Investigating the fluidization of disk-like particles in a fluidized bed using CFD-DEM simulation

Fluidization of monodispersed disk-like particles with different aspect ratios in the fluidized bed is simulated by CFD-DEM, with disk-like particles being modeled by the super-ellipsoids. The relatively comprehensive investigations are performed in order to understand the fluidization behaviors of disk-like particles and to evaluate how the aspect ratio influences the fluidization. The results obtained demonstrate that disk-like particles with a larger aspect ratio possess stronger particle movement and more apparent fluidization. Comparisons between spherical particles and disk-like particles elucidate their differences in the fluidization behavior. Particle orientation is also investigated in this paper due to its important influence on the fluidization. Particles possess different preferred orientations in the static bed and in the fluidization state, and a reduced aspect ratio can drive particles to be in the preferred orientation. The existence of the walls will prompt particles to align their cross sections to be parallel to the plane of the walls.     

Stationary states of a binary fluidized bed

Steady-state vertical flows and fluidized beds of a polydisperse material are considered based on the hypothesis on the collisional mechanism of energy and momentum exchange between particles. Representations are obtained for the effective energy of particle pulsations and the partial pressures, produced by the latter, in a binary fluidized bed. A stationary particle distribution with respect to the height of the bed is investigated.Ural State University, Ekaterinburg, Russia. Kazakh Chemicometallurgical Institute, Karaganda, Kazakhstan. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 65, No. 3, pp. 259–269, September, 1993.     

Bed expansion ratio of mono-sized and binary mixtures in fluidized,spouted, and spout-fluid beds

Studies on bed expansion ratio were carried out in fluidized, spouted, and spout-fluid beds. A single column has been used to compare the characteristics of fluidized, spouted, and spout-fluid beds. Experiments were carried out using air and glass beads under fluidized, spouted, and spout-fluid bed conditions separately to study the effect of gas velocity, bed mass, and particle size on bed expansion ratio. Glass beads of different sizes (0.75, 1.2, 1.7, and 3.075?mm) have been used as solid bed material. Bed expansion ratio was determined for mono-size particles and binary mixtures (different diameter ratios and composition). It was found that the bed expansion ratio decreases with increase in bed mass for only spouting condition and spout-fluidization conditions. The bed expansion ratio increases with increase in bed mass for only fluidization condition.     

Investigating the flow structures in semi-cylindrical bubbling fluidized bed using pressure fluctuation signals

Hydrodynamic characteristics of a gas-solid semi-cylindrical fluidized bed was experimentally investigated and compared with that of a cylindrical bed by analysis of pressure fluctuations. Pressure fluctuations were analyzed in time and frequency domains using standard deviation, power spectral density function and discrete wavelet transform methods. Experiments were carried out in two semi-cylindrical and cylindrical fluidized beds of 14?cm in diameter each, operating in the bubbling fluidization regime at ambient pressure and temperature. Both beds were filled with glass beads of various sizes (120, 290 and 450?µm). The superficial gas velocity was varied in the range of 0.2–0.8?m/s. Results showed that although the minimum fluidization velocity is influenced by the particle size, it is not affected by the geometry of the bed. It was shown that the hydrodynamics of both beds are very similar and the difference is negligible. Number of large bubbles is slightly larger in the semi-cylindrical bed as compared with the cylindrical bed. Also, increase in the particle size and superficial gas velocity result in a greater difference between the number of large bubbles in both beds and the number of large bubbles in the semi-cylindrical bed increases slightly faster than in the cylindrical bed.     

Exact flow of a third grade fluid past a porous plate using homotopy analysis method

The flow of a third grade fluid past a porous plate is considered. An exact analytical solution of the governing non-linear differential equation is constructed using homotopy analysis method. It is observed that the relevant perturbation solution corresponds to a special case of the presented solution.     

Conversion air velocity at which reverse density segregation converts to normal density segregation in a vibrated fluidized bed of binary particulate mixtures

It is well known, when binary mixtures of different-density particles of the same size are vertically vibrated or fluidized by airflow through the bottom, the particles segregate by density. Reverse density segregation occurs in the vibrated bed; heavier particles move upward and lighter ones move downward, and normal density segregation occurs in the fluidized bed; lighter particles move upward and the heavier ones move downward. In this study, we investigated the particles’ behavior in a vertically vibrated fluidized bed at various air velocity using two types of particulate mixtures of glass beads (GB) and stainless steel powder (SP) or iron powder (IP) of same size. We found that reverse segregation converts to normal segregation at a certain air velocity; here we call it “conversion air velocity”. Then, we investigated the likely origin of the conversion air velocity considering the minimum fluidization air velocity u_mf determined for the three monocomponent particles (GB, SP and IP) with and without vibration. We found that the conversion air velocity is close to the u_mf of the lower density particles (GB) with vibration, indicating that the conversion from reverse segregation to normal segregation occurs around u_mf of lighter particles with vibration.     

Heat transfer between a fluidized bed and a plate during drying

Journal of Engineering Physics and Thermophysics - Experimental data is given for the heat transfer between a fluidized bed and a plate during drying. Criterial equations are given for the...     

Mixing characteristics of binary mixtures in a spout-fluid bed

Mixing characteristics of binary mixtures in a flat-bottom cylindrical spout-fluid bed using glass beads and air are reported in this work. Experiments were carried out to investigate the mixing characteristics for binary mixtures at three flow conditions, i.e., only spouting, only fluidization and spout-fluidization. The experiments were performed at different gas velocities, diameter ratios of binary mixtures and three different bed arrangements. Mixing index was determined for fluidized bed and static bed conditions. It was found that, in all cases, lowest-diameter ratio mixture gave good mixing index values. For all flow conditions, mixing index for large–small bed arrangement was increasing with time, whereas for small–large bed arrangement, the mixing index deteriorated with time. However, in both cases, the mixing index reached almost a constant value. For well-mixed bed arrangement and spout-fluidization flow condition, segregation and re-mixing were observed.     

Selective extraction of pesticides from lipid-containing matrixes using supercritical binary gas mixtures

When supercritical carbon dioxide is used for extraction of trace compounds from lipid-rich samples, the resulting extract can contain a substantial amount of lipid coextractive which interferes in the subsequent chromatographic analysis. In this case, a cleanup step, which is time-consuming, is required in order to remove or reduce the lipid content in the extract. In this study, we report on a new approach for the extraction of trace compounds which significantly reduces the quantity of lipid coextractives, thereby eliminating the need for a sample cleanup step. An autoclave high-pressure reactor equipped with a mechanical stirring device was used for mixing gases, such as carbon dioxide and nitrogen, to generate the desired fluid mixtures. The composition of the mixtures could be adjusted by two mass flow controllers prior to the autoclave mixing device. The generated carbon dioxide/nitrogen binary mixtures were then employed to facilitate supercritical fluid extraction (SFE) at high pressures and elevated temperatures. The pressurized CO(2)/nitrogen binary fluid mixture demonstrated sufficient solvation power for quantitative recoveries of trace fortified organophosphorus and incurred organochlorine pesticides from poultry fat while significantly reducing lipid solubility in the fluid. This allowed the development of a method that produced an extract with minimal lipid content that could be used directly for gas chromatographic analysis, thereby eliminating the need to clean-up the extract.     

Removal of sulfur dioxide from a continuously operated binary fluidized bed reactor using inert solids and hydrated lime

Sulfur dioxide pollutant was treated in the laboratory with hydrated lime particles having a mean diameter of 9.1 microm in a continuously operating binary fluidized bed reactor also containing inert sand particles with sizes varying from 500 to 590 microm. The influence of temperature (500, 600, 700 and 800 degrees C) on the reaction medium, of the superficial velocity of the gas (0.8, 1.0 and 1.2 m/s), and of the Ca/S molar ratio (1, 2 and 3) on the SO2 removal efficiency were investigated for an inflow gas concentration of 1000 ppm and an initially static bed height of 10.0 cm. The pollutant removal efficiency proved to depend on the temperature and the velocity of the gaseous flow and was strongly influenced by the Ca/S molar ratio. The maximum efficiency of 97.7% was achieved at a temperature of 700 degrees C, a Ca/S ratio of 3 and a velocity of 0.8 m/s. The lime particles' mean residence time was determined by an indirect method, which consisted of integrating the gas concentration curves normalized with respect to time. Based on a calculation of the critical transition velocities, it was concluded that the reactor operated in a bubbling regime under each condition investigated here.     

Features of hydrocarbon mixtures filtration in a porous medium

The filtration process of a mixture of hydrocarbons (methane-n-butane) in a porous medium has been considered. The possibility of the existence of auto-oscillations in such a system has been shown. A mechanism explaining their origin has been proposed. The one-dimensional numerical model of the filtration process of a hydrocarbon mixture has been elaborated. The main parameters affecting the properties of the self-oscillating system have been determined.     

Thermal diffusion in binary gas mixtures

The temperature dependence and the pressure dependence of the thermal diffusion coefficient as well as its dependence on the concentrations of interdiffusing components is evaluated with the aid of the (12-7, ) model potential. The results of calculations are found to agree with experimental data within the accuracy of measurements.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 49, No. 2, pp. 284–287, August, 1985.     

Thermal conductivity of binary gas mixtures

The main methods of analysis of heat transfer in mixtures of nonreacting gases are discussed. A new model and method of calculating the thermal conductivity is proposed.     

Prediction of segregation behavior of binary mixture in a pulsed fluidized bed

A three-dimensional simulation is carried out to investigate the impact of pulsation flow on segregation behavior of binary mixture in a fluidized bed via the multi-fluid model. The simulated results are compared against the experimental data. The impacts of pulsation frequency and operating condition on flow and segregation behavior of binary mixture are discussed. The results reveal that an excessive increase of pulsation frequency and operating temperature is not beneficial to the enhancement of segregation efficiency. The pulsation frequency plays a more important role in segregation efficiency under a small size discrepancy of binary mixture. Meanwhile, the effect of pulsed air flow waveform on segregation efficiency of particles is also analyzed.     

The flow of a viscoelastic fluid past a porous plate

Summary The flow of a second order viscoelastic fluid past a porous plate is considered. It is characterized by a boundary value problem in which the order of the differential equation exceeds the number of available boundary conditions. The boundary value problem is solved by making a plausible assumption, namely that the variation of the normal derivative of the velocity at the plate withk is sufficiently smooth, wherek is the viscoelastic fluid parameter. Under this assumption it is shown that dual solutions exist for values ofk less than a critical value. Beyond this value, no solution exists.     

Experimental determination of critical injection on a porous plate

Experimental data are presented on determination of the critical injection parameter on a porous plate with turbulent boundary layer. The test results give satisfactory confirmation of the theoretical results of [1].     

Calculation of the temperature distribution on a porous plate

On the basis of the relations obtained in [6, 7], a graph is proposed which makes it easy to calculate the temperature distribution on a porous wall with uniform injection of a homogeneous gas. The calculation is compared with available experimental data.