Theoretical models for the thermo-gravitational separation process in porous media filled by N-component mixtures

The aim of this work is to present a theoretical analysis of the separation of an N-component mixture. In this study, two analytical models explaining the thermo-gravitational separation of components in N-component mixtures for vertical cavity filled by a porous medium are presented and assessed. The basic state and the separation are expressed in terms of the separation ratio, and the Lewis, cross-diffusion and Rayleigh numbers. Our computational analysis confirms that, for the given values of the mass fractions, thermodiffusion can be measured with a thermo-gravitational column, strongly supporting the experimentally determined transport coefficients

Thermal gravitational separation of ternary mixture n-dodecane/isobutylbenzene/tetralin components in a porous medium

Our present work focuses on the coupling between thermal diffusion and convection in order to improve the thermal gravitational separation of mixture components. The separation phenomenon was studied in a porous medium contained in vertical columns. We performed analytical and numerical simulations to corroborate the experimental measurements of the thermal diffusion coefficients of ternary mixture n-dodecane, isobutylbenzene, and tetralin obtained in microgravity in the international space station. Our approach corroborates the existing data published in the literature. The authors show that it is possible to quantify and to optimize the species separation for ternary mixtures. The authors checked, for ternary mixtures, the validity of the “forgotten effect hypothesis” established for binary mixtures by Furry, Jones, and Onsager. Two complete and different analytical resolution methods were used in order to describe the separation in terms of Lewis numbers, the separation ratios, the cross-diffusion coefficients, and the Rayleigh number. The analytical model is based on the parallel flow approximation. In order to validate this model, a numerical simulation was performed using the finite element method. From our new approach to vertical separation columns, new relations for mass fraction gradients and the optimal Rayleigh number for each component of the ternary mixture were obtained

Couplage thermodiffusion-convection dans une colonne thermo-gravitationnelle en vue de la séparation des espèces d'un mélange multiconstituants.

Nous proposons, dans ce travail, une étude analytique et numérique permettant d'étendre aux mélanges multiconstituants la théorie établie pour les mélanges binaires par Furry, Jones et Onsager (Théorie FJO)[1]. Cette théorie permet de calculer le coefficient de thermodiffusion à partir des mesures, à l'état stationnaire, de la fraction massique des constituants d'un mélange binaire en différents points de la colonne verticale de séparation. Nous analysons pour cela les transferts convectifs et massiques qui s'opèrent au sein d'un fluide à n constituants remplissant une fente verticale délimitée par deux parois maintenues à température uniforme T1 et T2. L'espacement entre ces deux plaques verticales est très faible comparé à leurs hauteur et profondeur. Cette fente est le siège d'un écoulement unicellulaire conduisant, à l'état stationnaire, à un gradient de fraction massique entre le bas et le haut de la colonne. Nous avons étendu les résultats traitant de la séparation des espèces des solutions binaires aux mélanges ternaires et ensuite aux multiconstituants dans les colonnes verticales. Pour mener à bien les calculs analytiques et numériques pour les mélanges ternaires et les multiconstituants, nous avons eu recours d'une part à : -l'hypothèse de l'écoulement parallèle (PFA) que nous avons validée numériquement dans le cas de cavités d'épaisseur de 2 à 4 mm et de hauteur de 5 à 10 cm, ce qui est le cas dans de nombreuses expériences traitant de la séparation des espèces. - Le vecteur des coefficients de thermodiffusion DT' est simplifié par : DT' = F(C) DT = F(C0) DT . De plus nous avons admis que l'ensemble des coefficients de transport du multiconstituant sont supposés constants pour de faibles variations de température et de fraction massique autour d'une température moyenne du mélange T0 et d'une concentration initiale C0 = (C10, C20, C30.....)= [Ci0]. Nous avons également vérifié, au niveau de cette contribution traitant des multiconstituants, que l'hypothèse de l'effet oublié (non prise en compte de la contribution de la fraction massique au niveau des forces de gravité dans l'équation de conservation de la quantité de mouvement) dû à Fury, Jones et Onsager (FJO) conduit à de bons résultats pour le mélange ternaire, tétraline, isobutylbenzène et n-dodécane avec des fractions de masse 0.8-0.1-0.1. Les valeurs des fractions massiques déterminées analytiquement ont été comparées aux expériences de P. Costesèque [2], les résultats théoriques et expérimentaux sont en bon accord. En utilisant ce modèle analytique nous avons aussi proposé [3] une méthode pour valider indirectement les expériences réalisées dans la station spatiale internationale en utilisant des résultats de mesures des fractions massiques en différents points placés à différentes hauteurs dans le champ de gravité. [1] P. Costesèque, A. Mojtabi and JK. Platten, Thermodiffusion phenomena, Comptes Rendus Mécanique 339 , 275-279, (2011) [2] P. Costesèque and J.-C. Loubet, Influence des concentrations relatives sur la diffusion thermogravitationnelle en milieu poreux des constituants d'un mélange ternaire d'hydrocarbures (système dodécane-isobutylbenzene-tétraline) Entropie 34, 53-59 (1998) 144(24),  [3] MA. Larabi , D. Mutschler and A. Mojtabi, Thermal gravitational separation of ternary mixture n-dodecane/isobutylbenzene/tetralin components in a porous medium J. of Chemical Physics 144(24), 244902, (2016

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Abstract Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries