Joanna Karcz

An Effect of a Baffle Length on the Power Consumption in an Agitated Vessel

Abstract An effect of the baffle length L on power consumption has been studied for an agitated vessel of inner diameter D =0.6 m equipped with short baffles. The measurements were carried out for the following agitators: Rushton and Smith turbines, pitched blade turbine ( β =45°, Z =3) and propeller. Power characteristics Ne =f( Re ) for different geometrical parameter L / H of the baffles were obtained within the turbulent regime of the fluid flow in the agitated vessel. The results of the experiments were approximated by means of Eqs. (7)-(13) .

Heat transfer in jacketed agitated vessels equipped with non-standard baffles

Abstract The effects of the geometrical parameters of non-standard baffles on heat transfer coefficient were experimentally studied for agitated vessels equipped with a Rushton disc turbine, pitched-blade turbine and propeller. The following geometrical parameters of the baffles were tested: number J, width B, length L and distance p between the lower edge of the baffle and the bottom of the vessel. Measurements were carried out in accordance with a second-order rotatable experimental design. The results of the investigations have been approximated analytically.

Experimental studies of power consumption for agitated vessels equipped with non-standard baffles and high-speed agitator

Abstract The influence of the geometrical parameters of non-standard baffles on power consumption has been investigated for agitated vessels equipped with a high speed agitator (Rushton disc turbine, pitched-blade turbine or propeller) The following geometrical parameters of the baffles have been tested: number J, width B, length L and distance p between the lower edge of the baffle and the bottom of the vessel. Measurements were carried out according to a second-order rotatable design of experiment, using the strain gauge technique. The results of the experiments have been approximated in the form of equations.

A mathematical model of mixing of particulate solids

Abstract A mathematical model of mixing of particulate solids accompanied by segregation is presented. The model has been constructed on the assumption of diffusional mechanisms of both phenomena occurring when the mixing takes place, i.e. homogenisation and segregation. For the mechanism of diffusional segregation a “Law of Diffusional Segregation” has been formulated, analogous to Ficks Second Law. The model has been solved for a two-component system mixed radially in a horizontal rotating drum mixer. A solution has been obtained in the form of the dependence of the concentration of the key component upon the time and position. After introducing the statistical definition of the degree of mixing, based on the concentration standard deviation in the system, a rate equation has been obtained.

Experimental determination of the optimal geometry of baffles for heat transfer in an agitated vessel

Abstract Experimental determination of the optimum values of geometrical parameters of baffles for heat transfer in a jacketed agitated vessel is the purpose of this research. The influence of the geometrical baffle parameters (number, width, length and distance between the lower edge of the baffle and the bottom of the vessel) upon both power consumption and heat transfer was examined for an agitated vessel with an inner diameter of 0.45 m. The experiments were performed with a disc turbine, a pitched-blade turbine and a propeller. An experimental design strategy was used in this research. The results of the experiments were approximated analytically. Based on the optimization criterion, an agitated vessel equipped with a disc turbine and optimally designed baffles is proposed as the most advantageous for heat transfer processes.

Mass Transfer in Multiphase Mechanically Agitated Systems

In this chapter, the results of the experimental studies concerning the volumetric mass transfer coefficient kLa obtained for mechanically agitated gas – liquid and gas – solid – liquid systems are discussed. Mechanically agitated gas – liquid and gas –solid – liquid systems are widely used in many processes, for example oxidation, fermentation or wastewater treatment. In such cases, oxygen mass transfer between gas and liquid phases in the presence of solid particles can be described and analyzed by means of the volumetric mass transfer coefficient kLa. In the gas – liquid and gas – solid – liquid systems, the kLa coefficient value is affected by many factors such as geometrical parameters of the vessel, type of the impeller, operating parameters of the process (impeller speed, aeration rate), properties of the continuous phase (density, viscosity, surface tension, etc.) and also by the type, size and loading of solid particles. To improve the efficiency of the processes conducted in gas – liquid and gas – solid – liquid three – phase systems two or more impellers on the common shaft are often used (Kielbus—Rąpala & Karcz, 2009). Multiple – impeller stirred vessels due to the advantages such as increased gas hold – up, higher residence time of gas bubbles, superior liquid flow characteristics and lower power consumption per impeller are becoming more important comparing with single – impeller systems (Gogate et al., 2000). As the number of energy dissipation points increased with an increase in the impellers number on the same shaft, there is likely to be an enhancement in the gas hold – up due to gas redistribution, which results into higher values of volumetric gas – liquid mass transfer coefficient (Gogate et al., 2000). Correct design of the vessel equipped with several agitators, therefore, the choice of the adequate configuration of the impellers for a given process depends on many parameters. That, which of the parameters will be the most important depends on the kind of process, which will be realized in the system. For the less oxygen demanding processes the designer attention is focused on the mixing intensity much more than on the volumetric mass transfer coefficient. When the most important thing is to achieve high mass transfer efficiency of the process, the agitated vessel should be such designed that the configuration of the agitators used ensure to get high both mixing intensity and the mass transfer coefficient values (Kielbus-Rąpala & Karcz, 2010).