A Fickian diffusion model for the spreading of liquid plumes infiltrating in heterogeneous media

ANNUAL LITERATURE SURVEY 1996 Fluidized sand-beds are efficient and cost-effective methods for biological treatment within recirculating aquaculture systems. This article summarizes and applies techniques developed in other disciplines for calculating fluidization hydraulics, based solely upon characteristics of the granular medium, for the purpose of designing biological fluidized-bed units for use in recycle aquaculture. Solutions to fluidization calculations are presented as simplified curves useful for sensitivity analysis for optimizing unit design. This article also discusses the characteristics which make a medium suitable for use in nitrifying fluidized beds in aquaculture, design criteria for proper distribution of water at the bottom of the flnidized bed, and special issues involving fluidization hydraulics and the application offluidized beds to aquaculture. Two-phase air/oil flow in aero engine bearing chambers: characterization of oil film flows Glahn A. & Wittig S., Transactions - ASME." Journal of Engineering for Gas Turbines and Power, 1996, 118/3 (578-583). In English. For the design of secondary air and lubrication oil systems, a sufficient knowledge of two-phase flow and heat transfer phenomena under bearing chamber flow conditions is required. The characterization ofoil film flows at the bearing chamber walls is one of the major tasks for a better understanding of these processes and, therefore, a necessity for improvements of the efficiency of aero engines. Utilizing a fiber-optic LDV setup, measurements of oil film velocity profiles have been performed in our high-speed bearing chamber rig simulating real engine conditions. All data have been compared with different theoretical approaches; which have been derived from a force balance at a liquid film element, including geometric conditions and temperature dependent fluid properties, and by approaches for the eddy viscosity available in the literature. Mechanism and effects of predominant parameters regarding limitation of falling water in vertical countercurrent two-phuse flow Sudo Y., Transactions - ASME: Journal of Heat Transfer, 1996, 118/3 (715-724). In English. In this study, an investigation was carried out to clarify the mechanism of countercurrent flow limitation (CCFL) or flooding, that is, limitations in the falling water mass flux in countercurrent two-phase flow in vertical channels, and to identify the effects or predominant parameters regarding CCFL, adopting the criterion that the CCFL condition be given by an envelope of momentum equation applied for the entire length of the channel with respect to any void fraction. As a result, it was found that the analytical model proposed could adequately predict all existing experimental results investigated in this study. In search of two-phase flow Hewitt G.F., Transactions - ASME: Journal o f Heat Transfer, 1996, 118/3 (518-527). In English. The objective of this paper is to take an overview of progress in the search for knowledge in two-phase flow over the past three and half decades, and to try to draw conclusions about future directions from this historical perspective. Rather than to try to cover the whole range of possible topics, two have been selected for examination, namely flooding and disturbance waves in annular flow. A Fickian diffusion model for the spreading of liquid plumes infiltrating in heterogeneous media Pruess K., Transport in Porous Media, 1996, 24/1 (1-33). In English. Infiltration of water and non-aqueous phase liquids (NAPLs) in the vadose zone gives rise to complex two- and three-phase immiscible displacement processes. Physical and numerical experiments have shown that everpresent small-scale heterogeneities will cause a lateral broadening of the descending liquid plumes. This behavior of liquid plumes int'dtrating in the vadose zone may be similar to the familiar transversal dispersion of solute plumes in single.phase flow. Noting this analogy we introduce a mathematical model for phase dispersion in multiphase flow as a Fickian diffusion process. Determination of permeability teusors for two-phase flow in homogeneous porous media: theory Lasseux D., Quintard M. & Whitaker S., Transport in Porous Media, 1996, 24/2 (107-137). In English. This paper continues previous studies of the closure problem for two-phase flow in homogeneous porous media, and shows how the closure problem can be transformed to a pair of Stokes-like boundary-value problems in terms of pressures that have units of length and velocities that have units of length squares. To determine the geometry associated with the closure problem, one needs to solve the physical problem; however, the closure problem can be solved using the same algorithm used to solve the physical problem, thus the entire procedure can be accomplished with a single numerical code. Experimental determination of the flow transport coefficients in the coupled equations of two-phase flow in porous media Dullien F.A.L. & Dong M., Transport in Porous Media, 1996, 25/1 (97-120). In English. The transport coefficients in the coupled equations of two-phase flow are defined if the pressure gradient in one of the two flowing fluids is equal to zero. This definition has been used in experiments with oil and water in a sandpack and the four transport coefficients have been measured over wide water saturation ranges. The values of the cross coefficients were found to be significant as they ranged from 10 to 35% of the value of the effective permeability to water and from 5 to 15 % of the effective permeability to oil, respectively. Pore-scale network model for drainage-dominated three-phase flow in porous media Pereira G.G., Pinczewski W.V., Chan D.Y.C., Paterson L. & Oren P.E., Transport m Porous Media, 1996, 24/2 (167-201). In English. Drainage displacements in three-phase flow under strongly wetting conditions are completely described by a simple generalisation of well understood two-phase drainage mechanisms. As in two-phase flow, the sequence of throat invasions in three-phase flow is determined by fluid connectivity and threshold capillary pressure for the invading interface. A three phase, two-dimensional network model based on the pore-scale fluid distribu-

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