Professor Geoffrey Evans

In the present work, an experimental analysis was performed to characterise the flow field around a single bubble of different diameters ~ 2.77¿3.53 mm) rising in a quiescent medium aiming to determine the effect of bubble size on kinetic energy distribution. The velocity field was measured using a non-intrusive particle image velocimetry (PIV) technique and kinetic energy spectrum was determined in both transverse and longitudinal directions applying a Fast Fourier Transformation (FFT). Both small- and large-scale motions of the flow field were identified and separated using a discreate wavelet transformation (DWT) method. It was found that the energy spectrum of the large-scale motions depended on the bubble size while the small-scale energy spectrum was nearly independent of it. The slopes of the energy spectrum were found to be close to -5/3 and -3 for the large- and small-scale regimes, respectively and the transition of slope was observed to occur at the wavenumber corresponding to the bubble diameter. Using the measured velocity field data, a turbulence kinetic energy (TKE) budget analysis was performed involving five components namely kinetic energy production, turbulent transport, pressure diffusion, viscous diffusion, and energy dissipation. Overall, it was observed that in the vicinity of bubble surface, turbulence production term was not entirely balanced by the dissipation term; and turbulent transport and pressure diffusion term also had significant contributions.

The new three-phase fluidized bed flotation column (TFC) hydrodynamics characteristics, such as gas holdup, bubble diameter and bubble surface area flux have been carried out, and this study focuses on bed fluid hydrodynamic parameters of the TFC. The bed hydrodynamic characteristics viz., bed fluctuation ratio (r), bed expansion ratio (R) and bed voidage (e) of the TFC have been studied using air as the discontinuous phase and water as the continuous phase, respectively. The effects of the system parameters studied include superficial gas, liquid velocities and initial static bed height (H0). Experimental studies based on the Response surface methodology (RSM) have been made to investigate the mathematical model of hydrodynamic parameters (r, R, e) and bubble diameter (Db) of the TFC. The results show that the models which were established by operating variables can predict the r, R, e and Db of the TFC well. Based on the previous investigation of the optimization of bubble performance parameters which has been caried out by Liu et al. (2020), the correlation of Db has been carried out, and the result shows that H0 is the boundary condition that determines the variation of Db. The optimization of Db by RSM shows that relatively small bubbles can be obtained when H0 is greater than 0.290 m within the range of parameters studied. The values of the experiment have been compared with those predicted by the proposed models and have been found to agree well.

In flotation, interactions of bubble-particle aggregates with turbulent flow structures in the liquid medium result in particle detachment. This study aims to simulate this phenomenon involving a bubble-particle aggregate (bubble diameter ~ 3 mm and particle diameter ~ 314 µm) interacting with a turbulent flow structure manifested as a confined vortex in a square cavity connected to a square cross-section channel. An interface resolved three dimensional (3D) computational fluid dynamics (CFD) model was developed to quantify the bubble-vortex interaction dynamics over a range of channel Reynolds numbers. The CFD model produced a good agreement with the experimentally measured vorticity magnitude, local energy dissipation rate, and bubble motion. It was shown that a bubble-particle aggregate could be captured within the vortex by suitably varying the channel Reynolds number, eventually leading to particle detachment. A separate force balance analysis was performed to determine a criterion for particle detachment utilising the CFD model predicted vorticity and local energy dissipation rate. It was shown that a critical local energy dissipation rate ~ 1.59 m2/s3 was required for particle detachment to occur, which was also verified experimentally.

Structured packings are widely used in oil & gas industries, as they can provide substantial surface area and high void fraction, thus enabling high mass transfer efficiency at a low pressure drop. This study investigates the hydrodynamic performance of two structured packings, namely, Mellapak 250Y and Montzpak B1-500. The pressure drop and liquid distribution are reported for a column of 200 mm diameter and 400 mm packing height. Wire-mesh sensor (WMS) is used to monitor the liquid distribution at the location of packing transitions. Packing replicas manufactured using a Fused Deposition Modelling (FDM) 3D printer is compared with commercial packings in terms of pressure drop and liquid distribution. A Computational Fluid Dynamics (CFD) model is initially validated using experimental data and then is used to investigate the effects of packing features, such as plate thickness, packing corrugation angles, holes, and packing transitions. The 3D-printed replicas show consistent performance compared to the commercial packings but can provide more information when measuring liquid distribution. The methodology and results discussed in this study can provide in-depth insights into the performance of structured packings, which is of critical importance when optimising packing parameters and testing new designs.

In this study, the role of cavitation bubbles in the bubble-particle interaction dynamics was investigated using high-speed imaging. A lab-scale conceptual flotation cell was designed involving an ultrasonic field with adjustable power output and a continuous liquid recirculation stream. Coarse size range hydrophobic glass Ballotini particles were suspended in the cell by the combined action of a confined vortex and turbulence created by periodic ultrasonic pulses. Ultrasonic pulses in the liquid medium led to the generation of numerous fine size range cavitation bubbles which were observed to form particle clusters. These particle clusters were observed attaching to relatively larger size carrier bubbles forming stable bubble-particles aggregates, which subsequently floated. It was noted that a favourable state of bubble-particle interactions was achievable to produce such stable bubble-particles aggregates by suitably controlling the input power and period of the applied ultrasonic pulse.

In the iron ore sintering process, the resistance to air flow is a major factor in deciding the flame front speed, which influences the sinter productivity and quality. In this work, pressure drop during sintering and the resistance to air flow was investigated in milli-pot sintering for different coke rates. The sintering experiments were conducted in a milli-pot (diameter 53 mm, height 400 mm) and pressure and temperature were measured at the same locations in the bed by four taps located equidistant to each other. The yield of sinter product was measured following a modified drop test and the mineralogy of the sinter product was analysed. The results from milli-pot sintering were then compared to the reported results from standard pilot-scale sintering, and it was found that the lower half of the milli-pot bed gave a reasonable representation of the pilot-scale sintering process. The results of sinter mineralogy, yield and productivity of the lower half of milli-pot at 5.5-8.0% coke rate were found to be similar to pilot-scale sintering tests at a corresponding coke rate from 3.5 to 5.5%. The maximum resistance to air flow in the bed was found to be in the region between the leading edge of the flame front at ~100°C and the trailing edge of the flame front at ~1 200°C. This suggests that the maximum resistance to air flow includes the effect of de-humidification and combustion in addition to the high temperature "flame front" region usually defined at temperatures above 1 100°C or 1 200°C.

In this study, we report the rising behaviour of the millimetric size ellipsoidal shaped particle-laden bubbles (particle diameter dP ~ 114 µm, bubble diameter dB ~ 2.76 and 3.34 mm) in the range of bubble surface loading (BSL) from 0 to 0.6 both in absence and presence of a surfactant (Sodium Dodecyl Sulphate, 20% CMC). High-speed imaging was used to capture the trajectory of the particle-laden bubble and an image processing methodology was developed to quantify the bubble surface loading. Three different regimes were observed - bubble shape transition (nearly spherical to ellipsoidal), particle detachment (at bubble rear end), and steady (for high BSL) or expansion (for low BSL) of the particle surface covered zone. A threshold for bubble surface loading (BSL ~ 0.40) was determined which had reasonable agreement with the experimental observations. Bubble rise velocity was observed to decrease with bubble surface loading but this trend was less steep in presence of surfactant. It was noted that loss of bubble surface mobility was higher in presence of surfactant, however in absence of surfactant, bubble surface loading contributed significantly to surface immobility. Finally, a correction factor to Schiller-Naumann drag coefficient model was proposed accounting for the bubble surface loading both in presence and absence of surfactant.

Hydrodynamic performance of an ultra low-pressure drop and high surface area, 3D printed structured packing (SpiroPak) was investigated in this study. Computational fluid dynamics (CFD) modelling combined with single-phase (dry) and irrigated (multiphase) experiments were carried out to validate the CFD modelling results. Experiments were conducted to measure the dry and wet pressure drop at a range of liquid load (0¿38.2 m3/m2·h) and F-factor (0¿1.2 Pa0.5). Liquid distribution was measured using Wire Mesh Sensor (WMS) for SpiroPak and compared with a commercial and 3D printed replica of Mellpak 250X and Montzpak B1¿500. The topology of the packing was analysed to calculate the specific surface area that could be available for mass transfer. It was found that the SpiroPak can have up to 50~200% more surface area per unit volume when compared with commercial packing. Experimental and modelling results showed that SpiroPak could reduce the dry pressure drop by approximately 50%. Parametric study found that reducing corrugation size to increase surface area and increasing the gap size to reduce the pressure drop were key design parameters of SpiroPak. Finally, scale-up and scale-out (tessellation) techniques were compared to determine the optimum element size for the application of SpiroPak on a large scale.

In order to get a better micromixing performance, an intensification reactor that couples a confined impinging jet reactor and high speed disperser (CIJR-HSD) was designed. The influences of operating and structural parameters on the micromixing performance were investigated by using the iodide-iodate reaction system. The results showed that the segregation index decreased with the increase of both the rotational speed and the number of rotors; whilst there was little influence due to both inlet flow rate and the presence of packing. The coupling distance between the centre of the CIJR and the first rotor of the HSD also had a non-negligible effect on segregation index. The micromixing time was determined by the Engulfment model, and could also be evaluated by the energy dissipation model based on fluid energy transformation. It was found that the micromixing time for the CIJR-HSD device was in the range of 0.1¿0.3 ms, while that for a single CIJR was in the range of 0.35¿0.5 ms.

This work presents a computational study based on Discrete Element Method (DEM) to investigate the capture of particles by bubbles in the presence of electrical double layer repulsion. In the DEM model a fully mobile boundary condition was assumed for the gas-liquid (bubble) interface. The forces acting on the particle were gravitational, buoyancy, hydrodynamic, as well as elastic and damping forces if/when the particle penetrated inside the bubble. Surface forces were considered and were evaluated through the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory. A preliminary theoretical analysis of the surface forces was carried out in order to determine the possibility of particle capture. This analysis included the determination of the interaction potential energy. Five different types of interaction energy curves were found. They were characterised by (1) a monotonic increase with distance; (2) the presence of a primary minimum; (3) the presence of an energy barrier and a primary minimum, (4) the presence of an energy barrier and a primary and a secondary minimum, and (5) a monotonic decrease with distance. DEM modelling was conducted to investigate the induction time for a single particle-bubble system. It was found that the induction time decreased with increasing contact angle and decreasing height of the energy barrier. In contrast, the primary minimum had very limited impact on induction time. Additionally, modelling of a more complex system consisting of a single bubble and multiple particles was also carried out. The multiple particle-single bubble simulation results showed that a decrease in induction time considerably enhanced collection efficiency. Finally, the concept of ¿contactless¿ flotation, which occurs in the case in which only a primary minimum exists, was also demonstrated through the use of DEM modelling.

Only when the process of particle detachment is well understood and modelled can minerals recovery using the flotation process be modulated to achieve a high efficiency by suitably changing the operating parameters. This is vitally necessary for the recovery of coarse particles in an energy efficient way, as detachment is the key limiting factor in the successful recovery of large particles. However, until the detachment mechanism is more fully understood, an upper limit on the floatable particle diameter still remains unidentified. To assess the current state of knowledge available in this area, a comprehensive literature review on the mechanisms and models of the bubble-particle detachment process in froth flotation is presented. In general, the detachment process is considered to be a stochastic process, and is usually attributed to the dynamic interactions with the turbulent flow structures (eddies) in the flotation environment which cause particles to detach because of dissipating energy. In this paper, previous studies on bubble-particle detachment have been critically analyzed with respect to the formulation of the models in predicting the detachment probability of particles. The models are classified into three different categories: force balance analysis; energy balance analysis and empirical analysis of particle size compared to maximum floatable particle size. Attention is also paid to an understanding of the mechanisms of bubble-particle detachment in quiescent and turbulent liquid flow fields. The predictions of all these models have been compared with the published experimental data and it was found that models which take an accurate consideration of the influence of eddies on a particle's detachment give the closest predictions. The generally held concept of bubble-particle detachment inside an eddy was experimentally validated, where a particle was observed to rotate on the surface of a bubble, resulting in a centrifugal acceleration 20 times that of gravitational acceleration. The aim of this paper is to review the developments and limitations of the existing models. The experimental work is reviewed so as to reveal the mechanisms of bubble-particle detachment. Therefore, the future development of models is identified in order to successfully predict particle detachment.

Liquid fluidised beds often operate with particles of different sizes and densities, encountering partial or complete segregation of solid particles at certain operating conditions. In this study, the segregation and dispersion of binary particle species of the same size but different densities in liquid fluidised beds have been investigated based on the analysis of computational fluid dynamics - discrete element method (CFD-DEM) simulation results.The vertical fluid drag force acting on the particles was found to be responsible for the particle segregation. The mechanisms governing the particle dispersion strongly depended upon the solid-liquid two-phase flow regime, which transited from pseudo-homogeneous to heterogeneous when the superficial liquid velocity reached a certain value. In the homogeneous or pseudo-homogeneous flow regime (Rep=40, ¿L, ave=0.74), particle collisions acted as the main mechanism that drove the dispersion of particles. However, after the system became heterogeneous, the magnitude of the vertical collision force decreased towards zero and correspondingly, the magnitude of the vertical fluid drag force was approaching that of the particle net weight force as the superficial liquid velocity increased. Therefore, in the heterogeneous flow regime (Rep>40, ¿L, ave>0.74), the local turbulence of the fluid flow and particle collisions (if there were any) were found to be the main mechanisms that drove the dispersion of particles in all directions. The dispersion coefficient of individual particles varied significantly throughout the system in the heterogeneous flow regime. The simulation results reasonably agreed with the experimental data and the prediction results by existing correlations.

Design and scale-up of fluid catalytic cracking (FCC) riser is still largely empirical, owing to limited understanding of inherent multiphase flow in this equipment. The multiphase flow of FCC riser has therefore been extensively investigated both experimentally and computationally. The experiments have provided significant insight into gas-solid flow patterns inside cold-flow risers, but simultaneous observations on flow and performance parameters (conversion and yields) in FCC riser are rarely found in literature. Consequently, computational fluid dynamic (CFD) models of FCC riser that can simultaneously account for flow, interphase interactions, droplet vaporization and cracking kinetics have been developed. The CFD modelling of FCC riser, despite several efforts, has still remained a challenge as it requires careful consideration of governing equations and closure models. This review presents state-of-the-art in CFD modelling and experimental analysis of gas-solid hydrodynamics and reactive flow of FCC riser. The CFD models are explained in greater detail with governing equations, constitutive relations, and physical significance of all the terms. A brief review of DNS studies on cluster formation, gas-solid drag, and turbulent interactions is also presented. Impact of important closure models such as drag models, viscous stress models, boundary conditions, droplet vaporization models, and kinetic models on predictions is critically examined. The review identifies major shortcomings of current CFD models and makes detailed recommendations for future work.

The capture of a falling particle at a horizontal gas¿liquid interface (film flotation) is determined by the particle impact velocity and the subsequent motion of the three phase contact line (TPCL) as the particle penetrates into the liquid. In this study, the three phase contact lines were observed experimentally using high speed video camera for a number of different particle liquid systems. The particles comprised hydrophilic glass bead particles with and without surface hydrophobicity treatment. The liquid comprised water, and NaCl, sucrose and hexadecyltrimethylammonium bromide (CTAB) aqueous solutions with different concentrations. Previous modelling of Liu et al. (2010a) was extended to include the advancing velocity of TPCL on dynamic contact angle. The critical fall height predictions by the modified model compared favourably with experimental measurements.

Two bubbles in conjunct condition are often encountered in high-viscosity liquids, but have received very little attention in the literature. The conjunct bubbles rise together with unchanged shapes and constant velocities, showing some unique properties compared to single bubbles. The current research built on the previous work of Cai et al.,[1] and extended the bubble size ratio (¿) to the range 1.0¿1.2. The formation and motion characteristics of conjunct bubbles made by direct collision of two in-line bubbles were investigated, including the effects of bubble volume, bubble size ratio, and liquid viscosity. Models for the conjunct bubbles and the single bubbles were provided for predicting the projected area diameters and the rising velocities respectively, and the predicted values closely agreed with the measurements in glycerol-water solutions with Morton numbers in the range of 1.690¿661.8. The dynamic forces on the conjunct bubbles were analyzed, and a succinct algorithm was proposed for calculating the drag forces on the conjunct bubbles and the interaction force between the two bubbles.

This paper presents a computer simulation analysis of the selective capture of binary particle mixtures by a central bubble, as influenced by the relative strength of the hydrophobic interaction assigned to each type of particle. The analysis was carried out for a quiescent fluid using two different configurations of initial particle positions, namely: spherical (particles released from within a spherical shell surrounding the bubble) and top (particles released from a horizontal plane located above the bubble) distributions. The top distribution was also used to study the effect of fluid velocity (< 0.05 m/s). The results show that in the case of a quiescent fluid the collection efficiency was greater for the top distribution than for the spherical one. In addition, when the strength of the hydrophobic force was less than the net particle weight, particles easily detached from the bubble surface. In the presence of fluid flow the collection efficiency followed an exponential decay with the fluid velocity and a quadratic relationship with an effective cross-section for the particle-bubble collision. The latter closely follows the collision models in the literature. Importantly, we have shown that selective capture only occurs when one type of particle possesses a hydrophobic force magnitude close to or less than the net particle weight, while the hydrophobic force for the second type needs to be much larger than the net weight of the particle. Therefore, we have concluded that selectivity does not depend solely on the hydrophobicity differences, but also requires that one type of particle has to be weakly interacting with the bubble.

Flotation in mechanically agitated cells has been the workhorse of the mining industry, but our quantitative understanding of the effect of microturbulence generated by agitation on flotation is still very limited. This paper aims to review the literature on quantifying the microturbulence effects on bubble-particle interactions in flotation. The particular focus is on the stochastic description of bubble-particle interactions in the turbulent flow which is a random field. We briefly review the stochastic description of microturbulence and motions of particles of micrometre sizes and bubbles of millimetre sizes in the isotropic turbulence of mechanical flotation cells. The key starting point is the generic equation of motion, which can be decomposed into the mean turbulent variables and fluctuating turbulent variables. The turbulent flow of the carrying liquid is characterised using isotropic turbulence theory. The next focus is on reviewing bubble-particle turbulent collision and detachment interactions. Bubble-particle turbulent collision is poorly quantified; no quantitative models of the bubble-particle turbulent collision efficiency relevant for flotation are available. Current theories on bubble-particle turbulent detachment face some deficiencies. In assessing the microturbulence effect on bubble-particle detachment, the majority of studies only considers the particle acceleration in the centrifugal direction but ignore the transverse acceleration of particles, which is due to turbulent shear flow. Critically, contact angle required in quantifying the detachment is not constant, single-valued as considered in the theories, but can vary from receding to advancing value during the relaxation of the triple contact line on the particle surface. The latest experiments show that multiple-valued contact angle can significantly affect stability and detachment of floating particles. Finally, quantifying the microturbulence effect on flotation requires further research.

The thrust of this paper concerns flow visualizations around a bubble-particle aggregate in oscillating grid turbulence where no net flux is presented. The influences of a turbulent liquid's motion on the detachment of a bubble from a particle are explored. The methods of analysing the two dimensional velocity fields are compared, including: Reynolds' decomposition, Galilean decomposition, Gaussian filtering and discrete wavelet transform (DWT). The decomposed velocities that are extracted using the different methods on a snapshot of a velocity field series are illustrated and compared. In terms of the flow structure visualizations, the DWT proved to be advantageous over the other methods for the reasons that no a priori cut-off frequency needed to be defined and the flow structures could be decomposed, scale to scale. The DWT was a sufficient method to decompose the velocity fields and to achieve flow structure visualizations, which is conducive to understanding the mechanisms of bubble-particle detachment in a turbulent field. This method was extended to analyse the instantaneous velocity fields around a bubble detaching from a stainless steel particle and the influences of eddies on the detachment. Under the same operating conditions, different detachment modes were identified from the instantaneous velocity fields around the detaching bubble in the oscillating-grid turbulence, including: ¿ the sliding of a bubble resulting from the shearing force in the turbulent flow field; ¿ the stretching of a bubble resulting from the pulling force in the turbulent flow field; ¿ the entrainment of a bubble into an eddy, so that the bubble followed the movement of the eddy.

In this paper we present a new method for studying the detachment of particles from bubbles in a rotating turbulent eddy. The eddy is formed in a wall cavity in a two-dimensional water tunnel with transparent walls. When water flows through the tunnel, a vortical flow field develops in the cavity. The properties of the eddy can be modulated by changing the free-stream velocity of the water in the tunnel. Bubbles are pre-loaded with one or more particles in a fluidized bed flotation device located beneath the vortex cavity. Loaded bubbles are released one at a time into the cavity, and the motion of the bubble-particle aggregate is studied using a high-speed video camera. The diameters of the particles and the bubbles, and the number of particles initially attached to the bubble, can be varied. The trajectories taken by the bubbles are quite complicated. In some cases, the bubble moves to the centre of the eddy, and particles rotate around its axis. If the rotational speed is sufficient, particles may detach due to centrifugal force. However, other modes were observed, including inertial detachment due to rapid changes in direction of the surface of the bubble, because of changes in trajectory of the bubble as a whole, or because of pulsations and oscillations of the bubble surface. Clusters of bubbles held together by particles were seen to form and reform. In the traditional explanation for the detachment of particles in flotation cells, it is assumed that particles detach from bubbles rotating in an eddy due to centrifugal force (Schulze, 1977) [1]. Although the conditions assumed in Schulze's theory may exist, it is only one of a range of phenomena that can lead to the detachment of particles from bubbles in a turbulent vortex. The interactions between bubbles and particles is stochastic in nature, and it is impossible to model precisely the series of events that take place when a particle and a bubble make contact with each other and move through the liquid. There can be no simple model for the recovery of hydrophobic particles in flotation machines.

Rapid advancement in computer technology makes it possible to perform simulations of large particulate systems using Discrete Element Method (DEM). However, it is still a challenge to adjust the DEM simulation parameters, especially the interparticle forces, in order to obtain rational results. Many of these forces diverge as the distance between particle surfaces approaches zero. Therefore, a cut-off distance needs to be considered in order to avoid such a problem. This work presents the results of the computational analysis of the influence of the cut-off distance, which is required to avoid the divergence of the van der Waals force, on the collision of a single particle against a flat surface. Hence, the effect of the cut-off distance on the coefficient of restitution, collision duration and maximum overlap has been studied. In addition, we have theoretically derived an expression for the minimum velocity under which the particle remains adhered to the surface (critical velocity) as a function of the cut-off distance. The simulation predictions of the critical velocity are within the range of experimental data published in the literature. We demonstrate that the cut-off distance has a profound influence on particle rebound and therefore, a careful selection of this parameter should take place when simulating bulk particle behaviour. Given that the hydrophobic force is usually simulated using the same expression as the van der Waals force, the results presented here could also be considered in the context of the simulation of the hydrophobic force.

This work investigates the effects of multiple jet interactions and single jet instability on jet breakup and droplet size using experimental and computational techniques. In particular, the jet separation distance, jet breakup length and droplet diameter were measured as a function of initial nozzle separation distance and jet volumetric flow rate. It was found that the two jets moved closer to each other to reach an equilibrium separation distance that was approximately 70% of the spacing between the two nozzles. The distance at which the instabilities were first observed on the surface of the jet was also a function of the initial separation distance. However, it was weakly dependent on the jet velocity. The jet breakup length and resultant droplet diameter were both influenced by flow rate and nozzle separation distance. The jet breakup length was found to decrease with reduction in nozzle spacing at the high flow rates. Interestingly, a linear relationship between droplet diameter and breakup length was found that was largely independent of nozzle spacing and consist with conventional Rayleigh jet breakup theory. The implications of the experimental observations on the design of multi-jet systems are discussed. Furthermore, computational fluid dynamics simulations were also used to identify the mechanism and dynamics of jet instability in the single jet systems. The simulation results were analysed to study the effect of instability on various parameters such as jet breakup, droplet formation and size of emulsion droplets. It was found that at higher volumetric flow rates, the droplets size increased during the jet breakup due to an asymmetric instability. The asymmetric instability was caused by the pressure gradient in the continuous phase and was prevented in double jet systems.

Vaporization of atomized feedstock is one of the critical processes in fluid catalytic cracking (FCC) risers; which is more often ignored in most of the FCC riser modelling studies. In this study, two different vaporization mechanisms of feedstock namely homogeneous mode and heterogeneous mode were studied. Different homogeneous models duly validated for various pure component droplets were applied to predict the vaporization time of the feed droplets typically expected in FCC feed vaporization zone. A new physical model for heterogeneous vaporization considering droplet-particle collision mechanics was also developed in the present study which compared well with the other existing heterogeneous modelling approaches. Comparison of the two vaporization modes indicates that under typical operating conditions of FCC riser, vaporization time of feed droplets predicted by heterogeneous mode is always lower than the homogeneous mode at least by an order of magnitude due to significant increase in heat transfer coefficient which accounts for droplet-particle contact. It is expected that actual vaporization time of feed droplets in an industrial FCC riser should lie in the range predicted by these two vaporization mechanisms which actually set the two limiting modes of vaporization. Obtained results predicted by the models could be used to aid design of the FCC feed vaporization zone.

Interfacial water in close proximity to an adsorbed surfactant layer plays an important role in many areas. Here, we systematically investigate the interfacial water structure at the adsorption layer of cetyltrimethylammonium bromide (CTAB) from low concentrations to its critical micelle concentration. Our sum frequency generation (SFG) spectroscopy results show that, with increasing CTAB concentration, the water SFG signals first increase, reaching maximum intensities at 0.1 mM, and then drop, whereas the ppp SFG signals of the terminal-methyl asymmetric stretch reach maximum intensities and saturate at 1 mM, which is the critical micelle concentration of CTAB. Our analysis reveals that the interfacial water layer adopts the most orderly arrangement when the interfacial potential of the adsorption layer reaches saturation and not at the surfactant concentration of adsorption saturation. Most importantly, our SFG data provide direct evidence for the antagonistic effects of the interfacial potential and thickness compression of the electrostatic field of the surfactant adsorption layer, leading to the strongest water SFG signals at 0.1 mM. Below 0.1 mM, the increased interfacial potential can have a pronounced effect on the increase of the overall dipole moment of the interfacial water layers. Above 0.1 mM, the decreased Debye screening length significantly reduces the water dipole moment. Finally, the newly proposed adsorption model cannot explain our SFG results.

The success of many industrial processes largely depends on the structural characteristics of aggregates. In intensive aerobic digestion process for wastewater treatment applications, the structural characteristics namely aggregate shape, size and therefore the aggregate surface area strongly influence the transfer of dissolved oxygen from the aeration process to aggregates of harmful contaminants/microorganisms. The aim of this study was to apply Discrete Element Modelling (DEM) techniques to the aggregation of suspended particles (microorganisms) to quantify the available surface area for convection and diffusion as a function of particles number concentration and surface charge. The simulation inputs included particle and fluid characteristics such as particle size and density, solid concentration, suspension pH and ionic strength. A post processing method based on the Go-chess concept was developed to quantify the surface area of aggregate structure. The simulation results showed that whilst an increase in connection points increases the total surface area of the aggregate, this does not necessarily translate into an increase in the surface area available for oxygen transfer as combinations of open and close pores are formed. Aggregate surface area was directly determined by aggregate structural characteristics, and increased rapidly when the coordination number was below 3.5 and the fractal dimension was less than 1.5. A correlation for prediction of aggregate external surface area was also proposed as a function of aggregate structural characteristics in terms of fractal dimension and coordination number.

It is critical to have an efficient energy budget in all the industrial process applications involving multiphase flow system where a significant amount of power is invested to achieve a desired outcome such as valuable particle collection and recovery in mineral flotation circuits. In order to achieve this aim there needs to be an ability to properly characterise the energy dissipation in the system; and from this knowledge to develop methodologies so that the supplied energy is distributed suitably among the eddies of different sizes which are responsible for enhancing different transport events such heat/mass transfer, mixing etc. The aim of the study was to obtain the 2D instantaneous velocity field in a homogeneous near isotropic turbulence field using particle image velocimetry (PIV) and then compute the space and time averaged specific energy dissipation rate from velocity field using four different methods, namely: (1) dimensional analysis, (2) velocity gradient, (3) structure function, and (4) energy spectrum. The system was studied in the Taylor Reynolds number range of 24-60, where it was found that the difference between the computed specific energy dissipation rates could be as much as 100 percent. Whilst it was found that there were uncertainties in all four methodologies, it is argued that the energy spectrum method is likely to give the most realistic quantification of the specific energy dissipation rate value since it was shown to satisfy the system energy balance which was not possible to do so for the other three methods. The energy spectrum method also had the added benefit of incorporating integral scale, Taylor microscale and Kolmogorov length scales in the quantification of the specific energy dissipation rate; whereas the other three methods are limited to either integral scale or Taylor microscale only. The limitation of the energy spectrum method, however, is the resolution of the energy spectrum down to the Kolmogorov length scale due to the noise in the measurement; and to resolve this problem a filter was applied to denoise in the dissipation range.

A liquid marble is a droplet coated with hydrophobic particles. A floating liquid marble is a unique reactor platform for digital microfluidics. The autonomous motion of a liquid marble is of great interest for this application because of the associated chaotic mixing inside the marble. A floating object can move by itself if a gradient of surface tension is generated in the vicinity of the object. This phenomenon is known as the Marangoni solutocapillary effect. We utilized a liquid marble containing a volatile substance such as ethanol to generate the solutocapillary effect. This paper reports a qualitative study on the operation conditions of liquid marbles containing aqueous ethanol solutions in autonomous motion due to the Marangoni solutocapillary effect. We also derive the scaling laws relating the dynamic parameters of the motion to the physical properties of the system such as the effective surface tension of the marble, the viscosity and the density of the supporting liquid, the coefficient of diffusion of the ethanol vapour, the geometrical parameters of the marble, the speed, the trajectory and the lifetime of the autonomous motion. A self-driven liquid marble has the potential to serve as an effective digital microfluidic reactor for biological and biochemical applications.

A flotation detachment model is developed by considering energy balance in the process. Energies concerned are surface energy increment and kinetic energy supplied by turbulent liquid motion. Surface energy increment is the work of adhesion by surface forces which is reflected by surface tension and contact angle. What makes this model outstanding from other detachment models of energy balance perspective is more accurate account of kinetic energy supplied from turbulent liquid motion. Eddies in the same scale as attached particles are considered accountable for particle detachment in the close vicinity. In this way, detachment probability is written as a function of energy dissipation rate. Predictions from different models are compared to experimental results. It is demonstrated that previous models overestimate the influence from turbulent liquid motion. Notably, with more accurate account of eddies' influence, the new model predicts particle detachment in accordance with experimental results.

Turbulence plays a critical role in detachment process of bubble from a solid surface. To investigate this effect, detachment process of a stationary air bubble from a nozzle in both quiescent and turbulent liquid field was studied. A stationary vertical (flat-ended) needle of ID 1.24mm was used as a nozzle to generate a bubble which was anchored to the needle tip. Different sizes of bubbles were generated in quiescent liquid. Volume and contact angle for these bubbles were measured precisely using microscopic imaging technique and correlated. In the quiescent case experiments, a constant contact angle of 90° and bubble diameter of 3.05±0.004mm were obtained consistently. A simple force balance approach was proposed assuming bubble in equilibrium to determine this maximum bubble diameter during detachment. The detached bubble size calculated using this approach agreed fairly well with the experimental results. An oscillating grid device capable of operating at different frequencies was then applied to generate a homogeneous, near-isotropic turbulent velocity field around the anchored bubble. It was observed that for detachment of smaller bubbles, higher turbulence intensity was indeed necessary. The turbulent flow field was quantified using particle image velocimetry (PIV) technique and resolved into flow structures (eddies) of different length scales using a Gaussian filter. It was concluded that smaller eddies perturbed the bubble interface whilst the larger eddies contributed to weakening of the capillary force causing the bubble detachment. Energy dissipation profile obtained from the PIV images indicated significant energy dissipation near the bubble compared to the bulk fluid which supported the fact that strong interactions between bubble and eddies were indeed responsible for bubble detachment.

Accurate prediction of the interactions between evaporating liquid droplets and solids are critical for many industrially important processes. A model based on coupled Level Set-Volume of Fluid approach was developed to simulate the interaction of evaporating liquid droplets with hot solid surfaces. The model incorporates appropriate source terms in the multiphase calculations to account for the heat and mass transfer. Accurate and stable numerical procedure was developed and incorporated in open source solver OpenFOAM. A brief discussion on the model development along with several key issues that are associated with this process was presented. The resulting numerical model was validated through the experimental data of Chandra and Avedisian (Chandra, S., Avedisian, C.T., 1991. Proc. R. Soc. Lond., Ser. A 432, 13-41). Although some discrepancies were found between the numerical results and experimental data, the model was found to be capable of reproducing the reduced droplet spreading rate as the temperature of the surface is increased away from the saturation temperature. The decrease in rate of surface wetting results from the combined effects of surface tension, viscous forces and evaporation at the liquid-solid-vapour contact line. Further, the effects of increased pressure at the solid-liquid interface resulting from the rapid evaporation of the liquid, which in some cases can be quite severe such that the liquid gets lifted-off from the surface, were also captured, in good agreement with experimental observations. Finally, the effects of the solid temperature on the evaporation and heat transfer rates of the droplets were presented and analysed. © 2014 Elsevier Ltd.

In a liquid fluidised bed system, the motion of each phase is governed by fluid-particle and particle-particle interactions. The particle-particle collisions can significantly affect the motion of individual particles and hence the solid-liquid two phase flow characteristics. In the current work, computational fluid dynamics-discrete element method (CFD-DEM) simulations of a dense foreign particle introduced in a monodispersed solid-liquid fluidised bed (SLFB) have been carried out. The fluidisation hydrodynamics of SLFB, settling behaviour of the foreign particle, fluid-particle interactions, and particle-particle collision behaviour have been investigated. Experiments including particle classification velocity measurements and fluid turbulence characterisation by particle image velocimetry (PIV) were conducted for the validation of prediction results. Compared to those predicted by empirical correlations, the particle classification velocity predicted by CFD-DEM provided the best agreement with the experimental data (less than 10% deviation). The particle collision frequency increased monotonically with the solid fraction. The dimensionless collision frequency obtained by CFD-DEM excellently fit the data line predicted by the kinetic theory for granular flow (KTGF). The particle collision frequency increased with the particle size ratio (dP2/dP1) and became independent of the foreign particle size for high solid fractions when the fluidised particle size was kept constant. The magnitude of collision force was 10-50 times greater than that of gravitational force and maximally 9 times greater than that of drag force. A correlation describing the collision force as a function of bed voidage was developed for Stp>65 and dP2/dP1=2. A maximum deviation of less than 20% was obtained when the correlation was used for the prediction of particle collision force. © 2014 Elsevier Ltd.

In this study, microwave irradiation was applied to hanging droplets of both water and ethylene glycol. Once the irradiation had ceased and the droplet was allowed to return to its original temperature, it was found that the surface tension of ethylene glycol returned to its original value. In contrast, the water surface tension remained well below its original value for an extended period of time. Similar observations have been reported for magnetically treated water, but this is the first time that such a lasting effect has been reported for microwave irradiation. The effect can be attributed to the unique hydrogen bonds of interfacial water molecules. While the irradiation intensities used in this study are well above those in household devices, there is certainly the potential to apply the methodology to industrial applications where the manipulation of surface tension is required without the use of chemical addition. © 2014 American Chemical Society.

The maximum liquid fraction that stable pneumatic foam can support is studied in this paper in order to illuminate change of flow regime from turbulent foam flow to the "emulsion regime" in which the distinct interface between the foam layer and the bubbly liquid is lost; this regime transition is nominated as "flooding". With further increases in gas flow rate, large (or "gross") bubbles can appear and rise in the column, the existence of which depends on the absolute pressure at the column bottom. Experiments are carried out using foam stabilized by sodium dodecyl sulfate, and the liquid fraction of both the foam layer and the bubbly liquid are measured using a pressure gradient method. The maximum liquid fraction is found to be at a critical point when the interface between the foam and the bubbly liquid layer disappears. The predicted maximum liquid fraction in the foam is given by e* = (n - 1)/(n + 1), where n is an adjustable constant that depends upon the characteristics of the gas-liquid interface, and the predictions have been experimentally verified. © 2014 American Chemical Society.

Film flotation is highly dependent upon how well wanted and unwanted particles are separated at the gas-liquid free surface. Single particle experiments and modelling analysis can be undertaken to determine a critical impact velocity at which the optimum separation is likely to occur. However, in commercial film flotation systems the higher loading density of the free surface can result in interactions that change the critical impact velocity. To investigate this influence, film flotation experiments have been undertaken with 4, 5 and 6 mm diameter spherical polypropylene particles with water, sucrose and surfactant (CTAB) solutions contained within vessels of varying dimensions and wettability (static contact angle). Experimentally it was observed that for a given particle diameter the critical impact velocity was found to decrease with decreasing vessel diameter, especially when the particle-to-vessel diameter ratio increased beyond about 0.2. Conversely, the critical impact velocity was found to be relatively independent of the liquid depth; but did decrease with decreasing static contact angle in the region where the vessel wall had an influence. The experimental system was also modelled using the Young-Laplace equation using both static and advancing contact angle measurements for both the particle and vessel surfaces. The model predictions were generally in good agreement with the experimental observations, including showing an increase in particle penetration depth with increasing vessel diameter and meniscus profiles, both at the particle impact point and the wall of the vessel. The predictions were improved when the advancing contact angle was used, especially for the smaller diameter vessels where there was more liquid motion. Finally, a model to determine the critical (minimum) diameter of vessel required so that the cavity profile generated by the impacting particle is unlikely to be influenced by the vessel walls is presented. © 2013 Elsevier Ltd. All rights reserved.

The Jones-Ray effect is shown to be governed by a different mechanism to enhanced anion adsorption. Halide ions at sub-molar concentrations are not exposed to the vapour phase; instead their first-solvating shell intimately interacts with the outmost water layer. Our novel proposal opens challenges for predicting related interfacial phenomena consistently. © the Partner Organisations 2014.

In this study the transition from homogeneous to heterogeneous flow in a solid-liquid fluidized bed (SLFB) is examined both experimentally and numerically. The experimental apparatus comprised a refractive index-matched SLFB, comprising 5. mm diameter borosilicate glass and sodium iodine solution, which allowed for both instantaneous particle image velocimetry of the liquid flow field and solids hold-up measurements to be undertaken for superficial liquid velocities in the range of 0.06-0.22. m/s. The motion of individual, spherical steel balls (with diameters 6, 7, 8, 9. mm) was then tracked as it settled through the fluidized bed for differing superficial liquid velocities. It was observed that, for all the steel balls covered in this work, there was a change in slope in their respective classification velocity curves at a superficial liquid velocity of 0.08. m/s. This value was very close to the critical velocity of 0.085. m/s predicted from 1-D linear stability analysis; and therefore deemed to be the critical condition that marked the transition from homogeneous to non-homogenous flow. It is proposed that the change in slope of the classification velocity curve is due to the encounter of the settling foreign particles with liquid bubbles whose presence marks the onset of heterogeneous flow. Additional computational analysis, involving both Eulerian-Eulerian (E-E) and Eulerian-Lagrangian (E-L) approaches, is used to confirm the presence of liquid bubbles at a critical liquid hold-up of 0.54, which corresponds to that predicted from 1-D linear stability analysis. In summary, the study has highlighted that experimentally the transition condition for a SLFB can be obtained simply by observing the behavior of the classification velocity of a single foreign particle at different superficial liquid velocities. This transition condition was found to agree with the 1D linear stability criterion, Eulerian-Eulerian CFD (3D) and Eulerian-Lagrangian DEM (3D) approaches. © 2014 Elsevier B.V.

Volume of fluid and continuum surface force methodologies were applied to two- and three-dimensionally model the motion of a liquid jet injected vertically downward from a rectangular nozzle into another immiscible liquid. Grid independent solutions were obtained for a 10mm2 nozzle with aspect ratios in the range 1-10. It was found that unlike the 3D simulation, the 2D CFD model was not able to predict the necking and breakup features observed in the experimental system. The 3D model showed that upon exiting the rectangular nozzle the liquid jet underwent a transition before becoming circular in cross-section and eventually reaching an equilibrium diameter prior to breakup into droplets. For a given nozzle geometry it was found that equilibrium jet diameter increased with increasing liquid volumetric flowrate, with good agreement between CFD simulations and experimental observations. The 3D model was applied to rectangular nozzles with different aspect ratios and it was found that for a given liquid flowrate there was an optimum aspect ratio for generating minimum-sized droplets, which was approximately 30% less than for a circular nozzle with the same cross-sectional area. © 2011 Canadian Society for Chemical Engineering.

Particle image velocimetry measurements have been performed in a solid-liquid fluidized bed in the Reynolds number range 51-759. To do this, the refractive indexes of the solid and liquid phases were matched at approximately 1.47 using 3. mm diameter borosilicate glass beads and a solution of turpentine and tetra-hydronaphthalene. Paraffin oil was added in varying quantities to vary the dynamic viscosity between 0.0012 and 0.010. Pa. s without changing the refractive index of the solution. From the PIV measurements, at sampling rates of 2. Hz, the fluctuating velocity components were found to be quite uniform in both the axial and radial directions. Moreover, the computed turbulent kinetic energy dissipation rates were also found to be relatively constant throughout the bed, thus highlighting the homogenous nature of the turbulence within the system.Following from Reddy et al. (2010b), direct numerical simulations were undertaken at particle Reynolds numbers up to 200 for assemblages of 1, 9, 27, 100, 180 and 245 particles, which corresponded to a liquid volume fraction range of 0.687p¿Lp0.998. The effect of surrounding particles on the settling velocity (hindrance effect) and the wake dynamics was investigated. It was found that the average settling velocity decreased with an increasing number of particles, with the quantitative results being in good agreement with the well established empirical correlation of Richardson and Zaki (1954). The local energy dissipation rate was also computed, and for a particle Reynolds number of 51, it was found to be 5.5m2s-3. This value was approximately 18 times the average energy dissipation rate of 0.30m2s-3; and compared favourably with the 0.36m2s-3obtained by a volume-averaged energy balance of the experimental system. © 2012 Elsevier Ltd.

Electroflotation is used in the water treatment industry for the recovery of suspended particles. In this study the bubble formation and release of hydrogen bubbles generated electrolytically from a platinum cathode was investigated. Previously, it was found that both the growth rate and detachment diameter increased with increasing wire diameter. Conversely, current density had little effect on the released bubble size. It was also found that the detached bubbles rapidly increased in volume as they rose through the liquid as a result of decreasing hydrostatic pressure and high levels of dissolved hydrogen gas in the surrounding liquid. The experimental system was computationally modelled using a Lagrangian-Eulerian Discrete Particle approach. It was revealed that desorption of gaseous solutes from the electrolyte solution, other than hydrogen, may have a significant impact on the diameter variation of the formed bubbles. The simulation confirmed that liquid circulation, either forced or induced by the rising bubble plume, influences both the hydrogen supersaturation (concentration) in the neighbourhood of the electrode and the size of the resulting bubbles.

This study experimentally investigates the application of a solid-liquid micro-fluidised bed as a micro-mixing device. The experiments were performed in a borosilicate capillary tube with an internal diameter of 1.2. mm (i.e. near the upper-limit dimension of a micro-fluidic system) using borosilicate particles with a mean diameter of 98 µm. Refractive index matching technique using sodium iodide solution was employed to achieve a transparent fluidised bed. Mixing performance of the micro-fluidised bed in terms of mixing time was investigated using a dye dilution technique. Experiments were carried out in the creeping flow regime at Reynolds numbers ranging between 0.27 and 0.72. It was demonstrated that the micro-fluidised bed mixing time sharply decreases as the Reynolds number increases. That is because at relatively high Reynolds numbers, the particle oscillation is stronger creating larger disturbances in the flow. The energy dissipation rate in micro fluidised bed was estimated to be four orders of magnitude less than other passive micro mixers which operate in the turbulent regime. It was also demonstrated that the ratio of mixing time and the energy dissipation rate for fluidised bed micro-mixer was comparable to K-M, Tangential IMTEK, and interdigital micro-mixers. However, the fluidised bed micro-mixer was found to operate at much lower Reynolds numbers compared to other passive mixers, with a mixing time of the order of few seconds. © 2013 The Institution of Chemical Engineers.

A model for estimating world natural gas production to peak in 2043 has been developed and takes into account the conventional natural gas production peak by 2038, the world unconventional natural gas production peak in 2038 as well the decline in methane hydrate. The model approximates coalbed methane while natural gas demand is modeled by analyzing demand per person and population forecasts. Estimating the worldwide coalbed methane resource and the determination of a reasonable recovery factor yields he coalbed methane unconventional ultimately recoverable resources (URR) estimate. Another input comes from the determination of conventional natural gas URR estimate. The model estimates that methane hydrate resources are about 1,000 tcm.

The results of measurements of the mass transfer coefficient for CO 2 bubbles in 70% aqueous glycerol solution have been presented. The bubbles have been generated by means of a distributor made of a rotating cylinder. Such a type of gas distributor prevents formation of large bubbles in liquids of higher viscosity and hence supports intensification of the mass transfer process.

This paper presents an analysis on the dynamic adsorption of frothers and collectors onto air bubbles in flotation. The analysis was carried out using the theory on the surfactant transfer by diffusion and adsorption. The bubble size was considered when solving the diffusion equation for the dynamic surface excess. The adsorption kinetics was modelled employing the Langmuir adsorption isotherm and its extension with the inclusion of the lateral interaction of the adsorbed molecules (the Frumkin adsorption isotherm). The numerical computation was applied to solve the governing equations. The dynamic adsorption of the surfactants was measured in terms of the dynamic surface tension for sodium dodecylbenzene sulfonate (SDBS) and Dowfroth 250, using pendant bubble tensiometry. The results show that for air bubbles with diameter of the order of 1 mm, the bubble size effect on the dynamic surface tension is small and the solution of the diffusion equation for a planar gas-liquid surface can be used to describe the dynamic adsorption onto the air bubbles. The experimental data obtained with SDBS were well described by the Frumkin adsorption isotherm and the molecular diffusion. The model description for the experimental data obtained with Dowfroth 250 required the kinetic equations. The paper is relevant for further analysis of the role of the adsorbed surfactants in the particle collection.

The second stage of an undergraduate laboratory experiment based on the concepts of compressible flow was described. The second stage of the experiment involved discharging vessel to atmosphere through a converging nozzle and recording the pressure-versus-time relationship for the process. The discharging vessel was emptied from an initial pressure of approximately 730 kPa to ambient conditions and the variation in vessel pressure with time was recorded. The results show a linear relationship between vessel pressure and time with the absolute value of the gradient increasing with increasing nozzle diameter.

The results of CFD simulation of a rotating cylindrical gas sparger in a downflowing liquid are presented. The simulations cover one-phase flow (73% aqueous glycerol) and two-phase flow (air-water) with special care taken to modelling the gas cavity that forms under such conditions. The velocity field measured with the aid of Particle Image Velocimetry (PIV) is compared with the simulation results for the case of one-phase flow.

Coarse particle (typically more than 100 micrometers in diameter) flotation is adversely influenced by liquid motion resulting from energy input associated with mixing of the gas and solid phases. In particular, the collected particles can become detached from the bubble as the particle-bubble aggregate passes through regions of different turbulent levels. The dynamics of particle-bubble-turbulence interaction is almost impossible to visualize within a real flotation environment as the phases are in constant motion which changes with time and position. To study the phenomenon of the particle bubble detachment process the problem was mimicked in such a way as to have a bubble detaching from a stationary 3 mm diameter steel particle in the turbulent field. A bubble of known volume was firstly introduced onto the submerged particle surface via a syringe needle. Image analysis was used to determine the bubble-particle contact angle and radial position of the three phase contact line under quiescent conditions. An oscillating grid device was then used to generate turbulent liquid motion around the particle-bubble aggregate. Particle image velocimetry (PIV) was used to quantify the instantaneous velocity field around the disturbed bubble. Laser induced-fluorescence (LIF) was applied to filter out the (green) internally reflected light from the bubble so that only the (orange) light from the fluorescing seeding particles was collected. The PIV-LIF images were then analysed by firstly utilising a masking technique to eliminate spurious velocity vectors inside the bubble. The velocity data in an envelope surrounding the bubble was extracted to calculate local, instantaneous values of liquid velocity, turbulent kinetic energy and energy dissipation rate. It was found that the flow structures generated by the oscillating grids resulted in a lateral inclination of the gas-liquid interface at the three phase contact line. The subsequent change in the dynamic contact angle resulted in a reduction in the capillary (attachment) force, and at a high enough turbulence level it became less than the buoyancy (lift-off) force and detachment of the bubble from the particle surface took place. The detachment events observed in this study is analogous to what actually takes place in mineral flotation cells where the bubble-particle aggregate is in motion.

Surface tension of fluid is crucial for multiphase systems and is often manipulated during industrial processes by introducing surfactants. In this study, effect of microwave radiation on surface tension of aqueous solution was investigated for new physical method to manipulate the surface tension without using chemicals. It has found that surface tension profiles of aqueous solution during microwave are different with the salt concentration. Moreover, convections in the droplet during microwave radiation were compared to provide new understanding on the non-thermal effect of microwave. © 2014 SPIE.

In this study, microwave irradiation is applied to a liquid droplet and the surface tension, the circulation flow and temperature of water droplet are measured dynamically under the irradiation. The droplet was allowed to return to its original temperature after the irradiation, it was found that water surface tension remained well below its original value for an extended period of time. Surface tension reduction shown similar effect of "impurity" at molecular level during the microwave, and some "memory" after microwave, which might be caused by nano-bubble. On the other hand, microwave can introduce the circulation flow of higher rotation speed and will be expected to be applied for non-contact stirring method. © 2014 SPIE.

Transport phenomena occur frequently in industrial problems. Most of the turbulent transport properties can be directly associated with the turbulent energy dissipation rate; hence it is a very significant parameter in the design of chemical processing equipment. To develop a better chemical processing equipment design, a thorough knowledge of the effect flow structure on local turbulence parameters like turbulent kinetic energy, eddy diffusivity and the energy dissipation rate are required. Turbulence is heterogeneous in most of the process equipment. Hence, the use of spatial average energy dissipation rate causes error in modelling of turbulent transport processes. In this present work, particle image velocimetry (PIV) is used to obtain the energy spectrum from grid generated homogeneous turbulence velocity data. The model of energy spectrum given by Kang et al. (2003) has been fitted to this energy spectrum using energy dissipation rate. A different approach, based on a third order structure function and velocity gradient technique has been used to compute the energy dissipation rate. The model predictions have been verified by experimental PIV velocity data from oscillating grid apparatus.

Coal exports are an important source of revenue for Australia and for this reason Australian coal production and resources have been examined in detail. Two recoverable resource estimates, a Standard case and a High case, were determined. The Standard case calculated the likely recoverable coal resources in Australia to be 317 Gt, whereas the High scenario determined the maximal amount of recoverable coal resources at 367 Gt. The study performed forecasting by use of curve-fitting with Logistic and Gompertz curves as well as Static and Dynamic versions of a supply and demand model based on real world mineral exploitation. The different modelling approaches were used to project fossil fuel production and the outlooks were compared. Good agreement was found between the Logistic, Static and Dynamic supply and demand models with production peaking in 2119±6 at between 1.9 and 3.3 Gt/y. Contrasting these projections the Gompertz curves peak in 2084±5 at 1-1.1 Gt/y. It was argued that the Logistic, Static and Dynamic models are more likely to produce accurate projections than the Gompertz curve. The production forecast is based on existing technology and constraints and a qualitative discussion is presented on possible influences on future production, namely: export capacity, climate change, overburden management, environmental and social impacts and export market issues.

A recent paper [L. C. Nitsche, A. Nguyen and G. Evans, Chem. Phys. Lett., 397, 417-421 (2004).] developed a cohesive chemical potential (referred to here as "primary" cohesion) for treating liquid-liquid interfaces, which yielded the correct free-surface evolution of drops while seeming to circumvent the characteristic properties of interfacial tension. Diffusion of miscible interfaces was interpreted as a consequence of the same driving force, acting through a different propagator. In this work we refine the chemical potential formulation by semi-analytically subtracting out, at each point within a drop, the corresponding potential for a flat interface at the same distance. The new "secondary" cohesive potential is shown to be consistent with the usual interfacial stress-jump boundary condition, while allowing interfacial "information" to be spread over a significant volume of the drop(s). In other words, the numerically defined interfacial layer need not be "thin". Reduction of parasytic currents in computer simulations is considered. Secondary cohesion is contrasted with (i) two prevailing volumetric versions of interfacial tension, as used in volume-of-fluid and front-tracking numerics, and (ii) the diffuse interface method [D. M. Anderson, G. B. McFadden & A. A. Wheeler, Ann. Rev. Fluid Mech., 30, 139-165 (1998)]. Morphological energy penalties and representations of diffusion associated with the various interfacial chemical potentials are compared. In particular, the double-well mixing energy density of the diffuse interface model can be simplified for certain modeling purposes. Numerical simulations based upon swarms of fuzzy Stokeslets are compared with experiments involving trailing drops and surfaces.

Chemical engineering at the University of Newcastle has introduced a "Systems Thinking" approach in response to the changing needs of today's young engineers, particularly in relation to sustainable development and interaction with the wider community. The basic concepts are reinforced to the students in the form of case studies. The activities cover a broad range of traditional chemical engineering principles, including fluid mechanics, heat and mass transfer, process flowsheeting, and design. The case studies have the additional dimensions of life cycle modelling, environmental impact assessment, and direct interaction with the broader community. In this paper, two examples, involving Building Design and On-Site Water Management, are presented, including a brief description, desired learning outcomes, results and general observations. Generally, it was found that the case studies provided an excellent framework for establishing a systems approach to arriving at solutions, and acted as a focus for quantitative analysis using the various tools taught during the course. Most importantly, the material presented assisted students to understand the practices which contribute to the transition to a sustainable society.

In this study a computational model was developed to describe the motion of spherical particles, of different diameters and densities, in the liquid flow field generated by an axisymmetric, confined, submerged jet. Initially, a model was developed to predict the single (liquid) phase motion generated by the jet. The liquid velocity predictions were experimentally validated before proceeding to incorporate a coupled Lagrangian model to describe the motion of the particles. Finally, the model is currently being extended to include the influence of the particle on the fluid motion and the effect of particle-particle interactions.

For a submerged jet, there are many design characteristics to explore for better mixing of buoyant particles (BP). Industries are facing difficulties in mixing of BP. Higher turbulence favors mixing, but mixing of BP has always been an art. Submerged jet (SJ) or impinged jet (IJ) is one of the ways to disperse BPs. For a SJ, modeling of free surface is important when the jet is not deeply submerged (~ 10 mm) in the liquid bath. In this research project, the free surface (surface between air and liquid) for a SJ system in a cylindrical liquid bath and entrainment of BPs has been studied with CFD analysis. The solution parameters (velocity profile and center line velocity) are validated against experimental LDV data generated. The use of 2D axisymmetric geometries minimized the computational cost. To overcome the computational burden of tracking individual panicles, the dispersion of particles/turbulent fluctuations were determined by a Particle Cloud Model.