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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Transport in porous media 18 (1995), S. 1-13 
    ISSN: 1573-1634
    Keywords: Mixed convection ; thermal plume ; line source ; porous media
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract A boundary-layer analysis is presented for the mixed convection flow which is produced when a horizontal line heat source, which is embedded in an infinite fluid-saturated porous medium, generates heat at a constant rate. It is shown that the governing equations can be non-dimensionalized so that they do not involve any parameters and thus just one solution of the transformed boundary-layer equations is required. Series solutions which are valid both near the line source and far downstream are obtained and compared with the numerical solution of the full boundary-layer equations.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Transport in porous media 32 (1998), S. 329-355 
    ISSN: 1573-1634
    Keywords: mixed convection ; asymptotic expansion techniques impulsively heated horizontal circular cylinder
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract The mixed convection caused when a horizontal circular cylinder is suddenly heated is investigated in the situation when the initial flow past the cylinder is uniform and its direction either upwards or downwards. An analytical series solution, which is valid at small times, is obtained using the matched asymptotic expansions technique. A numerical solution, which is valid at all times and for any values of the Rayleigh and Péclet numbers, is also obtained using a fully implicit finite-difference method. Three different regimes, when either the free or forced convection is dominant or when they have the same order of magnitude, are considered. In the free convection dominated regime, two vortices develop near the sides of the cylinder in both situations of an upward or downward external flow. Comparisons between the analytical and numerical results at small times, as well as a detailed discussion of the evolution of the numerical solution are presented. The numerical results obtained for large Rayleigh, Ra, and Péclet Pe, numbers show that a thermal boundary-layer forms adjacent to the cylinder for any value of the ratio Ra/e. The steady state boundary-layer analysis, similar to that performed by Cheng and Merkin, is analysed in comparison to the numerical solution obtained for large values of Ra and Pe at very large times.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-1634
    Keywords: porous medium ; convection ; boundary layer ; transient ; heat flux.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract An analysis is made of the transient free convection from a vertical flat plate which is embedded in a fluid-saturated porous medium. It is assumed that for time $$\overline \tau 〈 0$$ a steady state temperature or velocity has been obtained in the boundary-layer which occurs due to a uniform flux dissipation rate $$q_1^{\prime \prime } $$ . Then at time $$\overline \tau = 0$$ the heat flux on the plate is suddenly changed to $$q_2^{\prime \prime } $$ and maintained at this value for $$\overline \tau 〉 0$$ . An analytical solution has been obtained for the temperature/velocity field for small times in which the transport effects are confined within an inner layer adjacent to the plate. These effects cause a new steady boundary layer. A numerical solution of the full boundary-layer equations is then obtained for the whole transient from $$\overline \tau = 0$$ to the steady state, firstly by means of a step-by-step method and then by a matching technique. The transition between the two distinct solution methods is always observed to occur very near to the turning point of the plate surface temperature, a time at which the fluid temperature is close to its steady state profile. The solution obtained using the step-by-step method shows excellent agreement with the small time analytical solution. Results are presented to illustrate the occurrence of transients from both small and large increases and decreases in the levels of existing energy inputs.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Transport in porous media 22 (1996), S. 181-193 
    ISSN: 1573-1634
    Keywords: natural convection ; boundary-layers ; surface heat flux
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract This paper presents a theoretical and numerical investigation of the natural convection boundary-layer along a vertical surface, which is embedded in a porous medium, when the surface heat flux varies as (1 +x 2)μ), where μ is a constant andx is the distance along the surface. It is shown that for μ 〉 -1/2 the solution develops from a similarity solution which is valid for small values ofx to one which is valid for large values ofx. However, when μ ⩽ -1/2 no similarity solutions exist for large values ofx and it is found that there are two cases to consider, namely μ 〈 -1/2 and μ = -1/2. The wall temperature and the velocity at large distances along the plate are determined for a range of values of μ.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Acta mechanica 112 (1995), S. 107-116 
    ISSN: 1619-6937
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary A mathematical theory is proposed for the analysis of the unsteady boundary-layer flow and heat transfer arising from a continously moving heated flat plate which is suddenly stopped and cooled. Full numerical and asymptotic solutions which are valid for both small and large values of time are obtained for a range of Prandtl numbers from 0.1 to 10. Results for the non-dimensional velocity and the temperature profiles, as well as for the skin friction and the heat transfer on the plate, are presented. The accuracy of the solution is discussed and the results are given in sufficient detail in order to provide useful guidelines for practical applications.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1619-6937
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary The method of matched asymptotic expansions is employed for investigating the growth of the free convection boundary-layer on a horizontal circular cylinder prescribed with a uniform heat flux, which is embedded in a porous medium. It is assumed that the Rayleigh number is large, but finite, and the time of investigation is short. It is shown that the solution contains terms that are absent from the solution based on the boundary-layer approximation and that vortices form at both sides of the cylinder. The development of the plume region near the top of the cylinder, as well as the local and average Nusselt numbers, are evaluated and presented in graphical form.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Acta mechanica 127 (1998), S. 25-38 
    ISSN: 1619-6937
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary In this paper the radial free jet which is produced by a continuous discharge of fluid from the space between two identical, parallel, circular, concentric discs into an infinite region of stagnant fluid of the same density and viscosity is investigated. Both laminar and turbulent jets are considered with analytical solutions being obtained near to the origin of the jet and at large distances along the jet. These asymptotic solutions are matched using a computational technique, and the numerical predictions show very good agreement with all the available experimental data.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Acta mechanica 110 (1995), S. 19-32 
    ISSN: 1619-6937
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary This paper considers steady laminar combined convection flows of power-law fluids between vertical parallel-plates with a uniform temperature gradient applied to the walls. The parabolic equations are written in an implicit finite-difference form and are solved using a marching technique. The governing parameters are Gr, Pr, andn. Various values of Gr andn are considered, including the forced convection solution, Gr=0, and the Newtonian case,n=1. Pr is set at a value of unity in order to present the numerical method and to compare with the existing results for Newtonian fluids. Under certain circumstances reverse flow regions appear, either at the centre or adjacent to the walls of the duct and these are present in the fully-developed flow. These reverse flow problems are dealt with using an iterative technique. In order to assess the effects of recirculation and pseudoplasticity on the flow and heat transfer characteristics, flow profiles, Nusselt numbers and friction factors are presented for various values of the governing parameters.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Acta mechanica 121 (1997), S. 35-49 
    ISSN: 1619-6937
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary Laminar combined convection of non-Newtonian fluids in vertical eccentric annuli, in which the inner and outer walls are held at different constant temperatures is considered and a new economical method of solution for the three-dimensional flow in the annulus is developed. Assuming that the ratio of the radial to the vertical scale, ε, is small, as occurs frequently in many industrial applications, then the governing equations can be simplified by expanding all the variables in terms of ε. This simplification gives rise to the presence of a dominant cross-stream plane in which all the physical quantities change more rapidly than in the vertical direction. The solution trechnique consists of marching in the vertical streamwise direction using a finite-difference scheme and solving the resulting equations at each streamwise step by a novel technique incorporating the Finite Element Method. The process is continued until the velocity, pressure and temperature fields are fully developed, and results are presented for a range of the governing non-dimensional parameters, namely the Grashof, Prandtl, Reynolds and Bingham numbers.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 23 (1996), S. 811-817 
    ISSN: 0271-2091
    Keywords: SIMPLE-like algorithms ; average correction technique ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: This note develops an average correction technique for accelerating the rate of convergence of the SIMPLE-like algorithm by implementing the average pressure correction method as proposed by Wen and Ingham (Int. j. numer. methods fluids, 17, 385-400 (1993); 19, 889-903 (1994)) with an average velocity correction. The technique is illustrated by considering the classical problem of fluid flow over a backward-facing step using (i) no average correction, (ii) an average velocity correction, (iii) an average pressure correction and (iv) both average velocity and pressure corrections. When both average velocity and pressure corrections are employed, it is found that the number of iterations required for convergence is almost independent of the initial guessed values of fluid velocity and pressure and the fastest rate of convergence may be achieved.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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