Predicting the Liquid Phase Mass Transfer Resistance of Structured Packings

Published correlations for estimating the liquid phase mass transfer coefficients of structured packings are compared using experimental evidence on the efficiency of Montz-Pak B1–250MN and B1–500MN structured packings as measured in total reflux distillation tests using the chlorobenzene/ethylbenzene system at two operating pressures. Large differences are found between different correlations with respect to both the absolute values of mass transfer coefficients and the fraction of liquid phase based resistance and their trends with respect to increasing vapor and liquid loads. A new Delft Model liquid side mass transfer coefficient correlation that incorporates a more appropriate definition of the liquid film exposure length is presented which now generates lower values. The revised liquid film model, combined with an enhanced turbulent vapor phase mass transfer coefficient, leads to doubling the fractional liquid phase resistance with respect to that based on penetration theory assuming equal contact times. This effect results in predicting efficiencies which are slightly more conservative and agree reasonably well with experimental HETP data presented in this paper.Process and EnergyMechanical, Maritime and Materials Engineerin

Augmenting Distillation by Membranes: Developments and Prospects

The growing consciousness for sustainable industrial processes has resulted in industrially developed countries in supporting research efforts toward thorough evaluation of possibilities for improving efficiency of energy intensive separations implying also significant reduction of related carbon dioxide emissions. Being inherently thermodynamically inefficient, distillation, which is by far the most widely utilised and energy intensive separation technology in chemical process industries, has become primary target of energy conservation projects in refining, petrochemical and chemical industries. Improvement is an ongoing activity, replacing still beyond comprehension and a great deal of academic effort is oriented towards augmenting distillation by combining it, where appropriate, with membranes, i.e. pervaporation or vapour permeation, which in conjunction with polymeric membranes proved to be an industrially viable alternative to conventional processes for dehydration of alcohols. Present paper addresses recent developments along this line striving for larger fluxes in alcohol dehydrations by utilising ceramic membranes, with focus on vapour permeation, as well as the potential for the recovery of organic solvents and reactants forming azeotropes with other organics

An Improved Shortcut Design Method of Divided Wall Columns Exemplified by a Liquefied Petroleum Gas Process

Designing a sustainable and economical distillation system is a big global challenge in the industrial chemical field. To address this issue, one of most promising solutions is the so-called dividing wall columns addressed in this work, which not only can cut energy cost but also use limited installation space. An improved shortcut design approach is developed in this work to provide accurate models for each section of dividing wall columns; meanwhile Underwood’s and Gilliland’s equations are employed to determine minimum reflux ratio and total number of stages in different column sections in terms of corresponding design specifications and operating conditions. This proposed approach has been applied to separations of mixtures of hydrocarbons and alcohol with different values on the ease of separation index. To test its effectiveness, the preliminary design parameters obtained through the improved proposed shortcut method are further validated by a rigorous simulation in Aspen HYSYS. Furthermore, the results indicate that this method could provide much more accuracy of average interconnecting stream composition of the prefractionator and main column than those of other methods. In practice, this method has been applied to a case of liquefied petroleum gas (LPG) separation with three targeted products in an industrial liquefied petroleum gas plant. The applications and efficiency of the shortcut method in this study lay a theoretical foundation for designing the separation of ideal mixtures involving dividing wall columns

Experiments and dynamic modeling of a reactive distillationcolumn for the production of ethyl acetate by consideringthe heterogeneous catalyst pilot complexities

Great effort has been applied to model and simulate the dynamic behavior of the reactive distillation as a successfulprocess intensification example. However, very little experimental work has been carried out in transient conditions.The work presents a series of experiments for the production of ethyl acetate from esterification of acetic acid andethanol in a reactive distillation pilot column. The steady-state approach performed experiments with both excessof alcohol and stoichiometric feed configuration. Predicted and measured results show good agreement and reveala strong dependency of the structured packing catalyst activity on the pilot geometry and its operating conditions.The transient process behavior of the heterogeneously catalyzed system was deeply investigated and continuousand dynamic data were collected for an equilibrium model validation, after different perturbations on parameters.The experimental validation is shown to be essential to provide realistic hydrodynamic parameters, to understandthe sensitive parameters such as heat losses and to adapt values for the catalyst holdup as a function of the system

Violence, dignity and HIV vulnerability: street sex work in Serbia.

Sex work can be contextualized by violence, social and material inequality, and HIV vulnerability. We undertook a qualitative study to explore female and transvestite sex workers' accounts (n = 31) of HIV risk environment in Belgrade and Pancevo, Serbia. Violence emerged as a key theme. Accounts emphasise the ubiquity of multiple forms of everyday violence - physical, emotional, social - in street sex work scenes, linked to police as much as clients. We highlight the salience of emotions in sex work risk management, in which the preservation of dignity is of prime importance. Accounts draw upon narratives of hygiene and responsibility which, we argue, seek to resist portrayals, normative to this setting, of sex workers as contaminated and irresponsible. Findings highlight how the ubiquity of the risk of violence in street sex work scenes reflects institutionalised social inequalities and injustices. Sex workers are inevitably participant in the cycle of symbolic violence they seek to resist. The challenges for HIV prevention are therefore considerable, and require interventions which not only seek to foster safer micro-environments of sex work but structural changes in the welfare, criminal justice and other social institutions which reproduce the cycle of violence faced by sex workers day to day

A model to advance nursing science in trauma practice and injury outcomes research

Aims: This paper presents a model to advance nursing science and practice in trauma care. Background: The continuum of clinical care provided to trauma patients extends from the time of injury through to long-term recovery and final outcomes. Nurses bring a unique expertise to meet the complex physical and psychosocial needs of trauma patients and their families to influence outcomes across this entire continuum. Data Sources: Literature was obtained by searching CINAHL, PubMed and OvidMedline databases for 1990 – 2010. Search terms included trauma, nursing, scope of practice and role, with results restricted to those published in English. Manual searches of relevant journals and websites were undertaken. Discussion: Core concepts in this trauma outcomes model include environment, person/family, structured care settings, long term outcomes and nursing interventions. The relationships between each of these concepts extend across all phases of care. Intermediate outcomes are achieved in each phase of care and influence and have congruence with long term outcomes. Implications for Policy and Practice: This model is intended to provide a framework to assist trauma nurses and researchers to consider the injured person in the context of the social, economic, cultural and physical environment from which they come and the long term goals that each person has during recovery. The entire model requires testing in research and assessment of its practical contribution to practice. Conclusion: Planning and integrating care across the trauma continuum, as well as recognition of the role of the injured person’s background, family and resources, will lead to improved long term outcomes

What drives athletes toward dietary supplement use: Objective knowledge or self-perceived competence? Cross-sectional analysis of professional team-sport players from Southeastern Europe during the competitive season

BackgroundIssues related to knowledge of nutrition and dietary supplementation(DS) are understudied in professional athletes. This study aimed to examine the possible association between knowledge of nutrition and DS (KN&DS) and dietary supplement use (DSU) among professional athletes involved in team sports.MethodsThe sample comprised professional team-sport athletes (N=912, age: 22.113.37years, 356 females) involved in four Olympic sports: basketball (N=228), soccer (N=324), volleyball (N=154), and handball (N=206). The participants were tested by previously validated questionnaires to examine their self-perceived competence on nutrition and DS (S/KN&DS), their objectively evaluated (tested) KN&DS (O/KN&DS), sociodemographic and sport-specific variables (predictors), and DSU (criterion). Associations between the predictors and the criterion (No-DSU - Irregular-DSU - Regular-DSU) were determined by multinomial regression analysis for the total sample and separately for the studied sports.ResultsDSU was found to be less prevalent in older and more successful players. The O/KN&DS and S/KN&DS were positively correlated with DSU, but S/KN&DS was a stronger predictor of DSU than O/KN&DS. Sport-specific associations between predictors and criterion were identified, with stronger correlations in sports with a higher prevalence of DSU.Conclusions Due to the low correlations between O/KN&DS and S/KN&DS in the studied players, this study highlights the necessity for more frequent monitoring of biomarkers of nutritional status and its usage by coaches and practitioners to provide quantitative instruction

Biomarker Pigment Divinyl Chlorophyll a as a Tracer of Water Masses?

The ecological preferences of different Phytoplankton types drive their temporal and spatial distributions, reflecting their dependence on certain temperature ranges, light levels, nutrient availability and other environmental gradients. Hence, some phytoplankton taxa can be used as water mass tracers (biotracers)