Micro and nanobubble technologies as a new horizon for water-treatment techniques: A review

For liquid flow, superficial velocity profiles inside a packed bed were obtained for monodisperse packings of spheres, deformed spheres, cylinders and Raschig-ring by averaging over several thousand local measurements of the axial flow components within a cross-section. At fully developed flow, the profiles are constant along the packing except for short inlet and outlet zones of about three particles layer length with either a buildup of the profile at the inlet or a degeneration at the exit of the packed bed. Besides velocity profiles, porosity distribution functions were also evaluated experimentally. These were introduced in the extended Brinkman equation which simulates the fluctuating profiles well if the average porosity of the packing is replaced by the radial porosity distribution. The effective viscosity is adjusted to obtain best agreement between measurements and solutions of the Brinkman equation. This effective property, however, influences the flow profile in the very near wall range only, up to approximately a distance of about half the particle diameter. The effective viscosity is found to depend on the porosity data close to the wall, on particle shape, on the Reynolds number, and on the pressure loss relation.

Measured and modeled superficial flow profiles in packed beds with liquid flow

DEM-CFD simulations of fixed bed reactors with small tube to particle diameter ratios

A study is presented of the relationship between the local flow field and the local wall heat flux in a packed bed of spheres. Computational fluid dynamics is used as a tool for obtaining the detailed velocity and temperature fields, for gas flowing through a periodic wall segment test cell. Results from the wall segment are demonstrated to reproduce those obtained from a full bed of spheres with tube-to-particle diameter ratio of N = 4. Attempts to correlate the local wall heat flux with local properties of the flow field, such as velocity components, velocity gradients, and components of vorticity, led to the conclusion that local heat transfer rates do not correlate statistically with the local flow field. Instead, a conceptual analysis was used to suggest that local patterns of wall heat flux are related to larger-scale flow structures in the bed. © 2004 American Institute of Chemical Engineers AIChE J, 50: 906–921, 2004

CFD study of fluid flow and wall heat transfer in a fixed bed of spheres

Comparison of CFD simulations to experiment for convective heat transfer in a gas-solid fixed bed

Fluid flow through catalyst filled tubes

Gas flow and heat transfer through catalyst filled tubes

Gas density affects the gas holdup in bubble columns. Even at atmospheric pressure, different gases produce varying gas holdups. This contribution explores the causes for variations in gas holdups occurring for different gases. Differences in the bubble size distribution resulting from varying rates of bubble breakup and coalescence as well as dissimilar bubble rise velocities are the most likely causes of differences. Correlations that include a term for gas density are able to qualitatively predict the effect of changing gas density, but no correlation can consistently predict the gas holdup for multiple systems.

Oliver Bey

Papers

Fluid flow through catalyst filled tubes

Gas flow and heat transfer through catalyst filled tubes

Effect of Gas Density on Gas Holdup in Bubble Columns

Bestimmung von Strömungsverteilung und Wärmetransportparametern in schüttungsgefüllten Rohren

Einfluss der Wechselwirkung von Reaktion und Fluiddynamik auf das Verhalten von Strahlschlaufenreaktoren