ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    Dependence of Intertrabecular Permeability on Flow Direction and Anatomic Site (1999)
    Springer
    Annals of biomedical engineering 27 (1999), S. 517-524 
    Details
    ISSN: 1573-9686
    Keywords: Trabecular bone ; Permeability ; Porous media ; Fluid flow ; Bone grafts ; Hydraulic stiffening
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The structure-function relationships for the permeability of trabecular bone may have relevance for tissue engineering, total joint replacements, and whole bone mechanics. To investigate such relationships, we used a constant flow rate permeameter to determine the intrinsic permeability of trabecular bone specimens, oriented longitudinally or transversely to the principal trabecular orientation, from the human vertebral body (n=20), human proximal femur (n=12), and bovine proximal tibia (n=24). Overall, the intertrabecular permeability ranged from 2.68 × 1011 to 2.00 × 108 m2. Significant negative nonlinear relations between intertrabecular permeability and volume fraction were found for each group except the longitudinal bovine proximal tibial specimens (r2=0.34-0.80). The average permeability ratio, a measure of the anisotropy, was 2.05, 6.60, and 23.3 for the human vertebral body, bovine tibia, and human femur, respectively. The permeability depended strongly on flow direction relative to the principal trabecular orientation (p 〈 0.0001) and anatomic site (p 〈 0.0001). In addition to providing a comprehensive description of intertrabecular permeability as a function of anatomic site and flow direction, these data provide substantial insight into the underlying structure-function relationships. © 1999 Biomedical Engineering Society. PAC99: 8719-j
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1114/1.195
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Unsteady forced and natural convection around a sphere immersed in a porous medium (1996)
    Springer
    Journal of engineering mathematics 30 (1996), S. 515-525 
    Details
    ISSN: 1573-2703
    Keywords: Porous media ; Unsteady convection ; Sphere ; Matched asymptotics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Technology
    Notes: Abstract Unsteady forced and natural convection around a sphere immersed in a fluid-saturated porous medium is investigated. The sphere is suddenly heated and, subsequently, maintains a constant temperature over the surface. For the forced convection problem, the method of matched asymptotic expansions is used to obtain an asymptotic solution of the energy equation in terms of the Peclet number. For the natural convection problem, asymptotic solutions in terms of the Rayleigh number are obtained by means of a regular perturbation method.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00036615
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Perceptions of chemistry: Why is the common perception of chemistry, the most visual of sciences, so distorted? (1996)
    Springer
    Journal of science education and technology 5 (1996), S. 193-201 
    Details
    ISSN: 1573-1839
    Keywords: Chemistry ; chemistry education ; multiple intelligences ; imagery ; visual-spatial thinking
    Source: Springer Online Journal Archives 1860-2000
    Topics: Natural Sciences in General , Technology
    Notes: Abstract Chemistry has evolved from a science dominated by mathematics into a science highly dependent on spatial-visual intelligence. Yet the chemical content of introductory courses remains taught essentially the same as 40–50 years ago. Chemistry, today, is recognized by chemists as the molecular science. Yet, school chemistry is alienated from that perception. Thanks to the computer, young people are more comfortable with visual imaging than their instructors were at the same age. Thus the time is rife to reinvigorate chemistry education by means of the visual-spatial approach, an approach wholly in conformance with the way modern chemistry is thought about and practiced.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01575303
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Influence of mixture sensitivity and pore size on detonation velocities in porous media (1995)
    Springer
    Shock waves 5 (1995), S. 89-95 
    Details
    ISSN: 1432-2153
    Keywords: Detonations ; Velocity deficits ; Porous media
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract Experiments have been carried out to determine the dependence of the detonation velocity in porous media, on mixture sensitivity and pore size. A detonation is established at the top end of a vertical tube and allowed to propagate to the bottom section housing the porous bed, comprised of alumina spheres of equal diameter (1–32 mm). Several of the common detonable fuels were tested at atmospheric initial pressure. Results indicate the existence of a continuous range of velocities with change in Φ, spanning the lean and the rich propagation limits. For all fuels in a given porous bed, the velocity decreases from a maximum value at the most sensitive mixture near Φ≈1 (minimum induction length), toV/V CJ≈0.3 at the limits. A decrease in pore size brings about a reduction inV/V CJ and a narrowing of the detonability range for each fuel. For porous media comprised of spherical particles, it was possible to correlate the velocity data corresponding to a variety of different mixtures and for a broad range of particle sizes, using the following empirical expression:V/V CJ=[1–0.35 log(d c /d p)]±0.1. The critical tube diameterd c is used as a measure of mixture sensitivity andd p denotes the pore diameter. An examination of the phenomenon at the composition limits, suggests that wave failure is controlled by a turbulent quenching mechanism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02425039
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    Propagation of nitromethane detonations in porous media (1995)
    Springer
    Shock waves 5 (1995), S. 115-119 
    Details
    ISSN: 1432-2153
    Keywords: Detonation ; Nitromethane ; Porous media ; Heterogeneous explosive
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract The characteristics of the propagation of a detonation in chemically sensitized nitromethane in a dense porous medium are investigated. By introducing liquid NM+15% (by weight) DETA into densely packed beds of solid spherical glass beads 66μm to 2.4 mm in diameter, a highly heterogeneous explosive mixture is obtained. The critical (i.e., failure) charge diameter of this mixture is systematically measured in unconfined charges over a wide range of bead sizes. Velocity measurements are also made for the various charges. It is found that there exists a critical bead size above which the critical diameter decreases with increasing bead size and below which it decreases with decreasing bead size. This result indicates an abrupt change in the mechanism of propagation at the critical bead size. Velocity measurements further support this by emphasizing the different behavior above and below the critical point.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02425043
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 6
    Electronic Resource
    Electronic Resource
    A theoretical analysis of vertical flow equilibrium (1995)
    Springer
    Transport in porous media 18 (1995), S. 107-129 
    Details
    ISSN: 1573-1634
    Keywords: Porous media ; vertical equilibrium ; asymptotics ; displacement processes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract The assumption of Vertical Equilibrium (VE) and of parallel flow conditions, in general, is often applied to the modeling of flow and displacement in natural porous media. However, the methodology for the development of the various models is rather intuitive, and no rigorous method is currently available. In this paper, we develop an asymptotic theory using as parameter the variable $$R_{{L}} = L/H\sqrt {k_{{V}} /k_{{H}} } $$ . It is rigorously shown that the VE model is obtained as the leading order term of an asymptotic expansion with respect to 1/R L 2 . Although this was numerically suspected, it is the first time that it is theoretically proved. Using this formulation, a series of special cases are subsequently obtained depending on the relative magnitude of gravity and capillary forces. In the absence of strong gravity effects, they generalize previous works by Zapata and Lake (1981), Yokoyama and Lake (1981) and Lake and Hirasaki (1981), on immiscible and miscible displacements. In the limit of gravity-segregated flow, we prove conditions for the fluids to be segregated and derive the Dupuit and Dietz (1953) approximations. Finally, we also discuss effects of capillarity and transverse dispersion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01064674
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 7
    Electronic Resource
    Electronic Resource
    A stream tube model for miscible flow (1995)
    Springer
    Transport in porous media 18 (1995), S. 245-261 
    Details
    ISSN: 1573-1634
    Keywords: Porous media ; miscible flow ; tracer ; dispersion ; convective flow ; stochastic ; stream tube ; continuous time random walk
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract A simple theoretical model is described for deriving a 1-dimensional equation for the spreading of a tracer in a steady flow at the field scale. The originality of the model is to use a stochastic appoach not in the 3-dimensional space but in the 1-D space of the stream tubes. The simplicity of calculation comes from the local relationship between permeability and velocity in a 1-D flow. The spreading of a tracer front is due to local variations in the cross-sectional area of the stream tubes, which induces randomness in travel time. The derived transport equation is averaged in the main flow direction. It differs from the standard dispersion equation. The roles of time and space variables are exchanged. This result can be explained by using the statistical theory of Continuous Time Random Walk instead of a standard Random Walk. However, the two equations are very close, since their solutions have the same first and second moments. Dispersivity is found to be equal to the product of the correlation length by the variance of the logarithm of permeability, a result similar to Gelhar's macrodispersion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00616934
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 8
    Electronic Resource
    Electronic Resource
    A stream tube model for miscible flow (1995)
    Springer
    Transport in porous media 18 (1995), S. 263-282 
    Details
    ISSN: 1573-1634
    Keywords: Porous media ; dispersion ; miscible flow ; heterogeneities ; stochastic ; stream tube ; layered ; fractal
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Large-scale dispersion in heterogeneous porous media is studied by using a simple model based on stochastic calculation of convective flow in a bundle of stream tubes. The advantage of this approach is that there is a local relationship between velocity and permeability in the 1-dimensional space of the stream tubes. Dispersion is due to the variation in stream tube cross-section, related to the permeability field. First, the arrival times of the tracer in the stream tubes are related to the stochastic properties of the permeability field (variance and covariance). Then, transport equations are derived from the moments of the arrival times. The results agree with more complicated studies. For a permeability field with long-range correlation, the transport equation is not unique. It depends on the assumptions involving moments higher than two. Assuming a Gaussian shape for the tracer flux leads to equations similar to the ones obtained in previous studies of time-dependent dispersivity. Without this approximation, the equation is non-local (integrodifferential) and leads to a memory effect. In the last part of this paper, the general results are illustrated with several correlation functions for the permeability field: purely random, exponential and power law covariance, and perfectly layered media.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00616935
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 9
    Electronic Resource
    Electronic Resource
    Migration of salts in the unsaturated zone caused by heating (1995)
    Springer
    Transport in porous media 19 (1995), S. 139-156 
    Details
    ISSN: 1573-1634
    Keywords: Porous media ; heat ; nonisothermal transport ; unsaturated zone ; evaporation ; precipitation ; diffusion ; salinity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Heat-transfer phenomena as well as moisture movement in unsaturated soils due to thermal gradients, have been extensively studied during the last four decades. Less attention has been devoted to the transport and redistribution of solutes caused by heating. Solar radiation, radioactive waste repositories, underground energy storage, buried electric cables and steam pipes, disposal of waste heat from power plants are examples of heat sources in the soil. Soil-water properties, such as surface tension, viscosity, density, as well as the equilibrium composition of phases, depend on temperature. Hence, nonuniform heating of a soil partially saturated by saline water has an effect on such processes as water flow under capillary and gravitational forces, evaporation, condensation and diffusion of vapor and transport and precipitation of salts. A mathematical model is presented for the migration of salts in the vadoze zone in the soil under nonisothermal conditions, taking into account the above-mentioned phenomena. The physical assumptions underlying the model are briefly discussed. The study of a particular case shows that under certain conditions, a heat source may attract dissolved salts, and cause their precipitation in the hot area.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00626663
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 10
    Electronic Resource
    Electronic Resource
    Two-dimensional interaction of a wetting front with an impervious layer: Analytical and numerical solutions (1995)
    Springer
    Transport in porous media 20 (1995), S. 251-263 
    Details
    ISSN: 1573-1634
    Keywords: Porous media ; water movement ; analytical solutions ; numerical solutions ; two-dimensional solutions ; impervious layers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Wetting-front movement can be impaired whenever the flow region includes boundaries such as the soil surface, seepage faces, planes of symmetry, or actual layers that are effectively impermeable, such as heavy clays or coarse materials below the water-entry pressure. An approximate analytical solution for interaction of flow from a line source with a parallel plane, impervious layer is derived. The solution ignores gravity and assumes a particular diffusivity that is related to the constant flow rate. It is exact until interaction begins, and provides an accurate approximation for short times thereafter. It can therefore be used to test the accuracy of numerical solutions of the flow equation, which can then be used with confidence for later times when the analytical approximation breaks down, for instance because gravity is ignored. A finite difference solution was tested in this way for both gradual and steep wetting fronts. Agreement between the two solutions was excellent for the gradual front, with the analytical approximation only slightly in error at later times. Numerical errors at the steep front were much greater; an accurate solution needed a finer spatial grid and a restart from the exact analytical values at the beginning of the interaction. The analytical approximation, though not as accurate as for the gradual front, was still ‘good’.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01073175
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 11
    Electronic Resource
    Electronic Resource
    On creeping detonation in filtration combustion (1994)
    Springer
    Shock waves 4 (1994), S. 109-112 
    Details
    ISSN: 1432-2153
    Keywords: Combustion ; Detonation ; Porous media
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract In porous media the local elevation of pressure slowly propagates in the adjacent layers of the gas causing the temperature rise there. In the presence of explosive gases this mechanism may lead to the formation of self sustaining combustion waves propagating at a constant speed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01418574
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 12
    Electronic Resource
    Electronic Resource
    Convection in anisotropic inclined porous layers (1994)
    Springer
    Transport in porous media 17 (1994), S. 271-283 
    Details
    ISSN: 1573-1634
    Keywords: Porous media ; convection ; layering ; mathematical model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Two-dimensional convective flow in a system of fluid-saturated porous layers is considered for small fluid velocities. The layers are inclined at an angle to the horizontal and there is a temperature gradient across them. A mathematical model of the system is constructed and the resulting series solution is numerically summed. The unique features of this model include its ability to represent non-symmetric multi-layered systems and materials whose permeabilities are anisotropic. The model is applied to various physical configurations. System aspect ratios, system symmetry and permeablity anisotropies are found to influence the effect that layers of different materials have on the convective flow.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00613587
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 13
    Electronic Resource
    Electronic Resource
    Jump conditions across strong compaction waves in gas saturated rigid porous media (1993)
    Springer
    Shock waves 3 (1993), S. 105-111 
    Details
    ISSN: 1432-2153
    Keywords: Porous media ; Shock compaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract Based on experimental results and some additional simplifying assumptions, the general macroscopic two phase equations governing the flow field which is developed in a gas saturated rigid porous medium domain were simplified to a form which enab led us to develop two analytical models for calculating the jump conditions across strong compaction waves. Predictions obtained by these two simplified analytical models are compared to the experimental results of Sandusky and Liddiard (1985) and to predictions of another more complicated model which was proposed by Powers et al. (1989). Fairly good to excelle nt agreements are evident.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02115890
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 14
    Electronic Resource
    Electronic Resource
    Fluid flow through heterogeneous porous media in a rotating square channel (1993)
    Springer
    Transport in porous media 12 (1993), S. 43-54 
    Details
    ISSN: 1573-1634
    Keywords: Porous media ; heterogeneous ; rotating flow ; square channel ; Coriolis acceleration ; secondary circulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract An analytical three-dimensional solution to the fluid flow problem through heterogeneous porous media in a rotating square channel is presented. The permeability of the fluid saturated porous domain varies in the vertical direction, thus affecting the imposed main flow in the channel. As a result of Coriolis acceleration, secondary circulation in a plane perpendicular to the main flow direction is created. A particular example of a monotonic distribution of the permeability function is analyzed leading to a single vortex secondary circulation. Nevertheless, multiple vortex secondary flow solutions are possible depending on the particular variation of the permeability in the vertical direction. No secondary motion is expected for isothermal flows in homogeneous porous media.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00616361
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 15
    Electronic Resource
    Electronic Resource
    An elastoplasticity model in porous media theories (1992)
    Springer
    Transport in porous media 9 (1992), S. 49-59 
    Details
    ISSN: 1573-1634
    Keywords: Porous media ; mixture theories ; volume fractions ; incompressible constituents ; granular solid matrix ; viscous pore liquid ; finite elastoplasticity ; kinematical hardening
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract In this article, porous media theories are referred to as mixture theories extended by the well-known concept of volume fractions. This approach implies the diverse field functions of both the porous solid matrix and the pore fluid to be represented by average functions of the macroscale. The present investigations are based on a binary model of incompressible constituents, solid skeleton, and pore liquid, where, in the constitutive range, use is made of the second-grade character of general heterogeneous media. Within the framework of geometrically finite theories, the paper offers a set of constitutive equations for the solid matrix, the viscous pore liquid and the different interactions between the constituents. The constitutive model applies to saturated as well as to empty solid materials, taking into account the physical nonlinearities based on elasto-plastic solid deformations. In particular, the constitutive model concentrates on granular materials like soil or concrete, where the elastic deformations are usually small and the plastic range is governed by kinematically hardening properties.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01039625
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 16
    Electronic Resource
    Electronic Resource
    Deletion of nondominant effects in modeling transport in porous media (1992)
    Springer
    Transport in porous media 7 (1992), S. 15-38 
    Details
    ISSN: 1573-1634
    Keywords: Porous media ; modeling ; scaling ; dimensionless numbers ; dominance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract A methodology for eliminating nondominant effects in models that describe transport phenomena in porous media is presented. The methodology is based on the introduction of dimensionless numbers and on a proper evaluation of the order of magnitude of terms. These dimensionless numbers are redefined as characteristics of transport and transformation phenomena in porous media. It is shown that different time scales and different length scales may have to be employed for different variables. A method for evaluating the order of magnitude of the error of prediction when terms are deleted, is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00617315
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 17
    Electronic Resource
    Electronic Resource
    Deformable porous media with double porosity. Quasi-statics. I: Coupling effects (1992)
    Springer
    Transport in porous media 7 (1992), S. 63-82 
    Details
    ISSN: 1573-1634
    Keywords: Porous media ; double porosity ; consolidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract We investigate the macroscopic quasi-static description of a deformable porous medium with a double porosity constituted by pores and fractures. For this purpose, we use an homogenization technique which gives the macroscopic modelling from the description at the pore and fracture levels. It appears that the macroscopic description is sensitive to the ratios between the different scales,l/l′ andl′/l″, wherel, l′ l″ are characteristic lengths of the pores, the fractures and the macroscopic medium, respectively. In the first paper we investigate the casel′/l″=(l/l′)2, which exhibits a coupling between the flows through the pores and the fractures. The macroscopic description is shown to depend on a single pressure field and exhibits a broken symmetry. Other situations will be examined in a subsequent paper. Large spectra of pore and fracture sizes are also evoked.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00617317
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 18
    Electronic Resource
    Electronic Resource
    Fractal porous media IV: Three-dimensional stokes flow through random media and regular fractals (1990)
    Springer
    Transport in porous media 5 (1990), S. 325-340 
    Details
    ISSN: 1573-1634
    Keywords: Porous media ; three-dimensional ; permeability ; random ; fractal
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract The three-dimensional Stokes flow of a Newtonian fluid through random and/or fractal media is numerically determined. The permeability of these media is derived. Results relative to these structures are presented and discussed. The validity of the Carman equation and of a simple scaling argument is questioned.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01141990
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 19
    Electronic Resource
    Electronic Resource
    Free convection from a vertical plate with nonuniform surface heat flux and embedded in a porous medium (1988)
    Springer
    Transport in porous media 3 (1988), S. 95-106 
    Details
    ISSN: 1573-1634
    Keywords: Free convection ; heat transfer ; Porous media ; natural convection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract An analysis is presented for the calculation of heat transfer due to free convective flow along a vertical plate embedded in a porous medium with an arbitrarily varying surface heat flux. By applying the appropriate coordinate transformations and the Merk series, the governing energy equation is expressed as a set of ordinary differential equations. Numerical solutions are presented for these equations which represent universal functions and several computational examples are provided.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00222688
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 20
    Electronic Resource
    Electronic Resource
    Fractal porous media III: Transversal Stokes flow through random and Sierpinski carpets (1988)
    Springer
    Transport in porous media 3 (1988), S. 185-198 
    Details
    ISSN: 1573-1634
    Keywords: Porous media ; permeability ; random ; fractal
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract The transversal Stokes flow of a Newtonian fluid through random and Sierpinski carpets is numerically calculated and the transversal permeability derived. In random carpets derived from site percolation, the average macroscopic permeability varies as (ε- ɛ c)3/2, close to the critical porosityɛ c. This exponent is found to be slightly different from the conductivity exponent. Results for Sierpinski carpets are presented up to the fourth generation. The Carman equation is not verified in these two model porous media.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00820345
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 21
    Electronic Resource
    Electronic Resource
    A new perturbation expansion for horizontal infiltration and sorptivity estimates (1988)
    Springer
    Transport in porous media 3 (1988), S. 133-144 
    Details
    ISSN: 1573-1634
    Keywords: Porous media ; sorptivity ; asymptotic series solution ; unsaturated flow
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract A new asymptotic expansion is proposed for the nonlinear diffusion equation used to model the horizontal infiltration of water into soils. The expansion is based on a small parameter associated with the nonlinearity in the diffusivityD. The expansion leads to simpler integral formulae than previous series solutions and most previous iterative methods. To first order, it yields a formula for sorptivity identical with the ‘double-integration’ result, derived in a less rigorous manner by Parlange (1975). Rigorous conditions for the validity of the asymptotic expansion and the double-integration technique are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00820341
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 22
    Electronic Resource
    Electronic Resource
    High velocity flow in porous media (1987)
    Springer
    Transport in porous media 2 (1987), S. 521-531 
    Details
    ISSN: 1573-1634
    Keywords: Porous media ; high velocity flow ; non-Darcy flow ; Forchheimer equation ; inertial effects ; constitutive equations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Experimental observations have established that the proportionality between pressure head gradient and fluid velocity does not hold for high rates of fluid flow in porous media. Empirical relations such as Forchheimer equation have been proposed to account for nonlinear effects. The purpose of this work is to derive such nonlinear relationships based on fundamental laws of continuum mechanics and to identify the source of nonlinearity in equations. Adopting the continuum approach to the description of thermodynamic processes in porous media, a general equation of motion of fluid at the macroscopic level is proposed. Using a standard order-of-magnitude argument, it is shown that at the onset of nonlinearities (which happens at Reynolds numbers around 10), macroscopic viscous and inertial forces are negligible compared to microscopic viscous forces. Therefore, it is concluded that growth of microscopic viscous forces (drag forces) at high flow velocities give rise to nonlinear effects. Then, employing the constitutive theory, a nonlinear relationship is developed for drag forces and finally a generalized form of Forchheimer equation is derived.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00192152
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 23
    Electronic Resource
    Electronic Resource
    Fractal porous media I: Longitudinal stokes flow in random carpets (1987)
    Springer
    Transport in porous media 2 (1987), S. 553-569 
    Details
    ISSN: 1573-1634
    Keywords: Porous media ; permeability ; random ; fractal
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Two-dimensional porous media whose random cross-sections are derived from site percolation are constructed. The longitudinal flow of a Newtonian fluid in the Stokes approximation is then computed and the longitudinal permeability is obtained. Two methods are used and yield the same result when porosity is low. The Carman equation is shown to apply within ±7% when porosity is within the range from 0 to 0.75. Finally, random structures derived from stick percolation are investigated; results are qualitatively the same, but the Carman equation yields a poorer approximation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00192155
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 24
    Electronic Resource
    Electronic Resource
    Fractal porous media II: Geometry of porous geological structures (1987)
    Springer
    Transport in porous media 2 (1987), S. 571-596 
    Details
    ISSN: 1573-1634
    Keywords: Porous media ; fractal ; permeability ; transport
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Some geological structures are analysed and found to be fractal. An interesting feature is the very large range of scales involved; the spreading dimension is also measured for some of them. The consequences of these measurements on the analysis of transport processes in porous media are presented - the existence of fractal structures multiplies the variety of actual porous media.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00192156
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...