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Settling Velocity (settling + velocity)

Distribution by Scientific Domains
Chemistry23%
Life Sciences17%

Selected Abstracts

Settling velocity and total ammonia nitrogen leaching from commercial feed and faecal pellets of gilthead seabream (Sparus aurata L. 1758) and seabass (Dicentrarchus labrax L. 1758)

AQUACULTURE RESEARCH, Issue 15 2009
María Asunción Piedecausa
Abstract The physico-chemical characteristics of particulate wastes of Sparus aurata and Dicentrarchus labrax were investigated. Changes in the dimensions, settling velocity and total ammonia nitrogen (TAN) leached from commercial feed pellets were investigated after soaking. Also, the settling velocity and TAN leached from faecal pellets of these fish were assessed at 15 and 25 °C. The settling velocity of feed pellets was influenced positively by pellet weight and negatively by immersion length as a result of changes in pellet dimensions after soaking. The settling velocity of faecal pellets was determined by pellet weight. The experimental design did not allow identification of any consistent effect of water temperature on settling velocity. Total ammonia nitrogen leaching over time from feed and faecal pellets was successfully explained by means of a first-order kinetic equation. For feed pellets, water temperature significantly affected the speed of the process and the time at which the maximum TAN leached was reached, but did not influence the maximum TAN leached. Leaching was related to feed pellet size, and so the smaller the pellet, the higher the leaching. Total ammonia nitrogen leaching from faecal pellets was greater per unit weight than in feed pellets. However, neither water temperature nor fish species influenced TAN leaching from faeces. [source]

Transport and settlement of organic matter in small streams

FRESHWATER BIOLOGY, Issue 2 2010
TRENT M. HOOVER
Summary 1.,After it enters streams, terrestrially derived organic matter (OM) rapidly absorbs water. Using field and laboratory experiments, we examined how this process affected the buoyancy, settling velocity, transport distance and retention locations of four types of organic matter typically found in Pacific coastal streams (,flexible' red alder leaves and three ,stiff' particle types , Douglas-fir needles, red cedar fronds and Douglas-fir branch pieces). 2.,Immersion in water rapidly changed the physical characteristics of alder leaves, Douglas-fir needles and red cedar fronds, which all reached constant still-water settling velocities after only a few days of soaking. In contrast, the settling velocity of branch pieces continued to increase for 13 days, eventually reaching much higher values than any other OM type. Dried alder leaves became negatively buoyant after only two days of immersion, while other types took substantially longer (up to 24 days) before the specific gravity of all particles was >1. 3.,We released saturated OM particles in an experimental channel and found that all particle types travelled further in a fast, shallow ,riffle' than a slow, deep ,pool'. Comparisons with a passive settlement null model indicated that leaves were retained more rapidly than expected in the riffle (by large protruding stones), while the three stiff particle types travelled further than expected (probably due to turbulent suspension) and were retained when they settled in deeper water between larger stones. In pools, passive settlement appeared to dominate the retention of all OM types, with leaves travelling furthest. 4.,These retention patterns corresponded well with those observed when saturated OM particles collected in the field were released in two pools and two riffles in a second-order coastal stream. 5.,When the experimental channel and in-stream data were combined, the retention rates of the three stiff OM types were closely related to calculated Rouse numbers (Rouse number = particle settling velocity/shear velocity), whereas the retention rate of alder leaves was not. This suggests that different physical mechanisms are responsible for the retention of leaves and stiff OM types in shallow streams. [source]

Evaluation of a laser-assisted particle sizing/settling velocity determination technique

HYDROLOGICAL PROCESSES, Issue 9 2006
Dr I. G. Droppo
Abstract The use of predictive models for the understanding and management of sediment and contaminant transport generally requires knowledge of particle size and settling velocity. Particle size is often obtained by direct measurements, and the settling velocities are usually predicted using the Stokes' law (or a modification thereof) for single-grained spherical particles. Such measurements and estimates are not satisfactory measures for cohesive sediments, which exist as agglomerated particles called flocs and whose behaviour is significantly different from that of the single-grained particles. Direct measurement of settling velocity and size using optical methods in settling columns has also been employed to improve these predictions; however, the subjectivity in determining which particles are in focus results in unreliable size data. An out-of-focus particle will generally possess a larger size than in reality. This paper evaluates a laser-assisted particle sizing/settling velocity determination technique's ability to eliminate the subjectivity and improve particle-sizing accuracy during settling column experiments. Although the diffraction of light by the translucent standard beads (used for evaluating the technique's accuracy for determining particle size) posed a problem, the results suggest that this technique has potential for assisting researchers to obtain the most accurate settling particle size data possible. Copyright © 2005 John Wiley & Sons, Ltd. [source]

FOAM, a new simple benthic degradative module for the LAMP3D model: an application to a Mediterranean fish farm

AQUACULTURE RESEARCH, Issue 11 2008
Patrizia De Gaetano
Abstract The modelling framework already introduced by Doglioli, Magaldi, Vezzulli and Tucci to predict the potential impact of a marine fish farm is improved following different directions, namely (1) real historic current-metre data are used to force the simulations, (2) settling velocity values specifically targeting Mediterranean fish species are used, and (3) a new benthic degradative module, the Finite Organic Accumulation Module, is added to the modelling framework. The Finite Organic Accumulation Module uses the output of the other functional units of the modelling framework to calculate the organic load on the seabed. The Finite Organic Accumulation Module considers the natural capability of the seafloor in absorbing part of the organic load. Different remineralization rates reflect the sediment stress level according to the work of Findlay and Watling. Organic degradation for both uneaten feed and faeces is evaluated by changing the release modality (continuous and periodical) and by varying the settling velocities. It is found that the maximum impact on the benthic community is observed either for quickly sinking uneaten feed released twice a day, or for less intense near-bottom current conditions. If both the above-mentioned scenarios coexist, a high stress level is established in the sediment. The model also suggests that the use of self-feeders in cages can reduce farm impacts significantly. These results show how the new and more complete modelling framework presented here is able to improve the objectivity in the decision-making processes and how it may be successfully used for planning and monitoring purposes. [source]

Determination of physical behaviour of feed pellets in Mediterranean water

AQUACULTURE RESEARCH, Issue 2 2006
Paolo Vassallo
Abstract Settled uneaten feed causes the most intense impact under sea cages, and settling velocity of the feed pellets represents a key parameter for waste dispersion models. Even if some data about physical properties of feed pellets have been published in the framework of salmonid rearing, there is a complete lack of information related to the Mediterranean Sea, as regards typical values of temperature, salinity and feed composition for Gilthead Sea Bream (Sparus aurata L.) and Sea Bass (Dicentrarchus labrax L.). In this study we try to fill this lack, determining dimensions, water adsorption properties, floating times and settling velocities of a typical growing sequence of pellets for the species mentioned above, under defined laboratory conditions reproducing Mediterranean Sea water. The settling velocity increases with pellet size from 0.087, for the smallest pellet (3 mm), to 0.144 m s,1, for the 5 mm pellet. The biggest extruded pellet (6 mm) falls slower (0.088 m s,1). The floating time before pellet's fall is found to be a critical parameter in determining settling velocity. The latter depends on pellet's size, water temperature and salinity. The examined pellets reach a 42% of weight increase after 10 min of immersion, while no appreciable dimension change is observed. Our results are in part different from previous ones and could play a role in evaluating and modelling Mediterranean aquaculture environmental impact. [source]

A study of the Coriolis effect on the fluid flow profile in a centrifugal bioreactor

BIOTECHNOLOGY PROGRESS, Issue 4 2009
Christopher J. Detzel
Abstract Increasing demand for tissues, proteins, and antibodies derived from cell culture is necessitating the development and implementation of high cell density bioreactors. A system for studying high density culture is the centrifugal bioreactor (CCBR), which retains cells by increasing settling velocities through system rotation, thereby eliminating diffusional limitations associated with mechanical cell retention devices. This article focuses on the fluid mechanics of the CCBR system by considering Coriolis effects. Such considerations for centrifugal bioprocessing have heretofore been ignored; therefore, a simpler analysis of an empty chamber will be performed. Comparisons are made between numerical simulations and bromophenol blue dye injection experiments. For the non-rotating bioreactor with an inlet velocity of 4.3 cm/s, both the numerical and experimental results show the formation of a teardrop shaped plume of dye following streamlines through the reactor. However, as the reactor is rotated, the simulation predicts the development of vortices and a flow profile dominated by Coriolis forces resulting in the majority of flow up the leading wall of the reactor as dye initially enters the chamber, results are confirmed by experimental observations. As the reactor continues to fill with dye, the simulation predicts dye movement up both walls while experimental observations show the reactor fills with dye from the exit to the inlet. Differences between the simulation and experimental observations can be explained by excessive diffusion required for simulation convergence, and a slight density difference between dyed and un-dyed solutions. Implications of the results on practical bioreactor use are also discussed. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009 [source]

Transport and settlement of organic matter in small streams

FRESHWATER BIOLOGY, Issue 2 2010
TRENT M. HOOVER
Summary 1.,After it enters streams, terrestrially derived organic matter (OM) rapidly absorbs water. Using field and laboratory experiments, we examined how this process affected the buoyancy, settling velocity, transport distance and retention locations of four types of organic matter typically found in Pacific coastal streams (,flexible' red alder leaves and three ,stiff' particle types , Douglas-fir needles, red cedar fronds and Douglas-fir branch pieces). 2.,Immersion in water rapidly changed the physical characteristics of alder leaves, Douglas-fir needles and red cedar fronds, which all reached constant still-water settling velocities after only a few days of soaking. In contrast, the settling velocity of branch pieces continued to increase for 13 days, eventually reaching much higher values than any other OM type. Dried alder leaves became negatively buoyant after only two days of immersion, while other types took substantially longer (up to 24 days) before the specific gravity of all particles was >1. 3.,We released saturated OM particles in an experimental channel and found that all particle types travelled further in a fast, shallow ,riffle' than a slow, deep ,pool'. Comparisons with a passive settlement null model indicated that leaves were retained more rapidly than expected in the riffle (by large protruding stones), while the three stiff particle types travelled further than expected (probably due to turbulent suspension) and were retained when they settled in deeper water between larger stones. In pools, passive settlement appeared to dominate the retention of all OM types, with leaves travelling furthest. 4.,These retention patterns corresponded well with those observed when saturated OM particles collected in the field were released in two pools and two riffles in a second-order coastal stream. 5.,When the experimental channel and in-stream data were combined, the retention rates of the three stiff OM types were closely related to calculated Rouse numbers (Rouse number = particle settling velocity/shear velocity), whereas the retention rate of alder leaves was not. This suggests that different physical mechanisms are responsible for the retention of leaves and stiff OM types in shallow streams. [source]

Evaluation of a laser-assisted particle sizing/settling velocity determination technique

HYDROLOGICAL PROCESSES, Issue 9 2006
Dr I. G. Droppo
Abstract The use of predictive models for the understanding and management of sediment and contaminant transport generally requires knowledge of particle size and settling velocity. Particle size is often obtained by direct measurements, and the settling velocities are usually predicted using the Stokes' law (or a modification thereof) for single-grained spherical particles. Such measurements and estimates are not satisfactory measures for cohesive sediments, which exist as agglomerated particles called flocs and whose behaviour is significantly different from that of the single-grained particles. Direct measurement of settling velocity and size using optical methods in settling columns has also been employed to improve these predictions; however, the subjectivity in determining which particles are in focus results in unreliable size data. An out-of-focus particle will generally possess a larger size than in reality. This paper evaluates a laser-assisted particle sizing/settling velocity determination technique's ability to eliminate the subjectivity and improve particle-sizing accuracy during settling column experiments. Although the diffraction of light by the translucent standard beads (used for evaluating the technique's accuracy for determining particle size) posed a problem, the results suggest that this technique has potential for assisting researchers to obtain the most accurate settling particle size data possible. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Terminal settling velocity and drag coefficient of biofilm-coated particles at high Reynolds numbers

AICHE JOURNAL, Issue 10 2010
Mehran Andalib
Abstract The drag force (Fd) on bio-coated particles taken from two laboratory-scale liquid,solid circulating fluidized bed bioreactors (LSCFBBR) was studied. The terminal velocities (ut) and Reynolds numbers (Ret) of particles observed were higher than reported in the literature. Literature equations for determining ut were found inadequate to predict drag coefficient (Cd) in Ret > 130. A new equation for determining Fd as an explicit function of terminal settling velocity was generated based on Archimedes numbers (Ar) of the biofilm-coated particle. The proposed equation adequately predicted the terminal settling velocity of other literature data at lower Ret of less than 130, with an accuracy >85%. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source]

Effects of Ammonium Chloride on the Rheological Properties and Sedimentation Behavior of Aqueous Silica Suspensions

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2000
J. Jiyou Guo
The influence of ammonium chloride (NH4Cl) on the rheological properties and sedimentation behavior of aqueous silica (SiO2) suspensions of varying solids volume fraction (,s) was studied. SiO2 suspensions with low NH4Cl concentration (,0.05M, pH 5.2) exhibited Newtonian behavior and a constant settling velocity (U). The volume fraction dependence was well described by the Richardson,Zaki form, U=U0(1 ,,s)n, where n= 4.63 and U0= 1.0419 × 10,5 cm/s. At higher NH4Cl concentrations (0.07,2.0M, pH 5.2), suspensions exhibited shear thinning and more complicated sedimentation behavior due to their aggregated nature. For all suspensions studied, however, the apparent suspension viscosity, characteristic cluster size, and initial settling velocity were greatest at ,0.5M NH4Cl and exhibited a similar dependence on salt concentration. Above 0.5M NH4Cl, considerable restabilization was observed. This behavior cannot be explained by traditional DLVO theory. [source]

Settling velocity and total ammonia nitrogen leaching from commercial feed and faecal pellets of gilthead seabream (Sparus aurata L. 1758) and seabass (Dicentrarchus labrax L. 1758)

AQUACULTURE RESEARCH, Issue 15 2009
María Asunción Piedecausa
Abstract The physico-chemical characteristics of particulate wastes of Sparus aurata and Dicentrarchus labrax were investigated. Changes in the dimensions, settling velocity and total ammonia nitrogen (TAN) leached from commercial feed pellets were investigated after soaking. Also, the settling velocity and TAN leached from faecal pellets of these fish were assessed at 15 and 25 °C. The settling velocity of feed pellets was influenced positively by pellet weight and negatively by immersion length as a result of changes in pellet dimensions after soaking. The settling velocity of faecal pellets was determined by pellet weight. The experimental design did not allow identification of any consistent effect of water temperature on settling velocity. Total ammonia nitrogen leaching over time from feed and faecal pellets was successfully explained by means of a first-order kinetic equation. For feed pellets, water temperature significantly affected the speed of the process and the time at which the maximum TAN leached was reached, but did not influence the maximum TAN leached. Leaching was related to feed pellet size, and so the smaller the pellet, the higher the leaching. Total ammonia nitrogen leaching from faecal pellets was greater per unit weight than in feed pellets. However, neither water temperature nor fish species influenced TAN leaching from faeces. [source]

A review of the biophysical properties of salmonid faeces: implications for aquaculture waste dispersal models and integrated multi-trophic aquaculture

AQUACULTURE RESEARCH, Issue 3 2009
G K Reid
Abstract Knowledge of the quantitative and qualitative properties of salmonid faeces is necessary for aquaculture waste dispersal models, and the design of integrated multi-trophic aquaculture (IMTA) systems. The amount and proximate composition of salmonid faeces can be estimated using a mass-balance, nutritional approach. Indigestible components of salmonid diets have the potential to affect faecal ,cohesiveness' or ,stability'. Nutrient content and density of faeces can vary depending on diet and submersion time. Faecal density has a greater influence on settling velocity than faecal size. Published settling velocity data on salmonid faeces are highly variable due to differences in fish size, rearing systems, collection time, water density, methodology, the mass fraction tested and diet. Most faecal settling data used in published salmonid waste dispersal models are rudimentary and recent information suggests that such models are highly sensitive to this input. The design of open-water IMTA systems and estimation of nutrient capture and recovery from co-cultured filter feeders is difficult due to limited information on particle size, digestibility, settleable and non-settleable mass fractions of salmonid faeces at cage environments. Implications of faecal properties on the accountability for the effects of aquaculture nutrient loading are discussed. [source]

FOAM, a new simple benthic degradative module for the LAMP3D model: an application to a Mediterranean fish farm

AQUACULTURE RESEARCH, Issue 11 2008
Patrizia De Gaetano
Abstract The modelling framework already introduced by Doglioli, Magaldi, Vezzulli and Tucci to predict the potential impact of a marine fish farm is improved following different directions, namely (1) real historic current-metre data are used to force the simulations, (2) settling velocity values specifically targeting Mediterranean fish species are used, and (3) a new benthic degradative module, the Finite Organic Accumulation Module, is added to the modelling framework. The Finite Organic Accumulation Module uses the output of the other functional units of the modelling framework to calculate the organic load on the seabed. The Finite Organic Accumulation Module considers the natural capability of the seafloor in absorbing part of the organic load. Different remineralization rates reflect the sediment stress level according to the work of Findlay and Watling. Organic degradation for both uneaten feed and faeces is evaluated by changing the release modality (continuous and periodical) and by varying the settling velocities. It is found that the maximum impact on the benthic community is observed either for quickly sinking uneaten feed released twice a day, or for less intense near-bottom current conditions. If both the above-mentioned scenarios coexist, a high stress level is established in the sediment. The model also suggests that the use of self-feeders in cages can reduce farm impacts significantly. These results show how the new and more complete modelling framework presented here is able to improve the objectivity in the decision-making processes and how it may be successfully used for planning and monitoring purposes. [source]

Determination of physical behaviour of feed pellets in Mediterranean water

AQUACULTURE RESEARCH, Issue 2 2006
Paolo Vassallo
Abstract Settled uneaten feed causes the most intense impact under sea cages, and settling velocity of the feed pellets represents a key parameter for waste dispersion models. Even if some data about physical properties of feed pellets have been published in the framework of salmonid rearing, there is a complete lack of information related to the Mediterranean Sea, as regards typical values of temperature, salinity and feed composition for Gilthead Sea Bream (Sparus aurata L.) and Sea Bass (Dicentrarchus labrax L.). In this study we try to fill this lack, determining dimensions, water adsorption properties, floating times and settling velocities of a typical growing sequence of pellets for the species mentioned above, under defined laboratory conditions reproducing Mediterranean Sea water. The settling velocity increases with pellet size from 0.087, for the smallest pellet (3 mm), to 0.144 m s,1, for the 5 mm pellet. The biggest extruded pellet (6 mm) falls slower (0.088 m s,1). The floating time before pellet's fall is found to be a critical parameter in determining settling velocity. The latter depends on pellet's size, water temperature and salinity. The examined pellets reach a 42% of weight increase after 10 min of immersion, while no appreciable dimension change is observed. Our results are in part different from previous ones and could play a role in evaluating and modelling Mediterranean aquaculture environmental impact. [source]

Improvement in biomass characteristics and degradation efficiency in modified UASB reactor treating municipal sewage: a comparative study with UASB reactor

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2009
Suprotim Das
Abstract Low strength wastewaters (LSWs) are difficult to degrade efficiently in the upflow anaerobic sludge blanket (UASB) reactor. The possible reasons for poor treatment of LSWs in UASB are: (i) low mixing due to low biogas production (ii) frequent biomass washout at higher hydraulic loading rate due to low settleability of biomass. In the present study, lab scale UASB reactor and modified upflow anaerobic sludge blanket (MUASB) reactor were operated with municipal sewage containing chemical oxygen demand (COD) in range of 180,210 mg L,1 as LSW at three different hydraulic retention times (HRTs) of 8, 6, and 4 h. The changes in the biomass characteristics as well as degradation efficiency were compared with respect to time. During this operation, samples of biomass were taken from both reactors to measure total suspended solids (TSS), settling velocity, granular size and specific methanogenic activity (SMA). The overall COD removal in MUASB reactor was higher compared to UASB (84 and 67% respectively). After 150 days of operation, the settling velocity and SMA of MUASB biomass increased, but no significant change in settling velocity and SMA of UASB biomass was observed. The study shows that MUASB could be preferred over UASB for the treatment of municipal sewage as LSW. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source]

Experimental Results and Models for Solid/Liquid Fluidized Beds Involving Newtonian and Non-Newtonian Liquids

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2004
M. Aghajani
Fluidization technology relies almost solely on fluid/particle interaction wherein the liquid phase may exhibit Newtonian or non-Newtonian behavior. The steady motion of particles and the velocity-voidage relationship are the most important design parameters for fluidization, providing the basis for the prediction of heat and mass transfer coefficients and information on hydrodynamic conditions. A summary of the literature on particle settling velocity, minimum fluidization velocity and velocity voidage relationship is supplemented by new experimental results, which extend the range of investigated solid and liquid phase physical properties. Correlations for particle settling velocity and velocity-voidage relationship are developed and verified against experimental data. [source]