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

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Abstract

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 μm.

The modified blade turbine, noted as TP3, was found to be more efficient than the standard turbine in complete and homogeneous suspension.

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Abbreviations

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 s n)

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 :

PL/ϱLN3d5 power number in liquid system (-)

(Ne) g :

Pg/ϱspN3d5 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 :

ϱspNd2/η 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)

ɛ js :

specific power input per mass at the complete suspension state (W/kg)

η a :

apparent viscosity under mixing conditions (Pa s)

ν L :

kinematic viscosity of the liquid (m2/s)

ϱ L :

density of liquid (Kg/m3)

ϱ s :

density of solid (Kg/m3)

ρ sp :

density of suspension (Kg/m3)

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Authors and Affiliations

  1. Research Centre for Antibiotics, Chemical Pharmaceutical Research Institute, 6647-Valea Lupului, 6600, Jassy, Romania

    R. V. Roman

  2. Faculty of Industrial Chemistry, Technical University “Gh. Asachi”, Splai Bahlui 71, 6600, Jassy, Romania

    R. Z. Tudose

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  1. R. V. Roman
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  2. R. Z. Tudose
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Roman, R.V., Tudose, R.Z. Studies on transfer processes in mixing vessels: suspending of solid particles in liquid by modified Rushton turbine agitators. Bioprocess Engineering 15, 221–229 (1996). https://doi.org/10.1007/BF00369486

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