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  • 1
    Electronic Resource
    Electronic Resource
    Chaotic heat transfer in a periodic two-dimensional flow (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 10 (1998), S. 2102-2104 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Chaotic heat transfer in the annular region between two confocal ellipses is analyzed with tools developed in previous mixing studies as well as specific ones presented here. In particular, we show that even though the Eulerian temperature field is periodic, the Lagrangian temperature of a particle can be either periodic or chaotic depending on its initial position. A potential mixing zone, very similar to the one defined by Kaper and Wiggins, is defined for modulated heteroclinic trajectories. The geometry and modulation protocol can be optimized so that a greater than 100% increase of heat transfer over that of conduction is obtained. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.869725
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  • 2
    Electronic Resource
    Electronic Resource
    Chaotic mixing and heat transfer between confocal ellipses: Experimental and numerical results (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 8 (1996), S. 677-691 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The annular region between two concentric, confocal ellipses is a new geometry which is particularly effective for either mixing of viscous fluids or heat transfer enhancement in the important limit of a high Péclet number. This geometry is in many respects similar to the annular space between two eccentric, rotating cylinders although it possesses two (instead of one) axes of symmetry. The recently obtained analytical solution of the Stokes flow equations in this geometry shows that at steady state and for counter-rotation of the inner and outer ellipses, two opposite saddle points (connected by two different streamlines) appear in the region of minimum gap. This flow characteristic is also exhibited by the eccentric cylinder system for some cases of co-rotation. The Poincaré sections obtained when the inner and outer ellipses are displaced using a discontinuous velocity protocol show that a more effective long term mixing is obtained for the counter-rotating case, this is confirmed by the experimental data we have obtained. The opposite conclusions (more effective mixing for co-rotation) have been given in the eccentric cylinder geometry.Photographs of the fluorescent dye after 5 periods are compared with remarkable success to numerical blob deformation experiments. Experimental results also confirm previous results based on an analysis of Poincaré sections. In particular, better mixing is obtained when the inner ellipse displacement per period increases. Finally, this geometry is shown to be particularly effective as a heat exchanger. For steady, counter-rotation of the two boundaries, the recirculation zones can lead to a heat transfer rate increase of 80% over that of pure conduction at high Péclet numbers, and, by an appropriate sinusoidal modulation of the angular velocity of one boundary, the heat transfer rate can be more than double that of pure conduction. Since an analysis of the experimental data also suggests that the mixing rate for a sinusoidal modulation of the angular velocity of the boundaries is better than for a discontinuous velocity protocol, we propose that the average Nusselt number per period could be one of the several useful tools in the global optimization of the mixing protocol. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.868853
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  • 3
    Electronic Resource
    Electronic Resource
    On the reduction of natural convection heat transfer in horizontal eccentric annuli containing saturated porous media (1997)
    Bradford : Emerald
    International journal of numerical methods for heat & fluid flow 7 (1997), S. 401-416 
    Details
    ISSN: 0961-5539
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Studies numerically natural convection in a saturated porous medium bounded by two horizontal, isothermal eccentric cylinders by solving the governing two-dimensional Darcy-Boussinesq equations on a very fine grid for different values of the eccentricity e. For a radius ratio of 2 and e 〈 0.5, both a bicellular and a tetracellular flow patterns remain stable for moderate Rayleigh numbers. For e = 0.5, the transition from one flow regime to the other occurs with one of the solutions losing stability. Suggests that in a real situation, insulation is more efficient if the eccentricity is set to the maximum value for which the four-cell flow pattern is physically realizable than to the value that minimizes the heat transfer when the flow pattern is bicellular. The net gain with respect to a concentric insulation can be of the order of 10 per cent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1108/09615539710165840
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  • 4
    Electronic Resource
    Electronic Resource
    A simulation model of a high-capacity methane adsorptive storage system (1995)
    Springer
    Adsorption 1 (1995), S. 17-27 
    Details
    ISSN: 1572-8757
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract A two-dimensional model is developed to describe the hydrodynamics, heat transfer and adsorption phenomena associated with the adsorptive storage of natural gas (NG) in cylindrical reservoirs. Intraparticle and film resistances to both heat and mass transfer are neglected. In the momentum equation, Ergun's law is considered locally valid and is extended to two dimensions. These assumptions are fully justified in the paper. Numerical results are presented concerning the pressurization and blowdown of an ultra-lightweight 50 litre cylinder, commercially available for the storage of compressed NG, if it were filled with an activated carbon having a good adsorptive storage capacity. A simple formula is also proposed to predict the filling times for fast charges. The predicted temperature changes in the packed-bed are in good agreement with those reported in the literature for an experimental charge/discharge.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00704143
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  • 5
    Electronic Resource
    Electronic Resource
    Charge dynamics of a methane adsorption storage system: Intraparticle diffusional effects (1996)
    Springer
    Adsorption 3 (1996), S. 117-125 
    Details
    ISSN: 1572-8757
    Keywords: methane adsorption ; on-board storage ; mathematical modeling ; numerical simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The charge of natural gas adsorption storage systems is studied numerically, With emphasis given to the impact on its dynamics of intraparticle diffusional resistances to mass transport. Besides adsorption kinetics and thermal effects, the simulation model takes into account both mass transport inside the adsorbent and hydrodynamics of flow through the packed bed. Numerical results are presented for change with methane of a 50 liter cylindrical reservoir, filled with hypothetical adsorbents with diffusional time constants in the range 10−3 s1 D/R p 2 ≤ ∞. and with the adsorption equilibrium curve of a commercially available activated carbon with a good adsorptive storage capacity. An attempt is made to assemble the charge histories for different values ofD/R p 2 , in a single cure by using a modilied time scale.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01650235
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