Radial variation in porosity in annular packed beds

Toit, C.G. Du

doi:10.1016/j.nucengdes.2007.12.018

Cited by 94 publications

(50 citation statements)

References 17 publications

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“…The small tank-to-particle diameter ratio of about 12 caused the void fraction to be larger close to the wall (Mueller, 1992;Ismail et al, 2002;Du Toit, 2008), which in turn resulted in a lower flow resistance and hence higher fluid velocities there (Schwartz and Smith, 1953;Newell and Standish, 1973;Chandrasekhara and Vortmeyer, 1979). According to (Schwartz and Smith, 1953), for tankto-particle diameter ratios smaller than 30, the peak velocity close to the wall can be 30-100% greater than the velocity at the center of the tube.…”

Section: Modelingmentioning

confidence: 99%

Experimental and numerical investigation of combined sensible–latent heat for thermal energy storage at 575°C and above

et al. 2015

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Section: Modelingmentioning

confidence: 99%

Experimental and numerical investigation of combined sensible–latent heat for thermal energy storage at 575°C and above

et al. 2015

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“…We do not know whether the impact of the flow maldistribution has yet been directly included in the numerical model of a packed-bed AMR. However, there are several models which enable the calculation of the radial porosity distribution [104] as well as the radial velocity distribution in the packed bed [105], but since the great majority of the packed-bed AMRs are 1-D, this cannot be directly applied. As explained previously in this chapter, in the 1-D models the thermohydraulic properties are included by using appropriate correlations (mostly Nusselt number and friction factor correlations).…”

Section: The Flow Maldistributionmentioning

confidence: 99%

Active Magnetic Regeneration

Kitanovski

Tušek

Tomc

et al. 2014

Green Energy and Technology

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It is well known that the magnetocaloric effect of most magnetocaloric materials at moderate magnetic fields (up to 1.5 T) is limited to a maximum adiabatic temperature change of 5 K [1,2]. This value is not sufficient for such materials to be directly implemented into a practical cooling or heating device where temperature span over 30 K is required. Therefore, in order to increase the temperature span, one and so far the best option is for a heat regenerator to be included in the magnetic thermodynamic cycle.A heat regenerator is a type of indirect heat exchanger where the heat is periodically stored and transferred from/to a thermal storage medium (regenerative material) by a working (heat-transfer) fluid. The regenerative material usually has a porous structure, through which a working fluid is pumped in an oscillatory, counter-flow manner (which is more efficient than a parallel flow system). During the 'hot period', a warmer fluid flows through the regenerative material, which cools down, while the material heats up. As a result, heat is stored in the material. During the 'cold period', a cooler fluid flows through previously heated regenerative material, so the fluid heats up, while the material cools down. The heat is therefore transferred back to the fluid (the same fluid or a different one) at a different phase of the thermodynamic cycle. After a certain number of such steps, a periodic steady state is reached and, as a result, a temperature profile can be established along the length of the regenerator [3].The need to apply heat regenerators in a magnetic refrigerator was already realized by Brown [4] in the first prototype of a magnetic refrigerator, built in 1976. He applied a regenerative Stirling-like thermodynamic cycle (very similar to AMR), which significantly increased the temperature span of the device [4,5]. A few years later Steyert [6] and Barclay and Steyert [7] presented and explained the active magnetic regenerator, which remains the most applied method for the exploitation of the magnetocaloric effect at room temperature. Furthermore, all prototypes of magnetic refrigerators built since then have been based on the AMR process [5]. An AMR, unlike a passive (regular) heat regenerator, contains a magnetocaloric material as the regenerative material. It has a double function in a magnetic regenerator, i.e. it works as a regenerator and enables an increase in the temperature span as well as working as a coolant and generating/absorbing heat between the particular phases of the

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“…There have been numerous research efforts during the past several decades to achieve a quantitative understanding of the porosity distribution in packed beds, and various researchers have proposed a number of empirical correlations to describe the radial variation of porosity. The correlations fall into two categories: oscillatory and exponential porosity correlations (du Toit, 2008; van Antwerpen et al, 2010). Table 2 summarises the relevant correlations for radial porosity distribution as well as their application/implementation in CFD simulation of TBRs in the literature.…”

Section: Computational Representation Of Flow Geometries For Packed Bmentioning

confidence: 99%

Modelling and simulation of trickle‐bed reactors using computational fluid dynamics: A state‐of‐the‐art review

2011

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Trickle-bed reactors (TBRs), which accommodate the flow of gas and liquid phases through packed beds of catalysts, host a variety of gas-liquid-solid catalytic reactions, particularly in the petroleum/petrochemical industry. The multiphase flow hydrodynamics in TBRs are complex and directly affect the overall reactor performance in terms of reactant conversion and product yield and selectivity. Non-ideal flow behaviours, such as flow maldistribution, channelling or partial catalyst wetting may significantly reduce the effectiveness of the reactor. However, conventional TBR modelling approaches cannot properly account for these non-ideal behaviours owing to the complex coupling between fluid dynamics and chemical kinetics. Recent advances in the application of computational fluid dynamics (CFD) to three-phase TBR systems have shown promise of achieving a deeper understanding of the interactions between multiphase fluid dynamics and chemical reactions. This study is intended to give a state-of-the-art overview of the progress achieved in the field of CFD simulation of TBRs over the past two decades. The fundamental modelling framework of multiphase flow in TBRs, advances in important constitutive models, and the application of CFD models are discussed in detail. Directions for future research are suggested.RÉSUMÉ Les lits fixes arrosésà co-courant descendant de gaz et de liquide sont le siège d'innombrables processus catalytiques triphasiques, en particulier dans le domaine du raffinage pétrolier et de la pétrochimie. Les caractères polyphasique et non-idéal de leur hydrodynamique ont des répercussions importantes sur la conversion chimique, la productivité et la sélectivité. Ceci se traduit par l'entremise de la maldistribution des fluides, le mouillage partiel du catalyseur ou desécoulements préférentiels qui peuventêtre déterminants en ce qui a traità l'efficacité du réacteur. La mise enéquation rigoureuse de ces non-idéalités et des couplages réaction-hydrodynamique a longtemps résisté aux approches de conceptualisation dites « conventionnelles ». Cette revue de synthèse s'attarde par conséquentà discuter les récentes avancées dans l'utilisation de la mécanique des fluides numérique comme outil «émergent et non-conventionnel » de description quantitative et fine desécoulements et des réactions catalytiques, et de leur interaction au sein de ces réacteurs. Spécifiquement, nous discuterons de la pertinence des différentes approches multi-fluides mises en oeuvre, des relations constitutives développées et de l'utilisation de la mécanique des fluides numérique pour des applications pratiques des lits fixes arrosés. Nous suggérerons en guise d'épilogue de nouvelles directions de recherche dans ce domaine.Mots clés: Lit fixe arrosé, mécanique des fluides numérique, hydrodynamique polyphasique,équations constitutives tive amination, liquid-phase oxidation, etc.). TBRs are also used for the catalytic abatement of aqueous biocidal compounds in *

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Radial variation in porosity in annular packed beds

Cited by 94 publications

References 17 publications

Experimental and numerical investigation of combined sensible–latent heat for thermal energy storage at 575°C and above

Experimental and numerical investigation of combined sensible–latent heat for thermal energy storage at 575°C and above

Active Magnetic Regeneration

Modelling and simulation of trickle‐bed reactors using computational fluid dynamics: A state‐of‐the‐art review

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