J.L. Stephenson

Bio: J.L. Stephenson is an academic researcher from University of Wisconsin-Madison. The author has contributed to research in topics: Reynolds number & Superficial velocity. The author has an hindex of 1, co-authored 1 publications receiving 72 citations.

A critical review of dispersion in packed beds

Abstract: The phenomenon of dispersion (transverse and longitudinal) in packed beds is summarized and reviewed for a great deal of information from the literature. Dispersion plays an important part, for example, in contaminant transport in ground water flows, in miscible displacement of oil and gas and in reactant and product transport in packed bed reactors. There are several variables that must be considered, in the analysis of dispersion in packed beds, like the length of the packed column, viscosity and density of the fluid, ratio of column diameter to particle diameter, ratio of column length to particle diameter, particle size distribution, particle shape, effect of fluid velocity and effect of temperature (or Schmidt number). Empirical correlations are presented for the prediction of the dispersion coefficients (D T and D L) over the entire range of practical values of Sc and Pem, and works on transverse and longitudinal dispersion of non-Newtonian fluids in packed beds are also considered.

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

Abstract: 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.

CFD as a Design Tool for Fixed-Bed Reactors

Abstract: Computational fluid dynamics (CFD) is a tool that is becoming more realistic for use in the description of the detailed flow fields within fixed beds of low tube-to-particle diameter ratio (N). The...

Refractive-index and density matching in concentrated particle suspensions: a review

Abstract: Optical measurement techniques such as particle image velocimetry (PIV) and laser Doppler velocimetry (LDV) are now routinely used in experimental fluid mechanics to investigate pure fluids or dilute suspensions. For highly concentrated particle suspensions, material turbidity has long been a substantial impediment to these techniques, which explains why they have been scarcely used so far. A renewed interest has emerged with the development of specific methods combining the use of iso-index suspensions and imaging techniques. This review paper gives a broad overview of recent advances in visualization techniques suited to concentrated particle suspensions. In particular, we show how classic methods such as PIV, LDV, particle tracking velocimetry, and laser induced fluorescence can be adapted to deal with concentrated particle suspensions.