Date of Award
Doctor of Philosophy (PhD)
The limiting current method was used to investigate the mass transfer to a wall of a rectangular Plexiglass channel operated as a flow reactor for Reynolds numbers ranging from 200 to 32000. Cathode and mode blocks with smooth nickel surfaces were mounted in opposite walls of the channel, flush with the interior surface. Isothermal and non-isothermal mass transfer experiments were performed with the entire horizontal flow channel
i. rotated in 30° increments so that the cathode position varied from facing up to facing down (angle α) ii. tilled in 30° increments so that the channel position varied from horizontal to vertical (angle β)
at various bulk solution and cathode surface temperatures.
lsothermaI experiments (3277 in total) were performed in a flow channel with an internal rectangular cross-section of 2 cm x 1.5 cm (width x height), the total length being 229 cm between inlet and outlet. The electrolyte bulk solution, comprised of 2 mol/l NaOH, 0.025 mol/l K₃Fe(CN)₆ and 0.025 mol/l K₄Fe(CN)₆, was varied in temperature from 25°C to 55°C.
While the bulk solution was maintained at 25°C and the cathode surface temperature varied from 35°C to 55°C, non-isothermal experiments (2394 in total) were conducted in the same apparatus as describe above.
Examination of the data revealed that the mass transfer in the laminar now regime, at Re < 1900, seems to be independent of the Reynolds number. For laminar now conditions an equation of the form
Sh = 0.116 (1 + 0.336 (sinα)²⁷⁶⁶ + 0.427 (sinβ)⁰⁸²⁶(GRmSc)⁰³²⁰
gives an adequate prediction for mass transfer rates at 0° ≤ α ≤ 180° and 0° ≤ β ≤ 60°, where GRm is the combined Grashof number for heat and mass transfer. Mass transfer rates for the channel in a vertical position (β = 90°) can be predicted by:
For Reynolds numbers greater than 1900, mass transfer was found to be controlled by free and forced convection, with the forced convection dominant. For the turbulent flow region the date for 0° ≤ α ≤ 180° and 0° ≤ β ≤ 60° can be predicted by:
Mass transfer rates for channel slopes of 90° were best correlated by:
The isothermal laminar and turbulent experimental mass transfer coefficients were found to be within ±10% of correlations presented by Rousar et al. (1971) and Pickett (1977), respectively. For non-isothermal mass transfer in a horizontal channel under laminar and turbulent flow conditions the correlations of Ajersch (1990) agree well with the experimental data. Non-isothermal operation was found to increase mass transfer approximately four times over the isothermal case under the optimum enhancement conditions.
Since the system under investigation is a couple one, no analytical solution of the growing equations is possible. The finite element solver FIDAP was used to obtain numerically the local mass transfer coefficients, local Reynolds numbers, local densities, stream functions and concentration and temperature profiles for isothermal and non-isothermal case studies. The numerically obtained average mass transfer coefficients agreed within 15% of the experiment values for both the isothermal and non-isothermal case.
Bendrich, Guido, "Mass Transfer in Liquid Flow through a Reclangular Channel with and without Thermal Gradients" (1992). Open Access Dissertations and Theses. Paper 3499.