Modeling the rheological behavior of waxy crude oils as a function of flow and temperature history

International audienceSynopsis The solidification of waxy components during the cool down of waxy crude oils in pipelines may provide complex yield stress fluid behavior with time-dependent characteristics, which has a critical impact for predicting flow restart after pipeline shut-in. Here, from a previous set of data at a local scale with the help of Magnetic Resonance Imaging and a new full set of data for various flow and temperature histories, we give a general picture of the rheological behavior of waxy crude oils. The tests include start flow tests at different velocities or creep tests at different stress levels, abrupt changes of velocity level, steady flow, after cooling under static or flowing conditions. We show that when the fluid has been cooled at rest it forms a structure that irreversibly collapses during the startup flow. Under these conditions, the evolution of the apparent viscosity mainly depends on the deformation undergone by the fluid for low or moderate deformation and starts to significantly depend on the shear rate for larger values. Even the (apparent) flow curve of statically cooled waxy crude oils was observed to be dependent on the flow history, more specifically on the maximum shear rate experienced by the material. After being sufficiently sheared, i.e., achieving an equilibrium state, the rheological behavior is that of a simple liquid for shear rates lower than the maximum historical one. A model is proposed to represent those trends experimentally observed. In contrast with most previous works in that field, the model is built without any a priori assumption based on classical behavior of a class of fluids. Finally, it is shown that this mode

Differential Scanning Calorimetry contribution to a better understanding of the aging of gelled waxy crude oils

International audienceBelow Wax Appearance Temperature (WAT), waxy crystals appear within the crude oil and make it viscous with yield stress and shear thinning properties. Particular attention has been paid during the past works on different parameters such as temperature, pressure, shear history, etc. Another important parameter is the holding time of the sample once it has gelled and left at rest under isothermal conditions. Actually, the network of waxy crystals is known to change with time. This phenomenon has been particularly observed in the case of deposit that is expected to harden. The set of rheological tests and calorimetric analysis that were performed on a real waxy crude oil confirm that a gel formed with waxy crystals may evolve with time and that the extent of this phenomenon depends on the thermo-mechanical past of the sample. Actually, a strengthening of the gel during holding time is observed in the case of fast cooling because the sample gets supersaturated. Aging takes place through isothermal crystallization that lasts a few minutes. The results have also shown that slowly cooled samples do not lead to any aging

Simulation numérique de l'écoulement d'un fluide viscoplastique thixotrope et faiblement compressible dans une conduite cylindrique : application au transport des bruts paraffiniques

Ce papier présente des simulations numériques de l'écoulement instationnaire d'un fluide viscoplastique thixotrope et faiblement compressible dans une conduite cylindrique. Le champ d'application de cette étude est lié au redémarrage d'un brut paraffinique dans une conduite pétrolière. Le fluide est décrit par un modèle de Houska, basé sur un modèle de Herschel-Bulkley dans lequel est introduit une équation d'évolution en temps pour prendre en compte les effets de la thixotropie. La compressibilité est prise en compte dans l'équation de conservation de la masse grâce à un facteur de compressibilité isotherme. La résolution numérique est basée sur une méthode Volumes Finis/Lagrangien augmenté qui permet de traîter la non-dérivabilité du modèle de fluide à seuil et la compressibilité du fluide. L'influence des effets combinés de la compressibilité et de la thixotropie sur la capacité et le temps de redémarrage est observée. D'un point de vue pratique, on observe que la pression de redémarrage P peut être inférieure à la pression prédite par la relation conservative P=4*tauy*L/D, où tauy est la contrainte seuil, L la longueur de la conduite et D son diamètre

Differential Scanning Calorimetry contribution to a better understanding of the aging of gelled waxy crude oils

Below Wax Appearance Temperature (WAT), waxy crystals appear within the crude oil and make it viscous with yield stress and shear thinning properties. Particular attention has been paid during the past works on different parameters such as temperature, pressure, shear history, etc. Another important parameter is the holding time of the sample once it has gelled and left at rest under isothermal conditions. Actually, the network of waxy crystals is known to change with time. This phenomenon has been particularly observed in the case of deposit that is expected to harden. The set of rheological tests and calorimetric analysis that were performed on a real waxy crude oil confirm that a gel formed with waxy crystals may evolve with time and that the extent of this phenomenon depends on the thermo-mechanical past of the sample. Actually, a strengthening of the gel during holding time is observed in the case of fast cooling because the sample gets supersaturated. Aging takes place through isothermal crystallization that lasts a few minutes. The results have also shown that slowly cooled samples do not lead to any aging

ETUDE DES TRANSFERTS THERMIQUES AU SEIN D'UN LIT DE PARTICULES CONTENANT UN MATERIAU A CHANGEMENT DE PHASE POUR LE STOCKAGE DE CHALEUR

Une solution de stockage d'électricité, le procédé AA-CAES (Advanced Adiabatic Compressed Air Energy Storage), consiste à comprimer de l'air en phase de stockage et à le détendre dans une turbine afin de récupérer une partie de l'énergie électrique utilisée pour la compression. Lors de la compression la température de l'air augmente de plusieurs centaines de degrés. Il est alors nécessaire d'abaisser sa température pour permettre son stockage. Afin d'augmenter le rendement du procédé, la chaleur évacuée lors de cette étape est récupérée dans des unités de stockage d'énergie thermique qui peuvent par exemple être constituées de lits (fixes ou fluidisés) de particules contenant un Matériau à Changement de Phase (MCP). L'étude de ces lits de particules est complexe car elle fait intervenir des phénomènes couplés entre eux ayant lieu à différentes échelles (micro : échelle de la particule, méso : d'une partie du lit et macro : de l'ensemble du lit). Le logiciel PeliGRIFF (http://www.peligriff.com) autour duquel s'axe le travail de cette thèse permet de modéliser des systèmes d'écoulements particulaires à l'échelle micro (toutes les interactions particule-particule et fluide-particule sont directement résolues) et méso (les interactions fluide-particule sont modélisées). Pour être en mesure d'y simuler une unité de stockage via les MCP en vue de son dimensionnement tout en gardant une puissance de calcul nécessaire raisonnable, il est alors nécessaire de modéliser les phénomènes ayant lieu à l'échelle de la particule et influençant de manière significative les transferts thermiques aux échelles supérieures, en particulier la convection naturelle au sein de la phase liquide du MCP et le changement de phase lors du stockage/de la libération de la chaleur. Etablir ces modèles demande l'étude préalable d'une particule isolée. Le travail réalisé a donc consisté à évaluer au travers de simulations l'impact de la convection naturelle au niveau de la particule et de déterminer comment et dans quelle gamme de nombres adimensionnels, il est nécessaire de prendre en compte ce phénomène. Pour cela, des simulations sous OpenFOAM d'une unique particule soumise à un gradient de température sous différents nombres de Rayleigh et de Prandtl permettant le déclenchement de la convection naturelle ont été réalisées. Les résultats obtenus ont permis de déterminer l'effet de la convection sur les échanges et d'établir une corrélation reliant le flux de chaleur moyen (échangé entre l'extérieur et le fluide contenu dans la particule) aux nombres de Prandtl et Rayleigh de la particule . Cette corrélation permet de recalculer l'évolution temporelle de la température moyenne de la particule à partir de la connaissance des nombres de Prandtl et Rayleigh. La température moyenne ainsi recalculée et la température moyenne obtenue par simulation sous OpenFOAM ont ensuite été comparées pour divers couples (Rayleigh, Prandtl) afin de valider cette corrélation

Intervention Packages to Reduce the Impact of HIV and HCV Infections Among People Who Inject Drugs in Eastern Europe and Central Asia: A Modeling and Cost-effectiveness Study

Abstract Background: We evaluated the effectiveness and cost-effectiveness of interventions targeting hepatitis C virus (HCV) and HIV infections among people who inject drugs (PWID) in Eastern Europe/Central Asia. We specifically considered the needle-syringe program (NSP), opioid substitution therapy (OST), HCV and HIV diagnosis, antiretroviral therapy (ART), and/or new HCV treatment (direct acting antiviral [DAA]) in Belarus, Georgia, Kazakhstan, Republic of Moldova, and Tajikistan. Methods: We developed a deterministic dynamic compartmental model and evaluated the number of infections averted, costs, and incremental cost-effectiveness ratios (ICERs) of interventions. OST decreased frequencies of injecting by 85% and NSP needle sharing rates by 57%; ART was introduced at CD4 <350 and DAA at fibrosis stage ≥F2 at a $2370 to$23 280 cost. Results: Increasing NSP+OST had a high impact on transmissions (infections averted in PWID: 42% in Tajikistan to 55% in Republic of Moldova for HCV; 30% in Belarus to 61% in Kazakhstan for HIV over 20 years). Increasing NSP+OST+ART was very cost-effective in Georgia (ICER = $910/year of life saved [YLS]), and was cost-saving in Kazakhstan and Republic of Moldova. NSP+OST+ART and HIV diagnosis was very cost-effective in Tajikistan (ICER =$210/YLS). Increasing the coverage of all interventions was always the most effective strategy and was cost-effective in Belarus and Kazakhstan (ICER = $12 960 and$21 850/YLS); it became cost-effective/cost-saving in all countries when we decreased DAA costs. Conclusion: Increasing NSP+OST coverage, in addition to ART and HIV diagnosis, had a high impact on both epidemics and was very cost-effective and even cost-saving. When HCV diagnosis was improved, increased DAA averted a high number of new infections if associated with NSP+OST

Building a successful minimally invasive mitral valve repair program before introducing the robotic approach: The Massachusetts General Hospital experience

BackgroundPatients with mitral valve prolapse (MVP) requiring surgical repair (MVr) are increasingly operated using minimally invasive strategies. Skill acquisition may be facilitated by a dedicated MVr program. We present here our institutional experience in establishing minimally invasive MVr (starting in 2014), laying the foundation to introduce robotic MVr.MethodsWe reviewed all patients that had undergone MVr for MVP via sternotomy or mini-thoracotomy between January 2013 and December 2020 at our institution. In addition, all cases of robotic MVr between January 2021 and August 2022 were analyzed. Case complexity, repair techniques, and outcomes are presented for the conventional sternotomy, right mini-thoracotomy and robotic approaches. A subgroup analysis comparing only isolated MVr cases via sternotomy vs. right mini-thoracotomy was conducted using propensity score matching.ResultsBetween 2013 and 2020, 799 patients were operated for native MVP at our institution, of which 761 (95.2%) received planned MVr (263 [34.6%] via mini-thoracotomy) and 38 (4.8%) received planned MV replacement. With increasing proportions of minimally invasive procedures (2014: 14.8%, 2020: 46.5%), we observed a continuous growth in overall institutional volume of MVP (n = 69 in 2013; n = 127 in 2020) and markedly improved institutional rates of successful MVr, with 95.4% in 2013 vs. 99.2% in 2020. Over this period, a higher complexity of cases were treated minimally-invasively and increased use of neochord implantation ± limited leaflet resection was observed. Patients operated minimally invasively had longer aortic cross-clamp times (94 vs. 88 min, p = 0.001) but shorter ventilation times (4.4 vs. 4.8 h, p = 0.002) and hospital stays (5 vs. 6 days, p &lt; 0.001) than those operated via sternotomy, with no significant differences in other outcome variables. A total of 16 patients underwent robotically assisted MVr with successful repair in all cases.ConclusionA focused approach towards minimally invasive MVr has transformed the overall MVr strategy (incision; repair techniques) at our institution, leading to a growth in MVr volume and improved repair rates without significant complications. On this foundation, robotic MVr was first introduced at our institution in 2021 with excellent outcomes. This emphasizes the importance of building a competent team to perform these challenging operations, especially during the initial learning curve

Executive Summary of the Second International Guidelines for the Diagnosis and Management of Pediatric Acute Respiratory Distress Syndrome (PALICC-2)

OBJECTIVES: We sought to update our 2015 work in the Second Pediatric Acute Lung Injury Consensus Conference (PALICC-2) guidelines for the diagnosis and management of pediatric acute respiratory distress syndrome (PARDS), considering new evidence and topic areas that were not previously addressed. DESIGN: International consensus conference series involving 52 multidisciplinary international content experts in PARDS and four methodology experts from 15 countries, using consensus conference methodology, and implementation science. SETTING: Not applicable. PATIENTS: Patients with or at risk for PARDS. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Eleven subgroups conducted systematic or scoping reviews addressing 11 topic areas: 1) definition, incidence, and epidemiology; 2) pathobiology, severity, and risk stratification; 3) ventilatory support; 4) pulmonary-specific ancillary treatment; 5) nonpulmonary treatment; 6) monitoring; 7) noninvasive respiratory support; 8) extracorporeal support; 9) morbidity and long-term outcomes; 10) clinical informatics and data science; and 11) resource-limited settings. The search included MEDLINE, EMBASE, and CINAHL Complete (EBSCOhost) and was updated in March 2022. Grading of Recommendations, Assessment, Development, and Evaluation methodology was used to summarize evidence and develop the recommendations, which were discussed and voted on by all PALICC-2 experts. There were 146 recommendations and statements, including: 34 recommendations for clinical practice; 112 consensus-based statements with 18 on PARDS definition, 55 on good practice, seven on policy, and 32 on research. All recommendations and statements had agreement greater than 80%. CONCLUSIONS: PALICC-2 recommendations and consensus-based statements should facilitate the implementation and adherence to the best clinical practice in patients with PARDS. These results will also inform the development of future programs of research that are crucially needed to provide stronger evidence to guide the pediatric critical care teams managing these patients.</p

Severe Asthma Standard-of-Care Background Medication Reduction With Benralizumab: ANDHI in Practice Substudy

Background: The phase IIIb, randomized, parallel-group, placebo-controlled ANDHI double-blind (DB) study extended understanding of the efficacy of benralizumab for patients with severe eosinophilic asthma. Patients from ANDHI DB could join the 56-week ANDHI in Practice (IP) single-arm, open-label extension substudy. Objective: Assess potential for standard-of-care background medication reductions while maintaining asthma control with benralizumab. Methods: Following ANDHI DB completion, eligible adults were enrolled in ANDHI IP. After an 8-week run-in with benralizumab, there were 5 visits to potentially reduce background asthma medications for patients achieving and maintaining protocol-defined asthma control with benralizumab. Main outcome measures for non-oral corticosteroid (OCS)-dependent patients were the proportions with at least 1 background medication reduction (ie, lower inhaled corticosteroid dose, background medication discontinuation) and the number of adapted Global Initiative for Asthma (GINA) step reductions at end of treatment (EOT). Main outcomes for OCS-dependent patients were reductions in daily OCS dosage and proportion achieving OCS dosage of 5 mg or lower at EOT. Results: For non-OCS-dependent patients, 53.3% (n = 208 of 390) achieved at least 1 background medication reduction, increasing to 72.6% (n = 130 of 179) for patients who maintained protocol-defined asthma control at EOT. A total of 41.9% (n = 163 of 389) achieved at least 1 adapted GINA step reduction, increasing to 61.8% (n = 110 of 178) for patients with protocol-defined EOT asthma control. At ANDHI IP baseline, OCS dosages were 5 mg or lower for 40.4% (n = 40 of 99) of OCS-dependent patients. Of OCS-dependent patients, 50.5% (n = 50 of 99) eliminated OCS and 74.7% (n = 74 of 99) achieved dosages of 5 mg or lower at EOT. Conclusions: These findings demonstrate benralizumab's ability to improve asthma control, thereby allowing background medication reduction

New genetic loci link adipose and insulin biology to body fat distribution.

Body fat distribution is a heritable trait and a well-established predictor of adverse metabolic outcomes, independent of overall adiposity. To increase our understanding of the genetic basis of body fat distribution and its molecular links to cardiometabolic traits, here we conduct genome-wide association meta-analyses of traits related to waist and hip circumferences in up to 224,459 individuals. We identify 49 loci (33 new) associated with waist-to-hip ratio adjusted for body mass index (BMI), and an additional 19 loci newly associated with related waist and hip circumference measures (P < 5 × 10(-8)). In total, 20 of the 49 waist-to-hip ratio adjusted for BMI loci show significant sexual dimorphism, 19 of which display a stronger effect in women. The identified loci were enriched for genes expressed in adipose tissue and for putative regulatory elements in adipocytes. Pathway analyses implicated adipogenesis, angiogenesis, transcriptional regulation and insulin resistance as processes affecting fat distribution, providing insight into potential pathophysiological mechanisms