Dispersion Height Research Articles

Tuning thermal stability of fluorine-free foam by nano-MDH inorganic flame retardant

Foams enhanced by nanoparticles (NPs) have become an important way to develop new type of fluorine-free firefighting foams. This study focuses on thermal stability of foams generated by the mixed dispersion of CoatOsil-77 silicone and BS-12 hydrocarbon surfactants as foaming agent and nano-magnesium hydroxide (nano-MDH) as foam stabilizer. The interaction between nano-MDHs and surfactants were studied. Thermal stability of nano-MDH enhanced foam was explored by investigating drainage and volume attenuation of foam and heat transfer in vertical foam blanket. Stabilization mechanism of nano-MDH enhanced foam under heat was clarified. Results show that nano-MDHs have a weak interaction with the BS-12 molecules and almost has no interaction with the CoatOsil-77 molecules. Initial foam height of mixed dispersion increases at the presence of nano-MDHs, but further increase in the concentration of nano-MDH decreases its foaming ability. At room temperature, foam drainage and coarsening are accelerated by low concentration nano-MDH (1 wt%) and delayed by high concentration nano-MDH (>1 wt%). Meanwhile, foam was strengthened by rising nano-MDH content after exceeding 1 wt%. Drainage and volume attenuation of foam and heat transfer in vertical foam blanket were significantly delayed and the corresponding thermal stability was strengthened by nano-MDHs. This study can offer a possibility for tuning thermal stability of fluorine-free foams based on nano-MDHs.

Investigating sedimentation process in the plutonium reconversion using Eulerian Two-Fluid simulations and experimental verification

Batch settling simulations were used to investigate the sedimentation behaviour of cerium oxalate particles (surrogate to plutonium) in the nitric-oxalic acid solution which will be useful for the design of continuous process equipment used in plutonium reconversion. The effects of overall solid fractions (OSF), initial dispersion height (ht), and cylinder diameter (d) on the settling curve were investigated numerically and comparisons were made with experimentally obtained results. Further, the solid volume fraction distributions of cerium oxalate obtained by varying the dispersion height, OSF, and cylinder diameter were numerically analysed. The increase in OSF (dispersed phase concentration) led to the presence of high solid volume fraction inside the settler. Since, the dispersed phase volume fraction is more and closely packed, it experiences the delay in settling time. The analysis of pressure variation was done by varying ht, d, and OSF. The bulk settling velocity was computed for different OSF and ht values. It was observed that the settling velocity was reduced with an increase in OSF and was independent of d. The changes in bulk settling velocity with time helped to explain the separation process in detail. The vorticity and velocity fluctuations obtained along the height of the batch settler confirmed the random motion of solid phase during settling. The clear liquid separated at the top region of the batch cylinder was investigated as a function of sedimentation velocity which will be helpful for any future design optimization of a continuous separation equipment.

Experimental investigation of sedimentation behaviour using cerium oxalate particles in oxalic‐nitric acid medium

AbstractSettling behaviour of cerium oxalate particles in the solution was investigated by batch settling tests. The settling curves were experimentally generated for different overall solid fractions (OSF), initial dispersion height (ht) and batch cylinder diameter (d). Settling curves were analysed to obtain bulk settling velocity, and it was observed that bulk settling velocity decreases with increase in OSF and remains unchanged with change in cylinder diameter. Bulk settling velocity was found more or less same with increase in initial suspension height as long as the OSF was maintained constant. The particle settling time is delayed at higher OSF due to dense particle population as the movement of one particle is affected by the presence of neighbouring particle. Regression analysis of the settling curve was performed to identify suitable mathematical model. Two parameter based model was found to represent the settling curve better in comparison to three and five parameter based models. Applicability of dispersion number for characterizing the solid–liquid suspension was checked, and it was found that the dispersion number was not unique for the solid‐liquid system where it was influenced by the operating and dimensional parameters.

Bacterial nanocellulose: Reinforcement of compressive strength using an adapted Mobile Matrix Reservoir Technology and suitable post-modification strategies

Bacterial nanocellulose (BNC) is a highly interesting biomaterial due to some outstanding properties especially when used in medical therapeutics and diagnostics. BNC is absolutely bioinert and is characterised by intrinsic properties such as high tensile stiffness and elasticity, high porosity, exceptional water uptake and swelling capacity. Furthermore, these properties can be adjusted in a very defined way by specifically changing the cultivation conditions or performing post-modifications such as crosslinking, functionalisation with additives, dehydration or drying.Especially the high tensile strength of the nanofibrillar material has been the subject of many investigations in the past couple of years. Nevertheless, the enormous tensile strength and elasticity of BNC is contrary to an almost purely viscous behaviour under compressive load.In the present study, different methods to influence the mechanical behaviour under compression with respect to load bearing applications of BNC are systematically investigated. The possibilities and limitations of the variable layer-by-layer cultivation known as Mobile Matrix Reservoir Technology (MMR-Tech) as well as the effect of different post-modification strategies of BNC are thoroughly investigated.Beside of commonly used indentation tests for characterising the mechanical properties of BNC, we introduce a novel evaluation methodology based on mechanical relaxation measurements and an evolutionary regression algorithm for the derivation of a viscoelastic material law, which for the first time allows standardised, comparative viscoelastic investigations of soft-matter biomaterials to be performed independently of the measurement setup.Using this methodology, we are able to show, that cultivation conditions for BNC and suitable post-modifications can result in different effects on the viscoelastic behaviour of the fabricated composites. We show that the cultivation conditions for BNC primarily affect the height of dispersion and the frequency of the relaxation centre which corresponds roughly to the mean value of the logarithmic distributed relaxation times, and that these effects could be enhanced by post-modifications.However, we also identify parameters, such as the width of the relaxation region, which corresponds roughly to the standard deviation of the logarithmic distributed relaxation times, on which the type of cultivation obviously shows no influence but which can be influenced exclusively by post-modifications. Our methodology enables for the first time a clear identification of those parameters which represent a significant factor of influence to the viscoelastic material behaviour, which should enable a more targeted and application-relevant development of BNC composites in the future.

Modeling the dispersal of wind-borne pests: Sensitivity of infestation forecasts to uncertainty in parameterization of long-distance airborne dispersal

Modeling dispersal of wind-borne pests can be a valuable tool in a broader context of areawide integrated pest management. In such models both biotic and abiotic factors play important roles. Many aspects of the life cycle and dispersal of the focal species are typically well studied and represented with robust measures. However, some important assessments may be either lacking or based on difficult to obtain measurements. For example, investigations of population processes occurring at broad spatial scales pose logistical difficulties, and consequently the corresponding estimates may be biased. This is true in the case of long-distance airborne dispersal, in which aloft characteristics of dispersal are particularly difficult to estimate. In this study we assessed the sensitivity of regional infestation forecasts of sorghum by sugarcane aphids [Melanaphis sacchari (Zehntner)] to uncertainty in parameterization of measures meant to represent important aspects of long-distance airborne dispersal in the southern-to-central Great Plains of North America. We focused on dispersal duration, take-off height, and maximum dispersal height as three critical parameters that control wind-borne long-distance dispersal of aphids. The 63 investigated combinations of values of these parameters had largely equivalent region-wide impact on timing of first forecasted infestation (equivalence margin of 7 days) and the impact on the probability of forecasted infestation was equivalent (equivalence margin of 0.1). The spatial variability in estimates depended on local specificity of the modeled landscape, and it was larger in areas where infestations were less frequent, primarily in eastern Kansas, Oklahoma, and northern Texas.

Eulerian[formula omitted]Lagrangian modelling of rotating detonative combustion in partially pre-vaporized n-heptane sprays with hydrogen addition

Rotating detonation combustion (RDC) fuelled with partially pre-vaporized n-heptane sprays and gaseous hydrogen is studied with an Eulerian-Lagrangian method and a simplified two-dimensional model. Our focus is the effects of various pre-vaporized n-heptane equivalence ratios and droplet diameters on detonation wave propagation and droplet dynamics in two-phase RDC. The results show that when the droplets are small, they are fully vaporized by the detonation wave. However, when the droplet diameter is relatively large and/or the detonation wave number is bifurcated, liquid droplets are observable beyond the refill zone. Moreover, the detonation speed is considerably influenced by the droplet pre-vaporization and diameter. The velocity deficits from our simulated two-phase RDC vary between 5% and 30%. Over 70% n-heptane is detonated in the simulated cases, and it is found that there exists a critical droplet diameter (about 20 µm), around which the detonated fuel fraction is minimal. Four droplet trajectories in RDC are identified, which are differentiated by various evaporation times, residence times and interactions between droplets and the basic RDC flow structures. Inside the refill zone, three droplet categories are qualitatively identified. Droplets injected at the right end of the refill zone directly interact with the deflagration surface and meanwhile have relatively long residence time. However, droplets injected closer to the travelling detonation front have insufficient time to be heated and vaporized. Novel technologies and implementations may be needed to enhance the in-situ droplet evaporation during the refill period in practical liquid fuelled RDE’s. Our results also demonstrate that when pre-vaporization level is low and initial droplet diameter is large, the liquid fuel droplets may disperse towards the combustor exit. Furthermore, the droplet dispersion height decreases with liquid fuel pre-vaporization, while increases with droplet diameter.

Advanced flow profiler for two-phase flow imaging on distillation trays

A profound knowledge of the two-phase cross-flow on large-scale distillation trays is pivotal to their efficient design and operation. For such trays, a novel flow profiler comprising of multiple dual-tip probes for simultaneous local conductivity measurements is proposed in this work. The profiler is applied for a DN800 air/water column simulator equipped with sieve trays. 3D distribution of liquid holdup and tracer-based liquid flow in the two-phase dispersion are assessed in high resolution. Non-uniform holdup is found along the dispersion height. Contrarily, the liquid flow is largely uniform and symmetric with respect to the tray centerline. Prior to measurements, the profiler design, electronic scheme, measurement principle and data processing schemes are described.

Numerical Study of the Composite Effects of Uneven Street Canyons and Time-varying Inflows on the Air Flows and Pollutant Dispersion

ABSTRACT The dispersion behavior of pollutants in realistic street canyons is dominated by the pattern of airflow, which is closely linked to the building layout and air inflow at the street canyon boundary. Although uneven building layouts and time-varying inflows have been individually investigated for their influence on air flow pattern and pollutant dispersion in street canyons, the combined effects of these two factors have not been examined. In this study, four street canyon models, one even and three uneven models with different occupying ratios of high-rise buildings, were numerically studied using large-eddy simulation under steady inflow and time-varying inflow conditions. The results showed that both the uneven building layouts and the time-varying inflow condition enhanced the air flow strength and pollutant removal efficiency inside the street canyon. However, the composite effects of these factors were not simply additive. The worst pollutant removal efficiency was observed for air flow in the even street canyon with the steady inflow, which is the typical benchmark case in studies. With the time-varying inflow, the induced updrafts prevented the relatively tall high-rise buildings from restricting the height of the pollutant dispersion during the inflow in the valley. The pattern of the pollutant isoconcentration plane and the time-series curves of normalized concentrations in the even and uneven street canyon models exhibited fluctuant features with the time-varying inflow.

Using an extended CFD–DEM for the two-dimensional simulation of shock-induced layered coal-dust combustion in a narrow channel

We used the computational fluid dynamics–discrete element method (CFD–DEM) model of compressible flow to numerically investigate the flame structure during shock-wave-induced layered coal-dust combustion, which poses a significant risk in coal mines. This represents the first attempt to apply a CFD–DEM model to compressible reactive gas–particle flow. The Eulerian–Lagrangian model for compressible gas–particle flow was extended to simulate shock–particle interactions in a reactive flow field. The particle interactions were predicted by the DEM, and source terms for homogeneous and heterogeneous reactions were included in the governing equations. The calculations were validated for inert particle dispersion from shock–particle interactions and flame propagation velocity in layered coal-dust combustion. The results were consistent with those from previous experiments. Furthermore, the flame structure in layered coal-dust combustion was revealed using the CFD–DEM approach. The simulation of the layered coal-dust combustion indicated that the shock wave was initially generated by gas detonation in a narrow channel with coal-dust particles at the bottom. The predicted propagation mechanism during layered coal-dust combustion was consistent with that reported in a previous numerical study based on the Eulerian–Eulerian approach (Hoium et al., 2015). Moreover, the flame comprised a leading shock wave and diffusion flame; the coal-dust particles were dispersed and heated by the shock wave and combustion products, respectively. The diffusion flame structure propagated at 350–500 m/s, resulting in devolatilization behind the reaction front. However, the CFD–DEM results indicated that the particle dispersion heights were higher than those predicted by the Eulerian–Eulerian approach (despite similarities in the inert particle dispersion results of these methods), attenuating the compression wave from the reaction front and slowing the leading shock wave.

The Weather Conditions for Desired Smoke Plumes at a FASMEE Burn Site

Weather is an important factor that determines smoke development, which is essential information for planning smoke field measurements. This study identifies the synoptic systems that would favor to produce the desired smoke plumes for the Fire and Smoke Model Evaluation Experiment (FASMEE). Daysmoke and PB-Piedmont (PB-P) models are used to simulate smoke plume evolution during the day time and smoke drainage and fog formation during the nighttime for hypothetical prescribed burns on 5–8 February 2011 at the Stewart Army Base in the southeastern United States. Daysmoke simulation is evaluated using the measured smoke plume heights of two historical prescribed burns at the Eglin Air Force Base. The simulation results of the hypothetical prescribed burns show that the smoke plume is not fully developed with low plume height during the daytime on 5 February when the burn site is under the warm, moist, and windy conditions connected to a shallow cyclonic system and a cold front. However, smoke drainage and fog are formed during the nighttime. Well-developed smoke plumes, which rise mainly vertically, extend to a majority portion of the planetary boundary layer, and have steady clear boundaries, appear on both 6 and 7 February when the air is cool but dry and calm during a transition between two low-pressure systems. The plume rises higher on the second day, mainly due to lighter winds. The smoke on 8 February shows a loose structure of large horizontal dispersion and low height after passage of a deep low-pressure system with strong cool and dry winds. Smoke drainage and fog formation are rare for the nights during 5–8 February. It is concluded that prescribed burns conducted during a period between two low-pressure systems would likely generate the desired plumes for FASMEE measurement during daytime. Meanwhile, as the fire smolders into the night, the burns would likely lead to fog formation when the burn site is located in the warm and moist section of a low-pressure system or a cold front.

Numerical simulation of gas dispersion during cold venting of natural gas pipelines

This article analyzes the effects of various factors on gas dispersion during cold venting based on the actual cold venting operations of long-distance natural gas pipelines in China. Under the circumstance that no obstacles existed, unified dispersion model and PHAST software were used to simulate the gas dispersion process of cold venting in order to study the changes of gas concentration along vertical and horizontal directions over time. FLUENT was used to make numerical simulations to analyze the effect of the existence of high obstacles on gas dispersion. The results indicated that (1) with an increase in wind speed, the concentration range in which the gas might explode (5%–15%) decreased along the vertical direction but slightly increased along the horizontal direction; (2) when the initial venting pressure gradually decreased with the proceeding of cold venting, the downwind distance that might trigger danger reduced significantly; and (3) with an increase in atmospheric stability, the dispersion height of vented gas first increased and then decreased continuously. High atmospheric stability could inhibit the gas dispersion height to a larger degree than the wind speed and aerostatic buoyancy could facilitate it.

Optimization of microalgae-sourced lipids production for biodiesel in a top-lit gas-lift bioreactor using response surface methodology

Microalgae bioreactors that capture industrial carbon dioxide (CO2) emissions to produce lipids for biodiesel are of significant interest. Sun-lit open raceways are generally considered the most economic method for mass cultivation, but the large physical footprint of these shallow systems can limit both industrial site availability and CO2 transfer into the culture medium. To address these issues, a deep top-lit only, gas-lift bioreactor to culture microalgae and capture CO2 was designed and investigated. The results show a three times increase in areal biomass and lipid productivities when compared to traditional raceways used in large-scale microalgae production. Operational factors exerting significant effects on areal biomass and lipid productivities were identified through Plackett-Burman experimental design as gas flow rate, feed gas CO2 content, and dispersion height. By employing response surface methodology, models to predict areal biomass and lipid productivities were derived. The resulting desirability function was then applied to obtain the optimal combination of operational parameters that maximize lipid production per unit area occupied by the bioreactor, whilst keeping biomass production low to reduce downstream processing costs. The optimum operational parameters that fulfill the requirements of the optimization function resulted in areal biomass productivity of 32.1 gdwm−2d−1 and areal lipid production of 198.4 gLipidm−2.

CFD simulation and optimization of membrane scouring and nitrogen removal for an airlift external circulation membrane bioreactor

Cost-effective membrane fouling control and nitrogen removal performance are of great concern in airlift external circulation membrane bioreactors (AEC-MBRs). Computational fluid dynamics (CFD) model incorporating sub-models of bio-kinetics, oxygen transfer and sludge rheology was developed for the cost-effective optimization of a lab-scale AEC-MBR. The model was calibrated and validated by extensive measurements of water velocities and water quality parameters in the AEC-MBR. The validated results demonstrated that the optimized height of gas-liquid dispersion was at around 300mm. The shear stress on membrane surface was equalized and had an average value of 1.2Pa under an air flowrate of 1.0m3h−1. The model further revealed that the high nitrogen removal efficiency (>90%) was achieved due to the high recirculation ratio driven by airlift force without destroying the oxygen deprivation and enrichment in the anoxic and oxic zone, respectively.

Experimental Study on the Effect of Parameters on Sedimentation and Coalescing Profiles in Liquid-liquid Batch Settler

Efficient separation of liquid-liquid mixture based on dispersion is often required in many industrial processes. Influence of mixing time, initial height of dispersion, mixing intensity and oil phase ratio on the separation time in liquid-liquid batch settler/separator were investigated in terms of coalescence and sedimentation profile. Experiments were carried out with oil in water type dispersion. Results showed that in most of cases coalescence controls the time of separation. The experiment results of liquid-liquid separation profiles were compared with the predefined model. MATLAB was used for the fitting of coalescence profile and calculating fitting constants. The data obtained from the batch experiments along with the mathematical model can be used as a good monitoring tool for studying the liquid-liquid dispersion behaviour in industrial units.

Motion Simulation of Cluster Warhead Based on MATLAB

External trajectory equations of a certain cluster warhead were established according to the analysis of force during the motion process. The distribution on ground and some related motion parameters were got by MATLAB to solve the external trajectory equations. The influence of some factors on the distribution and terminal motion parameters were researched. The results show that the dispersion height and dispersion velocity are the most important factors. This paper can provide some reference for the research on the distribution of cluster warhead and determining operational scheme.

Theoretical analysis of particle number density in steady aeolian saltation

Particle number density or particle concentration in aeolian saltation is one important input parameter to calculate the sand flux, kinetic energy and mid-air collision probability in the aeolian saltation and particle concentration is also related to the wind erosion capacity, hence, in the present paper, the vertical distribution of particle number density in steady aeolian saltation is analyzed based on two different types of probability density functions of vertical lift-off velocity of saltating particles: one is the PDF (probability density function) of vertical velocity of lift-off particles in the three-dimensional space defined as a type-A PDF which considers the number of particles in various velocity bins per unit volume; and the other is the PDF of vertical velocity of lift-off particles ejected from the sand bed surface in a period of time as a type-B PDF which considers the number flux of particles in various velocity bins per unit surface area. These two types of PDFs are from two different perspectives (i.e., volume- and surface-based perspectives, respectively), and can be deduced from each other. The half-normal and exponential distributions are recommended for the type-A PDF, and the corresponding type-B PDF is expressed by Rayleigh and Gamma(2) distributions. The PDF distribution pattern of vertical velocity of lift-off particles has an important influence on the vertical profile of particle number density. If the type-A PDF of vertical velocity of ejected particles is a half-normal distribution, the particle number density decays exponentially with height. If the type-A PDF is an exponential distribution, the particle number density also decreases with height. If the type-A PDF is Gamma(3) and Rayleigh distributions, the particle number density first increases, then decreases with height. The type-A and type-B height parameters, which are calculated according to the mean vertical lift-off velocity from the type-A and type-B PDFs, respectively, are not simply considered as the actual mean saltation height, although if the type-A PDF of vertical lift-off velocity is half-normal PDF, the mean dispersion height of particle concentration equals the mean saltation height. The vertical distribution of particle number density can determine the dislodgement rate on bed surface which further affects the surface bedforms.

Liquid dispersions under gravity: volume fraction profile and osmotic pressure

Many physical properties of concentrated dispersions of immiscible fluids are captured by the concept of an osmotic pressure, which measures how much energy is required to deform the bubbles or drops upon compaction. This pressure has a strong impact on the flow and drainage behavior of dispersions. Nevertheless, theoretical models describing its variation with the volume fraction ϕ of the continuous phase are so far available only in the limits of low or high ϕ and experimental data are scarce. We report an experimental study of osmotic pressure in foams and emulsions, showing how the effects of ϕ, disorder, grain size, polydispersity and interfacial tension can all be captured by a single law which satisfies previously established theoretical constraints. Building on this result, we propose the first equation which accurately describes the variation of the volume fraction with the height of a fluid dispersion under gravity.

Microalgae biomass and lipid production potential, and mechanical stress compliance

Microalgae bioreactors that capture industrial carbon dioxide (CO2) emissions to produce lipids for biodiesel are of significant interest. Sun-lit open raceways are generally considered the most economic method for mass cultivation, but the large physical footprint of these shallow systems can limit both industrial site availability and CO2 transfer into the culture medium. To address these issues, a deep top-lit only, gas-lift bioreactor to culture microalgae and capture CO2 was designed and investigated. The results show a three times increase in areal biomass and lipid productivities when compared to traditional raceways used in large-scale microalgae production. Operational factors exerting significant effects on areal biomass and lipid productivities were identified through Plackett-Burman experimental design as gas flow rate, feed gas CO2 content, and dispersion height. By employing response surface methodology, models to predict areal biomass and lipid productivities were derived. The resulting desirability function was then applied to obtain the optimal combination of operational parameters that maximize lipid production per unit area occupied by the bioreactor, whilst keeping biomass production low to reduce downstream processing costs. The optimum operational parameters that fulfill the requirements of the optimization function resulted in areal biomass productivity of 32.1 gdwm−2d−1 and areal lipid production of 198.4 gLipidm−2.

The dynamic properties of intermediate filaments during organelle transport

Intermediate filament (IF) dynamics during organelle transport and their role in organelle movement were studied using Xenopus laevis melanophores. In these cells, pigment granules (melanosomes) move along microtubules and microfilaments, toward and away from the cell periphery in response to alpha-melanocyte stimulating hormone (alpha-MSH) and melatonin, respectively. In this study we show that melanophores possess a complex network of vimentin IFs which interact with melanosomes. IFs form an intricate, honeycomb-like network that form cages surrounding individual and small clusters of melanosomes, both when they are aggregated and dispersed. Purified melanosome preparations contain a substantial amount of vimentin, suggesting that melanosomes bind to IFs. Analyses of individual melanosome movements in cells with disrupted IF networks show increased movement of granules in both anterograde and retrograde directions, further supporting the notion of a melanosome-IF interaction. Live imaging reveals that IFs, in turn, become highly flexible as melanosomes disperse in response to alpha-MSH. During the height of dispersion there is a marked increase in the rate of fluorescence recovery after photobleaching of GFP-vimentin IFs and an increase in vimentin solubility. These results reveal a dynamic interaction between membrane bound pigment granules and IFs and suggest a role for IFs as modulators of granule movement.

Secondary dispersal of Dioscorea japonica (Dioscoreaceae) bulbils by rodents

We examined rodent dispersal of Dioscorea japonica bulbils. Bulbils dispersed by rodents may travel farther from their parent plants than those dispersed by gravity alone. To confirm the presence of secondary dispersal and the types of vector, we used an automatic camera to photograph animals that approached bulbils. To clarify secondary dispersal distance, we set marked bulbils at eight sites and searched for the bulbils once they were removed from their original locations by a disperser. We took photographs of mice (Apodemus speciosus) approaching the bulbils. In June, 10 of 333 bulbils that were moved germinated. We also measured the primary dispersal distance at four sites by dropping bulbils from heights of 0.5, 3.0, and 12.0 m. We then compared primary and secondary dispersal distances. The mean secondary dispersal distance was significantly greater than the primary dispersal distance for dispersal heights of 0.5 and 3.0 m, but less than that for a 12.0-m dispersal height. This indicates that rodents may disperse bulbils farther than gravity alone when bulbils drop from lower heights but they contribute little to dispersal for bulbils that drop from greater heights (e.g., from the top of the canopy). Thus, we confirmed the occurrence of rodent dispersal of bulbils and rodents might to some extent contribute to the dispersal and establishment of bulbils.