Determination of Radial Dispersion Coefficient in Beds of Sand from Measurements of the Rate of Dissolution of Buried Cylinders Aligned with the Flow

Abstract

A method is presented for determining the coefficient of transverse dispersion in flow through packed beds, which is based on the measurement of the rate of dissolution of planar or cylindrical surfaces, buried in the bed and aligned with the flow direction. The underlying theory is initially explained and experiments are then described in which more than three hundred new data points were obtained. These data are for the flow of water, at interstitial velocities between 0.1 and 1.5 mm/s, through beds of silica sand with average particle sizes between 0.219 and 0.496 mm. The experiments were performed at a range of temperatures, between 20oC and 35oC, and this yielded dispersion data for values of the Schmidt number (Sc=μ/ρDm) between 1170 and 570. For all the data reported, the ratio between the coefficient of transverse dispersion and the coefficient of molecular diffusion was shown to correlate well with the Reynolds number (Re=udρ/μ), both for beds with narrow and with wide particle size distributions.