Experimental and numerical investigation of droplet formation and material interactions under different conditions

Abstract

This work focused on developing a framework of numerical models for simulating the formation of droplet under different situations. The formation of a pendant droplet was studied through an integrated experimental, numerical and theoretical procedures, establishing the key factors influencing the dynamics of a pendant droplet and examining key material parameters such as the density, viscosity, wetting coefficient and surface tension. A numerical model was developed using the volume of fluid (VOF) solver in ANSYS FLUENT and validated using qualitative and quantitative approaches (e.g. droplet shape, length, volume, separation time). The numerical data was correlated with an analytical solution based on pressure and velocity data from a mathematical approach and experimental; works on model materials with different properties. The program has been used to establish a range of models relevant to industrial processes, including droplet for semifluid material systems, formation of satellite droplets, merging of droplets from two inlets at an angle, multiphase liquid in micro channels and generating droplets smaller than the nozzles diameter through using a code to control the flowrate and cycles. The data from the numerical models is also coded into Matlab to automatically plot the contour and calculate the volume of the droplet. Some cases in the modelling of merging of liquid in welding of thin tubes, effect of contact angles on liquid dripping and use of numerical modelling in microchannel design, are also evaluated and key results are presented. The interaction between liquid droplet with a homogenous material and a matrix with an embedded thin stiffer layer is studied in comparison to a similar loading situation with rigid indenters of different shapes. A particular focus has been on the effect of material properties (Negative Possion’s ratio and layer depth) on the enhancement of the indentation resistance and material deformation. The FE results are correlated with an analytical solution for homogenous materials and results from a mathematical approach for embedded systems in an elastic half-space. The influence of auxeticity (i.e. negative Poisson’s ratio) on the indentation stiffness ratio between systems with an inserted layer against a homogenous matrix (no reinforcement) is established. The deformation of the embedded system under different conditions (indenter size, thickness and embedment depth of the embedded layer) is presented and key mechanisms of the Poisson’s ratio effect are highlighted