Dr Zhengbiao Peng

A three-dimensional hot flow model for simulating the alumina encapsulated Ni/NiO methane-air CLC system is developed. The temperature of particles (i.e., metal/metal oxides) is calculated based on exothermal/endothermal reactions and the convective heat transfer between particles and the gas mixture. The temperature of the gas mixture is solved by incorporating the energy exchange with the oxygen carrier particles into the governing equations. The motion of particles is tracked using the discrete element method, whilst the fluid flow is governed by the modified Navier-Stokes equations derived by replacing the point and fluid mechanical variables with locally averaged variables and the inclusion of local gas volume fraction. Two different CLC systems with different initial particle conversion rates have been simulated and the characteristics of the CLC hot flow system in terms of distributions of particle and gas mixture temperatures, solid circulation rate and particle conversion rate have been analysed and discussed. The results showed that the transient solid circulation rate varied but fluctuated around a certain value. Heterogeneous distributions of particle temperature and conversion rate have been observed in both fuel and air reactors. The model has been validated by comparing the predicted solid circulation rate and pressure distribution against the experimental data. The hot flow model proves capable of reproducing the CLC mechanism, i.e., transferring oxygen atom from the air reactor to the fuel reactor.

Theoretical modelling, design and operation of circulating and interconnected fluidized beds require an accurate prediction of solids holdup in the fully developed pneumatic conveying flow regime of the riser (i.e. the upper section of the riser). Existing empirical and semi-empirical solids holdup correlations have exhibited limited accuracy and application range. In this study, an empirical correlation was developed to predict the solids holdup at the upper section of the riser in circulating and interconnected fluidized beds with an improved level of accuracy for a broad range of operating conditions and riser dimensions. The correlation is based on a group of dimensionless quantities, which are typically used to describe the hydrodynamics of gas-solids fluidized beds, taking into account gas and particle properties, riser dimensions, and solid circulation rate. The reduced solids flux phenomenon also has been considered directly by introducing a system dependent exponent in the correlation. The correlation predicted 90% of the experimental data with an average deviation of 15%. The correlation is applicable for particle Reynolds numbers between 3.7 and 366.

Gas-solid fluidised beds are widely used in chemical, petrochemical, pharmaceutical, biochemical and powder industries. Particles used in gas-solid fluidised beds often differ in size and/or density, thus have the tendency to segregate under certain operating conditions. The results of our earlier work (Alghamdi et al., 2013) showed that for a given binary mixture, the transition from segregation to mixing occurred when the superficial gas velocity was increased over a critical value. In this study, force analysis at particle scale, including particle-particle, particle-wall and particle-fluid interacting forces, has been performed to investigate the underlying mechanisms that drive the occurrence of the transition. The results showed that as the superficial gas velocity increased, the system exhibited three sequential states: segregated, transition, and mixed. The vertical fluid force acting on the particles was found to be responsible for the occurrence of the transition from segregation to mixing, at which the bulk density of the heavy (small) particle species became smaller than the actual density of the light (large) species. After the occurrence of the transition, the particle collisional effects were dominant over the fluid viscous effects in governing the gas-solid two-phase flow. After the system became mixed, the net force of fluid and particle net weight forces conversely tended to separate the particles. However, the particle dispersion induced by particle collisions counterbalanced the particle segregation, acting as the main mechanism driving the good mixing of the binary particle species. The simulation results were in good agreement with the experimental data.

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 (Re =40, ¿ =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 (Re >40, ¿ >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. p L, ave p L, ave

The void fraction of computational cells in numerical simulations of particulate flows using computational fluid dynamics-discrete element method (CFD-DEM) is often directly (or crudely) calculated assuming that the entire body of a particle lies in the cell at which the particle centroid resides. This direct method is most inexpensive but inaccurate and may lead to simulation instabilities. In this study, a modified version of the direct method has been proposed. In this method, referred to as the particle meshing method (PMM), the particle is meshed and the solid volume in a fluid cell is calculated by adding up the particle mesh volume with the basic working principle being the same as that of the direct method. As a result, the PMM inherits the simplicity and hence the computational advantage from the direct method, whilst allowing for duplicating the particle shape and accurate accounting of particle volume in each fluid cell. The numerical simulation characteristics of PMM including numerical stability, minimum particle grid number, prediction accuracy, and computational efficiency have been examined. The results showed that for a specific cell-to-particle size ratio, there was a minimum particle grid number required to reach the stable simulation. A formula of estimating the minimum particle grid number was derived and discussed. Typically, a particle grid number of about 5 times the minimum number was suggested to achieve the best computational efficiency, which was comparable or even higher than that of simulations using the analytical approach. PMM also exhibited the potential to be applied for complex computational domain geometries and irregular shaped particles.

In a chemical looping combustor (CLC) system, the solid circulation rate (SCR) is a key parameter that determines the design, operating conditions and the overall efficiency of the system. In the present work, the gas-solid flow of a CLC cold flow model (10kW ) has been simulated by the computational fluid dynamics-discrete element method (CFD-DEM). The results showed that the SCR at different locations of the system fluctuates with time with different amplitude, and the variation of SCR is periodically stable. The turbulent gas-solid flow regime in the air reactor was found to be the main mechanism driving the fluctuation of SCR and determined the fluctuation frequency and amplitude. The SCR increased with the flow rates of air/fuel reactors and loop seals, and the total solid inventory. Changes in operating conditions directly induced the change in the mass of solids that were entrained into the riser from the air reactor and how fast the solids were transported therein. A correlation was subsequently proposed to describe the SCR as a function of solid hold-up and gas flow velocity in the riser. The particle residence time decreased in a power law as the SCR increased. Reasonable agreements were obtained between simulations and experiments in terms of solid distribution, gas-solid flow patterns, pressure drop profiles and SCR. th

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.

In chemical looping combustion systems, accurate measurement of the solid circulation rate (SCR) is crucial for optimising the system performance. Conventionally, the SCR is predicted using the riser total pressure drop leading to an overestimation of up to 70%. In this work, a model has been proposed for the SCR prediction using the pressure drop at the top section of the riser. The height of this top section was determined by the riser gas-solid flow characteristics, namely, the axial solid holdup profile and lateral solid flux profile. A kinematic model was developed to predict the axial solid holdup profile and the reduced solid flux model developed by Rhodes et al. (1992) was employed to predict the mass fraction of upwards flowing solids. The prediction results of the proposed model were validated against the experimental data obtained in this work and those reported in the literature, where the prediction accuracy of SCR was significantly improved (by up to 60%) with a deviation of around 15%.

The correct calculation of cell void fraction is pivotal in accurate simulation of two-phase flows using a computational fluid dynamics-discrete element method (CFD-DEM) approach. Two classical approaches for void fraction calculations (i.e., particle centroid method or PCM and analytical approach) were examined, and the accuracy of these methodologies in predicting the particle-fluid flow characteristics of bubbling fluidized beds was investigated. It was found that there is a critical cell size (3.82 particle diameters) beyond which the PCM can achieve the same numerical stability and prediction accuracy as those of the analytical approach. There is also a critical cell size (1/19.3 domain size) below which meso-scale flow structures are resolved. Moreover, a lower limit of cell size (1.63 particle diameters) was identified to satisfy the assumptions of CFD-DEM governing equations. A reference map for selecting the ideal computational cell size and the suitable approach for void fraction calculation was subsequently developed. © 2014 American Institute of Chemical Engineers.

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 (d /d ) 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 St >65 and d /d =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. P2 P1 p P2 P1

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.

Performance of chemical looping combustion processes can be improved drastically by enhancing the overall redox characteristics of the system through the use of binary mixtures of oxygen carriers. However, binary mixtures of oxygen carrier particles are often found to differ in both size and density and therefore have the tendency to segregate under certain operating conditions.In this work, a numerical study was conducted to investigate the mixing and segregation behaviour of binary mixtures of particles with different sizes and densities in a bubbling fluidized bed under conditions pertinent to the fuel reactor of a cold flow model (i.e. a non-reacting replica) of a 10kW chemical looping combustor. The motion of particles was tracked individually by discrete element model (DEM), whilst the gas flow was modelled by computational fluid dynamics (CFD). Gas-particle interactions were considered by a two-way coupling method. Further, a modified version of Lacey's method was developed to calculate the mixing index, taking into account both the heterogeneity of solids spatial distribution and particle size differences.Results showed that the modified Lacey's method provided very consistent and stable mixing indexes, proving to be effective for an in-situ quantitative description of mixing. It was also found that as the size ratio of the binary mixture of particles reduced, the mixing index increased indicating better mixing conditions. The agreement between the DEM/CFD model predictions and the experimental data was found to be satisfactory. The optimum conditions for mixing of binary mixtures appeared to be a function of bubble size, bubble rising rate and bubbling dynamics (e.g., splitting and coalescence). Application of the DEM/CFD model for prediction of layer inversion phenomenon in gas-solid fluidized beds was also demonstrated. © 2012 Elsevier B.V. th

Multiphase flows have received increasing attention over the past decades. This paper describes the research carried out in Thermo-Energy Engineering Institute of Southeast University in recent years, focusing on several common issues associated with multiphase flows in industry, such as: boiling of falling film and complex structure of gas-liquid flow under large difference in temperature, free surface flows involving liquid jets and drop formation, mixing behaviors of gas-liquid-solid three-phase flow, and fluidization characteristics of cylindrical particles. Numerical methods ranging from empirical to CFD models were developed for predictions, and experimental works were essentially conducted for validation and modification. For all cases, simulated results were validated with experiments and good agreements were obtained. Based on the combined modeling and experimental approach, fundamental understanding of multiphase processes in a specific circumstance is achieved under conditions relevant to the actual industrial-scale, such as transport phenomena, flow patterns, fluid dynamics and interactions between phases. © 2010.

Drop formation in liquid-liquid fluidized bed was investigated experimentally. The normal water was injected via a fine-capillary spray nozzle into the co-flowing No. 25 transformer oil with jet directed upwards in a vertical fluidized bed. Experiments under a wide variety of conditions were conducted to investigate the instability dynamics of the jet, the size and size distribution of the drops. Details of drop formation, drop flow patterns and jet evolution were monitored in real-time by an ultra-high-speed digital CCD (charge couple device) camera. The Rosin-Rammler model was applied to characterize experimental drop size distributions. Final results demonstrate that drop formation in liquid-liquid system takes place on three absolutely different developing regimes: bubbling, laminar jetting and turbulent jetting, depending on the relative Reynolds number between the two phases. For different flow domains, dynamics of drop formation change significantly, involving mechanism of jet breakup, jet length pulsation, mean size and uniformity of the drops. The jet length fluctuates with time in variable and random amplitudes for a specified set of operated parameters. Good agreement is shown between the drop size and the Rosin-Rammler distribution function with the minimum correlation coefficient 0.9199. The mean drop diameter decreases all along with increasing jet flow rate. Especially after the relative Reynolds number exceeds a certain value about 3.5 × 10 , the jet disrupts intensely into multiple small drops with a diameter mainly ranging from 1.0 to 1.5 mm and a more and more uniform size distribution. The turbulent jetting regime of drop formation is the most preferable to the dynamic ice slurry making system. © 2008 Elsevier Ltd. All rights reserved. 4

The syngas passing through a pool is scrubbed in scrubbing-cooling chamber of coal-water-slurry (CWS) entrained-flow coal gasifier. A three-dimensional Euler-Lagrange model was used to study the distribution of particles in scrubbing-cooling chamber. The simulation of gas and liquid turbulent flow described by RNG k-e model and the particle flow is modeled using the deterministic trajectory model. The collisions between particles were taken into account by means of direct simulation Monte Carlo (DSMC) method based on the hard-sphere model. Comparisons of computational results with experimental data were also made. The effects of operating conditions and size grading on the distribution of particle number concentration in the chamber was revealed through simulation and analysis. The results indicate that the axial distribution of particle number concentration becomes wave-shaped in pool of scrubbing-cooling chamber. Big particles are ease to subside and small particles are ease to suspend. With changing the particle size grading, the particle number concentration can be changed obviously. © 2008 Elsevier B.V. All rights reserved.

The optimization of gas-solid flow behaviors in circulating fluidized bed for flue gas desulfurization (CFB-FGD) was simulated. The particles trajectories were calculated by the direct simulation Monte Carlo (DSMC) method, and the gas motion was modeled by the improved k-e two-equation turbulent model. All equations were solved numerically on the unstructured meshes. Interactions of particle-fluid, particle-particle and particle-wall were considered rigorously based on the four-way coupling method. An effective model for searching the local unstructured mesh in which the individual particle lay was proposed to achieve 'one-to-one' interaction between phases. Gas-solid flow patterns before and after adjustment were obtained, as well as the distributions of the particle concentration and the gas/particle axial velocity. Further, critical factors that strongly influenced the residence time and collision frequency of particles were analyzed. Final results highly confirm the feasibility and effectiveness of the scheme chosen to optimize the gas-solid flow behaviors within the tower. After adjustment, the gas-solid flow field appears symmetrical ideally, and the interior space of the tower is utilized in full. Residence time of the particles with the same radius comes to be in chorus relatively. The particle residence time is related closely to the continuum flow field and the particle physical properties. Particle collision frequency decreases distinctly compared with that before adjustment.

Circulating fluidization of slender particles is applied widely in industry including combustion of biomass stalks and drying or wetting of cut-tobacco. The fluidizing behaviors of slender particles in the gas-solid flows are affected by several influence factors such as inter-particle collision, local flow velocity and so on. The three-dimensional particle-wall collision mathematical models were founded in the light of the kinetic of rigid and the momentum conservation law, and the effects of wall on the fluidizing behaviors of slender particles in a circulation fluidized bed were studied by using the established three-dimensional mathematical models. It is found that the orientation distribution and concentration of slender particles in the riser is evidently affected by wall, especially in the regions near the wall, and the variation of orientation distribution of slender particles according to the radial positions of the riser is affected by wall too.

A three-dimensional fluidization model of slender particles is established with the Euler-Lagrange method, rigid dynamics and fluid mechanics models. The effects of particle-wall collision model are included in this model. Based on the established model, the concentration features of slender particle are studied using actual parameters of structure and operating. It is found that the slender particles cannot form evident dense-phase zone and dilute-phase zone without the inert materials in the riser, and two-way fluidizing of slender particles cannot form in the dense-phase either. The slender particles move slowly from nearby region of wallto centre zone with the increment of position of height; that is to say, there is the phenomenon of migration during the process of fluidization. The concentration of slender particles of nearby region of wall is affected by fluidizing velocity and the wall.

By adopting a numerical calculation method combining direct simulation Monte Carlo Method (DSMC) with Euler method, studied was the influence of the solid-phase particulate mass carrying rate in a two-phase turbulent flow of a flue gas desulfuration tower on the gas-phase flow field. When the particulate Strokes number in the tower is kept in a range from 1 to 100, the gas-solid flow coupling characteristics in the tower was analyzed by gradually increasing the particulate mass carrying rate. As a result, under different particulate mass carrying rates the in-tower gas-solid flow characteristics, the particulate concentration distribution along the axial direction, the gas-phase axial speed radial distribution and the bed layer pressure drop curves have been obtained. It has been found that when the particulate mass carrying rate is not greater than 0.031, the particulate flow exhibits a relatively good follow-up nature and assumes a pneumatic transmission flow state. In such a case, the particulate movement has an extremely small influence on the continuous phase field and can be neglected. When the particulate mass carrying rate is greater than 0.031, the gas-solid flow coupling action in the bed will be enhanced, and the discrete particulate movement will exercise a conspicuous influence on the gas-phase flow field. The gas-solid two-phase flow characteristics are dependent on each other and exhibit an obvious unstable state and non-uniformity. When the particulate mass carrying rate is relatively big, the bed layer pressure drop is closely related to the discrete particulate field distribution.

A new technique for ice slurry production was explored. Multiple small water-drops were formed in another immiscible chilled liquid by a single-nozzled atomizer and frozen in the fluidized bed by direct contact heat transfer. Experiments were conducted to investigate the dynamic behaviors of the ice crystal making system. The results demonstrate that the ice crystals could be produced continuously and stably in the vertical bed with the circulating coolant of initial temperature below -5°C. The size distribution of the ice crystals appears non-uniform, but is more similar and more uniform at lower oil flow rate. The mean ice crystal size rests seriously with the jet velocity and the oil flow rate. It decreases with decreasing the oil flow rate, and reaches the maximum at an intermediate jet velocity at about 16.5 m·s . The ice crystal size is also closely related to the phenomenon of drop-coalescing, which can be alleviated considerably by reducing the flow rate or lowering the temperature of the carrier oil. However, optimization of liquid-liquid atomization is a more effective approach to produce fine ice crystals of desired size. © 2008 Chemical Industry and Engineering Society of China (CIESC) and Chemical Industry Press (CIP). -1

The experimental apparatus of liquid-liquid circulating fluidized bed for drops formation was built up, by which the mechanism of drops formation of water in another immiscible liquid was investigated systematically. The high-resolution digital CCD (charge coupled device) camera was employed to acquire the process of drops formation in real-time, and the phenomena of form transition were studied based on comparison of the presentation of the photographs. The data extracted from photographs was reduced and analyzed by means of image processing and numerical calculation. The results show that the course of drops formation rests seriously with the relative Reynolds number between the two phases. It takes on three absolutely different developing forms as increasing the relative Reynolds number. The bubbling form of drops formation converts into the continuous jetting form when the Reynolds number is at 1632, and then into the confused jetting form at 1.14 × 10. Furthermore, the drop-size decreases as increasing the relative Reynolds number, especially when the Reynolds number exceeds 1.62 × 10 , and decreasing sharply. In the confused jetting form, jet breaks up intensely into a large number of smaller drops, which is perfect in the technique of circulating fluidized bed for ice slurry production in liquid-liquid system. 5

Drop formation in liquid-liquid atomization processes is one of the key techniques of liquid-liquid circulating fluid bed (CFB). A high resolution digital camera and image processing were used to investigate the process of drop formation in a normal CFB experimental system. The photos and sizes of drops in the whole flux range were obtained from experiments, and the distribution function was used to analyze the drop-size distribution (DSD). Experimental results indicated that DSD from a specific flux was in good agreement with Rosin-Rammler distribution function, and the areas of drop formation were divided into single drop formation section, transition section, and multiple drop formation section. It was found that with increasing flux, the uniformity of drops decreased at first and then increased and the median diameter of drops always decreased in both single drop formation section and multiple drop formation section. The uniformity and median diameter of drops in the multiple drop formation section changed insignificantly, whereas they remained unchanged in the transition section. And the diameters of drops formed were mostly between 0.7 mm and 1.0 mm while the flux of water was 50 ml·min . The research results provide a reasonable flux range of drop formation for practical operation of CFB based on the design demand of particle-size. -1

The mechanism of jet breakup and subsequent drops formation was studied experimentally. A high-speed CCD (charge coupled device) camera was employed to acquire in real-time the process of drops formation. Crucial factors that strongly influence the mean drop-size, jet length and the appearance of drops formation were investigated systematically by means of image processing and numerical calculation. Further, the Rosin-Rammler function was applied to analyze the drop-size distribution. Final results show that the drop-size distributes non-uniformly even under the same condition and agrees relatively well with the Rosin-Rammler distribution function. When the flow rate of the ambient immiscible liquid maintains invariable, the mean drop-size and the jet length reach the maximum respectively at the jetting-velocity of 2.3 m/s and 3.5 m/s. However, for a constant jetting-velocity, the process of drops formation appears completely different as the flow rate of the immiscible liquid changes. The process of drops formation rests seriously with the jetting-velocity and the flow rate of the immiscible liquid, and the values specified for them play a key role in optimization and control of drops formation.

The phenomena of drops coalescence were studied in liquid-liquid circulating fluidized bed. Critical factors that influenced the frequency of drops-coalescing were investigated through varying the mass flow rate and temperature of the carried oil-medium at same velocity of jetting. The high-resolution digital CCD (charge couple device) camera was employed to acquire the drops flow regime in real-time at different heights. The variation tendency of the mean particle-size along the bed was analyzed via image processing and numerical calculation. Ice particles produced at the lowest temperature of the oil-medium were measured manually and then the results were sorted. Based on these the scheme to restrain drops-coalescing was explored. Final results show that the influence of drops coalescence on the distribution of the ice-particle size is strong and intense, and the drops-coalescing frequency decreases with decreasing the mass flow rate of the oil-medium. However, partial surface breakup and swift freezing-out of drops make the mean particle-size decrease along the bed when the oil-medium temperature is lower. The quality of crystals produced for ice slurries can be improved by means of prescribing reasonable temperature and flow rates for the cold oil-medium, taking cost related factors into account and promising no ice-agglomeration.

A platform for numerical simulation of liquid-liquid atomization mechanism and another one for experimental study have been established. By employing the above platforms, water jet atomization mechanism in indissolvable solutions has been studied and its atomization process numerically simulated by using a VOF-CSF multi-phase flow model. An experimental verification and comparison was performed under identical working conditions. The study shows that the mathematical model set up by the authors can successfully simulate a continuous jet-flow atomization process and the simulation results are in extremely good agreement with the experimental ones. Through a combination of numerical simulation and experiments an exploratory study has been conducted of the influence of such key factors as jet-flow cone height, jet flow speed, indissolvable working-medium velocity etc. As a result, the following relevant law has been identified: under a certain atomization condition, the particle diameters of the atomization liquid droplets appear to be discrete; with an increase in jet flow velocity, the movement mode of liquid droplets assumes a gradual transition from being regular in shape to becoming turbulent. When the jet flow velocity is 3.5 m/s and the indissolvable medium velocity 0.18 m/s, the development trend of the atomization jet-flow cone height will undergo a change. The research findings are of major significance and have practical value for understanding liquid-liquid jet-flow atomization mechanism and better guiding relevant engineering applications.

The particle diameter distribution of liquid droplets is one of the key factors involved in the technology for making fluid ice from a liquid-liquid circulating fluidized bed. On a fluidized bed test device, by using a method combining high speed photography with image processing, a study has been conducted of the liquid-liquid single-hole atomized jet-flow at a low flowing speed and its impact on the distribution of particle diameters of liquid droplets. In this connection, a mathematic-statistical method was employed to analyze the change in jet flow length and the distribution of particle diameters of liquid droplets. It has been found from the analysis that a jet flow emerges when its speed is greater than 1.14 m/s and the fluctuations in the jet flow length at various flow speeds assume a random and non-periodic character. Moreover, with an increase of the jet flow speed the mean value and variance of the jet flow length show an overall variation tendency of 'first increase and then decrease'. With the jet flow speed being 6.58 m/s, which is a turning point, a spherical or conical jet-flow top is formed at the peak point of the jet flow length fluctuations. This is the main reason why there emerged a difference in magnitude of the particle diameters of liquid droplets and their movement routes showed signs of wobbling. At various flow speeds, the distribution of particle diameters of the liquid droplets is in very good agreement with Rosin-Rammler distribution. The research results provide a reliable basis for controlling the distribution of particle diameters of liquid droplets resulting from atomization during the actual operation of a liquid-liquid circulating fluidized bed.

This work describes a new dynamic ice-making method for ice-storage air condition. A numerical model for modeling liquid-liquid-solid three phase flow and heat transfer in ice-making chamber is developed. The influence of operating parameters on phase change of droplets in the process of dynamic ice-making was specially discussed by use of Euler-Lagrange methods, such as the droplet diameter, the inlet temperature and velocity of liquid phase. The results indicate that phase change of droplets is mainly influenced by the droplet diameter and the inlet temperature and velocity of liquid phase under certain conditions, and it enhances with decreasing these parameters. While the droplet diameter has the most remarkable influence on phase change of droplets, the inlet velocity of liquid phase does less, and the inlet temperature does the least. The calculated results provided a theory basis for the first design of operating and configuration parameters of ice-making bed.

Liquid-liquid circulating fluidized bed, which can be used as a novel method of dynamic ice forming, was studied using direct contact heat transfer between droplets and the coolant for ice storage system. A numerical model for modeling multiphase flows and heat transfer in circulating fluidized bed is developed. Exergy is discussed for liquid-liquid circulating fluidized bed based on the second law of thermodynamics. The numerical method is used to study the influence of operating parameters (such as the droplet diameter and the inlet temperature or velocity average of liquid phase) on ice-making performance and exergy in the dynamic ice-making process. The research results indicate that ice-making performance always increases with decreasing droplet diameter and the inlet temperature of liquid phase and not so much with decreasing the inlet temperature of liquid phase. Moreover, to decrease the droplet diameter is considered to be the best way with consideration of the contradiction of ice-making performance and exergy.

In the paper the ice slurry production system is introduced and the phenomenon of drop formation is discussed. Drop formation in liquid-liquid atomization processes is one of the key technologies of liquid-liquid circulating fluid bed (CFB). A high resolution digital camera and image processing were employed to investigate the process of drop formation in a normal CFB experimental system. The photos and sizes of drops in the whole flux range were obtained from experiments, and the distribution function was applied to analyze the drop-size distributions (DSD). Experimental results indicate that DSD from a certain flux is in good agreement with Rosin-Rammler distribution function(RRDF). ©2010 IEEE.