Étude des interactions entre gouttelette et flamme par des approches expérimentales et numériques

Spray combustion applications involve complex phenomena such as atomization, droplet vaporization, mixing, turbulence, chemical kinetics, and the interaction of these processes. In two-phase combustion, one of the fundamental processes is the interaction of a single droplet with a flamelet. Therefore, it is essential to understand the physics of isolated droplet evaporation and its effects on the flame front to study more complex flames.The aim of this study is to investigate droplet evaporation, flame characteristics, and changes in the flame morphology for laminar flames in the presence of droplets via experimental and numerical approaches. The experimental part of the study is conducted in CNRS ICARE, including microgravity experiments to study the flame instabilities of spherically expanding ethanol/air flame in the presence of isolated ethanol droplets usingthe Schlieren method. Additionally, ground experiments are performed to investigate the evaporation characteristics of an ethanol droplet evaporating through flat methane/air flame and the structural changes in propane/air flames due to the passage of an ethanol droplet using optical laser diagnostics including PIV, PTV, ILIDS, Chemiluminescence. In the numerical part of the study, the YALES2 solver is utilized to simulate droplet evaporation under different ambient conditions at elevated temperatures via the Eulerian-Lagrangian approach. In this scope, stationary droplet evaporation is computed at burnt gas compositions via the Spalding model, as well as the evaporation of a moving droplet through a stagnation flame field via the Abramzon-Sirignano model. Finally, nonreactive and reactive simulations are performed with stagnation burner geometry.Les applications de combustion par pulvérisation impliquent des phénomènes très complexes tels que l'atomisation, la vaporisation des gouttelettes, le mélange, la turbulence, la cinétique chimique, ainsi que l'interaction de ces processus. Dans la combustion diphasique, l'un des processus de base est l'interaction d'une seule gouttelette avec une flammelette. Par conséquent, il est essentiel de comprendre la physique de l'évaporation des gouttelettes isolées et des effets sur le front de flamme pour étudier des flammes plus complexes.Le but de cette étude est d'étudier l'évaporation des gouttelettes, les caractéristiques de la flamme et les changements sur la morphologie de la flamme pour les flammes laminaires en présence de gouttelettes via des approches expérimentales et numériques. La partie expérimentale de l'étude est menée au CNRS ICARE, y compris des expériences de microgravité pour étudier les instabilités de flamme en présence de gouttelettes d'éthanol isolées pour une flamme éthanol/air à expansion sphérique à l'aide de la méthode Schlieren et des expériences au sol pour étudier les caractéristiques d'évaporation d'une gouttelette d'éthanol traversant une flamme stabilisée contre une plaque. Les modifications induites par le passage de la goutte dans la flamme sont détaillées à l'aide de différents diagnostics optiques tels que PIV, PTV, ILIDS et Chimiluminescence.Dans la partie numérique de l'étude, le solveur YALES2 est utilisé pour simuler l'évaporation des gouttelettes dans différentes conditions ambiantes à des températures élevées via une approche Eulérienne-Lagrangienne. Dans ce cadre, l'évaporation des gouttelettes stationnaires est calculée aux compositions de gaz brûlés via le modèle de Spalding, ainsi que l'évaporation d'une gouttelette en mouvement à travers un champ de flamme de stagnation via le modèle d'Abramzon-Sirignano. Enfin, des simulations non réactives et réactives sont réalisées avec une géométrie de brûleur à stagnation réelle

Vaporization characteristics of an isolated ethanol droplet at flame conditions

International audienceThe aim of this study is to investigate single ethanol droplet evaporation characteristics under premixed CH4/air flame conditions via experimental and numerical approaches. In the experimental part of the study, ethanol droplet with an initial diameter between 20 and 70 µm was injected through a flat laminar stagnant flame. Visualization of the flame front and temporal monitoring of the droplet evaporation at high temperatures up to 2200 K were performed using planar laser tomography. Droplet motion and its diameter change are captured simultaneously via PIV/PTV and ILIDS diagnostics, respectively. Velocity measurements indicated that the droplets are small enough to be carried by surrounding gas with a very small slip velocity. Variation in droplet diameter is successfully tracked through the flame via ILIDS and it is found to be more drastic in burnt gases. Hence, vaporization rates are reported at burnt gas temperature which is affected by the heat losses from flame to the stagnation plate due to the change in the temperature profile. In the numerical part of the study, single droplet evaporation under constant temperature and stagnant environment was studied with Spalding model using YALES2 solver. The variations of the droplet properties were computed under N2 atmosphere and under flame conditions. At elevated conditions, flame temperature is found to have a more dominant effect on the evaporation rate rather than the burnt gas composition

How Does Pregnancy and Type of Delivery Affect the Clinical Course of Hereditary Angioedema?

Introduction: Knowledge on the clinical course of hereditary angioedema (HAE) during pregnancy, delivery, and breastfeeding is very limited. In this study, we aimed to evaluate the course of HAE during these periods. Methods: The HAE attacks C1-INH prophylaxis before and during pregnancy and during breastfeeding, and the delivery types were retrospectively determined. The severity of attacks was assessed by a 10-point Visual Analogue Scale (VAS). Results: We evaluated 88 pregnancies in 48 HAE patients among whom 20 were primiparous. Among those who had a HAE diagnosis during pregnancy (n = 34), the median attack numbers before pregnancy, during pregnancy, breastfeeding, and after breastfeeding were 17, 39, 24, and 14 (before pregnancy vs. pregnancy, p < 0.001; during pregnancy vs. breastfeeding, p = 0.001). The mean VASs (SD) were 6.59 (1.82), 8.33 (1.58), 7.32 (1.66), and 6.95 (1.90) (before pregnancy vs. pregnancy, p < 0.001; during pregnancy vs. breastfeeding, p = 0.016), respectively. Among those who received a HAE diagnosis after pregnancy (n = 54), the number (59.3%) and the severity (60%) of HAE attacks were high in pregnancy. 47 of the deliveries were normal vaginal delivery (NVD). Regional anesthesia was applied in 8 NVDs. 20 of caesarean deliveries were performed under general anesthesia, and 21 were under spinal anesthesia. Lowest numbers of attacks were found in patients who did not receive anesthesia during NVD (p = 0.001). Conclusion: The course of HAE can be worse during pregnancy and breastfeeding. NVD is related to fewer HAE attacks and prophylaxis with C1-INH during NVD is not necessary to prevent a HAE attack

Atopy and Allergic Diseases Have No Impact on the Severity of COVID-19

Objective: The clinical features of COVID-19 range from asymptomatic disease to severe pneumonia or even death. Therefore, many researchers have investigated the factors that could affect the severity of COVID-19. We aimed to assess the impact of aero-allergen sensitization and allergic diseases on the severity of COVID-19