Computer-aided tools for molecular systems engineering and wavelet-morphometric analysis of the texture of nanomaterials

An analysis of present-day computer-aided tools for molecular systems engineering and the possibility of their use for developing the texture of new nanomaterials is performed. A wavelet-morphometric algorithm for a computer-aided analysis of the texture of nanomaterials using the original photomicrographs is proposed that includes the following main stages: the decomposition of the original photomicrographs into low-frequency and high-frequency components using a discrete wavelet transform, the calculation of energymechanical characteristics for the identified images of the texture elements of the high-frequency component, and further binary decomposition and calculation of morphometric parameters for the created images of energy-mechanical characteristics (parameters of texture elements). A system of energy-mechanical and morphometric parameters of the elements of the texture of nanocomposites is proposed that is based on the use of binary decomposition filtration of textural photomicrographs and the morphometric parameters of the identified images of clusters in the binarization sections.     

Computer simulation of transient gas flows in complex round pipes

A computer model and algorithms for predicting and analyzing the transient incompressible gas flows in standard assemblies of complex round pipes are developed. It is shown that the vibrational safety and reliability of complex pipes are most reasonable to provide by using the three-dimensional computer simulation of the distribution of velocities, pressures, and temperatures over different sections of the pipe. It is shown that the developed three-dimensional computer model and obtained results can be used for calculating the integral indices of transient gas flows in assemblies of complex pipes.     

Influence of threshold variation on determining the properties of a polymer electrolyte fuel cell gas diffusion layer in X-ray nano-tomography

Morphological parameters of a 3D binary image of a porous carbon gas diffusion layer (GDL) for polymer electrolyte fuel cells (PEFC) reconstructed using X-ray nano-tomography scanning have been obtained, and influence of small alterations in the threshold value on the simulated flow properties of the reconstructed GDL has been determined. A range of threshold values with 0.4% increments on the greyscale map have been applied and the gas permeability of the binary images have been calculated using a single-phase lattice Botlzmann model (LBM), which is based on the treatment of nineteen velocities in the three dimensional domain (D3Q19). The porosity, degrees of anisotropy and the mean pore radius have been calculated directly from segmented voxel representation. A strong relationship between these parameters and threshold variation has been established. These findings suggest that threshold selection can significantly affect some of the flow properties and may strongly influence the computational simulation of micro and nano-scale flows in a porous structure.     

Texture and fractal methods for analyzing the characteristics of unsteady gas flows in pipelines

Turbulent structures in two-dimensional model gas flows are analyzed by estimating the fractal dimension and the texture characteristics of the gas flows. The fractal dimension is estimated using the self-similarity indices of the power spectra for the following characteristics of the gas flows: the Coriolis and Boussinesq coefficients, average pressure, hydraulic resistance coefficient, velocity loss in a pipeline element, and curvature of the gas flow. The texture characteristics are calculated using the following texture indices: energy, entropy, inertia coefficient, uniformity coefficient, cluster excess coefficient, cluster asymmetry coefficient, and also information measure of cluster correlation. Computer experiments show that, in propagation of a shock wave, the wavelet spectra of the indices of the model gas flows contain a large number of self-similar figures, which is indicative of a hierarchical structure and a fractal character of the model gas flows.     

Investigation of gas–solids flow characteristics in a conical fluidized bed dryer by pressure fluctuation and electrical capacitance tomography

It is important to investigate the gas–solids flow characteristics of fluidized bed drying processes to improve the operation efficiency and guarantee the product quality. This paper presents research into fluidized bed drying processes measured by high-frequency differential pressure fluctuation and electrical capacitance tomography (ECT). Power spectra analysis is combined with dynamic calibration for ECT to reveal the complex gas–solids flow behavior. Bubble characteristics are visualized by cross-sectional and quasi-3D ECT images. In addition, results by discrete wavelet transform analysis are given and compared with the analysis results of previous sections. It has been found that bubbles would coalesce in different ways under different operation conditions, and discrete wavelet transform sub-signals of ECT measurements are sensitive to particle moisture. This work reveals the complex hydrodynamic behavior in the fluidized bed dryer and provides valuable information for process control.     

Wavelet morphometric neural network algorithm for analyzing nanomaterial porous texture

A wavelet morphometric neural network algorithm for analyzing the porous texture of a nanomaterial that differs from the use of the procedure for identifying the binary clusters for the morphometric analysis obtained as a result of the analysis of the neural network cluster of a micro photo image of a nanomaterial instead of the procedure for identifying binary objects on binary cross sections of the original micro photo image have been proposed. Using this algorithm, we calculated the quantitative morphometric estimations of the geometric parameters of the nanocluster texture of solid and porous components, which have been applied to predict the density distribution of pores inside of a nanomaterial.     

气液两相流管道中的瞬态流动及清管操作模型

对于气液两相流的瞬态模拟,需要对连续性方程、能量方程及动量方程进行复杂的计算.在油气管线中,可使用对气体连续性方程进行近似的稳态假设和对某一流态下的两相局部动量平衡的方法对连续性方程和动量方程进行适当的简化.使用的计算机编码程序将假设流体绝热的简化瞬态模型与流态转化准则结合应用,并通过实验数据对其模拟结果进行验证.该程...     

Numerical study of cluster formation in a gas–particle circulating fluidized bed

Simulations with two-way coupling are performed for two-dimensional gas–solid flow in a circulating fluidized bed with a total solids concentration of 3% in the riser. The motion of particles is treated by a Lagrangian approach, and particles are assumed to interact through binary, instantaneous, non-frontal, and inelastic collisions with friction. The model for the interstitial gas phase is based on the Navier–Stokes equations for two-phase flow with fluid turbulence calculated by using LES. Several porosity functions exist in the literature relating the drag force for a particle in a cloud to the drag force on an isolated particle. We have studied the influences of this porosity function, observing large differences in the local flow structure. The fluctuating gas–solid motion has been investigated showing a strong anisotropic flow behaviour, which is similar to experimental findings. The instabilities in these flows are strongly linked to the non-linear drag function due to the group effect of particles in a cloud. The collision parameters have been found to have an important influence on the cluster structures.     

Oil–water two‐phase flow in microchannels: Flow patterns and pressure drop measurements

This paper investigates oil–water two‐phase flows in microchannels of 793 and 667 µm hydraulic diameters made of quartz and glass, respectively. By injecting one fluid at a constant flow rate and the second at variable flow rate, different flow patterns were identified and mapped and the corresponding two‐phase pressure drops were measured. Measurements of the pressure drops were interpreted using the homogeneous and Lockhart–Martinelli models developed for two‐phase flows in pipes. The results show similarity to both liquid–liquid flow in pipes and to gas–liquid flow in microchannels. We find a strong dependence of pressure drop on flow rates, microchannel material, and the first fluid injected into the microchannel.     

Two-dimensional transient numerical simulation of solids and gas flow in the riser section of a circulating fluidized bed

A computational fluid dynamics software (CFX) was modified for gas/particle flow systems and used to predict the flow parameters in the riser section of a circulating fluidized bed (CFB). Fluid Catalytic Cracking (FCC) particles and air were used as the solids and gas phases, respectively. Two-dimensional, transient, isothermal flows were simulated for the continuous phase (air) and the dispersed phase (solid particles). Conservation equations of mass and momentum for each phase were solved using the finite volume numerical technique. Two-dimensional gas and particle flow profiles were obtained for the velocity, volume fraction, and pressure drop for each phase. Calculations showed that the inlet and exit conditions play a significant role in the overall mixing of the gas and particulate phases and in the establishment of the flow regime. The flow behavior was analyzed based on the different frequency of oscillations in the riser. Comparison of the calculated solids mass flux, solids density and pressure drop with the measured pilot-scale PSRI data (reported in this paper) showed a good agreement.     

Discrete Modeling and Suggested Measurement of Heat Transfer in Gas–Solids Flows

Abstract

This article presents a two-dimensional transient model for gas–solids flow and heat transfer through pipes using the coupled Computational Fluid Dynamics and Discrete Element Method approach. Numerical simulations have been conducted to examine the modification of fluid thermal structure due to the presence of particles in a pneumatic transport pipeline. Modeled results have demonstrated the key role of transversal motion of rebounding particles in the pipe cross section in altering fluid temperature. Further implementation of this modeling technique in air-drying processes is discussed and possible experimental methods for the measurement of in situ particle and fluid motion and temperature profile are cited.     

A Numerical Study of Heat Transfer Mechanisms in Gas-Solids Flows Through Pipes Using a Coupled CFD and DEM Model

A two dimensional numerical model has been developed to simulate heat transfer in gas-solids flows through pipes, in which the gas phase is modelled as a continuum using the Computational Fluid Dynamics (CFD) approach and the solids phase is modelled by the Discrete Element Method (DEM). This allows interactions between gas, particles, and pipe wall to be accounted at the scale of individual particles and convective and conductive heat transfers to be calculated using local gas and solids parameters. The predicted changes to the flow structures and the various heat transfer mechanisms due to the presence of particles were analyzed and compared with other workers' findings. This study has quantitatively demonstrated the crucial effect of particle transverse motion on heat transfers due firstly to the thermal energy transport by rebounding particles and secondly to the modification of the fluid thermal boundary layer characteristics.     

Modeling of the heat transfer in cross-flow heat exchangers

The heat transfer in plate heat exchangers with cross flows of heat-transfer media is considered. At constant values of thermophysical parameters using a model of a one-dimensional flow in cach channel, analytical expressions for the temperature and heat flux distributions are obtained. The efficiency of heat exchangers at different values of dimensionless parameters is estimated. A model is proposed to take into account the two-dimensional flow of heat-transfer media in channels on the basis of empirical relations for the flow resistance and the heat transfer in flat channels.     

Particle Transport and Deposition under High-Frequency Oscillatory Ventilation and Normal Breathing

The fluid mechanics of high-frequency oscillatory ventilation (HFOV) for gas transport in the pulmonary region of the human lungs have been thoroughly studied by different methods. The major concept of HFOV adaptation is to push gas into further generation of the bronchial tree, with adequate gas mixing and small tidal volume. However, particle transport and deposition under HFOV is a rarely studied case where different mechanisms, compared to the mechanisms of gas transport, may associate. The target of this study is to numerically compare the efficiency of particle drug deposition under HFOV to normal breathing (NB) and to further clarify the mechanisms of particle transport and deposition under oscillating flows. A fully Eulerian computational fluid particles dynamic (CFPD) model is used for studying the transport and deposition of several sizes of inertia particles, under different transient flow conditions, inside a single physiologically realistic bifurcation created by generations G3–G4 of the human lung. An insight into the particle dynamics under high-frequency oscillating flow fields is given and the results showed that the highly oscillating field (HFOV) displayed stronger secondary flows, thinner boundary layers, and strong counter flow that accumulate and deposit particles further than a lower frequency oscillatory field (NB).

Copyright 2014 American Association for Aerosol Research     

Die Berechnung des Druckverlustes in der dreiphasigen Schwallströmung von Wasser, Öl und Luft

Calculation of Pressure Drop in Ternary Slug Flow of Water, Oil, and Air. Ternary flow of two immiscible liquids and a gas have hardly been studied up to the present although they frequently occur in petroleum production and in boiling mixtures of liquids. The article first considers known facts about the various kinds of binary flow as limiting cases of ternary flow with special consideration of slug flow. The article then reports new experimental results on ternary flow of oil, water, and air. The frictional pressure drop for ternary flow can be determined with the aid of known calculation procedures valid for binary flow. The limits of the observed forms of flow can be read from a flow map extended to include ternary flow. The pressure drop of ternary slug flow cannot be calculated without a knowledge of the form of flow. The frequency of slug movement is calculated for ternary flow by considering the pressure drop on binary flow of oil and water and the modified slug formation of liquids with higher viscosity. For small volume flows of gas the slug is almost ungassed. The pressure drop can be calculated with considerable accuracy in this range. At higher gas volume flows this becomes possible on considering measured slug lengths.     

A Numerical Study of Heat Transfer Mechanisms in Gas–Solids Flows Through Pipes Using a Coupled CFD and DEM Model

Abstract

A two dimensional numerical model has been developed to simulate heat transfer in gas–solids flows through pipes, in which the gas phase is modelled as a continuum using the Computational Fluid Dynamics (CFD) approach and the solids phase is modelled by the Discrete Element Method (DEM). This allows interactions between gas, particles, and pipe wall to be accounted at the scale of individual particles and convective and conductive heat transfers to be calculated using local gas and solids parameters. The predicted changes to the flow structures and the various heat transfer mechanisms due to the presence of particles were analyzed and compared with other workers' findings. This study has quantitatively demonstrated the crucial effect of particle transverse motion on heat transfers due firstly to the thermal energy transport by rebounding particles and secondly to the modification of the fluid thermal boundary layer characteristics.     

Prediction of the Induced Gas Flow Rate from a Self‐Inducing Impeller with CFD

The complex task of describing computationally two‐phase turbulent flows in aerated stirred‐tank reactors was overcome by proposing that the gas flow rate in the hollow impeller can be estimated from single‐phase flow simulations of the liquid phase in the reactor: the pressure at the impeller surface obtained from liquid phase simulations can be related to the gas induction rate. A commercial lab‐scale reactor with a radial six‐bladed hollow impeller was chosen for the study. To validate the presented methodology, the induced gas flow rate was measured experimentally from the tracking of the position of bubbles in a dynamic sequence of flow images. Notwithstanding the simplifications assumed in the presented CFD methodology, good agreement has been obtained between numerical results and experiments.     

Characterization of dynamic behavior of a spout-fluid bed with Shannon entropy analysis

Differential pressure fluctuation time series were obtained at different locations in a two-dimensional spout-fluid bed with a cross section of 300 × 30 mm and height 2000 mm. Shannon entropy analysis of differential pressure fluctuations was developed to characterize the dynamic behavior. Effects of two important operating parameters (spouting gas velocity and fluidizing gas flow rate) on the Shannon entropy were examined. It was demonstrated that a spout-fluid bed at a high spouting gas velocity or fluidizing gas flow rate was a deterministic chaos system since the Shannon entropies at all bed locations increased sharply and asymmetric unstable flows occurred. Shannon entropies were found to be significantly different at various bed locations. Shannon entropies of different flow regimes were distinct, so they were used to identify the flow regimes. The results show that the Shannon entropy helps to grasp the complex characteristics of dynamic behavior in spout-fluid beds.     

A hybridized snapshot proper orthogonal decomposition-discrete wavelet transform technique for the analysis of flow structures and their time evolution

A novel hybrid technique has been proposed in order to reveal in a greater detail the turbulent flow structures and their time evolution, and to address the issues and limitations related to the application of snapshot proper orthogonal decomposition (POD) and wavelet transform technique. The proposed hybrid technique combines the inherent abilities of the snapshot proper orthogonal decomposition and the two-dimensional discrete wavelet transform technique. The POD gives us the overall view of the most energetic flow pattern in an ensemble by decomposing the flow field into spatial and temporal modes, while two-dimensional wavelet transform gives us the localized spatial information through scale wise decomposition of the flow field. In this work, we apply the wavelet transform on the POD spatial modes. This enables us to understand the space scale structure of the flow events captured by the spatial POD modes, and the scale wise selectivity of these spatial POD modes. Thus, we are able to relate the most energetic flow events over a period of time (as obtained in spatial modes of snapshot POD) with the localized dominant scales that are contributing to it. Further, this information is utilized in the selection of those pod spatial modes that can effectively reconstruct a flow structure and its time evolution. The proposed technique has also been able to address the issues in the literature concerning the application of POD when the flow is less deterministic, as then a single POD mode may not reveal the flow structure and combination of modes is required to reconstruct it. In the present work, this hybrid methodology has been used to reveal the near wall intermittent events in channel flow: the ascending streaks and the bursts and their time evolution, the vortex tube and leading edge vortices in jet and the Taylor-Couette and irregular small chaotic vortices in Taylor-Couette flow. The planar dataset used for such an analysis has been obtained from particle image velocimetry and large eddy simulation studies.     

一种新的钢塑复合管制造技术

介绍了一种新的钢塑复合管连续制造技术,其特点是：在钢带焊接成管时通人惰性气体进行冷却,将焊道温度降低到PVC分解温度以下,从而避免与之粘连的PVC树脂分解。由于采用了冷却的方式,焊接部位与两管结合部位的距离可以缩短,减少了挤出压力,提高了挤出速度;可以缩短芯棒和口模的距离,使二者易于调节同心,挤出的管材的壁厚均匀。由于冷却的惰性气体中不含氧,焊接管不会产生粗糙易脱落的氧化膜,两管复合时不会因此处的薄弱环节而分层。