Modelling criteria for flow simulation in gas stirred ladles: experimental study

Abstract

Criteria for modelling isothermal flows encountered in typical gas stirred ladles have been investigated both theoretically and experimentally. To this end, the phenomena of fluid mixing in ladles have been investigated in order to deduce the relationship between model and full scale gas flowrates, needed for maintaining dynamic similarity between the two. Starting with the governing equation for material transport, mixing times in geometrically and dynamically similar gas stirred systems were first correlated theoretically. On the basis of this, it is shown that, in the Froude dominated flow regime (typical of industrial ladle refining operations), the ratio of mixing times in geometrically and dynamically similar gas stirred systems can be represented in terms of the geometrical scale factor λ(=Lmod /Lfs ) according to τm,mod /τm,fs = λ1/2. To assess the adequacy and appropriateness of various scaling equations reported in the literature (namely Qmod /Qfs =λn, proposed values of nbeing 1·5, 2·5, and 2·75, respectively), extensive experimental measurements of mixing times were carried out in three differently sized water model ladles. To measure mixing times, the conventional conductivity measurement technique was adopted. Comparisons of experimental ratios of mixing times with the corresponding theoretical ratio (=λ1/2 ) confirm that, in the Froude dominated flow regime, the most appropriate criterion for dynamic similarity between model and full scale ladles is Qmod /Qfs = λ2·5. Such findings were also corroborated through consideration of empirical mixing time correlations reported for Froude dominated ladle flows.