Mass Transfer to Single Spheres

TLDR: In this article, the rate of mass transfer to single spheres, with the aid of a diffusion-controlled electrode reaction, was studied. But it was found that neither the results thus obtained nor those by previous investigators showed good agreement with the Ranz-Marshall's eq.

Abstract: Studies were made on the rate of mass transfer to single spheres, with the aid of a diffusioncontrolled electrode reaction:Microelectrodes used as anode were platinum spheres having 1.66mm and 2.74mm diameters respectively, each with PVC-coated platinum wire of 0.6mm diameter. The reference electrode used as cathode was a thin platinum plate of 50×120mm. The experimental apparatus employed was as shown in Fig. 1. To obtain uniform distribution of liquid velocity over the entire column cross-section, glass beads of 5mm diameter were packed to a height of 30mm, topped with 10 sheets of Saran screen of about 12 meshes. Below the packing and 8mm above the spherical electrode, a Saran screen of about 150 meshes was placed.From the measurements of limiting current 6), 8) at various liquid flow rates, the mass transfer coefficients, kf, were calculated by the equation:kf=i/nFAc (7)The experimental results are shown in Table 1. It was found that neither the results thus obtained nor those by previous investigators3), 9), 10), 14), 16) showed good agreements with the Ranz-Marshall's eq. (2)14).Thereupon, assuming that the empirical equation might be presented as:Sh-2=kRepScq (8)the authors determined the values of the constants k, p and q (Figs. 3, 4 and 5), obtaining an equation:Sh=2.0+0.52Re0.54Sc0.35 (9)The value of the exponent of the Schmidt group, 0.35, agrees well with 0.348 obtained by Frossling3) from his experimental data.