The rates of mass transfer at a vertical array of closely spaced horizontal tubes were measured by the limiting‐current technique under single‐phase flow, gas sparging and two‐phase flow. The single‐phase flow data were correlated by the equation: Sh = 0.75 Sc0.33 Re0.59. The gas sparging data with no net solution flow were correlated by the equation: J = 0.31(Reg.Fr)–0.22. For two‐phase flow, the gas flow was found to enhance the rate of array mass transfer by a factor ranging from 1.25 to 5.25, depending on Reg and Re. The enhancement ratio increases with decreasing Re and increasing Reg. For Re ≥ 2500, the rate of mass transfer approaches the value of single‐phase flow, regardless of the value of Reg, which ranged from 7 to 41. The importance of the present geometry in building electrochemical and catalytic reactors, where exothermic liquid‐solid diffusion‐controlled reactions take place, is highlighted. The present geometry offers the advantage that the outer surface acts as a turbulence promoter while the inner surface acts as a heat exchanger.