Imperial College London

Emeritus ProfessorGeoffreyHewitt

Faculty of EngineeringDepartment of Chemical Engineering

Emeritus Professor
 
 
 
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Contact

 

+44 (0)20 7594 5562g.hewitt

 
 
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Assistant

 

Mrs Sarah Payne +44 (0)20 7594 5567

 
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Location

 

507aACE ExtensionSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

224 results found

Valluri P, Spelt PDM, Lawrence CJ, Hewitt GFet al., 2008, Numerical simulation of the onset of slug initiation in laminar horizontal channel flow, International Journal of Multiphase Flow, Vol: 34, Pages: 206-225

Results are presented for the initiation of slug-type structures from stratified 2D, two-layer pressure-driven channel flow. Good agreement is obtained with an Orr–Sommerfeld-type stability analysis for the growth rate and wave speed of very small disturbances. The numerical results elucidate the non-linear evolution of the interface shape once small disturbances have grown substantially. It is shown that relatively short waves (which are the most unstable according to linear theory) saturate when the length of the periodic domain is equally short. In longer domains, coalescence of short waves of small-amplitude is shown to lead to large-amplitude long waves, which subsequently exhibit a tendency towards slug formation. The non-uniform distribution of the interfacial shear stress is shown to be a significant mechanism for wave growth in the non-linear regime.

Journal article

Costantini A, Falcone G, Hewitt GF, Alimonti Cet al., 2007, Using transient inflow performance relationships to model the dynamic interaction between reservoir and wellbore during pressure testing, Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE, Vol: 2, Pages: 813-821

The fundamental understanding of the dynamic interactions between multiphase flow in the reservoir and that in the wellbore remains surprisingly weak. The classical way of dealing with these interactions is via inflow performance relationships (IPR's), where the inflow from the reservoir is related to the pressure at the bottom of the well, which is a function of the multiphase flow behaviour in the well. Steady-state IPR's are normally adopted, but their use may be erroneous when transient multiphase flow conditions occur. Transient multiphase flow in the wellbore causes problems in well test interpretation when the well is shut-in at surface and the bottomhole pressure is measured. Pressure build-up (PBU) data recorded during a test can be dominated by transient wellbore effects (e.g. phase change, flow reversal and re-entry of the denser phase into the producing zone), making it difficult to distinguish between true reservoir features and transient wellbore artefacts. This paper introduces a method to derive the transient IPR's at bottomhole conditions in order to link the wellbore to the reservoir during PBU. A commercial numerical simulator was used to build a simplified reservoir model (single well, radial co-ordinates, homogeneous rock properties) using published data from a gas condensate field in the North Sea. In order to exclude wellbore effects from the investigation of the transient inflow from the reservoir, the simulation of the wellbore was omitted from the model. Rather than the traditional flow rate at surface conditions, bottomhole pressure was imposed to constrain the simulation. This procedure allowed the flow rate at the sand face to be different from zero during the early times of the PBU, even if the surface flow rate is equal to zero. As a result, a transient IPR at bottomhole conditions was obtained for the given field case and for a specific set of time intervals, time steps and bottomhole pressure. In order to validate the above simulatio

Journal article

Hale CP, Hewitt GF, Hu B, Richardson SM, Wong WLet al., 2007, Gammas and X-ray tomography of liquid-liquid and gas-liquid-liquid flows, Multiphase Science and Technology, Vol: 19, Pages: 241-267, ISSN: 0276-1459

This article describes work carried out at Imperial College, London, in which a variety of gamma and X-radiography techniques were applied to the study of flows with two liquid phases (i.e., liquid-liquid two-phase flows and liquid-liquid-gas three-phase flows). Using a series of single-beam, single-energy gamma densitometers, it was possible to obtain data on the evolution of slug velocity and frequency. Using a traversing-beam, dual-energy densitometer, it was possible to obtain tomographic data on average phase distribution and (by conditional sampling) the phase distribution in the slugs. Using a triple-beam, dual-energy gamma densitometer, it was possible to obtain transient phase distribution data in the cross section, though at limited locations. Finally, complete cross-sectional distributions of the phases were obtained using a multibeam X-ray system, again in a form suitable for interpretation using a tomographic algorithm.

Journal article

Issa RI, Barbeau S, Hale CP, Odozi U, Hewitt GF, Richardson SM, Wong WLet al., 2007, Measurement and prediction of slug characteristics in three-phase flows, 13th International Conference on Multiphase Production Technology, Pages: 153-169

This paper describes experimental and modelling studies of three-phase (oil-water-gas) flows in a 77.92mm diameter horizontal tube. Measurements were made of pressure gradient and of the spatial and temporal distribution of the contents of the respective phases. Phase content measurements were made using gamma- and X-ray systems capable of discriminating between the two liquid phases. Data were obtained for the time averaged liquid phase hold-ups and, by conditional sampling, the holdup in the bodies of the slugs. Data were also obtained on slug initiation and on the evolution of slug frequency along the (37m) channel. Slug evolution was found to be very different in water-continuous and oil-continuous systems. To predict the flows, the slug capturing methodology developed previously at Imperial College was extended to the prediction of gas entrainment in the liquid slugs. Here, the two-fluid model framework was retained for the three-phase flows by writing a single momentum equation for the combined liquid phases, taking account of the relative motion of the phases using a drift-flux model. Excellent agreement was obtained between the predictions and the experiments. © BHR Group 2007 Multiphase Production Technology 13.

Journal article

Barbosa JR, Cheah LW, Hewitt GF, 2007, Flow boiling of water in a vertical tube at sub-atmospheric pressures, JOURNAL OF THE BRAZILIAN SOCIETY OF MECHANICAL SCIENCES AND ENGINEERING, Vol: 29, Pages: 401-409, ISSN: 1678-5878

Journal article

Walker SP, Ammirabile L, Cotton M, Hewitt GF, Laurence Det al., 2007, Multi-pin PWR re-flood studies and large eddy CFD simulations, Nuclear Future, Vol: 3, Pages: 223-229

This paper outlines a multi-pin re-flood model and further work in hand on its development, and developments in LES for nuclear reactor applications, all being performed under the auspices of KNOO Work Package I

Journal article

Manley SS, Graeber N, Menner A, Stepanek F, Hewitt GF, Bismarck Aet al., 2007, New insights into the relationship between internal phase level of emulsion templates and gas/liquid permeability of open porous polymer foams, ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, Vol: 234, ISSN: 0065-7727

Journal article

Hu B, Yang H-M, Hewitt GF, 2007, Measurement of bubble size distribution using a flying optical probe technique: Application in the highly turbulent region above a distillation plate, CHEMICAL ENGINEERING SCIENCE, Vol: 62, Pages: 2652-2662, ISSN: 0009-2509

Journal article

Hu B, Matar OK, Hewitt GF, Angeli Pet al., 2007, Mean and turbulent fluctuating velocities in oil-water vertical dispersed flows, CHEMICAL ENGINEERING SCIENCE, Vol: 62, Pages: 1199-1214, ISSN: 0009-2509

Journal article

Hewitt GF, Pugh SJ, 2007, Approximate design and costing methods for heat exchangers, HEAT TRANSFER ENGINEERING, Vol: 28, Pages: 76-86, ISSN: 0145-7632

Journal article

Al-Darmak S, Falcone G, Haie CP, Hewitt GFet al., 2006, Experimental investigation and modeling of the effects of rising gas bubbles in a closed pipe, Proceedings - SPE Annual Technical Conference and Exhibition, Vol: 6, Pages: 4116-4121

Transient multiphase flow in the wellbore causes problems in well test interpretation when the well is shut-in at surface and the pressure is measured down-hole. Pressure build-up (PBU) data recorded during a test can be dominated by transient wellbore effects (i.e. phase change, flow reversal and re-entry of the denser phase into the producing zone), making it difficult to distinguish between true reservoir features and transient wellbore artefacts (Gringarten et al., 2000). This paper is a follow up to SPE 96587 (Ali et al., 2005), which presented experimental results of phase redistribution effects on PBU data. Though the results of the experiments were revealing, they are complex as they reflect the real well situation. To obtain results in which the phase redistribution in the well is studied independently of the interaction with the reservoir, a further set of experiments were carried out, in which the tube (simulating the well) was isolated at both the top and the bottom at the same time. The pressure distribution was measured during the transient following shut-in and for the steady-state final condition in which there was a liquid-filled zone at the bottom of the test section and a gas-filled zone at the top. A substantial number of tests were conducted in the bubbly flow region and could therefore be analysed by a simple one-dimensional model for bubbly flow. The results of the comparison between the model and the experimental data are presented in this paper. Copyright 2006, Society of Petroleum Engineers.

Journal article

Ujang PM, Lawrence CJ, Hewitt GF, 2006, Conservative incompressible slug tracking model for gas-liquid flow in a pipe, 5th North American Confernce on Multiphase Technology, Vol: 2006, Pages: 373-388

A new slug tracking model which conserves mass exactly is presented. In the model, slug and stratified zones are treated as separate objects. In this model, gas entrainment has been represented as a process, with a correlation for the rate of gas entrainment. The primary variables for each object are the mass of gas and the length: these are integrated over time, and the remaining properties of each object are determined from them. A quasi-steady momentum balance is used for the stratified zones. This model is computationally efficient (computational times comparable to real time), whilst conserving the mass of liquid and gas exactly (errors of the order of machine precision). The initiation of hydrodynamic slugs is modelled as an uncorrelated Poisson process so that the time interval between the injection of new slugs is exponentially distributed. Good agreement with experimental data for several air-water flow conditions was obtained. © BHR Group 2006 Multiphase Technology 5.

Journal article

Hu B, Matar OK, Hewitt GF, Angeli Pet al., 2006, Population balance modelling of phase inversion in liquid-liquid pipeline flows, CHEMICAL ENGINEERING SCIENCE, Vol: 61, Pages: 4994-4997, ISSN: 0009-2509

Journal article

Liu L, Matar OK, Lawrence CJ, Hewitt GFet al., 2006, Laser-induced fluorescence (LIF) studies of liquid-liquid flows. Part I: Flow structures and phase inversion, CHEMICAL ENGINEERING SCIENCE, Vol: 61, Pages: 4007-4021, ISSN: 0009-2509

Journal article

Liu L, Matar OK, Hewitt GF, 2006, Laser-induced fluorescence (LIF) studies of liquid-liquid flows. Part II: Flow pattern transitions at low liquid velocities in downwards flow, CHEMICAL ENGINEERING SCIENCE, Vol: 61, Pages: 4022-4026, ISSN: 0009-2509

Journal article

Ujang PM, Lawrence CJ, Hale CP, Hewitt GFet al., 2006, Slug initiation and evolution in two-phase horizontal flow, INTERNATIONAL JOURNAL OF MULTIPHASE FLOW, Vol: 32, Pages: 527-552, ISSN: 0301-9322

Journal article

Hu B, Angeli P, Matar OK, Lawrence CJ, Hewitt GFet al., 2006, Evaluation of drop size distribution from chord length measurements, AICHE JOURNAL, Vol: 52, Pages: 931-939, ISSN: 0001-1541

Journal article

Hu B, Liu L, Matar OK, Angeli P, Hewitt GF, de Ortiz ESPet al., 2006, Investigation of phase inversion of liquid-liquid dispersions in agitated vessels, Tsinghua Science and Technology, Vol: 11, Pages: 202-206, ISSN: 1007-0214

In this paper we report results from on-going theoretical and experimental studies carried out jointly at Imperial College London and University College London. Laser-induced fluorescence (LIF) is used to investigate liquid-liquid phase inversion experimentally and to observe in detail phenomena that accompany the inversion process, such as secondary dispersions and drop coalescence and breakup. Theoretically, a two-region model together with a criterion based on a dynamic balance between drop coalescence and breakup is employed to predict phase inversion. The concept of a radial distribution function for hard spheres was also utilized in order to better model the interaction of drops at high dispersed phase holdup. The modeling work is capable of predicting the existence of ambivalent ranges which are in good agreement with experimental observations.

Journal article

Ali AM, Falcone G, Hewitt GF, Bozorgzadeh M, Gringarten ACet al., 2005, Experimental investigation of wellbore phase redistribution effects on pressure-transient data, Proceedings - SPE Annual Technical Conference and Exhibition, Pages: 2995-3000

Pressure transient analysis is a well established reservoir evaluation method. By analysing pressure and pressure derivative curves from build-up and drawdown tests, it is possible to identify reservoir characteristic parameters and heterogeneities. However, much of the pressure data recorded during a well test may be dominated by wellbore effects that can mask reservoir characteristics and lead to erroneous well test interpretations. This is particularly true when the well production rate is controlled at surface and more than one phase is flowing. These effects, which are transient in nature, include phase change, flow reversal, and re-entry of the denser phase into the producing zone. This paper presents the results of experiments carried out at Imperial College to investigate the effects of phase redistribution and phase re-injection on pressure build-up data. Single-phase and two-phase flow tests were conducted with air and water. An experimental rig was designed to emulate a reservoir connected, via a resistance, to the base of a flowing well. The "reservoir" is recreated by a pressurised vessel, while the "well" is simulated by a vertical pipe. The "well" was flowed at controlled rates to mimic those encountered in gas condensate reservoirs. After steady-state conditions had been attained, the "well" was shut-in at the top of the rig (i.e. at surface) and the associated transient phenomena monitored via distributed measurements of pressure, temperature, liquid hold-up and wall shear stress. Pressure build-up data were interpreted using established well test analysis techniques. The experiments provide a qualitative and quantitative understanding of the effects of gas rates, liquid rates and rising gas bubbles on wellbore phase redistribution and re-injection. The results yield an insight into the corresponding impact on well test transient pressure behaviour. Copyright 2005, Society of Petroleum Engineers.

Journal article

Hu B, Stewart C, Hale CP, Lawrence CJ, Hall ARW, Zwiens H, Hewitt GFet al., 2005, Development of an X-ray computed tomography (CT) system with sparse sources: application to three-phase pipe flow visualization, EXPERIMENTS IN FLUIDS, Vol: 39, Pages: 667-678, ISSN: 0723-4864

Journal article

Hu B, Angeli P, Matar OK, Hewitt GFet al., 2005, Prediction of phase inversion in agitated vessels using a two-region model, CHEMICAL ENGINEERING SCIENCE, Vol: 60, Pages: 3487-3495, ISSN: 0009-2509

Journal article

Hewitt GF, 2005, Three-phase gas-liquid-liquid flows in the steady and transient states, 3rd International Symposium on Two Phase Modelling and Experimentation, Publisher: ELSEVIER SCIENCE SA, Pages: 1303-1316, ISSN: 0029-5493

Conference paper

Valluri P, Matar OK, Hewitt GF, Mendes MAet al., 2005, Thin film flow over structured packings at moderate Reynolds numbers, CHEMICAL ENGINEERING SCIENCE, Vol: 60, Pages: 1965-1975, ISSN: 0009-2509

Journal article

Barbosa JR, Hewitt GF, 2005, A thermodynamic nonequilibrium slug flow model, JOURNAL OF HEAT TRANSFER-TRANSACTIONS OF THE ASME, Vol: 127, Pages: 323-331, ISSN: 0022-1481

Journal article

Hewitt GF, Vassilicos JC, 2005, Prediction of turbulent flows, ISBN: 9780521838993

© Cambridge University Press 2005 and Cambridge University Press 2009. The prediction of turbulent flows is of paramount importance in the development of complex engineering systems involving flow, heat and mass transfer, and chemical reactions. This book emerges from a major program at the Isaac Newton Institute in Cambridge, England. Utilizing modern computational fluid dynamics techniques, it reviews current approximation methods and their applicability to various industrial problems.

Book

Pugh SJ, Hewitt GF, Muller-Steinhagen H, 2005, Fouling during the use of seawater as coolant - the development of a user guide, HEAT TRANSFER ENGINEERING, Vol: 26, Pages: 35-43, ISSN: 0145-7632

Journal article

Liu L, Matar OK, de Ortiz ESP, Hewitt GFet al., 2005, Experimental investigation of phase inversion in a stirred vessel using LIF, CHEMICAL ENGINEERING SCIENCE, Vol: 60, Pages: 85-94, ISSN: 0009-2509

Journal article

Hewitt GF, Reeks MW, 2005, Computational modelling of multi-phase flows, Prediction of Turbulent Flows, Pages: 236-290, ISBN: 9780521838993

© Cambridge University Press 2005 and Cambridge University Press 2009. Introduction Computational modelling is assuming a greater and greater role in the study of multi-phase flows. Although it is not yet feasible to predict complex multi-phase flow fields over the full range of velocities and flow patterns, computational methods are helpful for a variety of reasons which include: They enable insights to be obtained on the nature and relative importance of phenomena and are a natural aid to experimental measurement. Indeed, it is often possible to compute quantities which cannot be readily measured. When coupled with experimental observations and empirical relationships, computational methods can give predictions which are reaching the stage of being useful in the design and operation of systems involving multi-phase flows, particularly for dispersed flow situations. This fact is reflected in the growing number of commercial computer codes which are available for application in this field. In this chapter, we will deal first with the application of single-phase prediction methods in the interpretation of two-phase flows. Here, a brief description is given of the available turbulence models and examples cited of the application of this approach (flows in coiled tubes, horizontal annular flow and waves in annular flow). An important class of two-phase flows is that where one of the phases is dispersed in the other, for example dispersions of bubbles in a liquid (bubble flow), dispersions of solid particles in a gas or liquid (gas-solids or liquid-solids dispersed flows) and dispersions of droplets of one liquid in another liquid (liquid-liquid dispersed flow).

Book chapter

Hunt JCR, Sandham ND, Vassilicos JC, Launder BE, Monkewitz PA, Hewitt GFet al., 2005, Developments in the understanding and modelling of turbulence, Prediction of Turbulent Flows, Pages: 5-49, ISBN: 9780521838993

© Cambridge University Press 2005 and Cambridge University Press 2009. Abstract Recent research is making progress in framing more precisely the basic dynamical and statistical questions about turbulence and in answering them. It is helping both to define the likely limits to current methods for modelling industrial and environmental turbulent flows, and to suggest new approaches to overcome these limitations. This chapter had its basis in the new results that emerged from more than 300 presentations during the programme held in 1999 at the Isaac Newton Institute, Cambridge, UK, and on research reported elsewhere. The objective of including this material (which is a revised form of an article which appeared in the Journal of Fluid Mechanics - Hunt et al., 2001) in the present volume is to give a background to the current state of the art. The emphasis is on the physics of turbulence and on how this relates to modelling. A general conclusion is that, although turbulence is not a universal state of nature, there are certain statistical measures and kinematic features of the small-scale flow field that occur in most turbulent flows, while the large-scale eddy motions have qualitative similarities within particular types of turbulence defined by the mean flow, initial or boundary conditions, and in some cases, the range of Reynolds numbers involved. The forced transition to turbulence of laminar flows caused by strong external disturbances was shown to be highly dependent on their amplitude, location, and the type of flow.

Book chapter

Hale CP, Hewitt GF, Manolis IG, Mendes MA, Richardson SM, Wong WLet al., 2005, Experimental and analytical studies of gas entrainment phenomena in slug flow in horizontal and near horizontal pipes, Multiphase Science & Technology, Vol: 17, Pages: 147-168, ISSN: 0276-1459

Journal article

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