Spray impact resistance of a superhydrophobic nanocomposite coating

The performance of a polyurethane/organoclay superhydrophobic nanocomposite modified with perfluoroalkyl methacrylic copolymer in the presence of a high‐pressure air‐water spray which mimics an icing cloud impact is investigated in this study. To quantify the average velocites of droplets impacting the superhydrophobic samples, a computational study was performed. Such a study is important to understand the interaction between the jet and surface. Impacting velocities for three different testing conditions were estimated to be 14.5, 4.5, and 3.4 m/s. Liquid saturation did not occur immediately, but over time, the high mass flow rate of water led to antiwetting performance degradation. Upon evaporation, contact angle returned to pretest values, indicating little mechanical erosion. This was consistent with scanning electron microscopy which showed that the nano and microstructure was preserved, and with energy‐dispersive X‐ray spectroscopy, which showed no surface chemistry change after testing. However, sliding angle showed stronger degradation, especially at higher impact velocities. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3025–3032, 2014     

Radial pressure profiles in a cold‐flow gas‐solid vortex reactor

A unique normalized radial pressure profile characterizes the bed of a gas‐solid vortex reactor over a range of particle densities and sizes, solid capacities, and gas flow rates: 950–1240 kg/m³, 1–2 mm, 2 kg to maximum solids capacity, and 0.4–0.8 Nm³/s (corresponding to gas injection velocities of 55–110 m/s), respectively. The combined momentum conservation equations of both gas and solid phases predict this pressure profile when accounting for the corresponding measured particle velocities. The pressure profiles for a given type of particles and a given solids loading but for different gas injection velocities merge into a single curve when normalizing the pressures with the pressure value downstream of the bed. The normalized—with respect to the overall pressure drop—pressure profiles for different gas injection velocities in particle‐free flow merge in a unique profile. © 2015 The Authors AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers AIChE J, 61: 4114–4125, 2015     

Coaxial Mixer Hydrodynamics with Newtonian and non‐Newtonian Fluids

The performance of several combinations of a wall scraping impeller and dispersing impellers in a coaxial mixer operated in counter‐ and co‐rotating mode were assessed with Newtonian and non‐Newtonian fluids. Using the power consumption and the mixing time as the efficiency criteria, impellers in co‐rotating mode were found to be a better choice for Newtonian and non‐Newtonian fluids. The hybrid impeller‐anchor combination was found to be the most efficient for mixing in counter‐rotating or co‐rotating mode regardless of the fluid rheology. For both rotating modes, it was shown that the anchor speed does not have any effect on the power draw of the dispersing turbines. However, the impeller speed was shown to affect the anchor power consumption. The determination of the minimum agitation conditions to achieve the just suspended state of solid particles (N_js) was also determined. It was found that N_js had lower values with the impellers having the best axial pumping capabilities.     

Continuous detonation in the regime of self-oscillatory ejection of the oxidizer. 2. Air as an oxidizer

Results of an experimental study of continuous detonation of a hydrogen-air mixture in a flow-type annular combustor 306 mm in diameter in the regime of air self-ejection are reported. The regime of pulsed detonation is also obtained. Stable regimes of continuous detonation with one and two transverse detonation waves having velocities D = 1.48−1.16 km/sec are observed in experiments. The frequency of the pulsed detonation wave is ≈1.4 kHz. The known condition for the continuous detonation regime (good mixing for the formation of a detonable layer) is validated. The size of the slot for air ejection, providing a necessary flow rate for detonation and a necessary ratio of the species in the mixture, is determined. Some methods for estimating the air flow rate are presented.     

Numerical investigation of monodisperse granular flow through an inclined rotating chute

A discrete element model of spherical glass particles flowing down a rotating chute is validated against high quality experimental data. The simulations are performed in a corotating frame of reference, taking into account Coriolis and centrifugal forces. In view of future extensions aimed at segregation studies of polydisperse granular flows, several validation steps are required. In particular, the influence of the interstitial gas, a sensitivity study of the collision parameters, and the effect of system rotation on particle flow is investigated. Shirsath et al. have provided the benchmark laboratory measurements of bed height and surface velocities of monodisperse granular flow down an inclined rotating chute. With a proper choice of the friction coefficients, the simulations show very good agreement with our experimental results. The effect of interstitial gas on the flow behavior is found to be relatively small for 3‐mm granular particles. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3424–3441, 2014     

Solids transport models comparison and fine‐tuning for horizontal,low concentration flow in single‐phase carrier fluid

We determined and fine‐tuned the solids transport models appropriate for predicting the single‐phase carrier fluid velocity to transport solid particles in conduits for horizontal, low concentration flow. A database with 538 experimental data points was compiled. A literature review was performed to determine the data ranges, forces, and mechanisms used to develop 44 models, and their velocity predictions were compared against the database using statistics. Using the dimensionless forms of the models and the data, the model parameters were adjusted to improve their accuracy and identify the dominant forces. At low concentrations: for liquid/solid flow from a bed of solids and gas/solid flow from the bottom of pipelines, the particle weight, and inertial and viscous forces dominate; for gas/solid flow from a bed of solids, the particle weight, and inertial, viscous, and adhesive forces play a role; and gaps exist in the data for large‐diameter pipes and high‐density gases. © 2013 American Institute of Chemical Engineers AIChE J, 60: 76–122, 2014     

生物质型煤热风干燥特性及模型研究

为降低生物质型煤干燥成本,提高干燥效率,研究热风干燥风速和温度对热风干燥特性的影响,拟合了生物质型煤在不同热风干燥条件下水分随时间变化的模拟曲线。结果表明:生物质型煤与多数多孔介质类似,干燥过程可分为加速干燥、恒速干燥、降速干燥3个阶段,其中恒速干燥阶段的干燥时间约25 min;热风温度越高,风速越大,生物质型煤的干燥速率越大,干燥时间越短,干燥时的裂纹率也越高。当干燥温度180℃,风速1.2 m/s时,生物质型煤热风干燥效果较好,干燥热效率最高为48.34%。通过对不同温度、风速条件下的生物质型煤干燥试验数据与常用干燥模型进行拟合分析,发现Sabbet干燥模型拟合度最好,当干燥温度180℃,风速1.2 m/s时相关性系数为0.997,二者相关性显著,因此Sabbet干燥模型可较好地反映生物质型煤在不同温度、风速下的干燥特性。     

Experimental Investigation of a Minihydrocyclone

A phase doppler particle analyzer (PDPA) was used to measure the liquid/solid two‐phase flow pattern in a 25 mm minihydrocyclone. The distributions of velocity, concentration, root mean square (RMS) velocities, and especially the average diameter of the particles were evaluated in this work. The measurements showed that in the upper section of the minihydrocyclone the particles accumulated in the outer helical flow near the line of zero velocity value (LZVV), which probably means that the inner helical flow has a more important influence on the separation. Strong turbulence occurred around the air‐core as well as around the zone near the wall. The RMS value indicated that the transformation of the axial flow direction takes place in the lower section of the conical length.     

Particle‐scale investigation of the solid dispersion and residence properties in a 3‐D spout‐fluid bed

Three‐dimensional modeling of the gas–solid flow in a spout‐fluid bed is conducted at the particle‐scale level. Both the local and systematic dispersion behaviors of solid phase are initially investigated. Then, the solid circulating and resident behaviors are discussed. The results demonstrate that vigorously lateral solid dispersion appears in the spout region and the periphery of the fountain, whereas intensely vertical dispersion exists in the central region of the bed. Moreover, the inlet configuration of bed strongly affects the distribution of lateral dispersion, while its influence on the vertical one disappears in the fountain. Strong anisotropy of solid dispersion along the three directions is obtained. Systematic dispersion intensity along the vertical direction is an order of magnitude larger than the lateral one. In addition, two circulating patterns of solid phase can be identified. Solid residence time is the smallest in the spout region and the largest in the bottom corner. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2788–2804, 2014     

Particles mixing induced by bubbles in a gas‐solid fluidized bed

The effect of bubble injection characteristics on the mixing behavior of a gas‐solid fluidized bed is investigated using a discrete particle model. The effect of different parameters including gas injection time, velocity, and mode are studied. Simulation results show that injecting gas at a constant gas flow rate in the form of small bubbles results in a better overall particle mixing. It was also found that the injection velocities have limited effect on particle mixing behavior for the same total gas volume injected into the bed. Moreover, the mixing index (MI) of continuous gas jet bubbling regime is compared with the MI obtained in uniform gas injection regime and the results revealed that the MI of continuous jet bubbling regime has a larger value than that of uniform gas injection regime at the fixed total gas flow rate. In both regimes, z‐direction MI is larger than x‐direction index. The differences between two direction indices are more noticeable in continuous jet bubbling in comparison with the uniform gas injection regime. © 2016 American Institute of Chemical Engineers AIChE J, 62: 1430–1438, 2016     

Modeling of Gas‐Particle Turbulent Flow in Spout‐Fluid Bed by Computational Fluid Dynamics with Discrete Element Method

Gas and solid turbulent flow in a cylindrical spout‐fluid bed with conical base were investigated by incorporating various gas‐particle interaction models for two‐way coupling simulation of discrete particle dynamics. The gas flow field was computed by a k‐ϵ two‐equation turbulent model, the motion of solid particles was modeled by the discrete element method. Drag force, contact force, Saffman lift force, Magnus lift force and gravitational force acting on individual particles were considered in the mathematical models. Calculations on the cylindrical spout‐fluid bed with an inside diameter of 152 mm, a height of 700 mm, a conical base of 60° and the ratio of void area of 3.2 % were carried out. Based on the simulation, the gas‐solid flow patterns at various spouting gas velocities are presented. Besides, the changes in particle velocity, particle concentration, collision energy, particle and gas turbulent intensities at different proportions of fluidizing gas to total gas flow are discussed.     

Hydrodynamic considerations on optimal design of a three‐phase airlift bioreactor with high solids loading

The hydrodynamic study of a three‐phase airlift (TPAL) bioreactor with an enlarged gas–liquid dual separator was carried out. Different lengths and diameters of the draft tube were tested to show how the design of the separator zone affects the hydrodynamic performance of the TPAL reactor. Ca‐alginate beads with entrapped yeast biomass at different loadings (0, 7, 14 and 21% v/v) were used in order to mimic the solid phase of conventional high cell density systems, such as those with cells immobilized on carriers or flocculating cells. Important information on multiphase flow and distribution of gas and solid phases in the internal‐loop airlift reactor (ALR) with high solids loading was obtained, which can be used for suggesting optimal hydrodynamic conditions in a TPAL bioreactor with high solids loading. It is finally suggested that the ALR with a dual separator and a downcomer to riser cross‐sectional area ratio (A_D/A_R) ranging from 1.2 to 2.0 can be successfully applied to batch/continuous high cell density systems, where the uniform distribution of solid phase, its efficient separation of particles from the liquid phase, and an improved residence time of air bubbles inside the reactor are desirable. Copyright © 2003 Society of Chemical Industry     

Understanding rate‐limiting processes for the sublimation of small molecule organic semiconductors

Organic small molecules continue to gain attention for application in light‐emitting devices in displays and solid‐state lighting. The purification of these materials by sublimation represents a critical obstacle for their high throughput processing. In this work, we find that the purification of the archetypical hole‐transporting material N,N′‐bis(naphthalen‐1‐yl)‐N,N′‐bis(phenyl)‐benzidine (α‐NPD) is controlled by a combination of viscous flow, Knudsen diffusion, and physical vapor deposition. In contrast with other commercially practiced sublimations, steps like diffusion within the solid feed, desorption from the feed particle surface, and mass transfer within the bed of feed particles, do not significantly affect the sublimation rate. This work provides guidelines for the large‐scale purification of organic semiconductor materials, and possibly for a broader range of high value small molecule specialty materials. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1347–1354, 2014     

Analysis of solar‐driven gasification of biochar trickling through an interconnected porous structure

The efficient transfer of high‐temperature solar heat to the reaction site is crucial for the yield and selectivity of the solar‐driven gasification of biomass. The performance of a gas‐solid trickle‐bed reactor constructed from a high thermal conductivity porous ceramic packing has been investigated. Beech char particles were used as the model feedstock. A two‐dimensional finite‐volume model coupling chemical reaction with conduction, convection, and radiation of heat within the packing was developed and tested against measured temperatures and gasification rates. The sensitivity of the gasification rate and reactor temperatures to variations of the packing's pore diameter, porosity, thermal conductivity, and particle loading was numerically studied. A numerical comparison with a moving bed projected a more uniform temperature distribution and higher gasification rates due to the increased heat transfer via combined radiation and conduction through the trickle bed. © 2014 American Institute of Chemical Engineers AIChE J, 61: 867–879, 2015     

Experiments on floating bed rotating drums using magnetic particle tracking

Magnetic particle tracking (MPT) was employed to study a rotating drum filled with cork particles, using both air and water as interstitial medium. This noninvasive monitoring technique allows for the tracking of both particle translation and rotation in dry granular and liquid–solid systems. Measurements on the dry and floating bed rotating drum were compared and detailed analysis of the bed shape and velocity profiles was performed. It was found that the change of particle–wall and particle–particle interaction caused by the presence of water significantly affects the bed behavior. The decreased friction leads to slipping of the particles with respect to the wall, rendering the circulation rate largely insensitive to increased drum speed. It was also found that the liquid–particle interaction is determining for the behavior of the flowing layer. The well-defined experiments and in-depth characterization performed in this study provide an excellent validation case for multiphase flow models.     

Effect of slip boundary conditions on the simulation of microparticle velocity fields in a conical fluidized bed

The hydrodynamic performance of micrometric TiO₂ particles has been experimentally studied in a conical fluidized bed and the results compared with numerical simulations. Local solid velocities in the bed have been measured by means of an optical fiber technique under different operating conditions of particle loading and air velocity. The radial profiles of axial solid velocities have been simulated to assess the sensitivity of grid size, and different drag models, namely, those by Syamlal and O'Brien, Ahmadi and Ma, Arastoopour et al., and Gidaspow, for no‐slip, partial‐slip, and free‐slip boundary conditions (BCs). The different drag models record almost similar results, but those provided by the Gidaspow and Ahmadi–Ma models, together with free‐slip BCs, are in somewhat better agreement with the experimental data for conical fluidized beds with smooth walls. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4502–4518, 2013     

PDA measurements in a three‐phase bubble column

Phase Doppler anemometry was used to quantify the flow characteristic of a three phases (liquid, solid, and bubbles) cylindrical bubble column driven by a point air source made of a 30‐mm diameter perforated air stone centrally mounted at the bottom. The cylindrical bubble column had an inner diameter of 152 mm and was filled with liquid up to 1 m above the point source. Acrylic beads with a nominal diameter of 3 mm were used as the solid phase. To match the density of the solid phase which was 1.05 kg/m³, the liquid density was raised to about 1.0485 kg/m3 by added salt. The bubble diameters generated were within the range of 600–2400 µm. The detailed turbulent characteristics of the liquid‐phase velocity, bubble diameter, bubble velocity, and solid velocity were measured at three different air rates, namely 0.4, 0.8, and 1.2 L/min (corresponding to average gas volume fraction of 0.0084, 0.0168, and 0.0258, respectively) for the homogeneous bubble column regime. With the addition of the solid phase, the flow field was found to be relatively steady compared to the two‐phase column referencing the probability density functions for both the liquid and bubble velocities. An analysis based on the determination of the drag forces and transversal lift forces was performed to examine the flow stability in the three‐phase bubble column. The analysis illustrated that how the added solid phase effectively stabilized the flow field to achieve a steady circulation in the bubble column and a generalized criterion for the flow stability in the three‐phase bubble column was derived. Further investigation for the transition and the heterogeneous bubble column regime with air rates at 2.0 and 4.0 L/min shown that this criterion can also be used as a general prediction of flow stability in this three‐phase bubble column. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2286–2307, 2013     

Influence of the mass flow rate of secondary air on the gas/particle flow characteristics in the near-burner region of a double swirl flow burner

The influence of the mass flow rate of secondary air on the gas/particle flow characteristics of a double swirl flow burner, in the near-burner region, was measured by a three-component particle-dynamics anemometer, in conjunction with a gas/particle two-phase test facility. Velocities, particle volume flux profiles, and normalized particle number concentrations were obtained. The relationship between the gas/particle flows and the combustion characteristics of the burners was discussed. For different mass flow rates of secondary air, annular recirculation zones formed only in the region of r/d=0.3–0.6 at x/d=0.1–0.3. With an increasing mass flow rate of secondary air, the peaks of the root mean square (RMS) axial fluctuating velocities, radial mean velocities, RMS radial fluctuating velocities, and tangential velocities all increased, while the recirculation increased slightly. There was a low particle volume flux in the central zone of the burner. At x/d=0.1–0.7, the profiles of particle volume flux had two peaks in the secondary air flow zone near the wall. With an increasing mass flow rate of secondary air, the peak of particle volume flux in the secondary air flow zone decreased, but the peak of particle volume flux near the wall increased. In section x/d=0.1–0.5, the particle diameter in the central zone of the burner was always less than the particle diameter at other locations.     

DEM study of granular flow characteristics in the active and passive regions of a three‐dimensional rotating drum

Three‐dimensional modeling of the solid motion in a lab‐scale rotating drum has been conducted via the discrete element method. After validating the simulated results with available experimental data, the active‐passive interface was identified, following which particle‐scale information in these two regions, in particular the influences of fill level and rotating velocity, were obtained. The results demonstrate that: (1) the total number of particles in the passive region is three times that in the active, (2) the transverse and axial velocities span a wider range in the active region, with the transverse values being greater, (3) the collision force is much higher in the active region, with the greatest magnitudes in the y direction relative to that in the x and z directions, (4) particle displacements are generally lower and have a narrower distribution in the active region, (5) the local solid residence time (SRT) distribution profiles are similar axially in that the highest SRT magnitudes are at the center region of the bed, while the other parts of the bed have uniform SRT magnitudes. © 2016 American Institute of Chemical Engineers AIChE J, 62: 3874–3888, 2016     

Experimental Simulation on Chemical-looping Combustion of Cold Model（英文）

The pressure profiles, gas velocities, solid circulation rate, solids flux, residence time distribution of gas and particles in chemical-looping combustion reactors and gas leakage were studied in a cold flow model unit. And these parameters in both air and fuel reactors were measured in the experimental stage. The experimental results show that gas fluidization velocity in the air reactor is 1.8 m/s, gas fluidization velocity in the fuel reactor 0.5 m/s, and the bed materials inventory of the two reactors between 1.2 to 3.15 kg. The first cold flow model results show that the solid circulation rates are sufficient. The appropriate operating conditions are optimized and the summary of final changes is made the on cold model. The proposed design solutions are currently being verified in a cold flow model simulating the actual reactor(hot) system. This paper presents an overview of the research performed on a cold flow model and highlights the current status of the technology.