DYNAMIC FILTRATION MODELING IN FOAM FILTERS FOR DIESEL EXHAUST

Diesel Particulate Filters (DPFs) are probably the most effective means for trapping the exhaust emitted particulate from diesel engines. Foam type filters become a promising alternative to the common wall flow filters, since they are effective in filtering small size particles and provide a larger specific surface area for catalytic coatings. A mathematical model taking into account the significant phenomena during the dynamic filtration of foam fitters is developed. The model predicts the filtration efficiency and the induced backpressure as function of the geometric filter properties and operating conditions. A novel approach is employed which considers both “deep-bed” and “cake”filtration characteristics in the filter. Due to the particular structure properties of the foam filters it is necessary to define a characteristic parameter, which differentiates among different filter types. This parameter, which has a physical meaning, is easily derived by simple experimental measurements. The model is employed to. identify and understand the critical parameters of the phenomenon. Indicative parametric runs are presented, which illustrate the applicability of the model in system optimization procedures.     

低压、常压系统结晶堵塞的原因及对策

分析二氧化碳汽提尿素装置低压、常压系统结晶堵塞的原因,提出了解决措施.     

纤维束滤料直接过滤废水的试验研究

论述了纤维束滤料直接过滤城市二级生化处理出水的试验情况。结果表明，纤维束过滤运行稳定，出水水质好，滤阻小，过滤周期长。     

管线和桶体设备带温带压堵漏的工艺安全设计

论述管线和桶体设备带温带压堵漏的特殊性,通过现场具体实时数据来计算带压堵漏时手动液压油泵的实际操作压力,以避免在实际堵漏过程中注胶压力过大造成管线失稳、断裂;采取加强圈的措施来提高管线和桶体设备的抗外压强度.     

新型AF滤料处理微污染水的过滤技术

本研究采用新型AF滤料在水厂进行了模型试验和生产性试验。模型试验结果表明：单层AF滤料滤池、双层AF-无烟煤滤料滤池在充氧条件下,滤速为4m／h时,对CODMn的去除率分别为17,4％和21．3％,对氨氮的去除率分别为55％和61％,出水水质均优于国家饮用水标准。生产性试验表明：双层AF-无烟煤滤料滤池的周期产水量是双层石英砂-无烟煤滤料滤池的1．5倍,出水水质前者优于后者,采用双层AF-无烟煤滤料滤池可为供水企业带来显著的经济效益。     

CFD MODELLING OF NATURAL CONVECTION HEAT AND MASS TRANSFER IN HYGROSCOPIC POROUS MEDIA

Abstract

This paper presents the derivation of a model to predict heat and mass transfer in a system consisting of a turbulently flowing fluid overlying a saturated hygroscopic porous medium. Comparisons with experimental and numerical simulations have been carried out to check the accuracy of components of the model. Finally, a case study using silica gel as a representative hygroscopic porous medium is presented as an application of the model. It is shown that moisture is convected from the warm interior of a bulk of porous medium to the relatively cool periphery. This result has profound practical implications when the hygroscopic medium is stored agricultural produce as the region of high moisture content may become moldy.     

RHEOLOGICAL PROPERTIES AND FLOW OF CONCENTRATED DISPERSE MEDIA I - MODELLING OF STEADY AND UNSTEADY BEHAVIOR

Abstract

A steady viscosity model, including both volume fraction and shear rate variables, is shown to be applicable to a large class of complex liquids which can be considered as highly concentrated disperse media. The effect of yield stress is taken into account. For unsteady measurements, this model, which includes thixotropy, can be simply extended to viscoelastic behaviour. Some examples of application will be given, specially to heavy crude oil emulsions.     

RHEOLOGICAL PROPERTIES AND FLOW OF CONCENTRATED DISPERSE MEDIA I - MODELLING OF STEADY AND UNSTEADY BEHAVIOR

A steady viscosity model, including both volume fraction and shear rate variables, is shown to be applicable to a large class of complex liquids which can be considered as highly concentrated disperse media. The effect of yield stress is taken into account. For unsteady measurements, this model, which includes thixotropy, can be simply extended to viscoelastic behaviour. Some examples of application will be given, specially to heavy crude oil emulsions.     

综合材料介入陶瓷艺术的形式规律

综合材料介入陶瓷艺术并不是把一大堆各式各样的材料随意堆积放置,而是要将这些材料通过艺术创作与陶瓷材料有机的结合构成艺术作品。本文运用形式美法则结合综合材料介入陶瓷艺术的创作进行分析研究,揭示综合材料介入陶瓷艺术的艺术规律:主从与重点、过渡与照应、节奏与韵律、质感与肌理、调和与对比、多样与统一。     

核级玻璃纤维滤材的研制

研制出能满足核电站使用的玻璃纤维滤材。其关键技术是防止或减少SiO2在硼酸和氢氧化锂水溶液中析出的核级滤材处理剂的研发,运用专有的玻璃纤维湿法造纸技术,生产出核级玻璃纤维滤材的坯纸,对其进行贵重添加剂处理,烘干后在坯纸的两面复合有机纤维保护层。现已成功用于巴基斯坦恰希玛核电站。     

DEVELOPMENT OF RADIAL MODELS FOR FORMATION DAMAGE IN POROUS MEDIA

The continuously changing velocities in radial geometry have a significant effect on process characteristics, making it an intellectually challenging problem. In practical operations, fluid is generally pumped down injection wells from where it flows radially outward. Simulating this radial system with linear models is definitely restrictive. Consequently, the need for developing radial models for flow and particle entrapment in porous media is both fundamental and applied.

A radial network model, covering a 120° angle, has been developed to simulate formation damage due to deep bed filtration (DBF) of injected suspensions. The models draws upon our previously developed concepts of “wave-front movement” and “flow-biased probability” for linear systems. Systematic studies have been performed on formation damage using monodispersed and polydispersed suspensions. Case studies have been presented for constant flow rate and constant pressure injections, and comparisons are made between linear and radial systems.

Results show that the results obtained from linear models are conservative in comparison to those obtained from radial models. Furthermore, the use of monodispersed particles in mathematical models would show smaller differences between linear and radial predictions than would actually occur for polydispersed particles.     

OPTIMIZATION AND NEURAL MODELLING OF PULSE COMBUSTORS FOR DRYING APPLICATIONS

ABSTRACT

Results of investigations of a valved pulse combustor to choose optimal geometry, which covered measurements of the flow rates of air and fuel, pressure oscillations, including pressure amplitude and frequency and flue gas composition are presented in the paper. Experimental studies compsiring the operation of the pulse combustor coupled with a drying chamber and working separately are described. It was found that coupling of the pulse combustor with a drying chamber had no significant effect on the pulse combustion process. Smoother runs of pressure oscillations in the combustion chamber, lower noise level and slightly higher NO_x emission were observed. The velocity flow field inside the drying chamber was measured by LDA technique. Results confirmed a complex character of pulsating flow in the chamber. A large experimental data set obtained from measurements enabled developing a neural model of pulse combustion process. Artificial neural networks were trained to predict amplitudes and frequencies of pressure oscillations, temperatures in the combustion chamber and emission of toxic substances. An excellent mapping performance of the developed neural models was obtained. Due to complex character of the pulse combustion process, the application of artificial neural networks seems to be the best way to predict inlet parameters of a drying agent produced by the pulse combustor     

2D MODELLING OF DRYING OF POROUS MEDIA: INFLUENCE OF EDGE EFFECTS AT THE INTERFACE.

TThis paper is essentially devoted to the study of the interfacial coefficient problem and to a characterization of the falling rate period.By means of a 2D numerical simulation, it is shown that the falling rate period is characterized by strong humidity heterogeneities at the interface. These heterogeneities affect significantly the interfacial mass transfer coefficient to be used in the traditional ID approach of drying. In this paper. the heterogeneities are due to the coupling between external and internal transfer in a boundary layer flow leading edge region.0ther phenomena that may also cause the occurence of humidity heterogeneities at the interface are discussed.     

OPTIMIZATION AND NEURAL MODELLING OF PULSE COMBUSTORS FOR DRYING APPLICATIONS

Results of investigations of a valved pulse combustor to choose optimal geometry, which covered measurements of the flow rates of air and fuel, pressure oscillations, including pressure amplitude and frequency and flue gas composition are presented in the paper. Experimental studies compsiring the operation of the pulse combustor coupled with a drying chamber and working separately are described. It was found that coupling of the pulse combustor with a drying chamber had no significant effect on the pulse combustion process. Smoother runs of pressure oscillations in the combustion chamber, lower noise level and slightly higher NO_x emission were observed. The velocity flow field inside the drying chamber was measured by LDA technique. Results confirmed a complex character of pulsating flow in the chamber. A large experimental data set obtained from measurements enabled developing a neural model of pulse combustion process. Artificial neural networks were trained to predict amplitudes and frequencies of pressure oscillations, temperatures in the combustion chamber and emission of toxic substances. An excellent mapping performance of the developed neural models was obtained. Due to complex character of the pulse combustion process, the application of artificial neural networks seems to be the best way to predict inlet parameters of a drying agent produced by the pulse combustor     

A THREE DIMENSIONAL NETWORK MODEL FOR CONSOLIDATED POROUS MEDIA. BASIC STUDIES

A three-dimensional porous medium model that pertains to consolidated permeable porous rocks and similar structures is proposed. The porous medium is considered as a network of chambers connected through long narrow throats and it is approximated as a network of unit cells of the constricted tube type. The skeleton of the network can be either regular or randomized, and the throat-to-chamber coordination number can be varied by randomly removing a number of throats. The sizes of contiguous chambers and throats can be cither independent random variables, or they can be correlated. This correlation can be positive (large chambers preferring large throats), or negative (large chambers preferring small throats). The permeability of the network is found to be minimal when the chambers and throats are completely uncorrected. The degree of correlation also affects the throat-to-chamber size ratio, a parameter which is very important in two-phase flows through porous media. A substantial correlation between the local intensity of the flow field on one hand and the local porosity and throat diameter on the other is found. @KEYWORDS: Pore network model, Consolidated porous media.     

ANALYSIS OF PERMEABILITY FOR ELLIS FLUID FLOW IN FRACTAL POROUS MEDIA

This work studies the flow characteristics of Ellis fluid in saturated porous media. A fractal model is developed for the effective permeability of Ellis fluid flow in porous media based on the assumptions that porous media consist of a bundle of tortuous capillaries, whose size distribution and tortuosity follow the fractal scaling laws. The average flow velocity and the effective permeability for Ellis fluid flow in porous media are derived. The proposed fractal model does not contain any empirical constant, and every parameter in the model has clear physical meaning. The model predictions are compared with the measured data, and good agreement between them is obtained.     

COMPARISON OF EXPERIMENTAL AND MODELLING STUDIES FOR THE MICROWAVE DRYING OF IRONBARK TIMBER

ABSTRACT

Temperature profiles through boards during the microwave-assisted drying of Australian Ironbark timber have been investigated in this work in order to explore evidence for timber degrade via “charring” at internal temperatures below those required for pyrolysis (Brooke et al., 1998). A previously published model (Turner and Jolly, 1990a) describing one-dimensional microwave power absorption, based on the solution of Maxwell's equations, has been reviewed and significant limitations identified and overcome. Improvements included the use of a linear-mixing approach for the dielectric constants, the incorporation of temperature and moisture dependencies for these dielectric properties and the inclusion of diffusion within an overall system model. A control-volume technique has been used for predicting both moisture and temperature distributions within the timber, with a second-order finite-difference method being used to solve Maxwell's equations. The final model showed     

Modelling the flow of power-law fluids through anisotropic porous media at low-pore Reynolds number

The flow of power-law fluids through fibrous media at low-pore Reynolds number is investigated using the homogenization method for periodic structures with multiple scale expansions. This upscaling process shows that the macroscopic pressure gradient is also a power-law of the volume averaged velocity field. To determine the complete structure of the macroscopic flow law, numerical simulations have to be performed on representative elementary volume of porous media. In this paper, this has been achieved on 2D periodic arrays of parallel fibers with elliptical cross section of different aspect ratios. It is found that macroscopic flow models already proposed in the literature fail in reproducing numerical data within the whole volume fractions of fibers and aspect ratios ranges. Consequently, a novel methodology is proposed to establish the macroscopic tensorial seepage law within the framework of the theory of anisotropic tensor functions and using mechanical iso-dissipation curves. This methodology is illustrated through our numerical results.