Estimation of the radial distribution of axial velocities in fixed beds of spherical packing

LUZI, CARLOS D.; MARIANI, NÉSTOR J.; ASENSIO, DANIELA A.; MARTINEZ, OSVALDO M.; BARRETO, GUILLERMO F.

CHEMICAL ENGINEERING RESEARCH & DESIGN

INST CHEMICAL ENGINEERS

Año: 2019 vol. 150 p. 153 - 168

0263-8762

tThe vessel wall of densely packed beds exert a strong influence on particle distribution thatgenerates a radial porosity profile and, in turn, a radial profile of axial velocity. A direct conse-quence is the appearance of an uneven flow distribution on the bed cross-section and radialvariations of transport properties. A widespread alternative for estimating such a veloc-ity profile is to solve the so-called extended Brinkman equation, using an available radialporosity profile. To this end, it is employed a local version of an expression quantifying thedrag force on the packing (usually the Ergun equation) and an effective viscosity to accountfor the radial transport of axial momentum. It is shown that the existing expressions toevaluate the effective viscosity are only suitable for a restricted range of Reynolds numbers.Supported on the expressions from averaging the microscopic conservation equations, itis reassessed the local evaluation of the drag force and the estimation of the effective vis-cosity. The use of the extended Brinkman equation with such changes allows a satisfactorydescription of the radial velocity profile for mono-sized spherical packing, as arisen from thecomparison with available experimental results and with an important number of resultsfrom pore-scale simulation.