The thesis investigates pipeline plugging mechanisms that have occurred during interim stabilization transfers at Hanford. A laboratory-scale saltwell pumping test loop was designed to evaluate a surrogate of Hanford Tank 241-SX-104 supernate. The effect of surrogate flow rate, cooling water flow rate and phosphate concentrations on plugging mechanisms was investigated. Critical parameters like particle and agglomerate size, velocity and bed growth rate were determined. Theoretical models were used to compare the experimental pressure rise and temperature drop of the surrogate in the channel. An operating region in which a plug would not form was developed, based on the experimental results. Experiments are also reported on plug remediation. Unplugging experiments at varying pump pressure heads and residence time of plug in the line were performed.

No description available.

No description available.

No description available.

This study focuses on deposition processes from sediment laden buoyant river plumes in deltaic regions. The goal is to experimentally examine the effects of various physical phenomena influencing the rate at which sediment is removed from the plume. Previous laboratory and field measurements have suggested that, at times, sedimentation can take place at rates higher than that expected from individual particle settling (i.e., C{W}_{s}). Two potential drivers of enhanced sedimentation are flocculation and interfacial instabilities. We experimentally measured the sediment fluxes from each of these processes using two sets of laboratory experiments that investigate two different modes of instability, one driven by sediment settling and one driven by fluid shear. The settling-driven and shear-driven instability sets of experiments were carried out in a stagnant stratification tank and a stratification flume respectively. In both sets, continuous interface monitoring and concentration measurement were made to observe developments of instabilities and their effects on the removal of sediment. Floc size was measured during the experiments using a separate floc camera setup and image analysis routines. Results from the stratification tank experiments suggest that the settling-driven gravitational instabilities do occur in the presence of flocs, and that they can produce sedimentation rates higher than those predicted from floc settling. A simple cylinder based force balance approach adopting the concept of critical Grashof number was used to develop a model for the effective settling velocity under settling-driven instabilities that is a function of sediment concentration in the plume only. Results from the stratification flume experiments show that under shear instabilities, the effective settling velocity is greater than the floc settling velocity, and increases with plume velocity and interface mixing. The difference between effective and floc settling velocity was denoted as the shear-induced settling velocity. This settling rate was found to be a strong function of the Richardson number, and was attributed to mixing processes at the interface. Conceptual and empirical analysis shows that the shear-induced settling velocity is proportional to U{Ri}^{-2}. Following the experiments, analyses were made among contributions of different mechanisms on the total deposition rate, and the locations that the various mechanisms may be active in the length of a plume. This analysis leads to a conceptual discretization of a plume into three zones of sedimentation behavior and Richardson number. The first zone is the supercritical near-field plume with intense interface mixing. Zone two represents the subcritical region where interface mixing still occurs, and zone three is the high Richardson number zone where mixing at the interface is effectively nonexistent. In zones one and two, individual floc settling and shear-induced settling mechanisms play the major roles in removing sediment from the plume. While, shear-induced settling rate was found to be maximum near the river mouth, its share of the total settling rate increases in the crossshore direction, since sand and large particulates deposit near the inlet and only small particles (with relatively low settling velocity) remain as the plume propagates. The third zone, starts when the interfacial mixing diminishes and leaking commences. / Ph. D.

Settling time is very important for data acquisition systems because it is the primary factor that defines the data rate for a given error level. Therefore settling time measurement is a crucial test. The goal of the project was to design, test and compare different measurement techniques. Three methods were tested to the accuracies of 0.1% and 0.01%. Also simulations were conducted to explain the parameters that affect the settling behavior. Additionally bench measurements were correlated to simulation results. This report is intended as a guide for settling time measurements.

Wax anti-settling additives (WASA) are used to mitigate against the problems caused by the settling of n-alkane wax crystals, which crystallise from petroleum diesel. This can result in the blocking of fuel filters and hence vehicle failure. However, the mode of action for such additives is not currently known and two mechanisms have been proposed: they reduce the wax crystal size to such an extent that they settle very slowly; or they induce gelation in the wax suspension. This project aims to elucidate the mechanism of WASA within the diesel system. A room temperature crystallising model diesel (10 wt% n-alkanes in dodecane) has been developed. This model system has given a good response to the additives, with the wax crystals reduced in size, and is hence suitable for mechanistic studies. Differential scanning calorimetry and infra-red spectroscopy both suggest that the WASA is incorporated in or onto the wax crystal. DSC shows that small amounts of WASA suppress the wax crystallisation temperature and change the shape of the heat flow curve. FT-IR shows the WASA amide stretch present within filtered and dried wax crystals. Intriguingly, electrophoresis experiments show that the WASA imparts a positive charge to the wax crystals, suggesting an electrostatic role in the WASA action. Rheological experiments show the presence of a weak gel in the WASA doped model diesel. However, the gel strength is not altered by the presence of an organic salt and thus cannot be purely electrostatic in origin. Small angle neutron scattering has been conducted to help locate the WASA in the system. It has shown that in solution WASA shows a collapsed polymer coil structure with a single molecule occupying a 28 Å diameter sphere and multiple WASA molecules forming a 2400 Å diameter sphere. In the presence of the wax the WASA scatter does not significantly change suggesting that the WASA is on the surface of the wax crystal. By combining these results, a mechanism of WASA action is proposed as WASA cations interactions bridging between the wax crystals causing a weak bridging flocculation gel with electrostatic and steric effects contributing to stabilisation. The WASA charges are partially dissociated thus giving the electrophoretic effect and the long chains on the cations can contribute to stability via steric stabilisation.

Batch sedimentation is a method that enables us to understand the mechanism of compaction and compression of sedimenting slurry. However, batch settling behaviour is a very complex phenomenon that is not easily described fully by a mathematical model. This causes unrealistically large empirical calculations when the thickener size estimations are required. Channelling, reverse concentration gradients and the initial concentration of the slurry have large effects on batch settling. Existing procedures do not provide clear relationships involving these three significant variables. In this study, batch sedimentation phenomena are examined in detail and possible explanations are given to clarify the complex behaviour using recent theories. Modern research has shown that channelling is an unwanted formation because channels can change the concentration at the bottom and top of the bed by carrying a great amount of flocs upwards. Batch sedimentation tests were performed using flocculated slurry of Calcium Carbonate at various initial concentrations such as 250 g/l, 500 g/l, 750 g/l and 1000 g/l to observe channelling and reverse concentration gradients. Flux plots for the batch system reveal behaviour which can be attributed to the upward flow of solids. In addition, photographic methods were used to observe settling processes, channelling mechanisms and flocs in the channels. One of the purposes of this work was to examine the phenomenological solid-liquid separation theory of Buscall and White (1987), which employs the material properties of the local volume fraction, compressive yield stress Py ()ö and hindered settling function R()ö to identify the material behaviour in batch sedimentation. Stepped-pressure filtration and batch settling tests were used to measure the material characteristics for the flocculated CaCO3 suspension. Experimental data were demonstrated using Height versus Time and Height versus Concentration graphs and displayed the possible region of reverse concentration gradients and channelling in the settling bed. Mathematical predictions adopted from Usher (2002) were performed employing material characteristics of the material and graphical documentations were presented. The results of mathematical predictions were compared to the experimental results and the modes of sedimentation explained by Lester et al. (2005). Fundamental theoretical models and experimental observations highlight that the main driving force for channelling is the high-pressure gradient at the bottom of the bed and the most important factors that cause channelling are high initial concentration of slurry and settling time. The predictions also show that the material and flocculant used for the batch settling tests demonstrate important effect on the settling process. The knowledge and information gained from this study is valuable to maximize the thickening process.

Investigating linkages between the compositions of suspended (seston) and benthic particulate matter is important to the understanding of organic matter (OM) cycling and nutrient retention in aquatic systems. We compared the quantity and quality of the truly suspended (TS) and settleable (SB) fractions of seston as well as benthic particulate matter in the tidal freshwater James River, Virginia. The mass of seston and OM was consistently higher in the TS fraction compared to the SB fraction. OM was preferentially retained in the TS fraction relative to seston. The proportional contribution of OM constituents (chlorophyll a, particulate organic carbon and nitrogen) to the two fractions was consistent across observed concentrations whereas increases in seston concentration resulted in decreased proportions in the TS fraction. Benthic constituent reservoirs were large relative to the SB fraction but the higher proportion of OM in the SB fraction suggests that the settleable material was more labile.

Hydraulic fracturing is a process for the extraction of hydrocarbons from underground formations. It involves pumping a specialized fluid into the wellbore under high pressures to form and support fractures in the rock. Fracturing stimulates the well to increase the production of oil and the natural gas which are the pillars of the energy economy. Key to this process is the use of proppants, which are solid materials used to keep the fractures open. Understanding the transport of proppant particles through a fluid is important to improve the efficiency and reduce environmental impact of fracturing. An increase of the settling velocity for instance, will impede the hydraulic fracturing process by reducing well productivity, or necessitate use of chemical additives. This thesis presents a theoretical investigation of the settling velocity of proppant particles. The effect of different parameters on the settling velocity were studied by manipulating the main factors that can influence particle transport. These include size of the particle (300 μm- 2000 μm), sphericity, density (1200 kg/m3-3500 kg/m3) and concentration. These typical values were obtained from commercially available proppants currently used in industry. Various correlations were investigated, assuming the carrier (fracturing) fluid to be an ideal Newtonian and as a power law (non-Newtonian) fluid. This will help predict the settling velocity for proppant particles in order to increase well productivity, and improve hydraulic fracturing efficiency. The models show that changing the carrier fluid viscosity and particle properties such as diameter, density, sphericity, and concentration leads to a significant change in the proppant settling velocity. For instance, reduction in particle size, density, and sphericity tend to reduce the settling velocity, while increasing the concentration of the particles and the fluid viscosity reduce the settling velocity.