Instability in pressure-driven displacement flow of one fLuid by another in a pipe

The pressure-driven displacement ow of one fluid by another has been widely studied in literature due to its relevance in many natural phenomena and industrial applications, such as pumping of crude oil, in food processing industry, in enhanced oil recovery, to name a few. The present thesis consists of two parts. In the first part, pressure-driven displacement ow of a less viscous fluid initially occupying an axisymmetric pipe by a highly viscous fluid is investigated by conducting numerical simulations. The fluids consist of two species di using at different rates. The fluids are assumed to be Newtonian, incompressible with the same density, but different viscosity modelled as an exponential function of the concentration of both the species. A parametric study investigating the effects of diffusivity ratio, log-mobility ratios of the slower and faster di using species and Reynolds number on the flow dynamics is conducted

A Numerical Investigation of Dimensionless Numbers Characterizing Meltpool Morphology of the Laser Powder Bed Fusion Process

Microstructure evolution in metal additive manufacturing (AM) is a complex multi-physics and multi-scale problem. Understanding the impact of AM process conditions on the microstructure evolution and the resulting mechanical properties of the printed component remains an active area of research. At the meltpool scale, the thermo-fluidic governing equations have been extensively modeled in the literature to understand the meltpool conditions and the thermal gradients in its vicinity. In many phenomena governed by partial differential equations, dimensional analysis and identification of important dimensionless numbers can provide significant insights into the process dynamics. In this context, we present a novel strategy using dimensional analysis and the linear least-squares regression method to numerically investigate the thermo-fluidic governing equations of the Laser Powder Bed Fusion AM process. First, the governing equations are solved using the Finite Element Method, and the model predictions are validated by comparing with experimentally estimated cooling rates, and with numerical results from the literature. Then, through dimensional analysis, an important dimensionless quantity interpreted as a measure of heat absorbed by the powdered material and the meltpool, is identified. This dimensionless measure of absorbed heat, along with classical dimensionless quantities such as Péclet, Marangoni, and Stefan numbers, are employed to investigate advective transport in the meltpool for different alloys. Further, the framework is used to study variations in the thermal gradients and the solidification cooling rate. Important correlations linking meltpool morphology and microstructure-evolution-related variables with classical dimensionless numbers are the key contribution of this work

Formation and Breakup of an Immiscible Compound Jet with Density or Viscosity Stratification

Formation of compound drops by breakup of an axisymmetric compound jet injected from a coaxial nozzle into another immiscible coflowing fluid, at various density and viscosity ratios, is numerically investigated. The fluids are assumed to be Newtonian and incompressible and gravity is neglected for simplicity. A Finite Difference Method with Front Tracking is used to track the evolution and breakup of the compound jet. The outcomes of our numerical results show how density and viscosity ratios affect the compound jet’s transition from dripping to jetting mode. The density ratios of inner-to-outer and intermediate-to-outer fluids affect compound jet breakup length, drop diameter and drop formation time more than comparable viscosity ratios. At high density and viscosity ratios, due to high inertia and viscous force respectively, the drop formation is more chaotic and mostly multi-core drops are formed

Ocular complications of herpes zoster ophthaimicus and post herpetic neuralgia A clinical study

Background: Herpes Zoster Ophthalmicus (HZO) affects the eye and adenexa and is often associated with severe ocular morbidity and neuralgic pain. It primarily affects the elderly and immunosuppressed people. Atypical clinical manifestations are more likely to occur in HIV positive patients than in immunocompetent individuals. Post herpetic neuralgia (PHN) forms one of the most chronic and distressing non-ocular complication of HZO. Objectives: To determine the spectrum of ocular complications, factors influencing visual prognosis, the effect of HIV-AIDS on the spectrum of ocular complications and the spectrum of post herpetic neuralgia in patients with Herpes Zoster OphthaImicus. Materials and Methods: In this prospective interventional study, all patients who presented to the Department of Ophthalmology branch within 3 weeks of the onset of active zoster-vesicle formation affecting the ophthalmic of the trigeminal nerve were included. Patients with post herpetic neuralgia were referred to the Department of Neuropsychiatry. Patients with pre-existing ocular disorders were excluded from the study. Results: The most common predisposing condition seen in this study was HIV infection, w h i c h w a s s e e n i n 4 4 . 2 % ( 1 9 / 43) of the patients. A peak incidence was seen in the age group, between 21-60 years. A positive Hutchinson's sign correlated significantly with the ocular manifestations of decreased corneal sensation, acute corneal lesions and uveitis. Corneal involvement was seen in 95.3% (41/ 43). Uveitis was seen in 44.2% (19/43) of the patients. The visual outcome in most of the patients was good with maximum patients having no visual loss. Acute herpetic pain was seen in 97.7% (42/43) patients. Postherpetic neuralgia was seen in 41.9% (18/43) patients. About 53% of the patients had no visual loss at 6 months follow-up, while 27.9% had mild-moderate visual loss and only 13.9% had severe visual loss There were only 6 patients who had severe visual loss. Conclusion: HZO is more frequently presenting at a younger age, due to an increasing incidence of HIV AIDS. Patients wi t h n a s o c i l i a r y a n d l a c r i m a l n e r v e involvement and the presence of Hutchison's sign are more likely to have serious ocular complications. Visual loss is more likely in this group, warranting close follow-up and prompt treatment. The spectrum of ocular complications in immunosuppressed did not significantly differ from the immunocompetent patients. The overall good outcome in this study is due to the u se of early intensive antiviral therapy

EUS-guided drainage of pancreatic fluid collections using lumen apposing metal stents: An international, multicenter experience.

INTRODUCTION: Lumen apposing metal stents (LAMS) have been used increasingly for drainage of pancreatic fluid collections (PFC). We present an international, multicenter study evaluating the safety and efficacy of LAMS in PFCs. METHODS: Consecutive patients undergoing LAMS placement for PFC at 12 international centers were included (ClinicalTrials.gov NCT01522573). Demographics, clinical history, and procedural details were recorded. Technical success was defined as successful LAMS deployment. Clinical success was defined as PFC resolution at three-month follow-up. RESULTS: 192 patients were included (140 males (72.9%), mean-age 53.8 years), with mean follow-up of 4.2 months ± 3.8. Mean PFC size was 11.9 cm (range 2-25). The median number of endoscopic interventions was 2 (range 1-14). Etiologies for PFC were gallstone (n = 82, 42.7%), alcohol (n = 50, 26%), idiopathic (n = 26, 13.5%), and other (n = 34, 17.7%). Technical success was achieved in 189 patients (98.4%). Clinical success was observed in 125 of 135 patients (92.6%). Adverse events included bleeding (n = 11, 5.7), infection (n = 2, 1%), and perforation (n = 2, 1%). Three or more endoscopy sessions were a positive predictor for PFC resolution and the only significant predictor for AEs. CONCLUSION: LAMS has a high technical and clinical success rate with a low rate of AEs. PFC drainage via LAMS provides a minimally invasive, safe, and efficacious procedure for PFC resolution