Transport phenomena in an agitated vessel with an eccentrically located impeller

Abstract

The paper presents results of an experimental analysis of the transport phenomena at the vicinity of the wall of an unbaffled agitated vessel with an eccentrically located impeller. Distributions of the transport coefficients were experimentally studied using an electrochemical method within the turbulent regime of the Newtonian liquid flow. Measurements were carried out in an agitated vessel with the inner diameter T = 0.3 m. Liquid height in the vessel was equal to the inner diameter, H = T. The agitated vessel was equipped with a Rushton or a Smith turbine or an A 315 impeller. Eccentricity of the impeller shaft was varied from 0 to 0.53. Local values of the dimensionless shear rate, shear stress, dynamic velocity and friction coefficient were integrated numerically for the whole surface area of the cylindrical wall of the vessel. Averaged values of these quantities were correlated with the impeller eccentricity and modified Reynolds number. The proposed Eqs. (5)–(8), with the coefficients given in Table 2, have no equivalent in open literature concerning this subject. Distributions of the shear rate, γ/n, and friction coefficient, f, at the vicinity of the cylindrical wall of the unbaffled vessel equipped with eccentric Rushton or Smith turbine or A 315 impeller are very uneven and they depend significantly on the impeller eccentricity, e/R. Maximum local values of these variables are located on the wall section closest to the impeller blades. From among the tested impellers, the greatest effects of the impeller eccentricity, e/R, and the liquid turbulence (described by the modified Reynolds number Re P,M) on the averaged dimensionless shear rate (γ/n)m and friction coefficient, f m, are found for the radial-flow Rushton turbine located eccentrically in an unbaffled agitated vessel.

Local Momentum Transfer Process in a Wall Region of an Agitated Vessel Equipped with an Eccentric Impeller

“…Local momentum transfer in the region of the cylindrical wall of the agitated vessel was studied using computer aided electrochemical method. This experimental method was described in detail by Karcz and Abragimowicz, as well as Karcz et al − In this method, nickel circular cathodes with a diameter 4 mm were used as measuring sensors. Cathodic reduction of the potassium ferricyanide K 3 Fe(CN) 6 was employed as a measuring system.…”

“…Electrochemical measurements were carried out within the turbulent liquid flow in the vessel of inner diameter T = 0.3 m. The results were described mathematically in the form of the equation which relates local friction coefficient f , obtained for the centric position of the propeller, with the dimensionless axial and angular coordinates ( z / H , φ/2π) and Re number. Momentum transfer process in the region of the wall of an agitated vessel was experimentally studied by Cudak and Karcz. − Graphical distributions of the shear rate on the vessel wall as a function of the impeller type (eccentrically located propeller, HE 3, A 315, Rushton or Smith turbines of diameter D = 0.33 T ) were determined. The dependences of the averaged dimensionless shear rate and friction coefficient on the Reynolds number and impeller eccentricity were approximated mathematically .…”

“…The dependences of the averaged dimensionless shear rate and friction coefficient on the Reynolds number and impeller eccentricity were approximated mathematically . Local momentum transfer was also analyzed experimentally for the system equipped with eccentric HE 3 impeller of diameter D = 0.5 T . The local and averaged momentum transfer quantities were correlated mathematically as a function of the impeller eccentricity and modified Reynolds number Re P,M (where Re P , M = (( P / M )ρ 3 T 4 /η 3 ) and M = V ρ).…”

“…Momentum transfer process in the region of the wall of an agitated vessel was experimentally studied by Cudak and Karcz. [21][22][23] Graphical distributions of the shear rate on the vessel wall as a function of the impeller type (eccentrically located propeller, HE 3, A 315, Rushton or Smith turbines of diameter D = 0.33T) were determined. The dependences of the averaged dimensionless shear rate and friction coefficient on the Reynolds number and impeller eccentricity were approximated mathematically.…”

“…21 Local momentum transfer was also analyzed experimentally for the system equipped with eccentric HE 3 impeller of diameter D = 0.5T. 22 The local and averaged momentum transfer quantities were correlated mathematically as a function of the impeller eccentricity and modified Reynolds number Re P,M (where Re P,M = ((P/M)F 3 T 4 /η 3 ) and M = VF). An effect of the impeller HE 3 diameter, impeller eccentricity and modified Reynolds number Re P,M on the averaged shear rate, friction coefficient, shear stress, and dynamic velocity was identified.…”