Novel design of triangular delta winglet pair for heat transfer enhancement

International audienc

Heat transfer enhancement of inclined projected winglet pair vortex generators with protrusions

Heat transfer enhancement in parallel plate-fin heat exchanger is examined by performing three-dimensional numerical simulations of longitudinal vortex generators (VG) with protrusions. The turbulence is modeled using the shear-stress transport (SST) κ-ω model and validated with correlations and experimental data at Reynolds number equal to 4600. Hemi-spherical protrusions are inserted downstream two VG configurations: delta winglet type (DWP) and a new VG configuration named inclined projected winglet pair (IPWP), in various locations, leading to the definition of six different configurations. Based on the streamwise distribution of Nusselt number and friction coefficient criteria in addition to vorticity, the local performance is analyzed. Some VGs with protrusions are examined and show better performance relative to VGs standing alone. The present study highlights the different mechanisms involved in the convective heat transfer intensification by generating multiple interacting vortices while adding protrusions with low pressure drop penalty. Finally, it is found that the IPWP with protrusions, set downstream in the middle, bestows the best global performance with about 7.1% heat transfer enhancement compared to DWP configuration

Novel design of delta winglet pair vortex generator for heat transfer enhancement

Heat transfer is a naturally occurring phenomenon that can be greatly enhanced with the aid of vortex generators (VG). Three-dimensional numerical simulations of longitudinal vortex generators are performed to analyze heat transfer enhancement in parallel plate-fin heat exchanger. The shear-stress transport (SST) κ-ω model is adopted to model the flow turbulence. Empirical correlations from the open literature are used to validate empty channel simulations. First, numerical simulations are conducted for the classical delta winglet pair (DWP) which is introduced as the reference case in this study. Then, an innovative VG configuration, named inclined projected winglet pair (IPWP), is examined and it shows superior performance relative to the DWP. The IPWP exhibits similar heat transfer rates than that of the DWP but with lower pressure drop penalty due to its special aerodynamic design. The local performance is analyzed based on the streamwise distribution of Nusselt number and friction coefficient criteria in addition to vorticity. This study highlights the different mechanisms involved in the convective heat transfer intensification by generating more vortices using more aerodynamic VG shape while decreasing the pressure drop penalty

Intensification des transferts par génération de vorticité

International audienc

Access-Site Complications in Transfemoral Neuroendovascular Procedures: A Systematic Review of Incidence Rates and Management Strategies

BACKGROUND: The femoral artery is the most common access route for cerebral angiography and neurointerventional procedures. Complications of the transfemoral approach include groin hemorrhages and hematomas, retroperitoneal hematomas, pseudoaneurysms, arteriovenous fistulas, peripheral artery occlusions, femoral nerve injuries, and access-site infections. Incidence rates vary among different randomized and nonrandomized trials, and the literature lacks a comprehensive review of this subject. OBJECTIVE: To gather data from 16 randomized clinical trials (RCT) and 17 nonrandomized cohort studies regarding femoral access-site complications for a review paper. We also briefly discuss management strategies for these complications based on the most recent literature. METHODS: A PubMed indexed search for all neuroendovascular clinical trials, retrospective studies, and prospective studies that reported femoral artery access-site complications in neurointerventional procedures. RESULTS: The overall access-site complication rate in RCTs is 5.13%, while in in non-RCTs, the rate is 2.78%. The most common complication in both groups is groin hematoma followed by access-site hemorrhage and femoral pseudoaneurysm. On the other hand, wound infection was the least common complication. CONCLUSION: The transfemoral approach in neuroendovascular procedures holds risk for several complications. This review will allow further studies to compare access-site complications between the transfemoral approach and other alternative access sites, mainly the transradial approach, which is gaining a lot of interest nowadays

Cancer immunotherapy: A comprehensive appraisal of its modes of application.

peer reviewedConventional cancer treatments such as chemotherapy and radiation therapy have reached their therapeutic potential, leaving a gap for developing more effective cancer therapeutics. Cancer cells evade the immune system using various mechanisms of immune tolerance, underlying the potential impact of immunotherapy in the treatment of cancer. Immunotherapy includes several approaches such as activating the immune system in a cytokine-dependent manner, manipulating the feedback mechanisms involved in the immune response, enhancing the immune response via lymphocyte expansion and using cancer vaccines to elicit long-lasting, robust responses. These techniques can be used as monotherapies or combination therapies. The present review describes the immune-based mechanisms involved in tumor cell proliferation and maintenance and the rationale underlying various treatment methods. In addition, the present review provides insight into the potential of immunotherapy used alone or in combination with various types of therapeutics

Letter: Thrombotic Neurovascular Disease in COVID-19 Patients.

Although the respiratory system is the primary target of the coronavirus, studies have demonstrated a strong tropism to the central nervous system (CNS).1,2 The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infects cells by binding to the angiotensin-converting enzyme 2 (ACE2) receptor. This receptor is also found in the CNS and plays a crucial role in autoregulating cerebral perfusion pressure.3,4 Additionally, epidemiological data demonstrated increased mortality due to cardiovascular and cerebrovascular diseases during flu pandemics due to a hypercoagulable state.5,6 The triad of neuroinvasion of SARS-CoV-2, induction of hypercoagulable state,5-9 and the inhibition of ACE2 blocking the formation of Angiotensin (1-7) serve as the pathophysiology for neurovascular insults.3,4 We present a case series of coronavirus disease 2019 (COVID-19) patients from 2 health systems developing cerebrovascular insult

Transradial approach for diagnostic cerebral angiograms in the elderly: a comparative observational study

Introduction: The transradial approach (TRA) reduces mortality, morbidity, access site complications, hospital cost, and length of stay while maximizing patient satisfaction. We aimed to assess the technical success and safety of TRA for elderly patients (aged ≥75 years). Methods: A retrospective chart review and comparative analysis was performed for elderly patients undergoing a diagnostic cerebral angiogram performed via TRA versus transfemoral approach (TFA). Also, a second comparative analysis was performed among the TRA cohort between elderly patients and their younger counterparts. Results: Comparative analysis in the elderly (TRA vs TFA) showed no significant differences for contrast dose per vessel, fluoroscopy time per vessel, procedure duration, conversion rate, and access site complications. Radiation exposure per vessel was significantly lower in the elderly TRA group. The second comparison (TRA in elderly vs TRA in the young) showed no significant differences for contrast dose per vessel, radiation exposure per vessel, procedure duration, access site complication, and conversation rate. A trend for prolonged fluoroscopy time per vessel was observed in the elderly TRA group. Conclusion/Discussion: TRA is a technically feasible and safe option for diagnostic neurointerventional procedures in the elderly. Our small elderly cohort was not powered enough to show a significant difference in terms of access site complications between TRA and TFA

Analyse des mécanismes d’intensification des transferts de chaleur dans un canal rectangulaire avec des tourbillons longitudinaux

Ce travail de thèse repose sur la conception et l’étude d’un nouveau générateur de vorticité (VG) permettant d’améliorer le transfert de chaleur dans des échangeurs de chaleur à plaques et ailettes. Un examen détaillé des techniques d'amélioration du transfert de chaleur est présenté, elles se divisent en trois catégories : les techniques passive, active et combinées. Les techniques passives sont plus couramment utilisées dans les échangeurs de chaleur car elles sont caractérisées par une meilleure efficacité, économie, facilité de fabrication et faible maintenance. Parmi les techniques passives, les générateurs de vorticité créent des écoulements secondaires, cassent la croissance de la couche limite et créent des écoulements tourbillonnants qui améliorent l'échange entre les parois et le fluide, intensifiant ainsi le transfert de chaleur. Cette étude basée sur l’analyse des mécanismes d’intensification, a permis de mettre en évidence une nouvelle conception de configuration pour des générateurs de tourbillons longitudinaux avec pour résultats une diminution des pertes de charges principalement causées par le générateur de vorticité et le maintien de tourbillons multi-échelles intenses qui améliorent les performances de transfert de chaleur et de mélange.The objective of this PhD thesis is to investigate and design a new vortex generator (VG) for enhancing heat transfer in parallel plate-fin heat exchangers. Detailed overview about heat transfer enhancement techniques was presented in a literature review, which are divided into three categories: passive, active and compound techniques. Passive techniques are more commonly used in heat exchangers since they are characterized by their efficiency, economy, ease of manufacturing and lower maintenance efforts. Vortex generators are one of the passive techniques that create secondary flows, disrupt the growth of the boundary layer and create swirling flows that enhance exchange between the walls and the core fluid, thus improving heat transfer. Finally, based on the analysis of the thermal enhancement mechanisms, a novel configuration for longitudinal vortex generators in common flow up was identified. It relies on decreasing the pressure drop across the channel mainly caused by the vortex generators while maintaining high intensity of multiscaled vortices that enhance the heat transfer and mixing performances