Thesis (M.S.)--Boston University / PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / 2031-01-01

Graduation date: 1995

Pressure drops over a packed bed of pebble bed reactor type are investigated. Measurement of porosity and pressure drop over the bed were carried out in a cylindrical packed bed facility. Air and water were used for working fluids. There are several parameters of the pressure drop in packed beds. One of the most important factors is wall effect. The inhomogeneous porosity distribution in the bed and the additional wetted surface introduced by the wall cause the variation of pressure drop. The importance of the wall effects and porosity can be explained by using different bed-to-particle diameter ratios. Four different bed-to-particle ratios were used in these experiments (D/dp = 19, 9.5, 6.33 and 3.65). A comparison is made between the predictions by a number of empirical correlations including the Ergun equation (1952) and KTA (by the Nuclear Safety Commission of Germany) (1981) in the literature. Analysis of the data indicated the importance of the bed-to-particle size ratios on the pressure drop. The comparison between the present and the existing correlations showed that the pressure drop of large bed-to-particle diameter ratios (D/dp = 19, 9.5and 6.33) matched very well with the original KTA correlation. However the published correlations cannot be expected to predict accurate pressure drop for certain conditions, especially for pebble bed with D/dp (bed-to-particle diameter ratio) </= 5. An improved correlation was obtained for a small bed-to-particle diameter ratio by fitting the coefficients of that equation to experimental database.

In unsteady flows, dune dimensions may vary considerably from fully-developed dimensions produced from a flat bed under a steady and uniform flow. Specifically, dune height and length are observed to lag discharge when the flow is non-steady, resulting in dimensions that are out of phase with the prevailing flow. This research attempts to provide some insight into the behaviour of dunes when the flow is suddenly changed, as well as the time-scale of the related dune changes. Nineteen experimental runs were carried out in the 21-m long, 0.76-m wide Sediment Transport Flume at Queen’s University. In ten of these runs the flow depth, h, was suddenly increased (h2/h1 > 1) and in nine runs the flow depth was suddenly decreased (h2/h1 < 1). In all runs, the slope of free surface was kept equal to the slope of the bed such that the change in flow rate is represented by the change in the flow depth. Seven ratios of the two flow depths, h2/h1 (varying between 0.49 and 2.29), were performed for three slopes (S = 1/792, 1/534, 1/341). The bed material was a coarse, poorly-graded silica sand (D50 = 1.0 mm). Longitudinal bed profiles were taken along the centreline of the flume approximately every 6–8 minutes to determine the transient dune dimensions and the time at which the dunes acquired their new equilibrium dimensions. This time is termed the duration of dune development, Td. Through dimensional and physical considerations, Bielenberg (2006) established that the dimensionless counterpart of Td should be a function of the material number, relative flow depth, relative flow intensity, and ratio of the flow depths h2/h1. The present experiments were carried out to investigate the influence of the relative flow intensity and h2/h1 on the duration of dune development. Results indicate that equilibrium dune dimensions do not depend on the initial shape of the bed. After the period Td, the dunes tend to be similar to those produced from a flat bed. It is found that Td is strongly dependent on h2/h1, and weakly dependent on the flow intensity. All other determining variables remaining the same, Td decreases with increasing values of flow intensity. Semi-empirical relations for the dimensionless duration of dune development are presented. / Thesis (Master, Civil Engineering) -- Queen's University, 2007-09-24 09:45:13.624

Thesis (M.H.A.)--University of Michigan, 1969.

Thesis (M.H.A.)--University of Michigan, 1969.

The Government of Ontario plans to ban the land application of untreated septage; however, most town wastewater treatment plants do not have the capacity to accept septage. A combined reed bed – freezing bed technology has been successfully developed to dewater and treat septage. Lab column studies established that freeze-thaw conditioning can restore drainage in clogged sand drying beds dosed with common biological sludges and that septage can be dosed at 10 cm/week for 2.5-5.0 months before clogging is observed. Pilot studies showed that freezing beds can operate without the need for a cover with the applied sludge effectively melting any snow cover in regions with moderate snowfall. Septage freezing was successfully modelled following an accepted model for ice formation on water bodies while septage thawing was modelled using a regression analysis with initial frozen depth and precipitation found to be insignificant and degree days of warming controlling the rate of thawing. Model results were utilized to produce a freezing bed design loading map for North America based on temperature normals. Field scale planted and unplanted reed bed – freezing bed systems were constructed and tested with varying hydraulic loading rates (1.9-5.9 m/y) and solid loading rates (43-144 kg/m2/y) over a 5 year period resulting in a recommended design hydraulic loading rate of 2.9 m/y or 75 kg/m2/y. Drainage rates doubled after freeze-thaw conditioning compared to during the growing season, suggesting that freeze-thaw conditioning restores filter hydraulic conductivity. No effect of solid loading rate, planted versus unplanted filters and 7 versus 21 d dosing cycles on filter drainage was observed; however, drainage varied significantly with hydraulic loading rate. The filters separated almost all contaminants with filtrate equivalent to a low-strength domestic wastewater which can be easily treated in any municipal or decentralized wastewater system. The dewatered sludge cake had similar nutrient and solid content to a solid dairy manure and met biosolid land application standards in terms of metals and pathogens. The combined reed bed-freezing bed technology can provide a low-cost solution for the treatment and reuse of septage in cold-climate regions.

No description available.

No description available.

No description available.