Particle image velocimetry for characterizing the flow structure of oil–water flow in horizontal and slightly inclined pipes

The simultaneous flow of oil and water in pipelines is a common occurrence in the chemical and process industry. An experimental investigation of oil–water flow in horizontal and slightly inclined pipes is presented in this paper. The experiments are performed in a 15 m long stainless steel pipe section with internal diameter 56 mm at room temperature and atmospheric outlet pressure. Exxsol D60 oil (density 790 kg/m³ and viscosity 1.64 mPa s) and water (density 996 kg/m³ and viscosity 1.00 mPa s) are used as test fluids. The pipe inclination is changed in the range from 5° upward to 5° downward. The measurements are made for two different mixture velocities, 0.50 and 1.00 m/s at water cut 0.50. The cross-sectional distribution of phase fractions in oil–water flow is measured using a traversable single-beam gamma densitometer. The different flow regimes are determined based on visual observations. The particle image velocimetry (PIV) is utilized in order to obtain non-invasive instantaneous velocity measurements of the flow field. Based on the instantaneous local velocities, mean velocities, root mean squared velocities and Reynolds stresses are calculated. Stratified flow with mixing at the interface is observed at mixture velocity 0.50 m/s. Interfacial waves are observed in upwardly and downwardly inclined flows. At mixture velocity 1.00 m/s, interfacial mixing is increased and dual continuous flows are observed. The degree of mixing largely depends on the pipe inclination. In general, higher water hold-up values are observed for upwardly inclined flows compared to the horizontal and downwardly inclined flows. The slip between the phases increases as the pipe inclination increases. The maximum mean axial velocity is detected in the more viscous oil phase at equal volumetric flow rates of oil and water. In addition, measured mean velocity and turbulence profiles show a strong dependency with pipe inclination. The largest root mean squared velocities and absolute values of the Reynolds stresses are observed close to the pipe wall due to higher mean axial velocity gradients. A damping effect of Reynolds stress is observed around the oil–water interface due to stable density stratification. The presence of interfacial waves enhances turbulence fluctuations in inclined oil–water flows.     

Coal–oil–water multiphase fuel: Rheological behavior and prediction of optimum particle size

As the coal–oil–water slurry is gaining importance in place of fuel oil, a better understanding of handling characteristics is in demand. Therefore, experimental investigations have been carried out to investigate the rheological properties of coal–oil–water suspension containing coal particles of different sizes. Different coal stocks with average particle sizes of 108 μm, 75.7 μm and 62.9 μm have been used. The concentration of solid for the experiment varies from 10% to 50% by weight. All experiments have been carried out in a cup and bob type coaxial cylindrical viscometer. Newtonian, shear thinning and shear thickening behavior of suspension has been observed depending on component content and operating conditions. Study with different particle sizes shows that it is possible to achieve an optimum particle size for better handling of such suspension. A generalized correlation has been developed to predict the apparent viscosity of coal–oil–water suspension incorporating the coal concentration, oil concentration, torque and particle diameter. The experimental data are in well agreement with proposed correlation.     

Processing of graded anode-supported micro-tubular SOFCs based on samaria-doped ceria via gel-casting and spray-coating

A simple gel-casting method was successfully combined with the spray-coating technique to manufacture graded anode-supported micro-tubular solid oxide fuel cells (MT-SOFCs) based on samaria-doped ceria (SDC) as an electrolyte. Micro-tubular anodes were shaped by a gel-casting method based on a new and simple forming technique that operates as a syringe. The aqueous slurry formulation of the NiO–SDC substrate using agarose as a gelling agent, and the effect of spray-coating parameters used to deposit the anode functional layers (AFLs) and electrolyte were investigated. Furthermore, pre-sintering temperature of anode substrates was systematically studied to avoid the anode–electrolyte delamination and obtain a dense electrolyte without cracks, after co-sintering process at 1450 °C. Despite the high shrinkage of substrate (～70%), an anode porosity of ～37% was achieved. MT-SOFCs with ～2.5 mm of outer diameter, 370 μm thick substrate, 20 μm thick AFLs and 15 μm thick electrolyte were successfully obtained. The use of AFLs with 30:70 and 50:50 wt% NiO–SDC allowed to obtain a continuous gradation of composition and porosity in the anode–electrolyte interface.     

Local Flow and Heat Transfer Behaviours in V-L-S Fluidized Bed Evaporator

The fluidized bed evaporator is a subject of considerable interest and can be employed in the process industries. However, the V-L-S flow behavior and heat transfer characteristics are still not well understood. In this work, a vertical fluidized bed evaporator with external natural-circulation flow boiling was established to investigate the local V-L-S flow behaviour and heat transfer characteristics and to reveal the influence of flow on heat transfer performance. It consists of a heated tube with inner diameter of 3.8 × 10⁻² m and height of 1.4 m and a circulating tube with the same inner diameter and height of 0.92 m. Both tubes are made of quartz glass plated with transparent electrically heating film. The solid particles added to the evaporator are glass, ceramic, Teflon™ and poly-formaldehyde beads or cylinders with the diameter ranging from 1.8 × 10⁻³ to 4 × 10⁻³ m. The particle volume changes from 0 to 1 × 10⁻³ m³ and heat flux varies from 5 × 10³ to 1.2 × 10⁴ W m⁻². The local velocity and holdup of solid particles, flow region transition, length of the V-L-S flow boiling, fluid circulating velocity and pressure drop in the V-L-S fluidized bed evaporator were visually investigated with CCD measuring technique. The main results on flow are as following. Axial solid holdup in heated tube of the evaporator decreases obviously for middle-density particle systems against the direction of the gravity. Three flow regions can be found in heated tube of the evaporator: L-S region, transition region and V-L-S region, and in transition region, the radial profile of solid holdups is relatively uniform. The increase of particle volume enlarges the length of V-L-S region and pressure drop, while decreases the circulating velocity of fluid mixture. The average heat transfer film coefficients of V-L-S flow boiling were estimated and a dimensionless correlation was obtained based on 120 sets of experimental data with a maximum relative deviation of 10.8%. The axial variation of the heat transfer coefficients has close relation to the axial distribution of the solid holdups.     

Study of solid–liquid mixing in agitated tanks through electrical resistance tomography

Electrical resistance tomography (ERT), which is a non-intrusive flow visualization technique, was used to investigate the solid–liquid mixing in an agitated tank equipped with a top-entering axial-flow impeller. The signals obtained from eight ERT planes were utilized to reconstruct the tomograms by using the linear back projection algorithm. The ERT measurements were correlated to solid concentration profiles by which the degree of homogeneity was quantified. In this study, the effect of important parameters such as impeller type (Lightnin A100, A200, A310, and A320 impellers), impeller speed (250–800 rpm), impeller off-bottom clearance (T/5–T/2, where T is the tank diameter), particle size (210–1500 μm), and solid concentration (5–30 wt%) on the degree of homogeneity were explored. The results showed that the degree of homogeneity in the solid–liquid mixing was improved with increasing the impeller speed. However, after reaching the maximum achievable homogeneity, further increase in impeller speed was not beneficial but might be detrimental. Hence, the measurement of the optimal impeller speed as a function of operating conditions and design parameters has vital role in achieving maximum homogeneity in a solid–liquid mixing system.     

Numerical study on pressure prediction and its main influence factors in pneumatic conveyors

The flow characteristics of multiphase gas–solid flow in a pneumatic conveyor were investigated numerically and experimentally to predict the important pressure within the pipeline. The effects of particle size, particle density, and bend radius ratio on pressure drop over the bend pipeline were also analysed. Experiments were conducted to obtain the static pressure at certain cross-sections of a fine powder pneumatic conveying pipeline with a length of 26 m and an inner diameter of 53 mm. The conveyed material was flyash with a mean particle size of 30 μm and the solids loading ratio was in the range 20–70. A numerical study of gas–solid flow in complex three-dimensional systems was undertaken by means of commercial CFD software Fluent 6.3. The simulation was performed using the Euler–Euler approach, accounting for four-way coupling. The calculated results of pressure gradient were found to be in good agreement with the measured data, with a fitting slope of 0.781 for the first horizontal straight pipeline and 1.017 for horizontal bend. It was also found that the pressure gradients increase with increase in particle diameter rapidly and reach the peak value when particle diameter is 150 μm, and then begin to decrease and show a slight steepening with increase in particle diameter with a value greater than 150 μm. An increase in particle density results in increase in pressure gradient. The pressure drop is much smaller when the roughness height is zero. The pressure gradient over the horizontal bend increases gradually with the increase of roughness height. The larger the roughness constant is defined, the greater the pressure drop will be. The bend pressure gradient decreases significantly when the bend radius ratio increases from 1 to 3, and then much slowly for bend radius ratios 3–6. With the increase of velocity difference, the pressure drop decrease is different at first, after 0.2–0.3 m, the pressure reduces the same.     

Microstructured ternary solid dispersions to improve carbamazepine solubility

The aim of this study was to investigate the improvement of the aqueous solubility of carbamazepine by preparing microstructured ternary solid dispersions using polyoxylglycerides and colloidal silicon dioxide. Microstructured solid dispersions were obtained in a spray dryer. The influence of the spray drying conditions on the properties of the microparticles was investigated using a full 3² factorial design in which the factors studied were the silicon dioxide content and the air outlet temperature. The microparticles were thoroughly characterized in terms of yield, solubility, angle of repose, particle size, drug content, moisture content, sorption isotherms, morphology, thermal behavior, infrared spectroscopy and crystallinity. The dissolution rates of carbamazepine and of the microparticles in water were also determined. In general, the microstructured solid dispersions demonstrated good yield, adequate flow and moisture content (< 3%), drug recovery (91.98 to 100.22%) and particle size (< 142.90 μm). Thermal and infrared analysis showed that there was no drug interaction during the process. On the other hand, the results of X-ray diffraction evidenced a partial polymorphic modification of carbamazepine. The solubility and dissolution rates of carbamazepine were remarkably improved. Therefore, the results confirm the high potential of the spray drying technique to obtain microstructured ternary solid dispersions.     

Effects of large scale eddies and stagnation surfaces on microcrystallization

A Lagrangian marker particle (LMP) method is applied to measure the toroidal large-scale eddies (LSEs) and their enveloping stagnation surfaces in a 280 l bottom-sweeping model crystallizer. The trajectories of a 0.4 cm diameter LMP show that these stagnation surfaces inhibit transport. Analysis shows that the velocity component normal to stagnation surfaces vanish. Therefore, stagnation surfaces act as a semi-permeable barriers to particle transport. Microconductivity measurements show that the stagnation surfaces are leaky at the molecular scale. Thus particle transport through stagnation surfaces is size-dependent. The LMP measurements reveal the structure of the LSEs. This consists of (1) an upward-swirling flow adjacent to the tank perimeter extending from the bottom to the top of the tank, (2) a central, quiescent zone, and (3) a downward return flow between (1) and (2) through a system of nested, smaller diameter, secondary toroidal flows concentric with the impeller axis. A cylindrical stagnation surface surrounds the central quiescent zone. These results are corroborated by measurements of inhomogeneous concentration profiles in an industrial scale 2000 l batch crystallizer. This leads to an understanding of the effects of LSEs on silver halide microcrystal particle size distribution in the industrial scale crystallizer.     

Effect of operating parameters on PVP/tadalafil solid dispersions prepared using supercritical anti-solvent process

Supercritical anti-solvent (SAS) process was employed to produce tadalafil solid dispersion sub-micron particles. Three independent variables for the SAS process (temperature, pressure, and drug concentration) were varied in order to investigate the effects on particle size and morphology of PVP/tadalafil solid dispersion (drug to polymer ratio 1:4). The mean particle size decreased with decreasing temperature (50 → 40 °C) and concentration (15 → 5 mg/mL) and increasing pressure (90 → 150 bar). Depending on the experimental variable, the mean particle size varied from 200 nm to 900 nm, and the dominant experimental variable was determined to be the drug concentration. Moreover, at a concentration of 15 mg/mL with any other process conditions, tadalafil tended to partially aggregate in crystalline form with irregular particle shapes. The results of in vitro dissolution experiments showed good correlation with mean particle size and crystallinity of the SAS-processed particles, in that the highest drug concentration showed the least dissolution rate and vice versa. Therefore, among the three variables studied, the drug concentration is the major factor that produces sub-micron particles in the SAS process.     

Crystallization of silibinin from organic solutions using supercritical and aqueous antisolvents

Silibinin, an anticancer drug, was crystallized from organic solutions using supercritical and aqueous antisolvents. Silibinin was dissolved in acetone and ethanol at concentration range of 0.01–0.04 g/mL, and the drug solutions were placed in contact with two different antisolvents, carbon dioxide and water. The mixing of the drug solutions and antisolvents led to the prompt precipitation of silibinin in a solid crystal form. The experimental variables, such as temperature, solution concentration, mixing rate and solution/antisolvent volume ratio were manipulated. When the experiments were conducted with a supercritical antisolvent, the effects of external additives on the crystal habit were examined. α-d-Glucose penta acetate, triton X-100 and urea were added to the solution at concentration range of 0.001–0.003 g/mL as external additives. The temperature increase of 20 °C induced 25% increase in particle size. As the solution concentration was increased from 0.01 to 0.04 g/mL, the average particle size decreased from 35.5 to 22.0 μm in supercritical antisolvent experiments, while the particle size increased from 8.9 to 30.4 μm in aqueous antisolvent experiments. The use of different kinds of external additives resulted in different modifications of the particle shape and structures.     

Reynolds number dependence of gas-phase turbulence in particle-laden flows: Effects of particle inertia and particle loading

A gas-particle flow experiment at a low particle loading (m = 0.4) in a vertical downward pipe is conducted at three different Reynolds numbers (Re = 6000, 10,000, and 13,000) to investigate the Re influence on the gas-phase turbulence modulation. The mean and fluctuating velocity data of both phases are acquired using a two-component LDV/PDA system. Two particles of varying degrees of inertia (i.e. high-density 70 µm glass beads and low-density 60 µm cenospheres) are used as the model particles to examine the effect of particle inertia on the trend in the turbulence modulation as a function of Re. An experiment at a higher particle loading (m = 4.0) using the glass beads is also conducted to examine the effect of particle concentration. In the presence of high inertia particles (St_T > 500) at a low particle loading, the gas-phase turbulence intensity in the pipe core is increased with increasing Re resulting in turbulence enhancement relative to the unladen flow. The turbulence enhancement is attributed to 1) a modification of the turbulence production by the Reynolds stress due to interparticle collision and/or 2) a reduction in the fluctuating drag force due to a change in the radial profile of the particle concentration. In contrast, the gas-phase turbulence intensity in the presence of low inertia particles (St_T < 500) is found to decrease with increasing Re similar to the trend in the unladen flow. Lastly, the turbulence enhancement at high Re is not observed at a high particle loading where the turbulent energy dissipation by the fluctuating drag force is dominant.     

Experimental investigation of solid bed depth at the discharge end of rotary kilns

The solid bed depth at the discharge end of rotary kilns was experimentally investigated for different mass flow rates, rotational speeds, inclination angles and materials using two lab kilns with sizes of 0.4 m (ID) ? 5 m (L) and 0.25 m (ID) ? 6.7 m (L), respectively. The solid depth at the discharge was found to be several more times higher than the particle diameter. All parameters according to Saeman's model were combined in a newly developed dimensionless ‘Bed depth number’ designated as ‘Bd’. The filling degree of a solid bed at the discharge can be correlated with F₀ = 1.75 ? Bd^0.5 (for an inclination angle between 1° and 4°). The range of the researched Bed depth number (Bd) is suitable for all industrial kilns. These values should be used as the initial condition, which was still unknown before, to solve the differential equation for the profile of the solid bed depth through the cylinder.     

Rotating fluidized bed with a static geometry: Guidelines for design and operating conditions

Computational fluid dynamics (CFD) simulations of the hydrodynamic behavior of rotating fluidized beds in static geometry (RFB-SG) are carried out for gas–solid flows. The rotating motion of the reactor bed is induced by the tangential injection of the gas along the circumference of the fluidization chamber. Steep gradients in the gas velocity fields both in radial and tangential direction generate turbulence. The radial and tangential drag forces fluidize the particle bed in both radial and tangential direction.An Eulerian two-fluid model is used. Gas phase turbulence is accounted for by a k–ε model adapted for rotational flows. The RFB-SG simulations provide guidelines for a design and operation with a high efficiency in gas–solid momentum transfer, excellent gas–solid separation and limited solids losses. Hydrodynamic variables like the centrifugal force, the injection pressure, the radial and tangential slip velocities, solids hold-up are calculated for both polymer particles (300 μm, 950 kg/m³, Geldart Group B) and glass beads (70 μm, 2500 kg/m³, Geldart Group A) to allow for a comparison among different fluidization chamber designs. Unstable bed behavior, like slugging and channeling, is also numerically predicted.     

Synthesis of dispersed CaCO3 nanoparticles by the ultrafine grinding

A one-step grinding process to obtain CaCO₃ nanoparticles from a micrometer-sized CaCO₃ was studied. A high-speed beads mill was employed to grind the particles, and poly(acrylic acid, sodium salt) was used to disperse the ground particles. The main parameters, which were investigated, were the slurry concentration, the rotor speed, the bead size, and the surfactant concentration. The larger bead size, higher slurry concentration, and faster rotor speed showed higher grinding efficiencies. However, there was severe agglomeration of the ground particles resulting in larger secondary particles as the grinding time increased after the certain point. The dispersion and enhanced grinding of particles were achieved by the surfactant. The particle size distribution of the ground particles had a narrow peak around 190 nm that was measured by the diffraction method. The primary particle size of the ground particles was around 40 nm.     

Effect of silica sol on the dispersion–gelation process of concentrated silica suspensions for fibre-reinforced ceramic composites

Sol gel process of silica powders dispersed in silica sol has been used to obtain a suitable suspension for the sol infiltration technique of fibre-reinforced ceramics. Efforts have been focused on analysing the effects of polyelectrolyte content, pH, solid load and concentration of gelling agent on the flow behaviour of silica suspensions. The most adequate suspension to manufacture the matrix of composites is a weak flocculated suspension with negligible thixotropic behaviour at pH ≥ 9.5, which is composed of silica microparticles dispersed in silica sol with 41 vol.% of solid load and 1.8 wt.% of Duramax D3005. This suspension easily undergoes a transition to a gel by a slight alteration of stability conditions adding 0.08 M of NH₄Cl, which reduces both the electrostatic repulsion and the pH to 8. Moreover, silica sol promotes the densification of ceramics up to 70% after sintering at 900 °C, allowing porous matrix processing of the composites.     

A miniature disk electrostatic aerosol classifier (mini-disk EAC) for personal nanoparticle sizers

We have developed a miniature disk electrostatic aerosol classifier (mini-disk EAC) for use in electrical mobility-based personal nanoparticle instrumentation for measurement of personal exposures to nanoaerosols. The prototype consists of two parallel disk electrodes separated by an electrically insulating spacer, to create the particle classification zone. The aerosol enters and exits the classification zone along the bottom disk electrode. An additional, particle-free sheath flow is used to improve the measurement resolution. The transmission measurement of the mini-disk EAC for DMA-classified particles shows that particle losses due to diffusion and electrical image forces were low. The particle penetration at 10 nm diameter (the designed lower size limit for the classifier) was 67% when the prototype was operated at the aerosol and sheath flow rates of 0.5 and 1.0 l min^?1, respectively. The performance of the mini-disk EAC was experimentally characterized using the particle cutoff curves that describe their penetration through the classifier as a function of applied voltage across the two disk electrodes. Based on the measurement of particle penetration at different aerosol and sheath flows, it was found that the aerosol and sheath flow rates of 0.5 and 1.5 l min^?1 were optimal for classifier operation. Finally, a semi-empirical model was also developed to describe the transfer function of the mini-disk EAC for non-diffusive particles.     

Mixing–segregation phenomena of binary system in a fluidized bed

A study on mixing–segregation phenomena in a gas fluidized bed of binary density system was performed by analysis of the residence time distribution and mixing degree. The effect of particle mixing on the residence time distribution and solid mixing was studied in a binary particle system with different densities. Residence time distribution curve and mean residence time of each particle were measured according to the flotsam particle size, mixing ratio and gas velocity in a gas fluidized bed (0.109 m I.D., 1.8 m height). The characteristics of residence time distribution and the deviation of mean residence time of each particle are consistent with previous mixing index based on the axial concentration of jetsam. From this study, mixing index of binary particle system with different densities should be considered by not only axial concentration distribution of jetsam particle but also characteristics of residence time distribution. This result suggests that the solid movement by fluidization gas is more important than solid axial dispersion.     

Production of fermentable sugars from enzymatic hydrolysis of pretreated municipal solid waste after autoclave process

A ligno-cellulosic concentrate from municipal solid waste (MSW) obtained after an autoclave separation process was investigated for its potential as a feedstock to produce fermentable sugars for ethanol production. A maximum enzymatic hydrolysis conversion of 53% of the cellulose and hemi-cellulose was found using a particle size range of 150–300 μm hydrolyzed in a 100 ml buffer solution containing 6 wt% lingo-cellulosic MSW concentrate with 90 mg cellulase at pH 4.8 held at 40 °C for 12 h. The hydrolysis rate leveled off at longer hydrolysis time and with increased substrate concentration and was related to enzymatic access to substrate. Lower hydrolysis rate at smaller particle size indicates that the grinding process may change the surface chemistry or morphology of the fibers making them less available for enzyme access. A drop in the hydrolysis rate was observed for the particles above 300 μm associate with the longer diffusion time for the enzyme into the fiber particles. The findings indicate that 152 L of ethanol could be obtained from a ton of lingo-cellulosic concentrate from MSW.     

DESIGN AND TESTING OF AN AEROSOL/SHEATH INLET FOR HIGH RESOLUTION MEASUREMENTS WITH A DMA

A modified aerosol/sheath inlet was designed for a differential mobility analyzer (DMA) for high resolution measurements based on field model calculations which include fluid flow, electric field, and convective/diffusive transport. To avoid the predicted flow recirculation for the current inlet design at an aerosol-to-sheath flow ratio of 0.05, the slit width is reduced and aerodynamically shaped so that the sheath velocity and aerosol velocity more nearly match. Numerical results are presented comparing the fluid flow of the old and new inlet. Problems associated with the old inlet include: flow unsteadiness at a flow ratio of 0.025, voltage shift at the peak particle concentration as a function of the flow ratio, and the historical observation that, while performing tandem differential mobility analyzer measurements (TDMA), the voltage applied on the second DMA for the peak particle concentration is higher than that for the first. Measurements demonstrate that all these problems are reduced or eliminated with the new inlet design. The TDMA measurements include flow ratios of 0.1, 0.05, 0.025 and 0.0125 at sheath flows of 166 and 333 cm³ s^-1 (10 and 20 l min^-1). The challenge of performing measurements at these low flow ratios will be discussed including flow calibration, flow matching, and pressure monitoring. The new inlet is applied to the measurement of the National Institute of Standards and Technology 0.1 μm Standard Reference Material 1963, and it is shown that the DMA can accurately measure the standard deviation of this narrowly distributed aerosol (σ/D_p=0.02).