Effective parameters for conductive contributions to radial heat transfer in fixed beds under stagnant conditions

FELIPE SUÁREZ; CARLOS DANIEL LUZI; NÉSTOR JAVIER MARIANI; GUILLERMO FERNANDO BARRETO

CHEMICAL ENGINEERING RESEARCH & DESIGN

INST CHEMICAL ENGINEERS

Año: 2017 vol. 119 p. 245 - 262

0263-8762

tNew expressions to evaluate the thermal conduction parameters in fixed beds of monosizedspheres are presented in this paper. The parameters are those introduced by the 2R2D modelproposed by Asensio et al. (2014): the effective thermal conductivity for the solid core of thebed es,ca heat transfer coefficient between the first layer of particles and the wall surfacehwpand a heat transfer coefficient between the first layer of particles and inner particles hpL.For a better comparison with experimental data those properties are readily associated withthe corresponding parameters for stagnant beds 0e,c, h0wpand h0pL. Expressions to evaluate thethree thermal parameters have been developed on common bases, consisting of a preciseapproximation for the confluence of flux lines in the particles towards the contact pointsand packing properties evaluated independently. It is shown that the coefficient h0pLcan bedirectly expressed in terms of 0e,c; therefore the practical number of conduction parame-ters are effectively reduced to 0e,cand h0wp. The results from the expressions proposed herefor 0e,cand h0wphave been compared with experimental data without employing any fittingparameter. In either case, the analysis of the estimations for particles of nearly sphericalshapes did not reveal significant systematic deviations. Experimental information at condi-tions outside the framework of the theoretical development, such as for rarefied gases andparticle shapes other than spherical, was also considered. The analysis of these cases washelpful in assessing effects requiring additional extensions.