CFD Prediction of Flow and Homogenization in a Stirred Vessel: Part I Vessel with One and Two Impellers

A simulation of flow field and tracer homogenization was performed using the commercial CFD software FLUENT 6.1. The aim is to investigate the potential of CFD software to predict concentration distribution of added tracer in cylindrical vessels. The calculated results – dimensionless velocity profiles, power and pumping numbers, dimensionless concentration curves, and mixing times – were compared with experiments in stirred vessels. In Part I, the study was performed for vessels agitated by one or two impellers on a centric shaft. Two different impellers were used – a 6‐bladed 45° pitched blade turbine and a standard Rushton turbine. The standard k‐? turbulence model and multiple reference frames method were used for the simulations. The influence of the grid type was also investigated; three types of grid – a structured, unstructured and a special user‐defined grid – were studied.     

Homogenization of liquids in tanks stirred by multiple impellers

The process of homogenization of liquids in a tall vessel equipped with a multiple impeller was studied. Up to four standard Rushton turbines and/or six pitched-blade turbines were used. The mixing time in the system was measured by the conductivity method. A continuous time history of the tracer concentration at several points in the system was recorded. The data were interpreted by means of an adapted cell model of the flow within the stirred vessel with several impellers based on the assumption of well mixed cells and intercellular flow of liquid. The liquid transfer flow rate between the cells, as a parameter of the model, was calculated from experimental data. A good agreement between the time dependence of concentration obtained experimentally and that calculated from theory was obtained. A direct relationship between the flow numbers between cells and those of impellers was established.     

Work, employment, and unemployment: Values, theories, and approaches in social research.

Argues against the idea that an encompassing theory of work could eliminate the existing shortcomings in empirical research in the field and discusses how specific theories can be exploited by adherents of one or the other dominant value positions: conservative, reformist, and radical. (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Thermal Analysis and Cone Calorimeter Study of Engineered Wood with an Emphasis on Fire Modelling

Fire Technology - Engineered wood products (EWPs) are a group of materials having a very similar chemical composition but having different and non-uniform thermo-physical properties throughout...     

Peptoid Efficacy against Polymicrobial Biofilms Determined by Using Propidium Monoazide‐Modified Quantitative PCR

Biofilms containing Candida albicans are responsible for a wide variety of clinical infections. The protective effects of the biofilm matrix, the low metabolic activity of microorganisms within a biofilm and their high mutation rate, significantly enhance the resistance of biofilms to conventional antimicrobial treatments. Peptoids are peptide‐mimics that share many features of host defence antimicrobial peptides but have increased resistance to proteases and therefore have better stability in vivo. The activity of a library of peptoids was tested against monospecies and polymicrobial bacterial/fungal biofilms. Selected peptoids showed significant bactericidal and fungicidal activity against the polymicrobial biofilms. This coupled with low cytotoxicity suggests that peptoids could offer a new option for the treatment of clinically relevant polymicrobial infections.     

Liquid Homogenization in Aerated Multi‐Impeller Stirred Vessel

The macroflow of fluid in a tall cylindrical vessel stirred with multiple stirrers was studied in the case of aeration of a liquid charge. The time of homogenization of the charge (mixing time) was calculated from the time dependency of the tracer concentration measured at various locations. Two types of stirrer were used in the experiments: six‐bladed Rushton turbines and/or pitched‐blade turbines with inclined blades pumping the liquid down or up. Four stirrers of the same type were located on the shaft. Other variables during the experiments were the stirrer frequency and the gas flow rate. It was found that the liquid macroflow in the vessel could be interpreted by the cell model or by the axial dispersion model for unaerated as well as for aerated systems. The influence of the aeration on the macroflow and mixing time was explained by the interaction of buoyancy and radial forces, and equations for the model parameters were proposed containing gas flow numbers and Froude numbers.     

Effect of gravity forces on oil recovery in a Hele‐Shaw cell

The effect of gravity on oil recovery was studied in a Hele‐Shaw cell. An immiscible two fluid system consisting of light paraffin oil as the displaced phase and distilled water as the displacing phase was used. Oil recovery at breakthrough was found to be almost linearly dependent on the Bond number. Maximum recovery was obtained in the case of upward flooding with the cell positioned vertically. The minimum oil recovery occurred when flooding was performed in the downward direction with the cell also placed in the vertical position. The recovery results obtained for the experiments carried out at a 45 degree incline and in the horizontal position were situated between these extremes.     

Political attitudes and judgments of other people.

"The hypothesis was set up that in judging other people, subjects tend to associate favorable personal characteristics with political attitudes of which they themselves approve." The data tend to support the hypothesis. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A limited view of adult development.

Comments on an article by Daniel J. Levinson (see record 1986-19674-001) on adult development and the life course. M. Jahoda takes exception to the article on two counts: (1) For a growing number of people adult development does not end at 65 when old age begins and (2) The study of the life cycle is not a newly emerging field and is not limited to the United States. (PsycINFO Database Record (c) 2010 APA, all rights reserved)