Development of theoretical model that
characterizes the system of impinging
jet to electrodes.
The goals of this work (con’d):
• Comparison between experimental and
theoretical limiting currents
• Prediction of flow and concentration
profiles at complex geometry system by
using numerical simulation program
(PHOENICS) with the proper boundary
conditions.
The experimental system
Results
•Mass transfer coefficients increased
as we increased the linear velocity of
the electrolyte jet at the nozzle exit
•Mass transfer coefficients for the
submerged hemisphere electrode, are
higher than the coefficients for a
sphere electrode.
Results
•Mass transfer coefficients decrease
by increasing the nozzle-electrode
distance. However, the influence is
more pronounced at smaller distances
Scheme of solution domain
Theoretical model and PHOENICS settings
•The grid distribution was divided into
two sections (in Y-axis):
1- Near the electrode surface (20 cells)
the distribution was according to a
power-law expanding grid
2- In the electrolyte bulk (20 cells) the
distribution was according to a
uniform grid
Theoretical model and PHOENICS settings (cont’d)
• The model employed a 41x37 grid cells
(BFC) in the y-z plane.
• The cells region was divided into two
frames:
1- zone where the solution flows out of the
nozzle. The method of the interpolation of
internal points was transfinite (TRANS)
Theoretical model and PHOENICS settings(cont’d)
2- zone where the solution impinging the
electrode and flows over it to the outlet.
The method of the interpolation of internal
points was “Laplace”-like equation (LAP).
Concentration profile of impinging jet over a submerged sphere
electrode
Flow vectors map of impinging jet over a submerged sphere electrode
Theoretical results for impinging jet on a
submerged sphere electrode
• At the impingement zone we observed
a sharp concentration profile that is
influenced by jet impingement on the
electrode surface.
• Because of the vortex (at the flow
vectors map) on the electrode sides we
observed the concentration profile to
become wider along Z-axis
Comparison between Experimental and Theoretical limiting currents
PHOENICS characteristics
• PHOENICS X11 – Version 2.1.3
• Operating system – UNIX
• Convergence
The number of iterations - 2000
PHOENICS characteristics
Relaxation
The Relaxation factors for the variables:
•P1(pressure) linear relaxation (LINRLX)- 0.01
•C1(mass fraction of ferricyanid ion) linear
relaxation (LINRLX) - 0.01
•C2 (mass fraction of water)linear relaxation
(LINRLX) - 0.01
•V1(velocity vector in Y-axis) false-time-step
relaxation (FALSDT) - 1*10-5
• W1(velocity vector in Z-axis) false-time-step
relaxation (FALSDT) - 1*10-6
CONCLUSIONS
1. Using a numerical simulation code
(PHOENICS), enables us to develop a method
to predict the theoretical limiting current
values
2. Calculated limiting currents from the
concentration field distribution, were in a
good agreement (0.5-10 %) by comparison to
experimental results.
RECOMMENDATIONS
1. Development of theoretical model for
submerged hemisphere electrode and
compare the results with the
experimental one
2. Developments of theoretical model
for unsubmerged sphere and
hemisphere electrode, and compare the
results with the experimental one.