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Turbulent Conditions (turbulent + condition)
Selected AbstractsExperimental Study and Design of a Submerged Membrane Distillation BioreactorCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 1 2009J. Phattaranawik Abstract A hybrid process incorporating membrane distillation in a submerged membrane bioreactor operated at elevated temperature is developed and experimentally demonstrated in this article. Since organic particles are rejected by an ,evaporation' mechanism, the retention time of non-volatile soluble and small organics in the submerged membrane distillation bioreactor (MDBR) is independent of the hydraulic retention time (mainly water and volatiles). A high permeate quality can be obtained in the one-step compact process. The submerged MD modules were designed for both flat-sheet membranes and tubular membrane configurations. The process performance was preliminarily evaluated by the permeate flux stabilities. The module configuration design and air sparging used in the MDBR process were tested. Flux declines were observed for the thin flat-sheet hydrophobic membranes. Tubular membrane modules provided more stable permeate fluxes probably due to the turbulent condition generated from air sparging injected inside the tubular membrane bundles. The experiments with the submerged tubular MD module gave stable fluxes of approximately 5,L/m2 h over 2,weeks at a bioreactor temperature of 56,°C. The total organic carbon in the permeate was consistently lower than 0.7,mg/L for all experiments. [source] Ilim Pulp, blending former Russian state enterprises, creates a corporate university to change culture, become an industry leaderGLOBAL BUSINESS AND ORGANIZATIONAL EXCELLENCE, Issue 5 2010Marina O. Latuha This article describes the establishment of a corporate university in a Russian company. Following the economic restructuring of the country, training and personnel development became vital ingredients in the company's long-term strategy. In these turbulent conditions, the company realized that it needed to have the training and personnel development characterized by continuity on the one hand and revolutionary changes in organizational culture on the other. If this could be achieved, it would encourage entrepreneurship, innovation, and change in the internal processes of the organization. The case describes the stages, programs, and basic components of the corporate university model. It not only illustrates the basic issues in the application of corporate training theory, but also analyzes the risks and problems for the company in the project's realization. The article concludes with a description of how the corporate university developed after its initiation, and some conclusions about the overall success of the project. © 2010 Wiley Periodicals, Inc. [source] Climatic effects on the phenology of lake processesGLOBAL CHANGE BIOLOGY, Issue 11 2004Monika Winder Abstract Populations living in seasonal environments are exposed to systematic changes in physical conditions that restrict the growth and reproduction of many species to only a short time window of the annual cycle. Several studies have shown that climate changes over the latter part of the 20th century affected the phenology and population dynamics of single species. However, the key limitation to forecasting the effects of changing climate on ecosystems lies in understanding how it will affect interactions among species. We investigated the effects of climatic and biotic drivers on physical and biological lake processes, using a historical dataset of 40 years from Lake Washington, USA, and dynamic time-series models to explain changes in the phenological patterns among physical and biological components of pelagic ecosystems. Long-term climate warming and variability because of large-scale climatic patterns like Pacific decadal oscillation (PDO) and El Niño,southern oscillation (ENSO) extended the duration of the stratification period by 25 days over the last 40 years. This change was due mainly to earlier spring stratification (16 days) and less to later stratification termination in fall (9 days). The phytoplankton spring bloom advanced roughly in parallel to stratification onset and in 2002 it occurred about 19 days earlier than it did in 1962, indicating the tight connection of spring phytoplankton growth to turbulent conditions. In contrast, the timing of the clear-water phase showed high variability and was mainly driven by biotic factors. Among the zooplankton species, the timing of spring peaks in the rotifer Keratella advanced strongly, whereas Leptodiaptomus and Daphnia showed slight or no changes. These changes have generated a growing time lag between the spring phytoplankton peak and zooplankton peak, which can be especially critical for the cladoceran Daphnia. Water temperature, PDO, and food availability affected the timing of the spring peak in zooplankton. Overall, the impact of PDO on the phenological processes were stronger compared with ENSO. Our results highlight that climate affects physical and biological processes differently, which can interrupt energy flow among trophic levels, making ecosystem responses to climate change difficult to forecast. [source] Turbulent Flow Through Porous MediaGROUND WATER, Issue 5 2001Douglas W. Barr The pressure driving flow through porous media must be equal to the viscous resistance plus the inertial resistance. Formulas are developed for both the viscous resistance and the inertial resistance. The expression for the coefficient of permeability consists of parameters which describe the characteristics of the porous medium and the permeating fluid and which, for unconsolidated isotropic granular media, are all measurable. A procedure is proposed for testing for the occurrence of turbulence and calculating the effective permeability when it occurs. The formulas are applied to a set of data from 588 permeameter runs ranging from laminar to highly turbulent. The equations fit the data from the permeameter closely through the laminar flow conditions and quite closely through the turbulent conditions. In the turbulent range, the plotting of the data separates into three distinct lines for each of the three shapes of particles used in the tests. For the porous medium and fluid of these tests, turbulence begins at a head gradient of about 0.1. [source] Effect of flow field heterogeneity in coagulators on aggregate size and structureAICHE JOURNAL, Issue 10 2010Lyonel Ehrl Abstract Aggregate size and structure were investigated under turbulent conditions in stirred tank (ST) and Taylor,Couette-type (TC-type) devices. Root-mean-square radius of gyration, ,Rg,, and zero-angle intensity of scattered light, I(0), were acquired as a function of stirring intensity, characterized by an experimentally obtained average hydrodynamic stress, ,,,exp, determined by torque measurements. Evaluating aggregate images revealed that aggregate structure and shape are independent of the device type. However, in TC-type devices, the aggregates grow to three to four times larger sizes than inside ST, although the same ,,,exp was used in both coagulators. As confirmed by computational fluid dynamics, this can be attributed to the differences in the maximum hydrodynamic stress in ST compared with those in TC-type devices. In contrast, the power-law scaling of ,Rg, and I(0) with ,,,exp is preserved for all investigated devices, with an exponent approximately equal to ,0.5 and ,0.7, respectively. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source] Dependence of initial cluster aggregation kinetics on shear rate for particles of different sizes under turbulenceAICHE JOURNAL, Issue 12 2009Lyonel Ehrl Abstract Initial aggregation kinetics for three particle sizes and broad range of Péclet numbers were investigated under turbulent conditions in stirred tank. This allowed us to observe the transition from diffusion-controlled to purely shear-induced aggregation. The evolution of the root-mean-square radius of gyration, zero-angle intensity of scattered light, and obscuration was obtained by small-angle static light scattering. For a given particle size the measured evolution of all integral quantities obtained for various volume average shear rates ,G,, scales with a dimensionless time, ,exp = ,exp × ,G, × , × t. The experimentally obtained aggregation efficiency ,exp, follows the power law ,exp = Pe,n, where Pe is the primary particle Péclet number. With increasing particle size a decrease in n is observed in accordance with theory and literature data. As previously predicted by population balance equation simulations three aggregation regimes were observed experimentally. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] | ||||||||||