On the modeling of viscoelastic droplet impact dynamics

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.In this paper, a numerical modeling of the impact, spreading, and eventually rebound of a viscoelastic droplet is reported. The numerical model is based on the volume of fluid (VOF) method coupled with the FENE-CR constitutive equations, and accounts for both the surface tension and the substrate wettability. The FENE-CR constitutive equations are used to model the polymer solution, while taking advantage of its rheological characterization. The comparison is performed between droplets of Newtonian solvent and a monodisperse polymer solution. The droplet impact on both hydrophilic and superhydrophobic substrate is analyzed through a detailed analysis of the spreading diameter evolution. It is found that while the droplet kinematic phase seems independent of the substrate and fluids properties, the recoiling phase is highly related to all of them. In addition the model infers a critical polymer concentration above which the droplet rebound from a superhydrophobic substrate is suppressed. The simulation is of particular interest to ink-jet processing, and demonstrates the capability of the model to handle complex non-Newtonian droplet dynamics

The matching of polymer solution fast filament stretching, relaxation, and break up experimental results with 1D and 2D numerical viscoelastic simulation

this work was supported by EPSRC grant number RG5560

Prediction and evolution of drop-size distribution of an ultrasonic vibrating microchannel

This paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.We report in this paper the evolution of a physically-based drop size-distribution coupling the Maximum Entropy Formalism and the Monte Carlo method to solve the distribution equation of a spray. The atomization is performed by a new Spray On Demand (SOD) device which exploits ultrasonic generation via a Faraday instability. The Modified Hamilton’s principle is used to describe the fluid structure/interaction with a vibrating micro-channel conveying fluid excited by a pointwise piezoactuator. We combine to the fluid/structure description a physically based approach for predicting the drop-size distribution within the framework of the Maximum Entropy Formalism (MEF) using conservation laws of energy and mass coupling with the three-parameter generalized Gamma distribution. The prediction and experimental validation of the drop size distribution of a new Spray On Demand print-head is performed. The dynamic model is shown to be sensitive to operating conditions, design parameter and physico-chemical properties of the fluid and its prediction capability is good. We also report on a model allowing the evolution of drop sizedistribution. Deriving the discrete and continuous population balance equation, the Mass Flow Algorithm is formulated taking into account interactions between droplets via coalescence. After proposing a kernel for coalescence, we solve the time dependent drop size distribution using a Monte Carlo Method which is shown to be convergent. The drops size distribution upon time shows the effect of spray droplets coalescence

Binary-mixture droplet evaporation: Lubrication approximation and coffee ring formation

This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.In this paper the dynamics of an evaporating sessile droplet spreading on a horizontal substrate is reported. A mathematical model based on the lubrication approximation is developed accounting for Marangoni effect, contact line motion, and multi-component fluid. After validating the model through pure liquid spreading and evaporation, an extension of the model is performed on a binary component liquid in which composition changes occur during the drying process. Furthermore, the presence of particles in the fluid enables to retrieve the coffee-ring formation. A good qualitative and quantitative agreement between the model and experimental observations is found.This study is funded from ANR PAN’H 2008 CATIMINHY project

Granulome inguinal inflammatoire sur hydrocèle bilatérale : une association inhabituelle

Le granulome inguinal ou encore appelé donovanose, désigne une maladie provoquée par la bactérie Klebsiella Granulomatis. Il se manifeste par des ulcères indolores au niveau de l'appareil génital. Nous rapportons un cas clinique qui illustre une présentation clinique atypique de la forme des granulomes inguinaux inflammatoires sur hydrocèle bilatérale chez le même patient. Le patient a bénéficié d’une exérèse de lymphœdème plus la cure bilatérale de l’hydrocèle

The observation and evaluation of extensional filament deformation and breakup profiles for Non Newtonian fluids using a high strain rate double piston apparatus

This paper reports a new design of experimental double piston filament stretching apparatus that can stretch fluids to very high extensional strain rates. Using high speed photography, filament deformation and breakup profiles of a strategically selected range of fluids including low and higher viscosity Newtonian liquids together with a viscoelastic polymer solution, biological and yield stress fluids were tested for the first time at extensional strain rates in excess of 1000 s−1. The stretching rate was sufficiently high that observation of low viscosity Newtonian fluid stretching, end pinching and break was observed during the stretching period of the deformation, whereas for a higher Newtonian viscosity, filament thinning and breakup occurred after the cessation of piston movement. Different fluid rheologies resulted in very different thinning and breakup profiles and the kinetics, in particular of yield stress fluids showed a striking contrast to Newtonians or viscoelastic fluids. Surprisingly all the tested fluids had an initial sub millisecond “wine glass” profile of deformation which could be approximately captured using a simple parabolic mass balance equation. Subsequent deformation profiles were however very sensitive to the rheology of the test fluid and where the final breakup occurred before or after piston cessation. In certain cases the thinning and break up was successfully matched with a 1D numerical simulation demonstrating the way numerical modelling can be used with the fluids correct rheological characterization to gain physical insight into how rheologically complex fluids deform and breakup at very high extensional deformation rates.</p

The matching of polymer solution fast filament stretching, relaxation, and break up experimental results with 1D and 2D numerical viscoelastic simulation

this work was supported by EPSRC grant number RG5560