Measurement of the coefficient of transverse dispersion in flow through packed beds for a wide range of values of the schmidt number

Abstract

Experimental values of the coefficient of transverse dispersion (DT) were measured withthe system 2-naphthol/water, over a range of temperatures between 293 K and 373 K, which correspondsto a range of values of viscosity (µ) between 2.83 × 104 Ns/m2 and 1.01 × 103 Ns/m2and of molecular diffusion coefficient (Dm) between 1.03×109 m2/s and 5.49×109 m2/s. Sincethe density () of water is close to 103 kg/m3, the corresponding variation of the Schmidt number(Sc= µ/Dm) was in the range 1000 50. More than 200 experimental values of the transversedispersion coefficient were obtained using beds of silica sand with average particle sizes (d) of0.297 and 0.496 mm, operated over a range of interstitial liquid velocities (u) between 0.1 mm/sand 14 mm/s and this gave a variation of the Reynolds number (Re= du/µ) between 0.01 and 3.5.Plots of the dimensionless coefficient of transverse dispersion (DT/Dm) vs. the Peclet number(Pem = ud/Dm) based on molecular diffusion bring into evidence the influence of Sc on transversedispersion. As the temperature is increased, the value of Sc decreases and the values of DT/Dmgradually approach the line corresponding to gas behaviour (i.e. Sc 1), which is known to bewell approximated by the equation DT/Dm = 1/ + ud/12Dm, where is the tortuosity withregard to diffusion