ARTICLE:

• HEAT TRANSFER BETWEEN DEFORMABLE MAGNETIC BEDS AND IMMERSED SURFACES: Cases of gas-fluidized beds  download article

Jordan Y. Hristov
Department of Chemical Engineering, University of Chemical Technology and Metallurgy, 1756 Sofia, 8 Kl. Ochridsky str., Bulgaria

ABSTRACT

The paper considers heat transfer between immersed surfaces and deformable magnetic particle beds in special cases of applications magnetically stabilized bed techniques. The first attempt to analyze the data [1-3] yielded uniform presentation of the existing results. The major efforts were stressed to recognize the effect of the fluidization regime on the heat transfer coefficients and to present the data via Nusselt number [1-3] and Chilton-Colburn dimensionless correlations [3].
The aforementioned investigations did not investigate the effect of the changing bed porosity of the stabilized bed on the heat transfer coefficients. The main problem hindering the studies in the past is the absence of information about the links between the deformation characteristics of the porous medium (the deformable magnetic bed) and its hydraulic characteristics. The recent results [4-6] demonstrate the applicability of the Richardson-Zaki (1954) scaling law, U/U_t = εⁿ to the bed expansion. This result relates the superficial fluid velocity, the overall bed porosity and the effect of the magnetic field on the scaling exponents.
The present work focuses on scaling relationships between the bed porosity and the internal length scale of the granular bed (the permeability K of the Forchheimer equation). The main condition imposed is a velocity independent pressure drop during the deformation.
The results confirm qualitatively those obtained experimentally [3]. Moreover, the scaling relationships allow to apply two models: thermally boundary layer model with Danckvertz penetration theory and entropy based model of particle mixing.

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