Local and average interphase heat transfer coefficients in a randomly packed bed of spheres

Abstract

Local and average heat transfer coefficients have been measured for a sphere in a randomly packed bed. A steady state technique was employed in which internally heated spheres were placed in a bed 35 in. deep and 12 in. sq. Air passed through the bed in downflow, the range of Reynolds numbers being from 120 to 1,700 based on the sphere diameter and the superficial velocity.Average heat transfer coefficients have been measured at twenty-five positions permitting the assessment of the effect of position. An entrance region limited to the first two particle layers in the bed has been verified.Distributions of the local heat transfer coefficient on the surface of a single sphere in the top layer and in the nineteenth layer of the bed have also been measured. These distributions indicate that a laminar boundary layer exists over portions of the sphere surface.In the analysis and design of fixed bed reactors, adsorbers, etc., prudent account of interparticle and inter-intraphase transport events is desirable. This is particularly true in the case of the nonisothermal catalytic reactor wherein local surface reaction rates are governed by concentrations and a temperature dictated by transport of mass and heat between the bulk fluid phase and the sites of catalysis (21, 27).Our concern in this instance is with interphase transfer of heat; that is, rates of heat transfer between a flowing fluid and the external surface of spheres comprising the fixed bed. As our ultimate interest resides in realizing greater understanding of the detailed structure of heat, mass, and momentum transfer in fixed beds, it follows that the initial inquiry must be focused upon local transfer rather than overall integral coefficients.

Closure of a macroscopic turbulence and non-equilibrium turbulent heat and mass transfer model for a porous media comprised of randomly packed spheres

“…Since we have proposed a Nu fs correlation, it is worth comparing the correlation and the obtained results against the existing Nu fs literature. In this respect, the correlations and their derived results proposed by Wakao et al [51], Gillespie et al [52] and Achenbach [53] were found to be in the similar range as proposed by the present work.…”

A multiscale mass transfer model for gas–solid riser flows: Part 1 — Sub-grid model and simple tests

“…Gas-solid heterogeneous reactions require well contact between phases, and hence the related mass transfer research is important in applications of CFB reactors. For all that, in comparison with research for packed beds (Appel and Newman, 1976;Gillespie et al, 1968;Guo and Thompson, 2001;Jolls and Hanratty, 1969;Mcconnachie and Thodos, 1963;Sullivan et al, 2005) and for bubbling fluidized beds (Hsiung and Thodos, 1979;Kato et al, 1970;Kunii and Levenspiel, 1969;Wen and Fane, 1982), the mass transfer behavior in CFB risers are less reported (Yu and Jin, 1994) and the results in point are hardly in fair agreement. For instance, a recent review finds that the values of mass transfer coefficient in the literature may differ by up to 7 orders of magnitude (Breault, 2006).…”

Review of the experimental research on the thermal‐hydraulic characteristics in the pebble bed nuclear reactor core and fusion breeder blankets

“…The local Nusselt number along the axial direction of randomly packed pebble‐bed test section was found to rise firstly and went down to a constant value after five to eight pebble layers, at the same Reynolds number 64 . Gillespie et al 78 concluded that the entrance effect was limited within the first two pebble layers.…”