Experimental investigation and numerical simulation of heat transfer in quenching fluidised beds

Fluidisation characteristics at different surfaces of a work-piece of complex geometry are conducted in a fluidised bed at various conditions including fluidising number, bed temperature and fluidising medium. The quenching of the work-piece is performed experimentally. In particular, the major frequency and energy of the pressure fluctuations are measured as a function of either fluidising velocity or heat transfer position and the results are used to develop a mathematic model. A computational model is developed to simulate gas dynamics and heat transfer between the fluidised bed and the work-piece surface, as well as simulating the temperature within the work-piece. The predicted cooling curves are in good agreement with the experimental results. Based on the simulation results, the flow characteristics of the gas and the temperature of the dense gas-solid phase near the work-piece surface are analysed to understand the heat transfer mechanism in the fluidised bed.

Population dynamics of the infaunal bivalve, Soletellina alba

The population dynamics of the infaunal bivalve Soletellina alba was investigated at three sites situated within close proximity to the mouth of the Hopkins River estuary. The initial study design was planned to examine the importance of winter flooding to the persistence of this bivalve mollusc within the Hopkins estuary, since mass mortalities have been observed during previous years coincident with periods of winter flooding. Unfortunately, the climatic conditions experienced during this study were atypical compared to the long-term average, so detailed sampling was limited to two, unanticipated, non-flood years rather than two, highly anticipated, flood years. This hampered my ability to conduct complete tests of the importance of winter flooding. Patterns of river discharge and the frequency and duration of mouth opening and closing differed greatly from that expected. Unexpectedly, periods of mouth closure were not always associated with periods of minimal river discharge; low salinities were another unexpected result during an extended period of mouth closure during 1998. As expected, salinities varied considerably with increasing water depth when the estuary mouth was open. Mouth closure lead to salinities becoming more uniform between water depths but hypoxic and anoxic conditions became evident via stratification in the water column at 1 m below the Australian Height Datum (AHD). Other than trends associated with increased water depth, significant variation was not evident between measurements of salinity taken from three sites within close proximity of the estuary mouth (approximately 500 m), or during changes in tide. The most pertinent anomaly was the absence of winter flooding. The distribution and abundance of juvenile and adult S. alba was variable across all Dates, Sites and Channel elevations (i.e. water depths) sampled during this study. An experimental test comparing the recruitment of juveniles at different channel elevations and in sediments of varying particle size was conducted during an exceptionally successful period of recruitment during 1999. The results of these tests showed that recruitment was greatest at the shallowest channel elevation used, and there was little evidence that sediment particle size influenced recruitment. In contrast to 1999, recruitment during 1997 or 1998 was extremely poor. Growth rates were monitored using tagged individuals held in caged and uncaged plots, which revealed that growth was highly variable among individuals, but not between Sites. These tests also revealed that growth was negligible during the colder, winter months, and that the fastest growing individuals were capable of growing 0.2 mm/day. Mixed results were obtained for tests of potential cage artifacts and the influence of handling. Caging and differing amounts of handling did not appear to influence growth, but there was evidence that cages and handling influenced bivalve condition and number of mortalities. These direct tests appeared to be the most appropriate method for determining growth rates of this species, since attempts to analyse length-frequency data were made difficult by the apparent convergence of cohorts, and shell aging is difficult due to the thin, fragile nature of the shell. As expected, mass mortalities were observed during the flood of 1996, but not during the two non-flood years of 1997 and 1998. There were, however, some considerable declines in abundances at some channel elevations during the two non-flood years. However, these declines were attributable to the complete disappearance of individuals, rather than the sudden presence of numerous, recently dead individuals that typify observed declines during winter flooding. The complete disappearance of individuals suggest that S. alba may be capable of post-settlement emigration, or that they were consumed by an unknown predator. Salinity tolerance tests showed that bivalves exposed to low salinities (≤6 ppt), exhibited poorer condition and took longer to re-burrow into sediments than those exposed to greater salinities (≥14 ppt), while death of bivalves exposed to salinities ≤1 ppt occurred after 8 days of exposure. These tests provide evidence that low salinities are probably the principal cause of mass mortalities during winter flooding, although the interaction between salinity, temperature and turbidity also deserve consideration. The results of this study indicate that certain aspects of winter flooding, especially salinity, are responsible for the mass mortalities of S. alba rather than the result of a short-lived life history. I hypothesise that the survival of very young juveniles (between 0.5 and 1 mm shell length) and rapid growth rates are important features of the life history of S. alba that explain its successful persistence within the Hopkins River estuary. The rapid rates of growth suggest that it may be possible for juveniles that survive winter flooding to grow, reach sexual maturity, and reproduce before the onset of the next flood event. Unfortunately, the increased survivorship of juveniles during periods of winter flooding was not demonstrated by this study because of the absence of winter flooding and also relatively poor recruitment. It is highly likely that this species is capable of completing it entire life cycle within the estuary since the absence of other nearby populations, together with periods of mouth closure, are likely to greatly limit the potential contribution made by larvae entering from the surrounding marine environment. This study has added considerably to our knowledge of how infauna cope with life in the intermittently closing estuaries that typify semi-arid coastlines in the Southern Hemisphere.

A microfluidics device to monitor platelet aggregation dynamics in response to strain rate micro-gradients in flowing blood

This paper reports the development of a platform technology for measuring platelet function and aggregation based on localized strain rate micro-gradients. Recent experimental findings within our laboratories have identified a key role for strain rate micro-gradients in focally triggering initial recruitment and subsequent aggregation of discoid platelets at sites of blood vessel injury. We present the design justification, hydrodynamic characterization and experimental validation of a microfluidic device incorporating contraction–expansion geometries that generate strain rate conditions mimicking the effects of pathological changes in blood vessel geometry. Blood perfusion through this device supports our published findings of both in vivo and in vitro platelet aggregation and confirms a critical requirement for the coupling of blood flow acceleration to downstream deceleration for the initiation and stabilization of platelet aggregation, in the absence of soluble platelet agonists. The microfluidics platform presented will facilitate the detailed analysis of the effects of hemodynamic parameters on the rate and extent of platelet aggregation and will be a useful tool to elucidate the hemodynamic and platelet mechano-transduction mechanisms, underlying this shear-dependent process.

Dynamics of interactions involving deformable drops : hydrodynamic dimpling under attractive and repulsive electrical double layer interactions

A model developed previously to analyze force measurements between two deformable droplets in the atomic force microscope [Langmuir 2005, 21, 2912-2922] is used to model the drainage of an aqueous film between a mica plate and a deformable mercury drop for both repulsive and attractive electrical double-layer interactions between the mica and the mercury. The predictions of the model are compared with previously published data [Faraday Discuss. 2003, 123, 193-206] on the evolution of the aqueous film whose thickness has been measured with subnanometer precision. Excellent agreement is found between theoretical results and experimental data. This supports the assumptions made in the model which include no-slip boundary conditions at both interfaces. Furthermore, the successful fit attests to the utility of the model as a tool to explore details of the drainage mechanisms of nanometer-thick films in which fluid flow, surface deformations, and colloidal forces are all involved. One interesting result is that the model can predict the time at which the aqueous film collapses when attractive mica-mercury forces are present without the need to invoke capillary waves or other local instabilities of the mercury/electrolyte interface.

Investigation of process dynamics and control of polystyrene batch reactor using hybrid model

The effects of operating conditions such as initiator and monomer concentration as well as reactor temperature of polymerization reactors are studied in this work. A recently developed hybrid model for polystyrene batch reactor is utilized in simulation study. The simulation results reveal the sensitivity of polymer properties and monomer conversion to variation of process operating conditions. In the second phase of this study, the optimization problem involving minimum time optimal temperature policy is considered for control study. An advanced neural network-based model predictive controller (NN-MPC) is designed and tested online. The experimental studies reveal that the developed controller is able to track the optimal setpoint with a minor oscillation and overshoot.

Tracking single bubble in Hall-Héroult aluminium cell : an experimental and numerical study

In simulations of the hydrodynamics of the multiphase flow in gas– liquid systems with finite sizes of bubbles, the important thing is to compute explicitly the time evolution of the gas–liquid interface in many engineering applications. The most commonly used methods representing this approach are: the volume of fluid and the phase field methods. The later has gained significant interest because of its capability of performing numerical computations on a fixed Cartesian grid without having to parametrise these objects (Eulerian approach) and at the same time it allows to follow the interface ( for example bubble’s shape) that change the topology. In this paper, both numerical (phase field method) and experimental results for the bubble shapes underneath a downward facing plane is presented. Experiments are carried out to see the bubble sliding motion underneath a horizontal and inclined anode. It is assumed that the bubble formed under the anode surface is deformed (flattened) due to buoyant field before it goes around the anode corner. The bubble elongates to form a tail-like shape. The change in shape of the bubble is almost instantaneous and has a significant effect on the localised hydrodynamics around the bubble, which could influence the dynamics of the flow patterns in the Hall–Héroult cell. This deformation is the main cause of the bubble wake and the induced flow field in the aluminium cell. Various parameters such as bubble size, deformation and its sliding mechanism at different surface tensions are discussed and compared with experimental results.

Modeling propagation dynamics of social network worms

Social network worms, such as email worms and facebook worms, pose a critical security threat to the Internet. Modeling their propagation dynamics is essential to predict their potential damages and develop countermeasures. Although several analytical models have been proposed for modeling propagation dynamics of social network worms, there are two critical problems unsolved: temporal dynamics and spatial dependence. First, previous models have not taken into account the different time periods of Internet users checking emails or social messages, namely, temporal dynamics. Second, the problem of spatial dependence results from the improper assumption that the states of neighboring nodes are independent. These two problems seriously affect the accuracy of the previous analytical models. To address these two problems, we propose a novel analytical model. This model implements a spatial-temporal synchronization process, which is able to capture the temporal dynamics. Additionally, we find the essence of spatial dependence is the spreading cycles. By eliminating the effect of these cycles, our model overcomes the computational challenge of spatial dependence and provides a stronger approximation to the propagation dynamics. To evaluate our susceptible-infectious-immunized (SII) model, we conduct both theoretical analysis and extensive simulations. Compared with previous epidemic models and the spatial-temporal model, the experimental results show our SII model achieves a greater accuracy. We also compare our model with the susceptible-infectious-susceptible and susceptible-infectious- recovered models. The results show that our model is more suitable for modeling the propagation of social network worms.

Molecular dynamics study of response of liquid N,N-dimethylformamide to externally applied electric field using a polarizable force field

The behavior of Liquid N,N-dimethylformamide subjected to a wide range of externally applied electric fields (from 0.001 V/nm to 1 V/nm) has been investigated through molecular dynamics simulation. To approach the objective the AMOEBA polarizable force field was extended to include the interaction of the external electric field with atomic partial charges and the contribution to the atomic polarization. The simulation results were evaluated with quantum mechanical calculations. The results from the present force field for the liquid at normal conditions were compared with the experimental and molecular dynamics results with non-polarizable and other polarizable force fields. The uniform external electric fields of higher than 0.01 V/nm have a significant effect on the structure of the liquid, which exhibits a variation in numerous properties, including molecular polarization, local cluster structure, rotation, alignment, energetics, and bulk thermodynamic and structural properties.

Fish responses to experimental fragmentation of seagrass habitat

Understanding the consequences of habitat fragmentation has come mostly from comparisons of patchy and continuous habitats. Because fragmentation is a process, it is most accurately studied by actively fragmenting large patches into multiple smaller patches. We fragmented artificial seagrass habitats and evaluated the impacts of fragmentation on fish abundance and species richness over time (1 day, 1 week, 1 month). Fish assemblages were compared among 4 treatments: control (single, continuous 9-m(2) patches); fragmented (single, continuous 9-m(2) patches fragmented to 4 discrete 1-m(2) patches); prefragmented/patchy (4 discrete 1-m(2) patches with the same arrangement as fragmented); and disturbance control (fragmented then immediately restored to continuous 9-m(2) patches). Patchy seagrass had lower species richness than actively fragmented seagrass (up to 39% fewer species after 1 week), but species richness in fragmented treatments was similar to controls. Total fish abundance did not vary among treatments and therefore was unaffected by fragmentation, patchiness, or disturbance caused during fragmentation. Patterns in species richness and abundance were consistent 1 day, 1 week, and 1 month after fragmentation. The expected decrease in fish abundance from reduced total seagrass area in fragmented and patchy seagrass appeared to be offset by greater fish density per unit area of seagrass. If fish prefer to live at edges, then the effects of seagrass habitat loss on fish abundance may have been offset by the increase (25%) in seagrass perimeter in fragmented and patchy treatments. Possibly there is some threshold of seagrass patch connectivity below which fish abundances cannot be maintained. The immediate responses of fish to experimental habitat fragmentation provided insights beyond those possible from comparisons of continuous and historically patchy habitat.

Molecular dynamics approach to the structural characterization and transport properties of poly(acrylonitrile)/N,N-dimethylformamide solutions

Poly(acrylonitrile) (PAN) in N,N-dimethylformamide (DMF) is a popular solution for producing large variety of polymer products. To precisely describe the behaviours of PAN and DMF in the synthesis processes, it is significant to call for more details about the structure, some thermodynamic and dynamical properties of PAN-DMF solutions. A PAN-DMF solution was simulated via molecular dynamics with an all-atom OPLS type potential in both the NPT and NVT ensembles. The simulation results were evaluated with quantum mechanical calculations (MP2/6-311 ++G(d,p) and counterpoise procedure) and were compared with available experimental results. The liquid structure was illustrated with pair correlation functions and transport and dynamics properties were calculated with the mean-square displacements MSD and the velocity autocorrelation functions. The strong H-bonds of C≡N « H-C=O, CH » O=C-H and CH2 O=C-H, with distances of 2.55 Å, 2.55 Å and 2.65 Å, respectively, were found. The largest interaction energy of - 7.157 kcal/mol between DMF molecules and PAN molecules was found at 4.9 Å center-of-mass distance. A potential profile of intermolecular interaction of DMF with PAN along the interaction distance was presented, clearly showing an increase of DMF vaporisation heat when it getting close to PAN molecules. This provided very useful information to analyse the vaporisation behaviours of DMF at the microscopic level, which is essential to comprehensively understand molecular rearrangements towards the design of synthetic processes. The impact of the presence of the PAN on the DMF solution properties were also benchmarked with pure DMF solution.

Social network analysis resolves temporal dynamics of male dominance relationships

Social organization is often studied through point estimates of individual association or interaction patterns, which does not account for temporal changes in the course of familiarization processes and the establishment of social dominance. Here, we present new insights on short-term temporal dynamics in social organization of mixed-sex groups that have the potential to affect sexual selection patterns. Using the live-bearing Atlantic molly (Poecilia mexicana), a species with pronounced male size polymorphism, we investigated social network dynamics of mixed sex experimental groups consisting of eight females and three different-sized males over a period of 5 days. Analyzing association-based social networks as well as direct measures of spatial proximity, we found that large males tended to monopolize most females, while excluding small- and medium-bodied males from access to females. This effect, however, emerged only gradually over time, and different-sized males had equal access to females on day 1 as well as day 2, though to a lesser extent. In this highly aggressive species with strong social dominance stratifications, the observed temporal dynamics in male-female association patterns may balance the presumed reproductive skew among differentially competitive male phenotypes when social structures are unstable (i.e., when individual turnover rates are moderate to high). Ultimately, our results point toward context-dependent sexual selection arising from temporal shifts in social organization.