Effect of turbulent environments on the structure and stability of flocs based on experiments and CFD-DEM simulation

The influence of protruding filamentous bacteria on floc stability and solid-liquid separation in the activated sludge process

Floc size variability under strong turbulence: Observations and artificial neural network modeling

Flotation cell and flotation column are widely used as the separation equipment for coal slime. In order to obtain better flotation results for different particle sizes, different turbulence intensity of flow field need to be created, but the turbulence intensity is not easy to adjust in conventional flotation equipment. In this paper, a new fluidized bed flotation column was designed to control turbulence intensity by the liquid velocity and static bed height. The effects of liquid velocities (0.198 m/s,0.226 m/s,0.254 m/s) and static bed heights (0.317 m,0.343 m,0.380 m) on coal slime flotation with different particle sizes were studied, which were evaluated by the combustible recovery, ash content, and the yield of clean coal. The research results showed that the flotation performance of coarse particles is better with low turbulence caused by low liquid velocity and great static bed height than that in high turbulence. Under the condition of high liquid velocity and low bed height, a high turbulence intensity environment is created, and the fine particle separation efficiency is better than that in low turbulence.

Influence of extracellular polymeric substances (EPS) treated by combined ultrasound pretreatment and chemical re-flocculation on water treatment sludge settling performance

This paper presents the effect of the structure of cationic polyacrylamides (CPAMs) on flocculation of pulp suspensions and floc properties. A focused beam reflectance measurement (FBRM) probe was used to monitor flocculation, deflocculation, and reflocculation processes in real time. To carry out the study, 1% elemental chlorine free (ECF) eucalyptus kraft pulp containing 20% ground calcium carbonate (GCC) was used. Results show that the effect of the CPAM structure depends on charge density and polymer dose. Floc size does not always decrease with branching degree, whereas floc stability and reflocculation ability increased when highly charged and branched CPAM was used. These findings indicate that the use of highly branched CPAMs with very high molecular weight is very promising as a retention aid method to improve the papermaking process.

A universal math model has been developed for the irradiance fluctuations of an optical beam propagating through atmospheric turbulence. This new model was developed under the assumption that the field irradiance consists of two principal components, each of which has an amplitude that is m distributed. By comparing this model with our own experimental data, as well as comparable data of other researchers, we found both qualitative and quan­ titative agreement over all ranges tested and strengths of turbulence. The statistics used in making these comparisons were the first five normalized moments of the bearr intensity. Our own data were obtained over a very homogeneous environment with ranges from 180 m to 3 km. The data so obtained correspond to many conditions of turbulence, from weak where lognormal statistics are ordinarily valid, to superstrong turbulence where negative expo­ nential statistics exist in the limit. In the weak turbulence regime we found that the data support the lognormal and universal model, which both predict essentially the same re­ sults. For conditions of moderate to strong turbulence, both the K distribution and the universal model match the data. However, for very strong turbulence prior to the limiting form of the negative exponential distribution, only our universal model matched the data. One of the interesting observations that we made in our data was that the normalized mo­ ments follow a looped path in the vicinity of their maximum values when they are plotted as functions of the normalized second moment. None of the standard theoretical models (i.e., lognormal, K, and negative exponential distributions) predict this looping effect since they are only two-parameter models whereas our universal model is a three-parameter model.IntroductionIt is widely known that the propagation of an optical beam through clear-air turbulence will result in fluctuations of the beam intensity, commonly called irradiance fluctuations. These fluctuations are due almost exclusively to atmospheric temperature variations caused by heating of the earth's surface. Over the years there have been numerous experimental and theoretical investigations into the phenomenon of irradiance fluctuations,1 '18 irost of which have been directed at the statistics associated with the phenomenon. There is an abundance of experimental evidence that validates the Tatarskii theory, or lognormal model, for both the amplitude and intensity of the beam under conditions of weak turbulence.1 > 2 » u » 7 > 12 For conditions of moderate turbulence the K distribution matches much of the experi­ mental data,7 * 8 ' 12 and in the regime of super saturation the theoretically predicted nega­ tive exponential distribution is now widely accepted.1215 Unfortunately, none of these standard distributions universally fit all the available data on intensity fluctuations.During March and August, 1980, experimental data on the statistics of optical beam in­ tensity fluctuations were gathered over various path lengths up to 3 km. The propagation experiments were carried out at the Kennedy Space Center Space Shuttle Landing Facility, a concrete runway 4.9 km long and 90 m wide. The runway is extremely level and the edges totally clear of all structures and vegetation (except grass) for distances up to several hundred meters. These conditions made for a near-perfect test site ensuring homogeneous conditions the full length of the runway. The refractive-index-structure parameter C£ varied by several orders of magnitude, from 1014 in2/3 to 2 x 1010 nT2/3. These values correspond to many different conditions of turbulence -- from very weak to superstrong into the saturation regime. Such a wide range of data over various conditions of turbulence and path lengths gave us new insight into the phenomenon of irradiance fluctuations.In this paper we discuss the experiments conducted at the Kennedy Space Center as well as a universal math model that we developed that is seemingly applicable to all conditions of turbulence for which data is available. This universal model has characteristics of the lognormal distribution in the regime of weak turbulence, characteristics of the K distribu­ tion in the regime of moderate turbulence, and asymptotically approaches the limiting nega­ tive exponential distribution in the deep saturation regime.

Environmental turbulence refers to the unpredictable changes, developments, and uncertainties in a firm’s external environment. Environmental turbulence consists of market turbulence, technological turbulence, and competition intensity. It causes a shortening of firms’ product life cycles, changes in customer demands, and rapid technological developments. Companies do not control the changes in their external environment. In addition, they cannot manage change by using traditional methods where environmental factors are constantly changing. Thus, environmental turbulence and strategic plans might be reconsidered in today’s business world. This article examines the intensity of environmental turbulence from the strategic agility and innovativeness perspective. The study was conducted using data from Turkey, including medium-high or high technology firms that were located in a technopark or had an R&D center. The survey method was used to collect data for the study and the SPSS Process macro was used to analyze the effects of moderator variables on the relationship between strategic agility and firm innovativeness. Findings indicate that strategic agility positively affects firm innovativeness and that this effect might decrease due to increases in turbulence intensity. Moreover, firm innovativeness positively affects performance, and this effect becomes more robust with increases in turbulence intensity. This study provides practical implications for companies and researchers depending on environmental turbulence diversity.

We compared morphometry and total swimming costs of wild, farmed (first-generation hatchery progeny of wild progenitors) and domesticated (seventh-generation progeny of the Norwegian aquaculture strain) juvenile Atlantic salmon (Salmo salar). Respirometry experiments were performed to assess total swimming costs of fish ranging in size from 4.0 to 16.1 g wet mass at a water temperature of 15 °C. Fish were subjected to flow conditions of low and high turbulence. Total swimming costs increased significantly with intensity of turbulence and were, on average, 1.4 times higher at high than at low turbulence. Total swimming costs were 2.4- to 4.0-fold higher than predicted by forced swimming models developed under conditions that minimize flow heterogeneity. Total swimming costs of wild and farmed fish were not statistically different (average difference = 6.7%). Hence, swimming costs models developed using farmed fish may be used to estimate swimming costs of wild fish. However, domesticated fish had total swimming costs 12.0% to 29.2% higher than farmed or wild fish. This may be related to domesticated fish having deeper bodies and smaller fins.

3D characterisation of a large high rate algal pond for wastewater treatment

Conditions for maximizing chemical and mechanical filler retention were studied through a combination of laboratory, semi-pilot and pilot scale experiments. In the first part of this work, we investigated the impact of particle size on the mechanical retention of particles in a fibre network using a modified laboratory hand sheet former. Quartz particles of well-defined and narrow-size fractions were used to simulate pre-flocculated filler of different sizes. Five different size fractions were studied. The mechanical retention was found to increase linearly with both web fibre grammage for each quartz fraction and with particle size. These results were then validated through pilot- scale production trials where different filler floc sizes were created through pre-flocculation techniques. In the second part of this work, we studied the stability of pre-flocculated filler flocs through a set of semi-pilot scale ow loop trials. Trials were performed by pre-flocculating filler (PCC) with flocculating agents continuously and exposing the filler flocs to controlled levels of hydrodynamic shear created by ow through a partially closed gate valve. Changes in filler floc size were monitored continuously using Focused Beam Reflectance Measurements (FBRM). A clear reduction in the particle size was observed as the pressure drop increased. A major part of the floc degradation occurred at relatively low shear conditions while under the highest shear conditions, the pre-flocculated PCC floc size was reduced close to the unflocculated state. In the third part of this work, we investigated the effect of different forms of process related shear on retention polymer stability and its effect on chemical retention. A set of semi-pilot scale ow loop trials were performed to investigate the effect of elongational shear-strain and shear due to velocity differences created inside and outside a dosage nozzle respectively. We show that the effect of elongational strain created inside the dosage nozzle leads to significant retention polymer degradation while shear created outside the dosage nozzle due to velocity gradients has a smaller effect on polymer degradation. We investigate these results with a series of pilot scale production trials and show that high shear conditions created inside the dosage nozzle leads to significant reductions in chemical filler retention. However, pilot trials indicate that shear created outside the dosage nozzle can also have a significant effect on filler retention, although to a lesser extent.

Stability of particle flocs upon addition of natural organic matter under quiescent conditions

Pre-flocculation is a technique that aggregates filler particles by means of polyelectrolytes. The size of the filler flocs is a critical factor affecting the properties of the paper. Process variables including the concentration of the flocculants, the stirring speed, and the dilution of the suspension change the size of the flocculated fillers. Ground calcium carbonate and cationic polyacrylamide were used to investigate the influence of these variables on flocculation. The median particle size and size distribution were examined and the tensile and optical properties influenced by the floc size and ash levels were evaluated. The addition of high concentration C-PAM increased the median particle size. Stirring speeds in the range of 1000 ~ 3000 rpm were used to simulate various turbulent environments, and it was shown that high stirring speeds drastically decreased the floc size. Diluting and low speed stirring the flocculated GCC suspension was effective in keeping the particle size intact without disruption before sheet forming. Larger GCC flocs in the handsheets resulted in better mechanical properties.

The present studies address feeding of plankton in turbulent environments, discussed by a comparison of analytical results and field data. Various models for predator-prey encounters and capture probabilities are reviewed. Generalized forms for encounter rates and capture probabilities in turbulent environments are proposed. The analysis emphasizes ambush predators, exemplified by cod larvae Gadus morhua L. in the start-feeding phase (stage 7 larvae) collected in shallow waters near Lofoten, Norway. During this campaign, data were obtained at four sites with strongly turbulent conditions induced by tidal currents and long-wave swells, and one site where the turbulence had a lower level in comparison. The guts of the selected cod larvae were examined in order to determine the number of nauplii ingested. Analytically obtained probability densities for the gut content were compared with observations and the results used for estimating the rate of capture of the nauplii. This capture rate was then compared with analytical results using also data for the surroundings, such as measured prey densities and turbulence conditions, as quantified by the specific energy dissipation rate. Different from earlier studies, the presented data include conditions where the turbulence exceeds the level for optimal larval encounter-capture rates.

Effect of background turbulent field on ion current characteristics of methane-air premixed combustion

The performance of free space optical (FSO) links in a clear atmosphere is affected by the non-ideal characteristics of the communication channel. Atmospheric turbulence causes fluctuations in the received signal level, which increase the bit errors in a digital communication link. In order to quantify performance limitations, a better understanding of the effect of the intensity fluctuations on the received signal at all turbulence levels is needed. Theory reliably describes the behavior in the weak turbulence regime, but theoretical descriptions in the intermediate and strong turbulence regimes are less well developed. We have developed a flexible empirical approach for characterizing link performance in strong turbulence conditions through image analysis of intensity scintillation patterns coupled with frame aperture averaging on an FSO communication link. These measurements are complemented with direct measurements of temporal and spatial correlation functions. A He-Ne laser beam propagates 106 meters in free-space over flat terrain about a meter above the ground to provide strong atmospheric turbulence conditions. A high performance digital camera with a frame-grabbing computer interface is used to capture received laser intensity distributions at rates up to 30 frames per second and various short shutter speeds, down to 1/16,000s per frame. A scintillometer is used for accurate measurements of the turbulence parameter Cn 2 . Laboratory measurements use a local strong turbulence generator, which mimics a strong phase screen. Spatial correlation functions are measured using laterally separated point detectors placed in the receiver plane. Correlations and captured image frames are analyzed in Labview to evaluate correlation functions, Cn 2 , and the aperture averaging factor. Our correlation measurement technique represents a probe into the length scales of different flows and make for a “fingerprint” of the air conditions at the time. The aperture averaging results demonstrate the expected reduction in intensity fluctuations with increasing aperture diameter, and show quantitatively the differences in behavior between various strengths of turbulence. This paper will present accurate empirical data in the strong turbulence regime. Such results can help build upon existing empirical data and lead to the development of new theories.