Egwu E. Kalu

Cyclic voltammetric studies of the effects of time and temperature on the capacitance of electrochemically deposited nickel hydroxide

A cyclic voltammetric (CV) technique was used to study the combined effects of annealing temperature and time on the pseudocapacitance of thermally treated electroprecipitated nickel hydroxide thin films. Through the analysis of the areas of the CVs cycled between 0 and 0.35 V (versus Ag/AgCl) it is shown that the optimal treatment condition for maximum film capacitance occurs at 300°C for 3 h. On the other hand, using the anodic and cathodic peak currents of the CVs cycled between 0 and 0.5 V (versus Ag/AgCl), the maximum film capacitance is also shown to occur at a thermal treatment condition of 300°C and 3.5 h (or 320°C and 3.2 h for linear approximations). The two methods demonstrate simple ways of extracting useful information on the electrochemical performance properties of thin films.

Prediction of 10-mm Hydrocyclone Separation Efficiency Using Computational Fluid Dynamics

Abstract It has been estimated that particles within the flow field of a 10-mm or mini-hydrocyclone experience local accelerations as high as 10 000 gravitation units. Although their operation is simple, the turbulent, swirling flow field within these devices offers a unique challenge to computational fluid dynamics (CFD). In addition to the computational challenge, very few experimental measurements have been reported in the literature on the flow field of the mini-hydrocyclone to which the CFD results may be compared. This research addresses the issue of predicting the separation efficiency of a volute entry 10-mm hydrocyclone. The feed flow rate is 4.5 litres/m (l/m) yielding a Reynolds number (based on the hydrocyclone diameter) of 9500 and a swirl number of 8.4. Using previously published flow simulation data, a multiphase system (consisting of a discrete oil phase and a continuous water phase) was analyzed for the purpose of obtaining separation information. These separation data were compared with laboratory separation experiments. Results indicate differences less than 20% for each droplet diameter. This information increased the level of confidence in the simulated flow field since there are no published velocity field data for the 10-mm hydrocyclone.

Simultaneous electrosynthesis of alkaline hydrogen peroxide and sodium chlorate

Simultaneous electrosynthesis of alkaline hydrogen peroxide and sodium chlorate in the same cell was investigated. The alkaline hydrogen peroxide was obtained by the electroreduction of oxygen in NaOH on a fixed carbon bed while the chlorate was obtained by the reaction of anodic electrogenerated hypochlorite and hypochlorous acid in an external reactor. An anion membrane, protected on the anode side with an asbestos diaphragm, was used as the separator between the two chambers of the cell. The trickle bed electrode of dimensions 0.23 m high ×0.0362 m wide × 0.003 m thick was used on the cathode side. The anolyte chamber of the cell, 0.23 m high × 0.0362 m, wide × 0.003 m thick was operated at a fixed anolyte flow of 2.0 × 10−6 m3 s−1 while the oxygen loadings in the trickle bed was kept constant at 0.102 kg m−2 s−1. Other operating conditions include inlet and outlet temperatures of 27–33°C (anode side), 20–29°C (cathode side), cell voltages of 3.0–4.2 V (at current density of 1.2–2.4 kAm−2) and a fixed temperature of 70°C in the anolyte tank.The effects of superficial current density, NaOH concentration (0.5–2.0 M) and catholyte liquid loadings (0.92–4.6 kg m−2 s−1) on the chlorate and peroxide current efficiencies were measured. The effect of peroxy to hydroxyl mole ratio on the chlorate current efficiency was also determined.Depending on the conditions, alkaline peroxide solution and sodium chlorate were cogenerated at peroxide current efficiency between 20.0 and 86.0%; chlorate current efficiency between 51.0 and 80.6% and peroxide concentration ranging from 0.069 to 0.80 M. The cogeneration of the two chemicals was carried out at both concentrated (2.4–2.8 M) and dilute (0–0.5 M) chlorate solutions. A relative improvement on the current efficiencies at concentrated chlorate was observed. A chloride balance indicated a less than 0.4% chloride loss to the catholyte. The results are interpreted in terms of the electrochemistry, chemical kinetics and the hydrodynamics of the cell.

In Situ Degradation of Polyhalogenated Aromatic Hydrocarbons by Electrochemically Generated Superoxide Ions

This paper reports on the reduction of dioxygen in aprotic media which yields superoxide ions which react with polyhalogenated aromatic hydrocarbons by nucleophilic substitution. The degradation of hexachlorobenzene to bicarbonates and chlorides using in situ generated superoxide ions was carried out at room temperature in a flow cell system equipped with a gas fed, porous electrode. The effects of current, electrolyte flow, and aprotic media on the extent of the degradation of hexachlorobenzene are presented.

Thermal Analysis of Spirally Wound Li/BCX and Li / SOCl2 Cells

A thermal analysis of Li/BCX and high rate Li/SOCl[sub 2] cells is presented. The thermal model developed was used to study the effect of ambient temperature of discharge (0-40 C) on Li/BCX cells discharged at the same rate. The model predictions show that ambient temperature of discharge was critical in thermal management of the cell. For forced convection cooled cells, the model predicted that ambient temperature near room temperature (25 C) was required to achieve the lowest maximum temperature rise in the cell. Inclusion of the effects of reaction products to the model predictions showed that a constant composition assumption may be misleading. Heat transfer through the spiral constituted a smaller fraction of the total heat dissipation from the cell. In a comparison of the thermal performance of high rate Li/SOCl[sub 2] cell with Li/BCX cell, the model predicted a higher temperature rise in the Li/SOCl[sub 2] cell (assuming the temperature rise behaves linearly with discharge current) if both cells were discharged at the same rate.

Bulk thermal capacity determination for Li/BCX and Li/SOCl2 cells

Abstract The bulk heat capacities of Li/BCX and Li/SOCl 2 cells were determined at 0 and 100% depth-of-discharge for 2.0 V cut-off voltage, in the temperature range 0 to 60 °C by a method that did not involve the destruction of the cell nor the contact of cell with a liquid. The heat capacity of Li/BCX cell is an important parameter for the design of a thermal control system for Li/BCX batteries. The heat capacities are found to be dependent on state-of-charge — increasing with depth-of-discharge. The Li/BCX DD-cell has a lower heat capacity (0.154 to 0.201 cal/(g K)) than a high rate Li/SOCl 2 D-cell (0.191 to 0.221 cal/(g K)). The results obtained by this method compare favorably well with results reported in the literature through other methods. The bulk heat capacities of the cells did not change significantly in the temperature range 0 to 60 °C.

Measurements of the Fundamental Thermodynamic Parameters of Li/BCX and Li / SOCl2 Cells

Two experimental techniques - equilibrium or reversible cell discharge and measurement of open circuit potential as a function of temperature - are used to determine the thermodynamic data needed to estimate the heat generation characteristics of Li/BCX and Li/SOCl2 cells. The results obtained showed that the reversible cell potential, the temperature dependence of the reversible cell potential, and the thermoneutral potential of the BCX cell were 3.74 V, -0.857 +/- 0.198 mV/K, and 3.994 +/- 0.0603 V, respectively. The respective values obtained for the Li/SOCl2 cell were 3.67 V, -0.776 +/- 0.255 mV/K, and 3.893 +/- 0.0776 V. The difference between the thermoneutral potential of Li/BCX and Li/SCl2 cells is attributable to the difference in their electroactive components.

Application of the modified van der waals equation for unsaturated vapour and liquid states

Abstract The Law-Lielmezs (L-L) modification of the Van der Waals equation of state: P = RT /( V-b )- a ( T )/ V 2 where: a ( T ) = a ( T c )· a ( T c ·a(T ∗ ) and: a ( T ∗ ) = 1 + pT ∗ q has been extended to include unsaturated states in terms of a correcting function C f (such that the α( T ∗ ) term becomes: a ( T ∗ ) = 1 + p C f T ∗ q The proposed extension has been compared with the results obtained by the use of the original Van der Waals equation of state.

Calorimetric Determination of the Thermoneutral Potential of Li/BCX and Li / SOCl2 Cells

Results are presented of the calorimetric determination of the effective thermoneutral potential, Eetp, of Li/BCS and Li/SOCl2 cells in the temperature range 0-60 C through a continuous recording of the cell voltage, heat flow, and current. The average effective thermoneutral potential at 25 C was 4.0 and 3.84 V for BCX and Li/SOCl2 cells, respectively. Based on the classical approach, the reversible cell potential, Er, and temperature dependence of reversible cell potential, dEr/dT, for BCX cell were 3.74 V and -0.952 mV/K, respectively, and for Li/SOCl2, Er = 3.67 V and dEr/dT = 0.567 mV/K. The thermal polarization (Eetp-E1), where E1 is the load voltage, for both cells, showed that they are the most thermally efficient near 40 C. An overall reaction proposed for the BCX chemistry is supported by the calculated thermodynamic parameters.