Natural convection mass transfer behaviour of long vertical annuli

The natural convection mass transfer behaviour of the inner cylinder of a v ertical annulus was studied by measuring the limiting current of the cathod ic deposition of copper from acidified copper sulphate solution. Active cyl inder height and copper sulphate concentration were varied to provide a (Sc .Gr) range of 1.8 x 10(10) - 3.3 x 10(14); under these conditions which lie in the transition region, the data were found to fit the equation: Sh = 0.325(Sc.Gr)(0.28) Comparison between the present data and previous related data in mass and h eat transfer confirmed the fact that the product Sc.Gr is not the sole crit erion for laminar-turbulent transition but the value of Sc or Pr plays also an important role. The technical importance of the present work in the des ign and operation of annular mass transfer equipments, e.g., electrochemica l reactors and dialyzers was highlighted. (C) 2000 Elsevier Science Ltd.