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  • Feed channel spacer characteristics and their optimisation
    (1998) Cao, Zhiyi
    Thesis
    The optimization of the spiral wound module design generally refers to the optimization of feed channel spacers, which is investigated in this thesis. The feed channel spacers serve to improve the mass transfer by promoting turbulence and provide passage for the fluid. However, the presence of spacers also significantly increases the channel pressure drop and consequently increases the energy costs of the process. The spacer design could therefore have a significant effect on process economics. The main aim of this work was to study spacer characteristics and test its major geometrical characteristics. To achieve this, custom designed spacers were developed in the laboratory and CFD simulations were used to visualize the flow management that spacer can achieve. Through experiments and CFD simulation, it was found that the transverse filament was one of the dominating factors in spacer design. Most of the pressure drop in the spacer filled channel was caused by the form drag introduced by the transverse filaments. The variation in transverse filament distance can greatly affect the number of transverse filaments in the channel and consequently affect the pressure drop and mass transfer in the channel. The experimental results showed that the diameter of the transverse filament also had a significant effect on channel pressure drop and mass transfer, especially at high flow rates. Increasing transverse filament diameter may result in a rapid increase in pressure drop and mass transfer caused by increased from drag and enhanced turbulence. Voidage alone was found not to be efficient for quantifying the geometrical properties of spacer filled channels. Two ratios, transverse filament diameter/channel height and transverse filament diameter/transverse distance, were established for quantifying the performance of the spacer filled channels. Novel spacers were developed as the result of this research. They provide similar mass transfer performance to the benchmark commercial spacer with lower pressure drop. Optimal novel spacer design was analysis based on economics analysis.
  • Stability and properties of supersaturated vanadium electrolytes for high energy density vanadium redox battery
    (1998) Rahman, Faizur
    Thesis
    Saturation concentrations of vanadium(V) and vanadium(IV) species were established conducting solubility studies of vanadium pentoxide and vanadyl sulfate in sulfuric acid concentrations ranging from 0 to 9M over a temperature range of 10°C-50°C. Total vanadium and total sulfur in the liquid samples at equilibrium were determined by ICP. The solubilities were found to be strongly I to the second dissociation constant of H 2 SO 4 and temperature. It was not possible to determine the solubility Of V2 O3 because of transformation Of V2 O 3 to VOSO4 in sulfuric acid solutions. However, total vanadium(III) concentrations as high as 2M were achieved with reagent grade V2 O 3 in 5M H2 SO4 by simple dissolution at 20°C. Supersaturated vanadium(V) electrolytes were prepared by electrolytic oxidation of V(IV) solution in different sulfuric acid concentrations to investigate the stability and properties of V(V) solutions over a temperature range of 20°C-50°C. The evaluation of thew V(V) solutions based on desupersaturation experiments, properties such as density, conductivity, viscosity, and cyclic voltammetry and 51 V NMR studies indicated that 3.0-3.5M V(V) solution in 5-6M total sulfate/bisulfate is a suitable composition for a high energy density vanadium redox. battery. Further increase in V(V) concentration above 3.5M, decreases the conductivity, electrochemical activity and reversibility, and increases the viscosity exponentially. It was found that the induction time for the precipitation of V 2 O 5 from V(V) solutions increases with increasing sulfuric acid concentrations because of increases in H+ ions, formation of sulfate/bisulfate complexes and dimerisation/polymerisation of VO2+ ions. The kinetic study of thermal precipitation of V(V) solutions indicated that the growth rate follows first order kinetics; under the conditions of low supersaturations and it obeys a second order rate equation at high supersaturations. Supersaturated V(V) solutions when exposed to atmosphere absorbs significant moisture which affect the properties and precipitation behaviour. A large number of additives and their blends were evaluated to inhibit the precipitation of supersaturated V(V) solutions at 40°C. A phosphate based formulation, KS11, was found to increase the induction time of 4M V(V) solution in 6M total sulfate/bisulfate by about 10 times. The formulation KS11 also exhibited encouraging results against the precipitation of supersaturated V(II) and V(IV) solutions. pitation of supersaturated V(II) and V(IV) solutions.