The fermentation of syngas (a mixture of CO, CO2 and H2) to produce ethanol is of interest as an alternative fuel. Clostridium carboxidivorans, has been found to produce higher than average amounts of ethanol and butanol from CO-rich mixtures. This project sought to determine the effects of the redox level in the solution, partial pressures in the headspace and mass transfer limitations on the products obtained through fermentation of syngas. It was determined that cysteine sulfide has a greater effect on the redox level of the media used to grow bacteria, than does the gas composition. Therefore, changing gas composition during the process will have little effect on the redox. However, addition of cysteine sulfide may vary the redox level. When cells were first inoculated, the redox level dropped and leveled at -200 mV SHE for optimal growth. In addition, cells switch from acetic acid to ethanol production after a drop of 40-70 mV in the redox level. Different sizes of reactors were used, including 1 liter reactors (non-pressurized), 50 mL bottles (20 psig) and 100 mL bottles (20 psig). The 50 mL bottles have more than double the growth rate than the 100 mL bottles (0.57 day-1 compared to 0.20 day-1). Partial pressures were measured in these two sizes to determine the different consumptions and the effect of partial pressure on both growth and production of acetic acid/ethanol. It is clear that re-gassing the bottles every 12 hours to keep the pressure higher in the 100 mL bottles makes a significant difference in the growth, making them very similar to the 50 mL bottles. Both the 50 mL and 100 mL bottle were found to have essentially the same mass transfer rate (0.227 L/hr vs. 0.255 L/hr). However, because of headspace differences, there was more CO available for the 50 mL bottles (on a per liter basis) as compared to the 100 mL bottles. Mass transfer analysis proved useful in pointing out that all three reactors likely experienced mass transfer limitations such that mass transfer effects are critical to address when performing studies involving syngas fermentation.

Reverse osmosis (RO) and nanofiltration (NF) membranes are pressure driven, diffusion controlled process. The influence of surface characteristics on membrane process performance is considered significant and is not well understood. Current mass transport models generally assume constant mass transfer coefficients (MTCs) based on a homogeneous surface. This work evaluated mass transfer processes by incorporating surface morphology into a diffusion-based model assuming MTCs are dependent on the thickness variation of the membrane’s active layer. To mathematically create such a surface layer, Gaussian random vectors embedded in a software system (MATLAB) were used to generate a three-dimensional ridge and valley active layer morphologies. A “SMOOTH” script was incorporated to reduce the influence of outlying data and make the hypothetical surfaces visually comparable to the AFM images. A nonhomogeneous solution diffusion model (NHDM) was then developed to account for surface variations in the active layer. Concentration polarization (CP) is also affected by this nonhomogeneous surface property; therefore, the NHDM was modified by incorporating the CP factor. In addition, recent studies have shown that the membrane surface morphology influences colloidal fouling behavior of RO and NF membranes. With consideration of the spatial variation of the cake thickness along the membranes, a fouling model was established by assuming cake growth is proportional to the localized permeate flow. Flux decline was assumed to be controlled by the resistance of cake growth and accumulated particle back diffusion at the membrane surface. A series of simulations were performed using operating parameters and water qualities data collected from a full-scale brackish water reverse osmosis membrane water treatment plant. The membrane channel was divided into a thousand uniform slices and the water qualities were iii determined locally through a finite difference approach. Prediction of the total dissolved solid (TDS) permeate concentration using the model was found to be accurate within 5% to 15% as an average percentage of difference (APD) using the NHDM developed in this research work. A comparison of the NHDM and the modified NHDM for concentration polarization (CP) with the commonly accepted homogeneous solution diffusion model (HSDM) using pilot-scale brackish water RO operating data indicated that the NHDM is more accurate when the solute concentration in the feed stream is low, while the NHDMCP appears to be more predictive of permeate concentration when considering high solute feed concentration. Simulation results indicated that surface morphology affects the water qualities in the permeate stream. Higher salt passage was expected to occur at the valley areas when diffusion mass transfer would be greater than at the peaks where the thin-film membrane is thicker. A rough surface tends to increase the TDS accumulation on the valley areas, causing an enhanced osmotic pressure at the valleys of membrane. To evaluate the impact of surface morphology on RO and NF performance, fouling experiments were conducted using flat-sheet membrane and three different nanoparticles, which included SiO2, TiO2 and CeO2. In this study, the rate and extent of fouling was markedly influenced by membrane surface morphology. The atomic force microscopy (AFM) analysis revealed that the higher fouling rate of RO membranes compared to that of NF membranes is due to the inherent ridge-and-valley morphology of the RO membranes. This unique morphology increases the surface roughness, leading to particle accumulation in the valleys, causing a higher flux decline than in smoother membranes. Extended fouling experiments were conducted using one of the RO membranes to compare the effect of different particles on actual water. It was determined that membrane flux decline was not affected by particle type when the feed water iv was laboratory grade water. On the other hand, membrane flux decline was affected by particle type when diluted seawater served as the feed water. It was found that CeO2 addition resulted in the least observable flux decline and fouling rate, followed by SiO2 and TiO2. Fouling simulation was conducted by fitting the monitored flux data into a cake growth rate model. The model was discretized by a finite difference method to incorporate the surface thickness variation. The ratio of cake growth term (�1) and particle back diffusion term (�2) was compared in between different RO and NF membranes. Results indicate that �2 was less significant for surfaces that exhibited a higher roughness. It was concluded that the valley areas of thin-film membrane surfaces have the ability to capture particles, limiting particle back diffusion.

<p> Forced convection mass transfer rates from single gas bubbles, with accompanying chemical reaction, were determined experimentally in the intermediate Reynolds number range. The reacting system carbon dioxide-monoethanolaminc was chosen for this study. </p> <p> A mathematical model, describing forced convection mass transfer from a single sphere with accompanying first or second order reaction, was developed and solved using finite-difference techniques. Hydrodynamic conditions in the intermediate Reynolds number region were described using Kawaguti-type velocity profiles. </p> <p> The numerical solutions of the model have been compared with the experimental results of this study as well as with previous theoretical and experimental results. </p> / Thesis / Doctor of Philosophy (PhD)

Flow accelerated corrosion is a piping degradation mechanism that results in pipe wall thinning due to the dissolution of the magnetite oxide layer on carbon steel surfaces to the bulk flow. The rate limiting process of flow accelerated corrosion in piping system is the diffusion-controlled mass transfer. The surface roughness develops due to the mass transfer and can subsequently have a significant effect on the mass transfer. The naturally developing surface roughness in many dissolving surfaces, including carbon steel pipes, is a densely packed array of saucer shaped depression called scallops, which can have several length scales. Heretofore, the developing roughness on soluble walls has not been quantified, mainly due to the lack of a reliable measurement methodology. The overall objective of this research is to investigate the developing roughness and the corresponding mass transfer on soluble walls in different piping geometries. A wall dissolving method using gypsum test sections dissolving to water in a closed flow loop was used to mimic the mass transfer in carbon steel pipes due to a similar Schmidt number of 1200. A novel non-destructive measurement technique using X-ray CT scans was developed to measure the development of surface roughness and the corresponding mass transfer. The method was validated by performing experiments using straight pipe test sections and comparing against traditional measurements method using ultrasonic sensors, coordinate measurement machine and laser scans. The time evolution of surface roughness and the corresponding mass transfer were measured in pipe test sections at Reynolds number of 50,000, 100,000 and 200,000. The roughness scallops were observed to initiate locally and then develop until the surface is spatially saturated. The surface roughness was characterized by the RMS height, peak-to-valley height, integral length scale, density and spacing of the scallops. Two time periods of roughness development were identified: an initial period of slower growth in the roughness height followed by a relatively higher growth rate that corresponded to the period before and after the surface saturates with the scallops. The mass transfer enhancement due to the roughness in each of these time periods was also found to be different, with a higher increase in the first period followed by a slower increase once the streamwise spacing was approximately constant. Both the height and spacing of the roughness elements was found to affect the mass transfer enhancement. A new correlation is proposed for the mass transfer enhancement as a function of the height-to-spacing ratio of roughness, with a weak dependence on Reynolds number. The measurement methodology was extended to study the mass transfer and developing roughness in a complex S-shaped back to back bend at Reynolds number of 200,000. The mass transfer in bend geometry can be enhanced by both the local flow due to the geometry effect and the developing roughness. Two high mass transfer regions were identified: at the intrados of the first and second bends. The height-to-spacing ratio of the roughness was found to increase more rapidly in these high mass transfer regions. An additional one-time experiment was performed at a Reynolds number of 300,000. A higher surface roughness with smaller values of spacing-to-height ratio was found in the regions with high mass transfer. / Thesis / Doctor of Philosophy (PhD)

<p> A continuous bubble reactor was used to study the transfer of oxygen into solutions of acetaldehyde. The reaction was catalysed by cobaltous acetate. The parameters investigated included temperature, catalyst concentration, air flow rate and column height.</p> <p> A mathematical model based on Houghton's work (36) was used to describe the absorption rate in the bubble column. The equation derived was solved numerically. The Sherwood numbers predicted by the theory were compared with those obtained experimentally.</p> / Thesis / Master of Engineering (MEngr)

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The literature on stream reaeration was reviewed. A recirculating loop open channel system was desiqned and experiments were performed to study the effects of average stream velocity and temperature on the mass transfercoefficient for oxyqen dissolution into "clean" water. The applicability of the apparatus to the study of the effects of surfactants was also investigated. The velocity ranged from 0.1 to 0.9 ft/sec and the temperature from 5,0 to 25.o0c. The results indicated that the mass transfer coefficient varies approximately linearly with average stream velocity and that the temperature coefficient is a variable which depends on mixinq condHions. Furthermore, it was found that the temperature dependency of the mass transfer coefficient could be expressed as either a linear or power function. Correlations expressing the mass transfer coefficient in terms of easily measurable stream parameters. were developed and compared to those found in the recent literature / Thesis / Master of Engineering (ME)

Yes / This paper presents a simulation study of vacuum membrane distillation (VMD) for desalination. A simulation model was built on Aspen Plus® platform as user defined unit operation for VMD module. A simplified mathematical model was verified and the analysis of process performance based on simulation was also carried out. Temperature and concentration polarization effects are significant in the conditions of higher feed temperature and/or vacuum pressure. The sign of difference of the vapour pressures between at the membrane interfaces, is a pointer of the vacuum pressure threshold. Increasing the vacuum pressure at lower feed temperature is an effective way to increase the permeate flux and reduce the energy consumption simultaneously.