Effect of Blockage on Heat Transfer Phenomena of Spheroid Particles at Moderate Reynolds and Prandtl Numbers

Kishore, Nanda; Gu, Sai

doi:10.1002/ceat.201100007

Cited by 30 publications

(12 citation statements)

References 21 publications

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“…Over the years, numerous analytical, numerical, and experimental studies dealing with the drag and Nusselt number characteristics and wall effects for single and multiple spheroids in Newtonian fluids have been reported in the literature. The bulk of these studies have been reviewed, among others, by Clift et al in their classic treatise, and more recently by Michaelides and Kishore and co-workers. − All in all, the currently available numerical simulations in this field are generally limited to the axisymmetric flow regime, and scant experimental results are consistent with these predictions . The next generation of developments in this field have dealt with the prediction of the drag and Nusselt number for oblates and prolates in power-law fluids. − Not only are these numerical results restricted to the axisymmetric flow regime, but there are no experimental results available to substantiate or refute the numerical predictions of drag on prolates and oblates in power-law fluids.…”

Section: Introductionmentioning

confidence: 99%

Spheroids in Viscoplastic Fluids: Drag and Heat Transfer

Gupta

Chhabra

2014

Ind. Eng. Chem. Res.

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In the present work, the forced convection momentum and heat transfer aspects of isothermal spheroidal particles (both prolates and oblates) in Bingham plastic fluids have been numerically investigated in the steady axisymmetric flow regime. Extensive results on the detailed structures of the flow and temperature fields are presented and analyzed in terms of the streamline and isotherm contours, and the yield surfaces as well as their dependence on the pertinent influencing parameters, namely, Reynolds number (1 ≤ Re ≤ 100), Prandtl number (1 ≤ Pr ≤ 100), and Bingham number (0 ≤ Bn ≤ 100) are delineated. Five values of aspect ratio, e = 0.2 and 0.5 (oblates) and e = 2 and 5 (prolates), and the limiting case of a sphere, i.e., e = 1, are considered here to elucidate the effect of shape on both drag and Nusselt number values. Broadly, for a given shape (value of e), drag shows the classic inverse dependence on the Reynolds number and a positive correlation with the Bingham number. Similarly, the mean Nusselt number bears a positive dependence on each of these parameters, Re, Pr, and Bn, due to the sharpening of the temperature gradient in the thin thermal boundary layer. The present drag results have been correlated via the use of a modified Reynolds number whereas the heat transfer results have been consolidated in terms of the Colburn j H factor, thereby enabling their prediction in a new application.

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Section: Introductionmentioning

confidence: 99%

Spheroids in Viscoplastic Fluids: Drag and Heat Transfer

Gupta

Chhabra

2014

Ind. Eng. Chem. Res.

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“…It is necessary to introduce the effect of the particle shape on the drag force and heat transfer. Nanda et al 39 proposed a modified model for describing the non-spherical particles in terms of the drag force and heat transfer by modifying the drag force coefficient and Nusselt number, respectively. That is, the drag force coefficient C d for the ellipsoid particles proposed by Nanda et al 39 is used.…”

Section: Model Detailsmentioning

confidence: 99%

“…Nanda et al 39 proposed a modified model for describing the non-spherical particles in terms of the drag force and heat transfer by modifying the drag force coefficient and Nusselt number, respectively. That is, the drag force coefficient C d for the ellipsoid particles proposed by Nanda et al 39 is used. The coefficient K sg of the interphase momentum exchange is as follows:…”

Section: Model Detailsmentioning

confidence: 99%

“…Here, the modified Nusselt number modified by Nanda et al 39 is introduced for considering the influence of the aspect ratio of the ellipsoid particle on interphase heat transfer.…”

Section: Energy and Fuelsmentioning

confidence: 99%

“…Nanda et al proposed a modified model for describing the non-spherical particles in terms of the drag force and heat transfer by modifying the drag force coefficient and Nusselt number, respectively. That is, the drag force coefficient C d for the ellipsoid particles proposed by Nanda et al is used. The coefficient K sg of the interphase momentum exchange is as follows: The interphase heat exchange intensity between the solid phase and gas phase is driven by the temperature difference and calculated as follows: Here, the modified Nusselt number modified by Nanda et al is introduced for considering the influence of the aspect ratio of the ellipsoid particle on interphase heat transfer.…”

Section: Model Detailsmentioning

confidence: 99%

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Numerical Study of the Pyrolysis of Ellipsoidal Low-Rank Coal Briquettes

Zhuo

Wang

2018

Energy Fuels

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Low-rank coal (LRC) upgrading is essential to convert LRC to a more thermal-efficient and environmentally friendly fuel before utilization in coal-based industries. Briquetting and pyrolysis are the dominant route, where briquettes are usually in the shape of an ellipsoid through a two-roll briquetting process. In this work, an integrated numerical model is developed to predict the pyrolysis process of ellipsoidal LRC briquettes in a packed-bed pyrolyzer. A computational fluid dynamics (CFD) model is developed to describe the flow and thermochemical behaviors related to the pyrolysis of ellipsoidal LRC briquettes, including dewatering, pyrolysis, and other homo-and heterogeneous chemical reactions. A discrete element method (DEM) model is used to describe the packing density distribution of ellipsoidal briquettes. The model is validated against the measurements in a pilot-scale test rig in terms of the temperature history and gas species yields. Typical in-furnace phenomena are illustrated, including flow field, temperature field, and product evolution. Then, the effects of key variables, including briquette properties and heating conditions, on the pyrolysis behavior are investigated quantitatively. The effects of key parameters, including briquette moisture, final pyrolysis temperature, and briquette aspect ratio, on pyrolysis are studied, and the optimal values are identified under the given conditions. For example, more H 2 and less CH 4 are generated when the moisture content of initial briquettes is increased in the range of 2−15%, but in the range of 15−20%, H 2 is then decreased and CH 4 is increased. The maximum packing density is obtained when the aspect ratio of briquettes is 2.0. However, the highest temperature increase rate is observed when the aspect ratio is 1.7. An appropriate final pyrolysis temperature, 973 K in this study, is suggested to balance the pyrolysis rate and energy consumption. This model provides a cost-effective tool for optimizing the design and operation of pyrolyzers for ellipsoidal LRC briquettes.

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Effects of Wall Confinement and Power‐Law Fluid Viscosity on Nusselt Number of Confined Spheres

Reddy¹,

Kishore²

2013

Chem Eng & Technol

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Effects of wall confinement on the heat transfer phenomena of confined spherical particles in power‐law fluids are numerically investigated. The spherical particle is held at constant temperature and a power‐law fluid is flowing past the particle in a confining tube. Heat transfer takes place from the heated sphere to the surrounding fluid. The governing conservation equations of mass, momentum, and energy are solved using computational fluid dynamics‐based software. The numerical solver is thoroughly validated by comparing the present average Nusselt numbers with existing literature values. On the basis of numerical results, an empirical correlation for the average Nusselt number of a confined sphere in Newtonian and power‐law fluids is proposed which can be used in new applications.

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Effect of Blockage on Heat Transfer Phenomena of Spheroid Particles at Moderate Reynolds and Prandtl Numbers

Cited by 30 publications

References 21 publications

Spheroids in Viscoplastic Fluids: Drag and Heat Transfer

Spheroids in Viscoplastic Fluids: Drag and Heat Transfer

Numerical Study of the Pyrolysis of Ellipsoidal Low-Rank Coal Briquettes

Effects of Wall Confinement and Power‐Law Fluid Viscosity on Nusselt Number of Confined Spheres

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