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

Experimental values of the coefficient of transverse dispersion (D-T) were measured with the system 2-naphthol/water, over a range of temperatures between 293 K and 373 K, which corresponds to a range of values of viscosity (mu) between 2.83 x 10(-4) Ns/m(2) and 1.01 x 10(-3) Ns/m(2) and of molecular diffusion coefficient (D-m) between 1.03 x 10(-9) m(2)/s and 5.49 x 10(-9) m(2)/s. Since the density (rho) of water is close to 10(3) kg/m(3), the corresponding variation of the Schmidt number (Sc = mu/rhoD(m)) was in the range 1000 - 50. More than 200 experimental values of the transverse dispersion coefficient were obtained using beds of silica sand with average particle sizes (d) of 0.297 and 0.496 mm, operated over a range of interstitial liquid velocities (u) between 0.1 mm/s and 14 mm/s and this gave a variation of the Reynolds number (Re = rho du epsilon/mu) between 0.01 and 3.5. Plots of the dimensionless coefficient of transverse dispersion (D-T/D-m) vs. the Peclet number (Pe(m) = ud/D-m) based on molecular diffusion bring into evidence the influence of Sc on transverse dispersion. As the temperature is increased, the value of Sc decreases and the values of D-T/D-m gradually approach the line corresponding to 'gas behaviour' (i.e. Sc approximate to 1), which is known to be well approximated by the equation D-T/D-m = 1/tau + ud/12D(m), where tau is the tortuosity with regard to diffusion.