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ISBN : **978-1-56700-478-6**

Proceedings of the 24th National and 2nd International ISHMT-ASTFE Heat and Mass Transfer Conference (IHMTC-2017)

The present study aims to elucidate the effect of severe confinement of walls and viscosity ratio on the steady-state convective mass transfer from a single Newtonian fluid sphere steadily falling along the axis of a long cylindrical tube filled with power-law fluids. The species transport equations along with momentum transport equations of both phases, have been solved numerically using the finite element method. The effects of the external Reynolds Number (*Re*), Schmidt number (*Sc*), power-law index (*n*), internal to external fluid characteristic viscosity ratio (*k*), and confinement ratio (*λ*) on the local and average Sherwood number (*Sh*) have been analyzed over the following ranges of conditions: *Re* = 25, 1 ≤ *Sc* ≤ 100, 0.4 ≤ *n* ≤ 1.8, 0.1 ≤ *k* ≤ 10 and 0.5 ≤ *λ* ≤ 0.9, and the results are discussed in terms of iso-concentration contours, and plots of local and surface-averaged Sherwood number. It has been observed that for a moderate to high value of the Schmidt number, irrespective of the value of the power-law index and viscosity ratio, as the value of confinement ratio increases, the average Sherwood number increases. As the value of the power-law index increases, the mass transfer rate decreases for all values of Schmidt number and viscosity ratio hereby suggesting that shear-thinning behavior facilitates mass transfer, whereas shear-thickening behavior impedes it. It is also observed that at low values of the viscosity ratio, mass transfer rate is always higher than that for the high viscosity ratio at a fixed Reynolds Number, Schmidt number, confinement ratio and power-law index.