Imperial College London

Dr Victor Voulgaropoulos

Faculty of EngineeringDepartment of Chemical Engineering

Research Associate







ACE ExtensionSouth Kensington Campus





Experimental and numerical studies on the flow characteristics and separation properties of dispersed liquid-liquid flows

Physics of Fluids 31: 073304 (2019)

The local dynamics of spatially developing liquid-liquid dispersed flows are investigated. Detailed measurements with laser-based diagnostic tools are conducted at two axial pipe locations.The variations in drop concentration over the pipe cross-section along the pipe result in local changes of the physical properties of the mixture and consequently in asymmetrical velocity profiles, with the maxima of the velocity located in the drop-free region. Computational fluid dynamics simulations based on a mixture approach predict the experimental results close to the experimental uncertainties for the majority of the cases. It is found that the drops behave as suspensions of rigid spheres for the conditions investigated, despite the deformation effects, which are found experimentally to be stronger at the densely packed region.

computational fluid dynamics, emulsions, flow development, laser diagnostics, Poiseuille flow

POF 2019 - Flow Development

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Structured planar laser-induced fluorescence (S-PLIF) for the accurate identification of interfaces in multiphase flows

International Journal of Multiphase Flow 118: 193 (2019)

We present a novel adaptation of PLIF, which we refer to as structured PLIF (S-PLIF), which can suppress the errors in PLIF-derived film thickness measurements that arise due to total internal reflection (TIR) of the emitted fluorescence at the phase boundary of annular flows. The proposed measurement approach relies on the periodic modulation of the laser-light intensity and angled illumination of the examined region of the flow.

annular flow, interface identification, laser-induced fluorescence, thin films, wavesIJMF - Structured PLIFRead the paper

On the link between experimentally‐measured turbulence quantities and polymer‐induced drag reduction in pipe flows

AIChE Journal 65: 16662 (2019)

We investigate the hydrodynamics of polymer‐induced drag reduction in horizontal turbulent pipe flows, providing spatiotemporally resolved information of velocity and its gradients obtained with particle image velocimetry (PIV) measurements in solutions of water with dissolved polyethylene oxide (PEO). We find that the local magnitudes of important turbulent flow variables correlate with the measured levels of drag reduction irrespective of the flow Reynolds number, polymer weight and concentration. A relationship between the drag reduction and the turbulent flow variables is found.

drag reduction, laser diagnostics, particle image velocimetry, polymers, turbulent flows

AIChE J - Joint probability distributions

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Thermal Energy Processes in Direct Steam generation Solar Systems: Boiling, Condensation and Energy Storage (REVIEW)

Frontiers Energy Research 6: 147 (2019)

Direct steam generation is a promising solar-energy technology, which can reduce the growing dependency on fossil fuels. Of interest are the flow regimes, heat transfer coefficients and pressure drops that are experienced during the thermal processes present in direct steam generation systems. A brief overview of some energy storage options are also presented to motivate the inclusion of thermal energy storage into direct steam generation systems.

concentrated solar power, direct steam generation, energy storage, flow boiling, flow condensation

RS DFID Review

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Laser diagnostic tools in concentrated emulsions

Experiments in Fluids 58: 170 (2017)

Optical laser-based techniques and an extensive data analysis methodology have been developed to acquire flow  and  separation  characteristics  of  concentrated  liquid–liquid dispersed flows.

dispersed flows, drop size distribution, particle image/tracking velocimetry, planar laser-induced fluorescence, separationPLIF PTV PIV

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Coalescence of surfactant-laden drops

Physical Review E 94: 033101 (2016)

The effect of surfactants on the coalescence of an aqueous drop with a flat aqueous-organic interface was investigated in a Hele-Shaw cell

coalescence, Hele-Shaw cell, interfacial characteristics, particle image velocimetry, surfactants

Streamlines of a coalescing drop

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See the featuring on the Kaleidoscope Sep 2016 issue

bubble columns with complex fluids

Chemical Engineering Research and Design 95: 93 (2015)

Investigate how the addition of an organic surface active agent affects the characteristics of a bubble column equipped with a porous sparger and containing a non-Newtonian liquid.

bubble column, complex fluids, flow regimes, shear-thinning, surfactants

Clustering in bubble column

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show research

Augmented Boiling with nano-engineered surfaces and Eco-friendly Refrigerants (AmBER)

MIT International Science and Technology Initiatives (MISTI) Global Seed Funds

Department of Nuclear Science and Engineering, Massachusetts Institute of Technology

Clean Energy Processes (CEP) Laboratory, Department of Chemical Engineering, Imperial College London

Department of Mechanical and Aeronautical Engineering, University of Pretoria

Boiling of fluids, such as refrigerants or water, is a very effective way to transfer heat and is therefore employed in a wide range of applications. Our scope is to improve the understanding of this important process with the ultimate aim of enhancing the boiling performance of novel refrigerants. This is a necessary pathway for unlocking the efficient use and integration of next-generation, eco-friendly fluids in renewable heating, cooling and power systems. We are particularly interested in concentrated solar-power systems and fully-passive thermally-powered cooling systems that rely on the use of low global-warming potential refrigerants. To achieve this goal, we will perform world-first experimental studies in large-scale facilities using advanced laser-based and infrared diagnostic tools as well as nano-engineering techniques to modify the properties of solid surfaces. The research could also have potential impact on water-based applications such as steam generation, steam power-plant systems and solar cooking.

Multiscale Investigation of Nucleate-boiling and Interfaces (MINI)

Dame Julia Higgins Engineering Postdoc Collaborative Research Fund

Mirco Magnini, Department of Chemical Engineering, Imperial College London

Edward R Smith, Department of Mechanical Engineering, Imperial College London,

Victor Voulgaropoulos, Department of Chemical Engineering, Imperial College London

The objective of MINI is to integrate MD and CFD simulations with targeted experiments to perform a synergistic multiscale analysis of boiling. It will enhance fundamental knowledge and provide design guidelines for green heat exchangers. We aim to combine the aforementioned three approaches to answer fundamental questions: How does a bubble form? Can its molecular description be upscaled to practical bubble sizes (~1 mm)? Are the continuum-scale assumptions used to model phase change consistent with their molecular-level description? These insights will enable cooling devices based on newer eco-friendly refrigerants to achieve the same heat transfer capabilities of traditional polluting fluids.MINI

Coupled molecular and continuum simulation of nucleation and bubble rising by Edward R Smith