DISTRIBUTION OF ENERGY BETWEEN CONVECTIVE AND TURBULENT FLOW FOR THREE FREQUENTLy USED IMPELLERS


By jpeza - Posted on 25 Junio 2009

Datos del paper
Autor Principal: 
G. ZHOU
Volumen: 
74A
Página Inicial: 
379
Página Final: 
389
Abstract: 

Turbulence energy dissipation is important in the study of turbulent mixing

phenomena in stirred tanks. This paper investigates the characteristics of the

turbulence energy dissipation and the overall energy distribution in the impeller

region of a stirred tank. One radial flow impeller (Rushton turbine (RT)) and two axial

flow impellers (the pitched blade turbine (PBT) and a fluidfoil turbine (A31O))were used.

The mean and root-mean-square velocity (RMS) profiles close to the three impellers were

measured in a cylindrical baffied tank using laser Doppler anemometry (LDA). The

average turbulence energy dissipation, Ei was ca1culated using a macroscopic energy

balance equation over several control volumes. The local turbulence energy dissipation E

was estimated using E = Av3 /L with A = 1 and L = D / 10. Integration of the local

dissipation over a control volume consistently gave results within 6% ofthe macroscopic

energy balance. The bulk of the energy is dissipated in the small volume occupied by the

impeller and the impeller discharge stream for all three impellers: in order of increasing

percentages 38.1% (A31O), 43,5% (RT) and 70.5% (PBT). The dominant characteristics

of energy distribution are different for each impeller. The A310 was most efficient at

generating convective flow. The RT generated the most turbulence, and the PBT derived a

much larger portion of its energy from the return flow.

Dirección del Autor: 

Department 01 Chemical Engineering, University 01 Alberta, Edmonton, Alberta, Canada

Keywords: 
turbulent energy dissipation; impellers; stirred tanks; turbulence; mixing
Coautores: 

S. M. KRESTA