The discrete element model (DEM) is a very promising modelling strategy for two-phase granular systems. However, owing to a lack of experimental measurements, validation of numerical simulations of two-phase granular systems is still an important issue. In this study, a small two-dimensional gas- fluidized bed was simulated using a discrete element model. The dimensions of the simulated bed were 44mm × 10mm × 120 mm and the fluidized particles had a diameter dp = 1.2 mm and density ρp = 1000 kg/m^3. The comparison between DEM simulations and experiments are performed on the basis of time-averaged voidage maps. The drag-law of Beetstra et al. [Beetstra, R., van der Hoef, M.A., & Kuipers,J. A. M. (2007b). Drag force of intermediate Reynolds number flow past mono- and bidispersed arrays of spheres. AIChE Journal, 53,489-501 ] seems to give the best results. The simulations are fairly insensitive to the coefficient of restitution and the coefficient of friction as long as some route of energy dissipation during particle-particle and particle-wall contact is provided. Changing the boundary condition of the gas phase at the side-walls from zero-slip to full-slip does not affect the simulation results. Care is to be taken that the cell sizes are chosen so that a reasonable number of particles can be found in a fluid cell. 相似文献
We present some results of a one-dimensional fluid model with a floating electrode immersed in plasma with magnetic field
applied at an oblique angle. The model equations are integrated numerically in order to find the space profiles of the ion
velocities and electrostatic potential for various strenghts and angles of the magnetic field. We assume a collisionless magnetized
pre-sheath with isothermal ions. The results are then compared with the spatial profiles obtained by a computer simulation.
We use a BIT1 particle-in-cell code. The simulations input parameters are chosen in the way, that they resemble the fluid
model as much as possible. Because the results of the simulation are given in the absolute SI units, they have to be normalized
correctly. We evaluate the model results and compare them with the computer simulation results. Special attention is brought
on formation of the pre-sheath with magnetic field applied at intermediate angles. The results of the simulation are in good
qualitative agreement with the model. 相似文献
An experimental study was made of the thermal and hydraulic characteristics of a three-phase fluidized bed cooling tower. The experiments were carried out in a packed tower of 200 mm diameter and 2.5 m height. The packing used was spongy rubber balls 12.7 mm in diameter and with a density of 375 kg/m3. The tower characteristic was evaluated. The air-side pressure drop and the minimum fluidization velocity were measured as a function of water/air mass flux ratio (0.4–2), static bed height (300–500 mm), and hot water inlet temperature (301–334 K).
The experimental results indicate that the tower characteristics KaV/L increases with increases in the bed static height and hot water inlet temperature and with decreases in the water/air mass flux ratio. It is also shown that the air-side pressure drop increases very slowly with increases in air velocity. The minimum, fluidization velocity was found to be independent of the static bed height.
The data obtained were used to develop a correlation between the tower characteristics, hot water inlet temperature, static bed height, and the water/air mass flux ratio. The mass transfer coefficient of the three-phase fluidized bed cooling tower is much higher than that of packed-bed cooling towers with higher packing height. 相似文献
In this paper we establish an SIR model with a standard incidence rate and a nonlinear recovery rate, formulated to consider the impact of available resource of the public health system especially the number of hospital beds. For the three dimensional model with total population regulated by both demographics and diseases incidence, we prove that the model can undergo backward bifurcation, saddle-node bifurcation, Hopf bifurcation and cusp type of Bogdanov–Takens bifurcation of codimension 3. We present the bifurcation diagram near the cusp type of Bogdanov–Takens bifurcation point of codimension 3 and give epidemiological interpretation of the complex dynamical behaviors of endemic due to the variation of the number of hospital beds. This study suggests that maintaining enough number of hospital beds is crucial for the control of the infectious diseases. 相似文献
Nadolol, a beta-blocker used in the management of hypertension and angina pectoris, has three chiral centers and is currently marketed as an equal mixture of its four stereoisomers. Resolution of three of the four stereoisomers of nadolol was obtained previously by HPLC, with a complete separation of the most active enantiomer (RSR)-nadolol, on a column packed with perphenyl carbamoylated beta-cyclodextrin (beta-CD) immobilized onto silica gel. In this study, continuous separation of the target enantiomer of (RSR)-nadolol from its racemic mixture (which is a ternary mixture in the chromatographic system) was studied by non-linear SMB chromatography. Different regions of (2, 3) and (1, 2) complete separation regime were determined in the (m2, m3) region and the effect of non-linearity such as overall feed concentration and component composition on the separation performances was investigated. A direct simulation approach has been proposed to simulate the SMB separation performance for the pseudo-binary mixture of nadolol. The simulation was conducted on the basis of a shortcut method constituted only of the weak-key and strong-key components. The performance of the cyclic steady-state behavior of the SMB unit was predicted reasonably well. It was also discussed quantitatively that the complete separation region obtained from the shortcut method is a subset of the true complete separation region and the optimal separation conditions obtained differed slightly from the "true" separation. 相似文献
In analytical sciences the design of novel materials and stationary phases for the sample preparation and separation of analytes
from biological fluids is needed. In this work we present different strategies for modification of stationary phases to produce
tailored solutions for the analytical problem. In this context a novel shielded polymeric reversed-phase monolithic material
was prepared in the presence of different numbers of reactive groups and concentrations of the coating polymer. Chromatographic
experiments were performed using benzoic acid propyl ester in order to characterize the hydrophobicity and efficiency of the
different restricted-access continuous beds prepared. Inverse size-exclusion chromatography was used for investigation of
the pore structure properties of the beds. Capillary columns were applied for nanochromatography of biological fluids containing
a mixture of nitrazepamum and medazepamum.
Presented at the 11th International Conference on Chemistry and the Environment, 9–12 September 2007, Torun, Poland 相似文献
An experimental study was conducted on a layered-bed pressure-vacuum-swing adsorption, PVSA, process with adsorbents that differ in their adsorption properties. An oxygen, O2, PVSA process was employed as an example for investigating how the process performance is affected by bed-layering configuration under different operating conditions for specific purge, product purity, and cycle feature. For two adsorbents with similar nitrogen-to-oxygen, N2/O2, selectivity but different N2 and O2 capacities, placing the high-capacity adsorbent at the product end and the low-capacity adsorbent at the feed end of the adsorption bed results in a better performance than in the case of reversing the layer positions of those adsorbents. The benefit of placing the adsorbent with higher capacity at the product end becomes more significant at high O2 product-purity levels. The experimental data obtained in this investigation agree well with simulation results reported earlier. 相似文献
We quantified the microstructural disorder of packed beds and correlated it with the resulting eddy dispersion. For this purpose we designed a set of bulk (unconfined) monodisperse random sphere packings with a systematic, protocol-dependent degree of microstructural heterogeneity, covering a porosity range from the random-close to the random-loose packing limit (? = 0.366–0.46). With the precise knowledge of particle positions, size, and shape we conducted a Voronoï tessellation of all packings and correlated the statistical moments of the Voronoï volume distributions (standard deviation and skewness) with the porosity and the protocol-dependent microstructural disorder. The deviation of the Voronoï volume distributions from the delta function of a crystalline packing describes the origin of short-range disorder of the investigated random packings. Eddy dispersion was simulated over a wide range of reduced velocities (0.5 ≤ ν ≤ 750) and analyzed with the comprehensive Giddings equation. Transient dispersion was found to correlate with the spatial scales of heterogeneity in the packings. The analysis of short-range disorder based on the Voronoï volume distributions revealed a strong correlation with the short-range interchannel contribution to eddy dispersion, whereas transchannel dispersion was relatively little affected. The presented approach defines a strictly scientific route to the key morphology–transport relationships of current and future chromatographic supports, including their morphological reconstruction, statistical analysis, and the correlation with relevant transport phenomena. It also guides us in our understanding, comparison, and optimization of the diverse packing algorithms and protocols used in simulations and experimental studies. 相似文献