Research into Multi-scale Examination of MultiPHase physIcs in flowS (MEMPHIS)


Velocity field after coalescence of water droplet on an oil-water interface

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Domain decomposition over 163 = 4096 subdomains


Droplet dynamics in stratifying horizontal gas-liquid flow

1 Mar 2017

Many industrial products, i.e. milk, paint and shampoo, are emulsion-based systems and require drops of a preferred size. Microfluidic devices, such as flow-focusing channels, can provide narrow drop size distributions. In many cases surfactants are used to stabilise the emulsions, which  add complexity to the drop formation process. At UCL we investigate the hydrodynamic characteristics and velocity profiles of aqueous drops in a flow-focusing device with and without surfactants present. This study is part of a collaborative work with the University of Birmingham, within the MEMPHIS framework. Silicone oil (μ = 0.0046 Pa s, Sigma-Aldrich) was used as a continuous  [ Read More ]

27 Feb 2017

The animation below shows the interfacial wave structure in circumferential direction of a falling liquid (water) film using Multi-Pin Film Sensor (for more details on experimental setup, see my previous post on the following link):   This animation was taken at liquid Reynolds number, ReL=1670. The inner diameter of the test section is 127 mm. Unlike small diameter pipes where the waves are characterised as coherent rings, the waves found in this study with large diameter pipe are more localized.   [click on the image]    

24 Feb 2017

Microfluidics enables formation of emulsions and foams with drops/bubbles of a submillimetre size and a narrow size distribution. Surfactants are usually used in emulsification/foaming processes to protect drops/bubbles against coalescence through creating protective adsorption layers on the phase interfaces. However, a recent study performed at the University of Birmingham has shown that a protective surfactant layer does not always work when drops are moving in the confined geometry of microchannel. Frequent coalescence events were in particular observed in the channels with their height smaller than their width for surfactant-laden drops larger than the channel height. An example of such coalescence is  [ Read More ]

31 Jan 2017

  The Figure above shows a three-dimensional direct numerical simulation of an annular falling film reactor in a situation of a clean interface (left), insoluble (center) and soluble (right) surfactant. We adapt and extend a formulation for soluble surfactant transport in multiphase flows recently presented by Muradoglu & Tryggvason (JCP 274 (2014) 737-757) to the context of the Level Contour Reconstruction Method (Shin et al. IJNMF 60 (2009) 753-778) which is a hybrid method that combines the advantages of the Front Tracking and Level Set methods. Particularly close attention was paid to the formulation and numerical implementation of the surface  [ Read More ]

31 Jan 2017

Paper ‘On the effect of surfactants on drop coalescence at liquid/liquid interfaces‘ has been published in Chemical Engineering Science. Weheliye Hashi Weheliye, Teng Dong, Panagiota Angeli   Abstract In this work the effect of surfactants on the coalescence of a drop with a flat aqueous-organic interface was experimentally investigated. A high speed Particle Image Velocimetry (PIV) system was used to obtain velocity profiles and kinetic energy per unit mass distribution inside the coalescing droplets. Different mass ratios of surfactant to oil below the CMC value, up to ϕ   = 5 × 10−4, of a non-ionic surfactant dissolved in the organic phase were studied.  [ Read More ]

21 Dec 2016

  1.   Purpose and motivation: A very little information is known about the behaviour of high viscous liquids (>100 Pa.s) in two phase slug flows. The main aim of this experiment is to study the characteristics and parameters of gas-liquid slug flows with a very viscous oil  in a large diameter column. Experiments were carried out at the University of Nottingham to study the behaviour of air passing through silicone oil (360 Pa.s) in 240 mm diameter column using Electrical Capacitance Tomography, ECT. Parameters such as; void fraction; frequency of periodic structures; Taylor bubble velocity; lengths of Taylor bubbles and  [ Read More ]

9 Dec 2016

Results of collaborative work between University of Birmingham (experimental study) and Imperial College London (numerical simulations) were presented in three talks at 69th Annual Meeting of the American Physical Society Division of Fluid Dynemics 1. Experimental and numerical study of a complex cross-junction microchannel by Emilia Nowak, Mark Simmons,  Lyes Kahouadji, Richard Craster, Omar Matar, Damir Juric, Jalel Chergui, Seungwon Shin  Abstract Microuidic devices occur in various fields such as inkjet printing, DNA chips, lab-on-a-chip technology, micro-propulsion and droplet-based microuidics. Here, we examine drop and plug formation of immiscible liquids in a cross-shaped microchannel via high-speed imaging, shadowgraphy and PIV  [ Read More ]

30 Nov 2016

Paper on ‘Flow Pattern Transition in Liquid-Liquid Flows with A Transverse Cylinder’ has been accepted for publication in International Journal of Multiphase Flow. Flow pattern transition in liquid-liquid flows with a transverse cylinder Maxime Chinaud, Kyeong Hyeon Park, Panagiota Angeli Abstract The effect of a cylindrical bluff body on the interface characteristics of stratified two-phase, oil-water, pipe flows is experimentally investigated with high speed Particle Image Velocimetry (PIV). The motivation was to study the feasibility of flow pattern map actuation by using a transverse cylinder immersed in water in the stratified pattern, and particularly the transition from separated to dispersed  [ Read More ]

29 Nov 2016
18 Nov 2016

 A series of liquid falling film experiments in 127 mm diameter, 3.5 long pipe was conducted to study the interfacial structure of the falling film using Multi-Pin Film Sensor (MPFS) which is capable of providing film thickness data with high temporal and spatial distribution in axial and circumferential directions. Figure 1 shows a photo of MPFS with arrays of electrodes (64 electrodes in circumferential direction and 10 axial planes).                                                                    (a)                                                                    (b) Figure 1: Multi-Pin Film Sensor (MPFS), (a) top view, (b) from inside   The liquid falling film rig is fairly straightforward in which the liquid is  [ Read More ]


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