Chemical Engineering and Processing 48 (2009) 823–827 Contents lists available at ScienceDirect Chemical Engineering and Processing: Process Intensification journal homepage: www.elsevier.com/locate/cep Modelling of mass transfer in film flow of shear thinning liquid on a horizontal rotating disk I. Tsibranska ∗ , D. Peshev, G. Peev, A. Nikolova Department of Chemical Engineering, University of Chemical Technology and Metallurgy, 1756 Sofia, Bulgaria article info Article history: Received 10 April 2008 Received in revised form 15 August 2008 Accepted 29 October 2008 Available online 5 November 2008 Keywords: Shear thinning liquid Horizontal rotating disk Liquid film Modeling Mass transfer abstract A mathematical model for the mass transfer in radial nonwavy film flow of shear thinning power law liquid on a horizontal rotating disk has been assumed. Numerical simulations of the model are compared with experimental results for oxygen desorption from two water polymer solutions. It is established that the model underestimates the experimental mass transfer coefficients within the limits of the safety coefficients usually employed in the design of industrial equipment. Both the numerical and experimental data demonstrate a “synergetic” effect of the increase of disk revolutions and decrease of liquid rheology index in intensifying the mass transfer process. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Mass transfer in liquid film flow on a horizontal rotating disk has been an object of various investigations in the recent years [1–7]. They have shown that the process takes place very intensively on this device. It has already found a number of applications [8–10]. The major interest has been devoted to the process of absorption in a film of Newtonian liquid [1–4,6,7]. The fluid supplied on the disk however can be non-Newtonian as for example in the cases of blood oxygenation [11] and degassing of fiber-yielding polymer solutions before spinning [12] or such behaviour can arise due to processes of polymerization [9,10] or formation of dispersed phase [8]. For this reason Peev et al. [13] investigated the oxygen desorp- tion from two polymer solutions, described by the power-law of Ostwald–de Waele. They also developed a simplified model for the process, based on the short contact time approach and established a good qualitative agreement between the experimental results and the model predictions. The quantitative match however was found insufficient with a considerable overestimation of the predicted disk radius. In this paper, we present the results of a more accurate mathe- matical modelling, based on numerical solutions of the equations, describing the process. ∗ Corresponding author. Tel.: +359 28163301. E-mail address: tsibranska@yahoo.com (I. Tsibranska). 2. Description of the model assumed In more general case the mass transfer process (see Fig. 1 and the list of symbols) in the film is described by the convective diffusion equation ∂C ∂t + w r ∂C ∂r + w y ∂C ∂y = D  1 r ∂ ∂r  r ∂C ∂r  + ∂ 2 C ∂y 2  . (1) Scaling can easily show that diffusion in the radial direction is small and the first term in brackets on the right-hand side of Eq. (1) can be neglected. We shall consider the steady state mass transfer which takes place when the liquid feed has a constant volumetric flow rate and concentration of the diffusing species and the gas phase surround- ing the disk has an enormous volume as compared to the liquid film. The film on the disk is assumed radial, laminar and nonwavy. The axial velocity, w y , is much smaller than the radial one, but ∂C/∂r ≪ ∂C/∂y and this assumption needs special attention: - To the best of our knowledge there is no analytical solution for the velocity components in the steady state flow on a rotating disk even for the more simple case of Newtonian liquid. Com- bining of numerical solutions about the velocity components for shear thinning liquid and mass transfer will result in an extremely sophisticated model difficult for practical application. - The model which describes a non-Newtonian liquid is usually chosen by analyzing data for the shear rates and respective shear stresses obtained in simple one-dimensional flows (capillary, with coaxial cylinders, etc., viscometers). As far as the shear thin- 0255-2701/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.cep.2008.10.006