No description available.

There is a considerable volume of work available in literature which suggests that the performance of axial-flow hollow fibre membrane modules is limited by poorly distributed flow through the shell-side. This study was commissioned to examine the distribution of shell-side flow and its effect on mass transfer and to compare the performance measured by the axial-flow configuration to that obtained by a commonly used alternative known as the helically-wound module design. Laminar flow and mass transfer models have been developed to examine performance through axial-flow hollow fibre modules. These models also consider deviations from laminar flow in the form of turbulence and hydrodynamically undeveloped flow. Modelling analysis on four fibre bundle cross-sections quantify the extent to which channelling limits flow and mass transfer performance. Experimental flow and mass transfer work with locally fabricated hollow fibre modules demonstrated some inconsistencies with axial laminar flow modelling. Pressure drop and mass transfer results exceeded predictions from modelling. This thesis has hypothesised that fibres in axial-flow hollow fibre modules are not aligned as straight and parallel rods (as assumed in modelling) but interweave. Fibre interweaving results in flows between ducts. Such flows create mixing between ducts which results in more intimate contact between the flow and membrane surface, the consequence being higher pressure drop and higher mass transfer. The implication from this work was that axial flow and mass transfer modelling was limited in its use for characterisation of shell-side performance. The experience with helically-wound hollow fibre membrane modules (also fabricated locally) was that, by deliberately inducing flow between ducts, it was possible to considerably improve mass transfer performance. It was found that, whilst helically-wound modules could not be packed as tightly as axial-flow modules and required more sophisticated fabrication techniques, the benefit in their use arose from a substantial improvement in the level of shell-side mass transfer.

The effect of unsteady thermocapillary convection on the mass transfer rate of a solute between two immiscible liquids within a rectangular microscale channel with differentially heated sidewalls was numerically investigated. A computational fluid dynamic code in Fortran77 was developed using the finite volume method with Marker and Cell (MAC) technique to solve the governing equations. The discrete surface tracking technique was used to capture the location of the moving liquid-liquid interface. The code produced results consistent with those reported in published literature. The effect of the temperature gradients, the aspect ratio, the viscosity of liquid, and the deformation of the interface on the mass transfer rate of a solute were studied. The mass transfer rate increases with increasing temperature gradient. The improvement of the mass transfer rate by the thermocapillary convection was found to be a function of the Peclet number (Pe). At small Pe, the improvement of the mass transfer rate increases with increasing Pe. At high Pe, increasing the Pe has no significant effect on increasing the mass transfer rate. Increasing the aspect ratio of the cavity up to 1 increases the mass transfer rate. When the aspect ratio is higher than 1, the vortex moves only near the interface, resulting in decreasing the mass transfer rate. By increasing the viscosity of the liquid in top phase, the maximum tangential velocity at the interface decreases. As a result, the improvement of the mass transfer rate decreases. The deformation of the interface has no significant effect on the improvement of the mass transfer rate. By placing the heating source at the middle of the cavity, two steady vortices can be induced in a cavity. As a result, the mass transfer rate is slightly enhanced than that in the system with one vortex. By reversing the direction of the temperature gradient, the mass transfer rate decreases due to the decrease in the velocity of bulk fluid. The thermocapillary convection also promotes the overall reaction process when the top wall of the cavity is served as a catalyst. / Graduation date: 2005

Polycyclic aromatic hydrocarbons (PAH) have been identified as a serious environmental problem. In past research it has been proven that naphthalene, the simplest PAH, could be biodegraded using roller bioreactors and Pseudomonas putida. In this previous work it became apparent that the mass transfer rate of the hydrophobic naphthalene was the rate limiting factor in biodegradation, as the bacteria could degrade the naphthalene as fast as it entered solution. The challenge for the present research was to find a simple, inexpensive method for increasing the mass transfer rates within the framework of the previously successful reactor. <p>After some deliberation, the addition of inert particles (glass beads) was determined to be the preferred option to increase mass transfer. The inert particles visibly increased the turbulence in the reactor and significant increases in both mass transfer and bioremediation rates were achieved. The augmentation of mass transfer rates was found to be dependent on the type, size and relative loading of the particles. Two types of inert particles were investigated to increase mass transfer rates, spherical glass beads and Raschig rings. Glass beads were found to be far superior to Raschig rings for the intended purpose. Three sizes of spherical glass beads were then compared experimentally (1, 3, and 5mm). It was discovered that the 3mm beads were vastly superior to 1mm beads and 5 mm beads were slightly superior to 3mm beads. Different bead loadings (volume of particles / total working volume) were then explored with 10%, 25% and 50% bead loading investigated. Although slight increases in mass transfer were observed at higher bead loadings, the reduction in working volume for biodegradation meant that 50% was accepted as the optimum loading parameter. <p>The optimum conditions for maximum mass transfer occurred using 5 mm spherical glass beads at 50% loading. The increase in mass transfer and biodegradation rates compared to a traditional roller bioreactor were found to be 10 fold and 11 fold, respectively. The optimum mass transfer conditions were then applied to 2-methylnaphthalene with increases in mass transfer and biodegradation equal to 6 fold and 8 fold, respectively. The candidate bacteria used in this study was found incapable of degrading 1,5 dimethylnaphthalene although the mass transfer results demonstrate promise for the developed technology. To determine the effects of scale on the process, two larger reactors were finally studied. They were eight times and twenty-one times the size of the initial bioreactor. The process was shown to speed up at larger scale which shows great promise for future applications. The maximum degradation rate achieved in the larger reactor was 148 mgL-1h-1. This compares very well with the best result found in literature, 119 mgL-1h-1, which was achieved in a much more complex system. Clearly, the bead mill bioreactor designed during the present work is a simple concept that shows superior performance for the bioremediation of PAHs.

Polycyclic aromatic hydrocarbons (PAH) have been identified as a serious environmental problem. In past research it has been proven that naphthalene, the simplest PAH, could be biodegraded using roller bioreactors and Pseudomonas putida. In this previous work it became apparent that the mass transfer rate of the hydrophobic naphthalene was the rate limiting factor in biodegradation, as the bacteria could degrade the naphthalene as fast as it entered solution. The challenge for the present research was to find a simple, inexpensive method for increasing the mass transfer rates within the framework of the previously successful reactor. <p>After some deliberation, the addition of inert particles (glass beads) was determined to be the preferred option to increase mass transfer. The inert particles visibly increased the turbulence in the reactor and significant increases in both mass transfer and bioremediation rates were achieved. The augmentation of mass transfer rates was found to be dependent on the type, size and relative loading of the particles. Two types of inert particles were investigated to increase mass transfer rates, spherical glass beads and Raschig rings. Glass beads were found to be far superior to Raschig rings for the intended purpose. Three sizes of spherical glass beads were then compared experimentally (1, 3, and 5mm). It was discovered that the 3mm beads were vastly superior to 1mm beads and 5 mm beads were slightly superior to 3mm beads. Different bead loadings (volume of particles / total working volume) were then explored with 10%, 25% and 50% bead loading investigated. Although slight increases in mass transfer were observed at higher bead loadings, the reduction in working volume for biodegradation meant that 50% was accepted as the optimum loading parameter. <p>The optimum conditions for maximum mass transfer occurred using 5 mm spherical glass beads at 50% loading. The increase in mass transfer and biodegradation rates compared to a traditional roller bioreactor were found to be 10 fold and 11 fold, respectively. The optimum mass transfer conditions were then applied to 2-methylnaphthalene with increases in mass transfer and biodegradation equal to 6 fold and 8 fold, respectively. The candidate bacteria used in this study was found incapable of degrading 1,5 dimethylnaphthalene although the mass transfer results demonstrate promise for the developed technology. To determine the effects of scale on the process, two larger reactors were finally studied. They were eight times and twenty-one times the size of the initial bioreactor. The process was shown to speed up at larger scale which shows great promise for future applications. The maximum degradation rate achieved in the larger reactor was 148 mgL-1h-1. This compares very well with the best result found in literature, 119 mgL-1h-1, which was achieved in a much more complex system. Clearly, the bead mill bioreactor designed during the present work is a simple concept that shows superior performance for the bioremediation of PAHs.

No description available.

An experimental and analytical study of a microchannel ammonia-water desorber was conducted in this study. The desorber consists of 5 passes of 16 tube rows each with 27, 1.575 mm outside diameter x 140 mm long tubes per row for a total of 2160 tubes. The desorber is an extremely compact 178 mm x 178 mm x 0.508 m tall component, and is capable of transferring the required heat load (~17.5 kW) for a representative residential heat pump system. Experimental results indicate that the heat duty ranged from 5.37 kW to 17.46 kW and the overall heat transfer coefficient ranges from 388 to 617 W/m2-K. The analytical model predicts temperature, concentration and mass flow rate profiles through the desorber, as well as the effective wetted area of the heat transfer surface. Heat and mass transfer correlations as well as locally measured variations in the heating fluid temperature are used to predict the effective wetted area. The average wetted area of the heat and mass exchanger ranged from 0.25 to 0.69 over the range of conditions tested in this study. Local mass transfer results indicate that water vapor is absorbed into the solution in the upper stages of the desorber leading to higher concentration ammonia vapor and therefore reducing the rectifier cooling capacity required. These experimentally validated results indicate that the microchannel geometry is well suited for use as a desorber. Previous experimental and analytical research has demonstrated the performance of this microchannel geometry as an absorber. Together, these studies show that this compact geometry is suitable for all components in an absorption heat pump, which would enable the increased use of absorption technology in the small capacity heat pump market.

Thesis (Ph. D.)--Lehigh University, 2003. / Includes vita. Includes bibliographical references (leaves 104-107).

A novel approach to geologic CO₂ sequestration is the surface dissolution method. This method involves lifting native brine from an aquifer, dissolution of CO₂ into the brine using pressurized mixing and injection of the CO₂ saturated brine back into the aquifer. This approach has several advantages over the conventional approach, including minimization of the risk of buoyancy driven leakage and dramatic reduction in the extent of pressure elevation in the storage structure. The mass transfer coefficient for the CO₂/brine two-phase system and associated transport calculations allow efficient design of the surface equipment required to dissolve CO₂ under pressure. This data was not previously available in the literature. Original experimental data on the rate of dissolution of CO₂ into Na-Ca-Cl brines across a range of temperatures and wet CO₂ densities are presented. From this data, the intrinsic mass transfer coefficient between CO₂-rich and aqueous phases has been calculated. The statistically significant variation in the mass transfer coefficient was evaluated and compared with the variation caused by the experimental method. An empirical correlation was developed that demonstrates that the mass transfer coefficient is a function of the NaCl salinity, temperature and wet CO₂ density. For the conditions tested, the value of the coefficient is in the range of 0.015 to 0.056 cm/s. Greater temperature and smaller NaCl salinity increases the mass transfer coefficient. There is an interaction effect between temperature and wet CO₂ density, which increases or decreases the mass transfer coefficient depending on the value of each. CaCl₂ salinity does not have a statistically significant effect on the mass transfer coefficient. The transport calculations demonstrate that wellhead co-injection of CO₂ and brine is feasible, providing the same technical outcome at lower cost. For example, assuming a 2000 ft deep well and typical aquifer injection conditions, complete dissolution of the bulk COv phase can be achieved at 670 ft for bubbles of 0.16 cm initial radius. Using a horizontal pipe or mixing tank was also shown to be feasible. Gas entrainment was shown to provide a marked reduction in size of mixing apparatus required. / text

A basic physical model of electrodecantation has been developed and tested. Experimental data of Belongia (1999) were used to compare with computational results obtained from the model. The model was developed to calculate the transient velocity field, electric potential and particle distribution for the parameter space encountered in stable colloidal dispersions. The model included the effects of a spatially nonuniform electric field that existed in the experiments of Belongia (1999) because of the type and position of the electrodes used. As a result, the model required numerical methods for its solution. The problem was found to depend largely on three dimensionless groups: Re, a Reynolds number, Pe an electric Péclet number and ¤ a large dimensionless parameter denoting the Grashof number divided by the Reynolds number. Because A^(1/3) >> 1, nonuniform computational meshes were needed to resolve the exceedingly thin natural convection boundary layers that occur. Additionally, because Pe >> 1, a flux-limiting (FCT) numerical method was used to solve the particle transport equation. Results from the basic physical model show excellent agreement with the scaling of the experimental data but exhibit about 80% relative error when compared with experimental data on the decantation time. Consequently, a physicochemical model of electrodecantation was developed to include electrical conductivity variations that develop as ions transport during electrodecantation. Results show markedly better agreement (about 10% relative error) with experimental data concerning the decantation rate. Additionally, the physicochemical model is able to predict the pH and electrical conductivity stratification that was measured experimentally by Belongia (1999). A problem concerning the electrohydrodynamic deformation of miscible fluids, with differing electromechanical properties (electrical conductivity and dielectric constant), was also investigated. Numerical results predicting the sense and extent of deformation for various values of the two fluids’ electrical conductivity ratio compare well (less than 10% relative error) with measurements by Rhodes, et al. (1989). The role of dielectric constant differences in electrohydrodynamic deformations was also investigated. It was determined that an O(1) difference in the fluids’ dielectric constants is necessary to produce electrohydrodynamic deformations on the time scales reported by Rhodes, et al. (1989) and Trau, et al. (1995).