Mass transfer equations are derived and compared with dissolution experiments of C₆H₅COOH-H₂O and Cu-H₂SO₄-K₂Cr₂O₇ systems on single spheres (6 different sizes from 3/4" to 3"). In region I (long contact time with smooth laminar film), Sh converges
Sh=1.608 (GaSc/Pe^*)^1/3 or k=2.01 D√δ
(δ: mean film thickness) and increases with decreasing volumetric flow rate Q. In region II (short contact time with smooth laminar film), Sh converges
Sh=0.716 Pe^*1/9(GaSc)^2/9
The transition from region I to II occurs around Pe^*/(GaSc)^1/4≤10. In region III (short contact time with wavy film surface), Sh increases with Pe^* to the 1/3 - 1/2 power and is substantially higher than that in region II. A generalized short contact time equation using the measured local film thickness δ
Sh=0.501 Pe^*1/3{∫^π₀(d/δ)sinθdθ}^2/3
is valid in this region. Thus, main cause for enhancement in Sh is the reduction in film thickness relevant to the wave formation. The II-III transition is somewhere between wave inception and wave coverage flow rates. In the above, Sh=kd/D, Pe^*=Q/dD and Ga=gd³/v², in which k is based on a log-mean driving force.