Yes / Cooling towers are a relatively inexpensive and consistent method of ejecting heat from several industries such as thermal power plants, refineries, and food processing. In this research, an earlier model from literature was to be validated across three different case studies. Unlike previous models, this model considers the height of the fill as the discretised domain, which produces results that give it in a distribution form along the height of the tower. As there are limitations with the software used (gPROMS) where differential equations with respect to independent variables in the numerator and denominator cannot be solved, a derivative of the saturation vapour pressure with respect to the temperature of the air was presented. Results shown were in agreement with the literature and a parametric sensitivity analysis of the cooling tower design and operating parameters were undertaken. In this work the height of fill, mass flowrates of water and air were studied with respect to sensitivity analysis. Results had shown large variations in the outlet temperatures of the water and air if the mass flows of water and air were significantly reduced. However, upon high values of either variable had shown only small gains in the rejection of heat from the water stream. With respect to the height of the fill, at larger heights of the fill, the outlet water temperature had reduced significantly. From a cost perspective, it was found that a change in the water flowrate had incurred the largest cost penalty with a 1% increase in flowrate had increased the average operating cost by 1.2%. In comparison, a change in air flowrate where a 1% increase in flowrate had yielded an average of 0.4% increase in operating cost.

The purpose of this investigation was to determine meaningful values of interfacial area and contact time for mass transfer on a sieve-tray. These values were determined by measuring the rates of absorption of carbon dioxide into aqueous solutions and forcing the parameters to give answers consistent with the rates of absorption. These values were checked by comparing the interfacial area determinations with independent measurements. The interfacial areas and contact times were determined for liquid :eed rates of 10, 20, and 30 cubic centimeters per minute; slot velocities of 22, 26, 30, and 34 feet per second; hole diameters of 1/8, 1/4, and 3/8 inches; tray thicknesses of 1/16, 1/8, and 1/2 inches; free areas of 1.56, 3.52, and 7.04 percent; and depth of unaerated liquid or the tray of 1.00, 2.00, and 3.00 inches. The values of the interfacial area determined in this investigation were consistent with independent, previously measured values. The values of the contact times determined were about four times greater than previous estimations; this discrepancy was attributed to wall effects and differences in froth characteristics. / Ph. D.

It was the purpose of this investigation, using the ternary system acetone-toluene-water in the extraction of acetone from toluene using distilled water, to determine the operating characteristics of a pulse extraction column, and to determine the effects of solvent-to-feed ratio, feed concentration, and pulse amplitude on the overall mass transfer coefficient. The equipment used was operated at a temperature of 25±1 ºC, and consisted of a two-inch diameter glass column with eight sieve plates having 1/16-inch diameter holes on triangular centers, and a plate-free area of twenty-three per cent. The plate spacing used was eight inches. Pulsation of the liquids in the column was accomplished by means of a brass bellows actuated by a push rod driven by a motor-driven cam. The determination of the column operating characteristics resulted in curves defining the operating flow rates at which the column could be operated without light- or heavy-phase flooding. The shape of the curves was a function of the feed and solvent flow rates, but was independent of the pulse amplitude. Using flow rates taken from the column operating characteristic curves, a total or forty-five tests were made to determine the effect or pulse amplitude, feed concentration, and the solvent-to-feed ratio on the overall mass transfer coefficient. It was found that the overall mass transfer coefficient was the highest at a volumetric solvent-to-feed ratio of 0.50 for conditions of blowing, reached a minimum at a volumetric solvent-to-reed ratio of 1.00 at which there was no blowing or dumping, and increased slightly at a volumetric solvent-to-feed ratio or 1.50 at which dumping occurred. The overall mass transfer coefficient increased with increased feed concentration in a straight-line relationship. The overall mass transfer coefficient was also increased by an increase in the pulse amplitude. / Master of Science

The purpose of this investigation was to determine the effect of a homologous series of solutes on the overall mass-transfer coefficients for liquid-liquid extraction. The solutes used were ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether. The carrier solvent was water, and the extracting solvent was toluene. The phase diagrams for these systems were determined at 30 °C. The phase diagrams were found to be similar and to have maximum solubilities ranging from 69.9 to 76.7 weight per cent of solute.. Three of the systems exhibited solutropes, and the system containing tetraethylene glycol dimethyl ether approached a solutrope at a solute concentration of approximately 64 per cent. A countercurrent-flow, 1-1/2-inch diameter, horizontal, pyrex glass tube, eight feet long with an interfacial surface area of one square foot, was used for the extraction tests. The feed concentration ranged from 9.10 to 15.18 weight per cent of solute in water. The flow rates of the water phase varied from 15.20 to 34.72 pounds per hour, and the solvent phase flow rates varied from 18.86 to 33.83 pounds per hour. The overall mass-transfer coefficients based on the water phase were found to vary between 0.0098 and 0.0133, 0.0036 and 0.0051, 0.0035 and 0.0063, and 0.0023 and 0.0063, for the systems investigated. The solvent phase coefficients were found to vary between 0.0097 and 0.0149, 0.0057 and 0.0079, 0.0092 and 0.0172, and 0.0087 and 0.0237. The overall coefficients were not affected appreciably by changing the molecular weight of the solute. Also, experimentally determined values of the overall coefficients based on the solvent phase did not agree with those values of the coefficients calculated by previously determined equations. / Master of Science

Creosote, containing many high molecular weight hydrophobic polycyclic aromatic hydrocarbons (PAH's), is present in the subsurface environment at the Oneida Tie-Yard in Oneida, Tennessee. Phytoremediation using hybrid poplar trees was chosen as the remedial technology on-site. Since monitoring began, the contaminant plume has been shrinking consistently and evidence has shown that remediation is taking place. However, remediation may be rate-limited by the desorption and dissolution kinetics of the PAH's on-site. The objectives of this research are to: (1) estimate the desorption and dissolution rates of 10 PAH's found in the subsurface and (2) estimate the amount of each PAH and total mass of contaminant that is irreversibly sorbed to the soil. Three laboratory desorption and dissolution experiments were performed using contaminated soil samples from the Oneida Tie-Yard site. The first experiment was a batch desorption equilibrium experiment, the second was a batch desorption kinetics experiment, and the third was a soil column dissolution kinetics experiment. The target compounds in this study were: naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, chrysene, and benzo(b)fluoranthene. The resulting data for the desorption equilibrium experiment revealed that rates of equilibrium were truly not instantaneous in the systems studied. However, because approximately 76% of PAH's desorbed by the first sampling event (3 days), an equilibrium isotherm was considered appropriate. Results showed that there is a sorbed reversible concentration that readily desorbs to the aqueous phase for each PAH. Additionally, it was determined that the percent removal of sorbed PAH's decreases with increasing molecular weight. Desorption curves based on experimental data were found to exhibit linear behavior over large variations in aqueous concentration, but showed exponential behavior as concentrations approached zero. Freundlich sorption equilibrium isotherms for the 10 monitored PAH's on-site were generally found to have N coefficient values over 1, especially over large variations in solution phase concentration, indicating a non-uniform sorbent. Dissolution of resistant PAH's under field-like conditions was determined to occur over long periods of time. Dissolution rates calculated from experimental data were shown to generally decrease with increasing molecular weight. Overall, desorption and dissolution kinetics of PAH's were shown to be rate-limiting factors to remediation at the Oneida Tie-Yard. / Master of Science

It was the purpose of this investigation to ascertain the qualitative nature of the interracial tension equilibrium characteristics of the systems hexane-acetone-water and toluene-acetone-water by studying the effect of drop velocity on drop weight through use of the modified drop weight procedure, and comparing these results with those obtained from systems known to have time dependent interfacial tension relationships; to then evaluate the effect of interfacial tension on the rate or mass transfer by obtaining extraction data for the above systems in a horizontal, countercurrent liquid-liquid extraction tube for a series of interfacial tension values achieved through variation of the total acetone concentration in the system; and finally, to attempt to obtain an equation correlating the overall mass transfer coefficient based on the solvent film with the physical and operational variables of the systems and extractor. The observation that some three component, ternary systems containing high molecular weight solutes required time to reach interfacial tension equilibrium, prompted a more careful consideration of the assumption that determinations or this property obtained under static conditions represented the values existing under extracting conditions. The drop weight method was selected for comparison studies. An equation relating drop weight to drop velocity was derived, and took the form: m = 2πrσØ/g - Aρv²/g where: m = drop weight, gm 2, π = constants r = tip radius, cm σ = interfacial tension, dynes/cm g = acceleration due to gravity, cm A = cross sectional area of capillary tube, sq cm ρ = density of fluid flowing in capillary, gm/cu cm v = drop velocity, drops/min Ø = correction factor for non-ideal drop detachment from tip. The equation predicted that if (σ') and (Ø) were constants, a plot or drop weight (m) versus the square or the drop velocity (v²) would result in a straight line. The systems used to test the validity of the above equation were arabic acid and acetone as solutes with each of the following liquid pairs: benzene-water, cyclohexane-water, and toluene-water. From this study, it was concluded that 1. Adjustment of interfacial tension for the systems acetone in toluene, benzene, or cyclohexane with water was so rapid that equilibrium was reached as quickly as the drops could be formed. 2. The interfacial tension values of systems containing solutes having a molecular weight of 50 to 60 measured by equilibrium methods will be representative of the interfacial tension values for the systems under extracting conditions. 3. Equilibrium methods are not suitable for evaluating interfacial tension under extracting conditions for solutes having a molecular weight on the same order of magnitude as that for arabic acid. 4. The experimental method used in this investigation failed to show any transient values of interfacial tension less than the equilibrium values as postulated by Christiansen and Hixon. Extraction tests were made on the systems toluene-acetone-water and hexane-acetone-water at 25 to 29 °C, in an effort to determine the effect of interfacial tension on the overall mass transfer coefficient. Phase flow rates covered a range of 1,000 to 10,000 pounds per hour per square foot for both phases. Concentration ranged from 35 to 5 weight per cent acetone in the inlet water stream, and 20 to zero weight per cent acetone in the inlet toluene stream. For the hexane system. the concentrations varied from 45 to 15 weight per cent in acetone in the inlet water phase, and 5 to zero per cent acetone in the inlet hexane phase. The results of this study led to the following conclusions: 1. The overall mass transfer coefficient for acetone from water to hexane based on the hexane film, increased from 0.012 to 0.060 with an increase in interfacial tension from 7.6 to 24.0 dynes per centimeter, as controlled by decreasing acetone concentration. 2. The overall mass transfer coefficient for acetone from water to toluene based on the toluene film, decreased from 0.145 to 0.048 with an increase in interfacial tension from 6.6 to 22.5 dynes per centimeter, as controlled by decreasing acetone concentration. 3. Because of the opposite effect of interfacial tension on transfer of acetone from water to hexane and to toluene, no generalization as to the effect of interfacial tension on the overall mass transfer coefficient could be made. 4. The mass transfer coefficient for acetone to toluene was 0.1 to 0.025 ot the transfer coefficient for acetone from water to toluene. 5. The overall mass transfer coefficient based on the solvent phase concentrations can be correlated with 67 percent accuracy with the physical properties of the system by the equation: K_sd/D_s = 2.708 x 10⁻²¹(dσ/μ_sD_s)^0.7227(μ_w/μ_s)^4.0592(μ_s/ρ_sD_s)^5.4361(dG_s/μ_s)^0.4701(dG_w/μ_w)^0.3027 where: K_s = overall mass transfer coefficient based on solvent phase, lb/hr- sq ft-ΔC d = diameter of horizontal extraction tube, ft D_s = diffusivity of solute in solvent, sq ft/hr σ = interfacial tension, lb/hr² ρ_s = density of solvent phase, lb/cu ft μ_w, μ_s = viscosity of water and solvent phases, respectively, lb/ft-hr G_w, G_s = mass velocity of water and solvent phases, respectively, lb/hr-sq ft. 6. Equations correlating the individual film coefficients with physical properties of the system derived from binary extraction studies could not be used to predict ternary overall mass transfer coefficients. / Ph. D.

The migration of organic contaminants in the subsurface, due to leaking underground storage tanks, includes both discrete and dissolved phase plume movements through the porous media. Such problems always involve the multiphase flow and mass transport through three phases, namely air, oil, and water. A finite element model is developed in this thesis based on the theory of multiphase flow weakly-coupled with the theory of mass transport, in a three-dimensional setting. Galerkin's method is employed to derive the finite element formulations for multiphase flow and mass transport based on the appropriate governing differential equations. The equations for multiphase flow are based on van Genuchten's model for unsaturated flow for air and water. In this model, the saturation-pressure-conductivity relations are used to obtain the constitutive behavior. The solution procedure of the resulting time dependent nonlinear equation involves using a general 0-scheme, for time integration, and a modified Picard's method, for nonlinear iteration. The governing equation for mass transport in a three-phase system is derived based on the assumption of linear partitioning between the air, oil, water, and solid phases. The equations for flow and transport are weakly-coupled through the time lagged interphase mass transfer term. A computer program called IMFTP3D is developed. The program can solve problems related to (1) multiphase immiscible flow, (2) diffusion without flow, and (3) multiphase flow weakly-coupled with mass transport. The three-dimensional model is validated for all three options based on previous two-dimensional models and laboratory experiments present in the literature. Laboratory experiments where conducted involving gasoline movements through both a one-dimensional column and a two-dimensional flume. The computer program, IMFTP3D, was then used to investigate the usefulness of the model in predicting water outflow in for the column problem and plume movements in the flume experiment. / Master of Science

A vibrated bed is a mobile layer of solid particles contained in a vessel that is vertically vibrated. When a flow of gas is maintained through it , the bed is called an aerated vibrated bed and a vibrated gas-fluidized bed if the gas stream is greater than the minimum fluidization velocity of the particles. Mass transfer rates from solid particles coated with naphthalene to a nitrogen stream, the fluidizing gas, are determined using a gas chromatographic technique. Two kinds of coated beads of different densities are used: Master Beads and low-density glass beads. The investigation is done using a cylindrical vessel with bed depths of 24 mm, 12.7 mm, and 1 mm (ultra-shallow bed). A range of solid particles from 125 to 841 microns of geometric mean size is employed. Using a vibrational frequency of 25 Hz, the particle bed is vibrated at different intensities up to four times the gravitational acceleration. Vibrations increase the mass transfer rate to some extent depending on the bed depth. The mass transfer process is more important in shallow beds, where strong solid mixing occurs, than in deeper beds, where bulk-circulation patterns affect the naphthalene sublimation. Higher mass transfer rates are obtained with larger as well as heavier particles. / Master of Science

This document details the results of a study that employed a single element, spiral-wound, thinfilm composite nanofiltration (NF) membrane pilot to assess the treatment effectiveness for aerated and unaerated groundwater supplies. Phase 1 consisted of using raw, unaerated groundwater with standard cartridge filtration (CF) and scale inhibitor (SI) as pretreatment to NF. During the first phase, four water recoveries and crossflow velocities were evaluated to observe how operational conditions affected permeate water quality. Phase 2 involved the simulation of a 70-foot transmission pipeline and sand filter (SF) pilot in series with CF and SI addition pretreatment, prior to NF. Phase 3 employed tray aeration prior to the SF pilot. The pilot was operated for 1,483 run-hours over the three phases, whereupon operational and water quality monitoring ensued to assess NF efficiency. Biological activity tests and foulant analyses were performed to further characterize source water. It was determined statistically that changes in operational conditions in Phase 1 such as crossflow velocity did not significantly affect constituent mass transfer. Phase 2 demonstrated that NF removed total dissolved solids and total organic carbon content greater than 96 percent (%) and 86%, respectively. Phase 3, which exhibited operational difficulties and flux decline, suggested that additional pretreatment is required for NF operation using aerated groundwater. Dimensional analysis (DA) and diffusionbased mass transfer models were employed to predict permeate chloride content for each testing phase; it was determined that the DA overpredicted chloride concentrations by 10 magnitudes and diffusion models were predictive when compared to actual values. The transient response to feed water perturbations within the single-stage membrane process was determined to cause a log-logistic two-and-a-half-minute delay.

Recombinant Pichia pastoris is one of the important methylotropic yeast due to its robustness and ability to produce hormones like human chorionic gonadotropin (hCG), luteinizing hormone (LH) extracellularly. High growth on glycerol and strong protein expression on methanol by insertion of alcohol oxidase (AOX) promoter demand the fermentation to be a multistage operation. Methylotropic pathway demands more oxygen as methanol has to be converted to formaldehyde with half mole of oxygen. Moreover as fermentation progresses cell density in the reactor also increases. In case of Pichia pastoris fermentation cell density usually reaches very high (above 100 gm/lit) at the end of fermentation. Both these contribute in the increased oxygen demand in the fermentation and oxygen transfer turns out to be a limiting step. The present study focuses on the oxygen transfer process and its improvement in the fermentation. Oxygen transfer in bioreactor is a multistep process and involves different kinetic as well as mass transfer steps. In case of fermentation especially at high cell densities, oxygen transfer from bubbles to the broth becomes limiting step. The interface transport is governed by many physical as well as kinetic parameters. It is essential to screen these parameters from the whole set to identify the key parameters. Sensitivity analysis is carried out by using Metabolic Control Analysis (MCA) to quantify the effects of different parameters. It is found that bubble size and oxygen partial pressure are two such key parameters which can be manipulated. Use of pure oxygen to increase partial pressure and thereby solubility of oxygen in broth is a common approach. This work focuses on bubble size manipulation to increase the oxygen transfer rates.The idea behind this work is on to generate micron sized bubbles and utilize them effectively in the fermentation. There are many techniques reported to generate microbubble dispersions. In this work ’Spinning Disc microbubble Generator’ is fabricated to generate microbubbles. A flat disc surrounded by baffles with 5 mm gap in between, when subjected to 5000 rpm generates microbubbles. Some modifications are done to the set up to achieve desired properties of the bubbles. The bubbles generated fall in the range of 30-300 micron with mean size of about 60 micron. Use of Tween-20 surfactant stabilize the bubbles and hence offer a good resistance to coalescence and breakage. The liquid fraction in the bubbles can be as high as 40%. Contineous addition of this dispersion unnecessarily can dilute the fermentation broth. To overcome this volume constrain, a recirculation system is designed. Microbubble dispersion is added contineously to the reactor and equivalent fermentation broth is pumped back to the microbubble generator to achieve steady state to the liquid volume in both the vessels. Mass transfer studies with microbubbles show the potential of microbubble dispersion (MBD) to enhance mass transfer significantly. Decrease in volumetric mass transfer coefficient (KLa) due to surfactant is overcompensated by the increase in the interfacial area and net effect is, potential enhancement in KLa. The enhance- ment factor, that is, ratio of mass transfer coefficient with MBD to mass transfer coefficient with conventional sparging, is obtained to be about 4 to 5. Prior to utilization of bubbles in the recirculation system, cells are checked for the shear sensitiveness. Negligible lysis losses and almost no effect on growth patterns in shake flask culture confirm that the cells used are mechanically stable at operating conditions. Better growth patterns in shake flask are observed when microbubbles are pumped for predetermined duration in the broth. It shows possible use of MBD as oxygen carriers. Glycerol batch phase with MBD and conventional sparging is studied at different initial cell densities. Conventional sparging fails to grow the cells and Dissolved Oxygen (DO) levels close to zero suggest high oxygen demands which can not be sustained by conventional sparging. The same batch is run using MBD. Reasonably good growth patterns are observed. DO levels are well above 70% for most of the time during operation. High oxygen demand which can not be sustained by conventional sparging alone can be sustained by MBD. In this way in high den- sity cultures utilization of MBD can be a good alternative to fulfill required oxygen demand in fermentation.