Studies on transfer processes in mixing vessels: suspending of solid particles in liquid by modified Rushton turbine agitators

The modified blade turbines are attractive alternatives to the standard Rushton turbine as they do not require any modification in the electrical engine motor and drive assemblies are simple to manufacture and have a reduced power consumption.The modified blades were obtained through increase in the blade height of the Rushton turbine simultaneously with perforation of the blade surface. The field surface of the modified blade is equal to the blade surface of the standard Rushton turbine.In this study the modified blade turbine with the surface fraction of the perforations equal to 0.353 is used.The complete suspension speed and the power dissipation in transition and turbulent regimes using standard and modified Rushton turbine agitators positioned singly or doubly on same shaft, in five solid-liquid systems were investigated.The solid particles used have the mean diameter between 15–1000 m.The modified blade turbine, noted as TP3, was found to be more efficient than the standard turbine in complete and homogeneous suspension.List of Symbols A distance between turbine and the vessel bottom (m) - c dimensionless constant (-) - d agitator diameter (m) - d_p surface-to-volume mean diameter of the particle (m) - D vessel diameter (m) - (H_L)₁ suspension height for one turbine immersed (m) - (H_L)₂ suspension height for two turbines immersed (m) - K consistency index (Pa sⁿ) - l_k eddy-size characteristic (m) - N flow behaviour index (-) - N_p number of blades of the mixing system (-) - N agitator speed (s^–1) - N_js agitator speed that just causes complete suspension (s^–1) - Ne P_L/_LN³d⁵ power number in liquid system (-) - (Ne)_g P_g/_spN³d⁵ power number in solid-liquid system (-) - P_L power consumption in liquid system (W) - P_s power consumption in solid-liquid system (W) - r coefficient of correlation (-) - R distance between turbines (m) - Re _spNd²/_a Reynolds number (-) - S suspension parameter in Zwietering equation (2) (-) - S_C full surface of the blade (m²) - S_G surface of the perforations applied on the blade (m²) - S_G/S_C surface fraction of the perforations (-) - X particle concentration (g/l) - w baffle width (m) - _js specific power input per mass at the complete suspension state (W/kg) - _a apparent viscosity under mixing conditions (Pa s) - _L kinematic viscosity of the liquid (m²/s) - _L density of liquid (Kg/m³) - _s density of solid (Kg/m³) - _sp density of suspension (Kg/m³)