Mass transfer in gas-liquid slurry reactors

A critical review is presented on the mass transfer characteristics of gas¿liquid slurry reactors. The recent findings on the influence of the presence of solid particles on the following mass transfer parameters in slurry reactors are discussed: volumetric gas¿liquid mass transfer coefficients (kLa, kGa), liquid-side mass transfer coefficients (kL and kS) and specific gas¿slurry contact area (a). The second part of this paper reviews the recent progress in our knowledge and understanding of the enhancement of gas¿slurry mass transfer due to the presence of solids. Five different cases are distinguished, i.e. \ud \ud ¿ enhanced mass transfer by physical adsorption on small particles.\ud \ud ¿ enhanced mass transfer by fast homogeneous reactions in the slurry, due to inert particles,\ud \ud ¿ enhanced mass transfer by homogenous reaction in the liquid with dissolving particles,\ud \ud ¿ enhanced mass transfer due to reactive particles and\ud \ud ¿ enhanced mass transfer due to catalytic particles in heterogeneous reactive systems.\ud \ud Prospective areas for additional research are identified

Numerical calculation of simultaneous mass transfer of two gases accompanied by complex reversible reactions

A discretization technique is described, which makes it possible to calculate numerically mass transfer behaviour between two media in which complex chemical reactions occur. To show the stability of the technique it has been applied to the industrially well-known system of simultaneous absorption or desorption of H2S and CO2 to or from an amine solution, accompanied by simultaneously occurring strongly interfering overall chemical reaction(s) of complex, non elementary kinetics. For previously published limit cases of the transfer system considered, i.e. for the single transfer of H2S or CO2 accompanied by reversible chemical reaction, a comparison has been made with analytical and approximate solutions of previous authors. The agreement is very good. In studying simultaneous transfer of H2S and CO2, on which hardly any previous work was available, special attention has been paid to the effects of the reversibility of the reactions involved. It has been shown how, under certain conditions due to reversibility occurring in the transferzone, desorption takes place though absorption would be expected on basis of the driving forces. This revealed that not only enhancement factors larger than unity but also smaller, even negative values are possible

Mechanism of charge transfer in the discontinuous metal phase of a fluidized bed electrode

From measurements of double layer capacity, collision frequency and contact time during collision, it is concluded that models for charge transfer in the discontinuous phase of fluidized bed electrode that are based on ideal particulate fluidization cannot explain metal phase resistivities, experimentally observed.\ud Based on a literature survey it is shown that not only gas-solid but also liquid-solid fluidization is at least partially aggregative.\ud A preliminary model for charge transfer in the discontinuous phase, based on aggregative fluidization, is derived

Physical Activity : The interplay between individual and neighbourhood factors

Physical inactivity is among the most important and prevalent risk factors of many major diseases. Although the health benefits of regular exercise and a physically active lifestyle are well known, many people are still not active. Understanding why some population groups are physically active and others are not is therefore of key importance in developing strategies to improve population health. Physical activity is often believed to be influenced by both environmental factors, such as the neighbourhood lay-out, and individual factors, like p

Urban population density and mortality in a compact Dutch city

We investigated the association and underlying pathways between urban population density and mortality in a compact mid-sized university city in the Netherlands. Baseline data from the GLOBE cohort study (N = 10,120 residents of Eindhoven) were linked to mortality after 23 years of follow up and analyzed in multilevel models. Higher population density was modestly related to increased mortality, independently of baseline socioeconomic position and health. Higher population density was related to more active transport, more perceived urban stress and smoking. Increased active transport suppressed the mortality-increasing impact of higher population density. Overall, in dense cities with good infrastructure for walking and cycling, high population density may negatively impact mortality

Interactions of individual perceived barriers and neighbourhood destinations with obesity-related behaviours in Europe.

Perceived barriers towards physical activity and healthy eating as well as local availability of opportunities (destinations in the neighbourhood) are important determinants of obesity-related behaviours in adults. Little is known, however, about how these factors interact with the behaviours. Data were analysed from 5,205 participants of the SPOTLIGHT survey, conducted in 60 neighbourhoods in urban regions of five different countries across Europe. A virtual audit was conducted to collect data on the presence of destinations in each neighbourhood. Direct associations of, and interactions between, the number of individual perceived barriers and presence of destinations with obesity-related behaviours (physical activity and dietary behaviours) were analysed using multilevel regression analyses, adjusted for key covariates. Perceiving more individual barriers towards physical activity and healthy eating was associated with lower odds of physical activity and healthy eating. The presence of destinations such as bicycle lanes, parks and supermarkets was associated with higher levels of physical activity and healthier dietary behaviours. Analyses of additive interaction terms suggested that the interaction of destinations and barriers was competitive, such that the presence of destinations influenced obesity-related behaviours most among those perceiving more barriers. These explorative findings emphasize the interest and importance of combining objective (e.g. virtual neighbourhood audit) methods and subjective (e.g. individual perceived barriers collected in a survey) to better understand how the characteristics of the residential built environment can shape obesity-related behaviours depending on individual characteristics