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

Zhang H, Hewitt GF, 2016, New models of droplet deposition and entrainment for prediction of CHF in cylindrical rod bundles, Nuclear Engineering and Design, Vol: 305, Pages: 73-80, ISSN: 0029-5493

In this paper, we present a new set of model of droplet deposition and entrainment in cylindrical rod bundles based on the previously proposed model for annuli (effectively a "one-rod" bundle) (2016a). These models make it possible to evaluate the differences of the rates of droplet deposition and entrainment for the respective rods and for the outer tube by taking into account the geometrical characteristics of the rod bundles. Using these models, a phenomenological model to predict the CHF (critical heat flux) for upward annular flow in vertical rod bundles is described. The performance of the model is tested against the experimental data of Becker et al. (1964) for CHF in 3-rod and 7-rod bundles. These data include tests in which only the rods were heated and data for simultaneous uniform and non-uniform heating of the rods and the outer tube. It was shown that the predicted CHFs by the present model agree well with the experimental data and with the experimental observation that dryout occurred first on the outer rods in 7-rod bundles. It is expected that the methodology used will be generally applicable in the prediction of CHF in rod bundles.

Journal article

Angeli P, Azzopardi BJ, Hewakandamby B, Hewitt GF, Pain CC, Simmons MJH, Matar OKet al., 2015, Multi-scale exploration of multiphase physics in flows (MEMPHIS): A framework for the next-generation predictive tools for multiphase flows, Pages: 242-249

Ins this paper, we outline the framework that we are developing as part of the Multi-scale Exploration of Multiphase PHysIcs in flowS (MEMPHIS) programme to create the next generation modelling tools for complex multiphase flows. These flows are of central importance to micro-fluidics, oil-and-gas, nuclear, and biomedical applications, and every processing and manufacturing technology. This framework involves the establishment of a transparent linkage between input and prediction to allow systematic error-source identification, and, optimal, model-driven experimentation, to maximise prediction accuracy. The framework also involves massively-parallelisable numerical methods, capable of running efficiently on 105-106 core supercomputers, with optimally-adaptive, three-dimensional resolution, and sophisticated multi-scale physical models. The overall aim of this framework is to provide unprecedented resolution of multi-scale, multiphase phenomena, thereby minimising the reliance on correlations and empiricism.

Conference paper

Tajudin ZB, Diaz-Bejarano E, Coletti F, Macchietto S, Hewitt GFet al., 2015, 435539 Effect of friction factor correlations and propagation errors on differential pressure in a crude OIL fouling measuring RIG, Pages: 446-447

In order to detect crude oil fouling experimentally, primary measurements of differential pressure and temperatures must be obtained with high fidelity, accuracy and reproducibility at (or close to) industrial conditions. Information of the thermal and hydraulic effects of fouling can be studied by using robust models to decouple the various phenomena involved. To start with, it is important to have a reliable set of primary measurements in which the robust model could be validated against the experiment data.

Conference paper

Gimeno LS, Walker SP, Hewitt GF, Le Corre JM, Dasgupta A, Ahmad Met al., 2015, Validation and cross-verification of three mechanistic codes for annular two-phase flow simulation and dryout prediction, Pages: 6863-6875

The ability to predict the boiling transition, or dry-out, in annular two-phase flow is essential to Light Water Reactor (LWR) safety analysis. Common approaches include the use of empirical correlations or look-up tables which, although reliable, cannot be readily applied to complex cases outside the experimental range used for their development. Phenomenological models can widen the range of conditions in which dry-out can be predicted as they provide a better insight into the governing phenomena. These models however also employ empirical correlations to close the system of conservation equations and therefore require validation against experimental data. In this paper, three independently-developed codes for the phenomenological modelling of dry-out, GRAMP, MEFISTO-T and SCADOP, are compared against one another and validated against two experimental dry-out datasets. These data, on dry-out in tubes, were generated by BARC, in India, and Harwell, in the UK. The three codes are used to predict the location of: the onset of annular flow, the flow flow rate along the annular flow length, the dry-out power and the location of dry-out under broadly BWR operating conditions. A high level of consistency between the three codes is demonstrated, and good agreement is observed against the experimental data. Some areas of uncertainty are also discussed in this paper, with the focus on the applicability of the entrainment deposition correlations and the importance of the liquid entrained fraction at the onset of annular flow.

Conference paper

Tajudin Z, Martinez-Minuesa JA, Diaz-Bejarano E, Valkov I, Orzlowski P, Coletti F, Macchietto S, Hewitt GFet al., 2015, Experiment Analysis and Baseline Hydraulic Characterisation of HiPOR, a High Pressure Crude Oil Fouling Rig, ICHEAP12: 12TH INTERNATIONAL CONFERENCE ON CHEMICAL & PROCESS ENGINEERING, Vol: 43, Pages: 1405-1410, ISSN: 1974-9791

Journal article

Hewitt GF, Coletti F, 2014, Preface, ISBN: 9780128012567

Book

Coletti F, Hewitt GF, 2014, Concluding Remarks, Crude Oil Fouling: Deposit Characterization, Measurements, and Modeling, Pages: 321-323, ISBN: 9780128012567

© 2015 Elsevier Inc. All rights reserved. The final chapter (Chapter 6) summarizes the current state of knowledge on crude oil fouling and attempts to predict how the subject will develop into the future.

Book chapter

Coletti F, Crittenden BD, Haslam AJ, Hewitt GF, Jackson G, Jimenez-Serratos G, Macchietto S, Matar OK, Müller EA, Sileri D, Yang Jet al., 2014, Modeling of Fouling from Molecular to Plant Scale, Crude Oil Fouling: Deposit Characterization, Measurements, and Modeling, Pages: 179-320, ISBN: 9780128012567

© 2015 Elsevier Inc. All rights reserved. Chapter 5 describes a multiscale approach to modeling of crude oil fouling focused on improving understanding from the molecular level to industrial-scale systems. At the molecular scale, modeling work allows the determination of key parameters, such as diffusion coefficients and fluid physical properties, which can be used in thermodynamic equations of state and detailed fluid-dynamic models to predict fouling deposition in simple flows. At large scale, advanced system models of refinery heat exchangers and heat exchanger networks incorporate the lessons learned from the smaller scale models and provide the ability to predict the future course of fouling. It is shown how these models can be used for accurately assessing operational costs due to fouling, assisting in heat exchanger design, and devising improved operating strategies that minimize costs.

Book chapter

Hewitt GF, Coletti F, 2014, Crude Oil Fouling: Deposit Characterization, Measurements, and Modeling, ISBN: 9780128012567

© 2015 Elsevier Inc. All rights reserved. With production from unconventional rigs continuing to escalate and refineries grappling with the challenges of shale and heavier oil feedstocks, petroleum engineers and refinery managers must ensure that equipment used with today's crude oil is protected from fouling deposits Crude Oil Fouling addresses this overarching challenge for the petroleum community with clear explanations on what causes fouling, current models and new approaches to evaluate and study the formation of deposits, and how today's models could be applied from lab experiment to onsite field usability for not just the refinery, but for the rig, platform, or pipeline. Crude Oil Fouling is a must-have reference for every petroleum engineer's library that gives the basic framework needed to analyze, model, and integrate the best fouling strategies and operations for crude oil systems. • Defines the most critical variables and events that cause fouling • Explains the consequences of fouling and its impact on operations, safety, and economics • Provides the technical models available to better predict and eliminate the potential for fouling in any crude system.

Book

Crittenden BD, Hewitt GF, Millan-Agorio M, Rostani K, Venditti S, Yang Met al., 2014, Experimental Generation of Fouling Deposits, Crude Oil Fouling: Deposit Characterization, Measurements, and Modeling, Pages: 51-94, ISBN: 9780128012567

© 2015 Elsevier Inc. All rights reserved. In Chapter 3 experimental work concerning the generation of fouling deposits is described. The first part of the chapter describes deposit formation at a very small scale in microbomb reactors. These allow the determination of the temperature effects on deposition in the absence of fluid flow. The second part of the chapter describes a rotating cell for the generation of fouling in a compact device under controlled conditions of temperature, heat flux, and shear stress. Finally, the chapter discusses the construction and commissioning of a rig (HIPOR) for studying fouling in large-scale geometries, simulating those found in real heat exchangers.

Book chapter

Jimenez Serratos MG, Haslam AJ, Jackson G, Muller EAet al., 2014, 5. Modeling of Fouling from Molecular to Plant Scale5.2 Thermodynamic and Molecular Modeling, Crude Oil Fouling Deposit Characterization, Measurements, and Modeling, Editors: coletti, Hewitt, Publisher: Gulf Professional Publishing, ISBN: 9780128013595

With production from unconventional rigs continuing to escalate and refineries grappling with the challenges of shale and heavier oil feedstocks, petroleum engineers and refinery managers must ensure that equipment used with today’s crude ...

Book chapter

Morgan R, Markides CN, Zadrazil I, Hewitt GFet al., Investigation into Liquid-Liquid Flow Instability Mechanisms using Laser-Based Optical Diagnostic Techniques, The Geoff Hewitt Celebration Conference – Multiphase Flow: Theory, Modelling, Simulation and Experimentation

Conference paper

Angeli P, Azzopardi BJ, Hewakandamby B, Hewitt GF, Pain CC, Simmons MJH, Matar OKet al., 2014, The next-generation predictive tools for multiphase flows, Pages: 221-228

In this paper, we outline the framework that we are developing as part of the Multi-scale Exploration of Multiphase PHysIcs in flowS (MEMPHIS) programme to create the next generation modelling tools for complex multiphase flows. These flows are of central importance to microfluidics, oil-and-gas, nuclear, and biomedical applications, and every processing and manufacturing technology. This framework involves the establishment of a transparent linkage between input and prediction to allow systematic error-source identification, and, optimal, modeldriven experimentation, to maximise prediction accuracy. The framework also involves massivelyparallelisable numerical methods, capable of running efficiently on 105-106 core supercomputers, with optimally-adaptive, three-dimensional resolution, and sophisticated multi-scale physical models. The overall aim of this framework is to provide unprecedented resolution of multi-scale, multiphase phenomena, thereby minimising the reliance on correlations and empiricism.

Conference paper

Manning JP, Walker SP, Hewitt GF, 2014, A LOWER BOUND FOR THE DRYOUT QUALITY IN ANNULAR FLOW, 22nd International Conference on Nuclear Engineering (ICONE22), Publisher: AMER SOC MECHANICAL ENGINEERS

Conference paper

Angeli P, Azzopardi BJ, Hewakandamby B, Hewitt GF, Pain CC, Simmons MJH, Matar OKet al., 2014, Multi-scale exploration of multiphase physics in flows (MEMPHIS): A framework for the next-generation predictive tools for multiphase flows, Pages: 231-238

Copyright © American Institute of Chemical Engineers. All rights reserved. In this paper, we outline the framework that we are developing as part of the Multi-scale Exploration of Multiphase PHysIcs in flowS (MEMPHIS) programme to create the next generation modelling tools for complex multiphase flows. These flows are of central importance to microfluidics, oil-and-gas, nuclear, and biomedical applications, and every processing and manufacturing technology. This framework involves the establishment of a transparent linkage between input and prediction to allow systematic error-source identification, and, optimal, modeldriven experimentation, to maximise prediction accuracy. The framework also involves massivelyparallelisable numerical methods, capable of running efficiently on 105-106 core supercomputers, with optimally-adaptive, three-dimensional resolution, and sophisticated multi-scale physical models. The overall aim of this framework is to provide unprecedented resolution of multi-scale, multiphase phenomena, thereby minimising the reliance on correlations and empiricism.

Conference paper

Zhao Y, Markides CN, Matar OK, Hewitt GFet al., 2013, Disturbance wave development in two-phase gas-liquid upwards vertical annular flow, International Journal of Multiphase Flow, Vol: 55, Pages: 111-129, ISSN: 0301-9322

Disturbance waves are of central importance in annular flows. Such waves are characterised by their large amplitudes relative to the mean film thickness, their high translation velocities relative to the mean film speed, and their circumferential coherence. The present paper is concerned with the existence, development and translation of disturbance waves in upwards, gas–liquid annular flows. Experiments are described, which featured simultaneous high-frequency film thickness measurements from multiple conductance probes positioned circumferentially and axially along a vertical pipe, these measurements were aimed at studying the three-dimensional development of these interfacial structures as a function of distance from the tube inlet. From the results, it is found that disturbance waves begin to appear and to achieve their circumferential coherence from lengths as short as 5–10 pipe diameters downstream of the liquid injection location; this coherence gradually strengthens with increasing distance from the inlet. It is further shown that the spectral content of the entire interfacial wave activity shifts to lower frequencies with increasing axial distance from the inlet, with the peak frequency levelling off after approximately 20 pipe diameters. Interestingly, on the other hand, the frequency of occurrence of the disturbance waves first increases away from the inlet as these waves form, reaches a maximum at a length between 7.5 and 15 pipe diameters that depends on the flow conditions, and then decreases again. This trend becomes increasingly evident at higher gas and/or liquid flow-rates. Both wave frequency measures increase monotonically at higher gas and/or liquid flow-rates.

Journal article

Zadrazil I, Markides CN, Hewitt GF, Matar OKet al., Structure and Velocity Profiles in Downwards Gas-Liquid Annular Flow, 8th International Conference on Multiphase Flow

The downwards co-current gas-liquid annular flows inside a vertically oriented pipe have been experimentally investigated.The measurements and characterisation were performed using advanced optical non-intrusive laser-based techniques, namelyLaser Induced Fluorescence, and Particle Image/Tracking Velocimetry. The investigated conditions were in the range of ReL =306 – 1,532 and ReG = 0 – 84,600. Temporal film thickness time traces were constructed using the Laser Induced Fluorescenceimages. Based on these, the wave frequency was evaluated using direct wave counting approach and power spectral densityanalysis. Additionally, qualitative PIV observations revealed the presence of recirculation zones within a wave front ofdisturbance waves.

Conference paper

Ahmad M, Chandraker DK, Hewitt GF, Vijayan PK, Walker SPet al., 2013, Phenomenological modeling of critical heat flux: The GRAMP code and its validation, Nuclear Engineering and Design, Vol: 254, Pages: 280-290

Reliable knowledge of the critical heat flux is vital for the design of light water reactors, for both safety and optimization. The use of wholly empirical correlations, or equivalently “Look Up Tables”, can be very effective, but is generally less so in more complex cases, and in particular cases where the heat flux is axially non-uniform. Phenomenological models are in principle more able to take into account of a wider range of conditions, with a less comprehensive coverage of experimental measurements. These models themselves are in part based upon empirical correlations, albeit of the more fundamental individual phenomena occurring, rather than the aggregate behaviour, and as such they too require experimental validation. In this paper we present the basis of a general-purpose phenomenological code, GRAMP, and then use two independent ‘direct’ sets of measurement, from BARC in India and from Harwell in the United Kingdom, and the large dataset embodied in the Look Up Tables, to perform a validation exercise on it. Very good agreement between predictions and experimental measurements is observed, adding to the confidence with which the phenomenological model can be used. Remaining important uncertainties in the phenomenological modeling of CHF, namely the importance of the initial entrained fraction on entry to annular flow, and the influence of the heat flux on entrainment rate, are identified and partially quantified.

Journal article

Zhao Y, Zadrazil I, Markides CN, Matar OK, Hewitt GFet al., Wave structure in Upwards Gas-Liquid Annular Flows, American Physical Society - Division of Fluid Dynamics

A two-phase flow system in a vertical pipe in which the liquid around the pipe periphery is lifted by the gas core is referred to as an ``upwards annular flow'' (UAF). UAFs have a complex interfacial structure, which consists of short-lived, small-amplitude ``ripple'' waves, and large amplitude, high-speed ``disturbances'' waves. Two sets of flush-mounted electrically conducting probes together with axial view photography were used to study UAFs. The overall wave frequency decreased with increasing distance from the inlet until saturation. Disturbance waves were observed over a wide range (both low and high) of liquid Reynolds numbers, ReL, while ripples were observed at lower ReL. Disturbance ``bursts,'' which are a source of liquid entrainment into the gas core, were also observed, with increasing frequency at progressively higher ReL. The waves appeared more chaotic near the inlet, which hindered the formation of the correlated waves. As the small (ripple) waves coalesced into bigger waves with increasing distance from the inlet, the waves became more coherent around the pipe periphery. The results that will be presented comprise: (i) statistical film thickness data, and (ii) wave, frequency, velocity, and wavelength.

Conference paper

Zadrazil I, Hewitt GF, Matar OK, Markides CNet al., Wave Structure and Velocity Profiles in Downwards Gas-Liquid Annular Flows, American Physical Society, American Physical Society - Division of Fluid Dynamics

A downwards flow of gas in the core of a vertical pipe, and of liquid in the annulus between the pipe wall and the gas phase is referred to as a ``downwards annular flow'' (DAF). DAFs are conventionally described in terms of short-lived, small-amplitude ``ripples,'' and large-amplitude, high-speed ``disturbances.'' We use a combination of Laser Induced Fluorescence (LIF), Particle Image and Tracking Velocimetry (PIV, PTV) to study DAFs. We demonstrate through these techniques that the liquid films become progressively more complex with increasing liquid Reynolds number (ReL), while a similar increase of complexity is observed for increasing gas Reynolds number (ReG). Disturbance waves are observed for low and high ReL, and ripples for intermediate ReL. Additionally, a high degree of rolling breakdown of disturbance waves is observed in falling films at the highest ReL, which is a source of bubble entrainment into the film body. Our results will comprise: (i) statistical data on film thickness, and (ii) wave frequency, velocity, wavelength. In addition, a qualitative (e.g. re-circulation zones) and quantitative (e.g. mean/rms velocity profiles) velocity characterisation of the film flows will be presented.

Conference paper

Morgan RG, Markides CN, Zadrazil I, Hewitt GFet al., 2012, Characteristics of horizontal liquid-liquid flows in a circular pipe using simultaneous high-speed laser-induced fluorescence and particle velocimetry, International Journal of Multiphase Flow, Vol: 49, Pages: 99-118, ISSN: 1879-3533

This paper describes a set of experiments on liquid–liquid flows in a horizontal circular tube. The liquids used in the experiments were an aliphatic hydrocarbon oil (Exxsol D80) and an aqueous solution of glycerol. The concentration of glycerol in the solution was adjusted so that the two liquids had the same refractive index, and optical distortions due to the curvature of the (transparent) circular tube test section were corrected for with the use of a graticule technique. The test section was far downstream of an inlet section that established an initially stratified co-current flow of the two immiscible liquids, with the Exxsol D80 oil flowing over the glycerol/water solution. The flows were investigated at the test section with the application of laser-based optical diagnostic methods, which included high-speed simultaneous Planar Laser Induced Fluorescence (PLIF), Particle Image Velocimetry (PIV) and Particle Tracking Velocimetry (PTV). These techniques allowed the reliable evaluation of the nature of the investigated horizontal liquid–liquid flows (i.e., the flow patterns from phase distribution information), together with the detailed spatiotemporally resolved measurement of key flow characteristics such as phase and velocity distributions, and also of important parameters such as droplet size. The resulting PLIF images provide a clear indication of the distribution of the phases within a plane that passed through the channel centreline, and are used to obtain qualitative information about the arising flow patterns. The images were also used quantitatively to generate data on phase distribution, in situ phase fraction, interface level and droplet size distribution. Much of the PLIF data on in situ phase fraction and interface level agrees well with predictions from a simple stratified laminar–laminar flow model. The particle velocimetry methods (PIV and PTV) provide data on the velocity profiles in the investigated flows. Over the range of

Journal article

Zadrazil I, Markides CN, Matar OK, Naraigh LO, Hewitt GFet al., Characterisation of Downwards Co-Current Gas-Liquid Annular Flows, Turbulence, Heat and Mass Transfer 7, Publisher: Begell House

The hydrodynamic characteristics of downwards co-current two-phase (gas-liquid) flows inside avertical tube (ID = 32 mm) have been investigated experimentally. Advanced optical techniques, namely LaserInduced Fluorescence and Particle Tracking Velocimetry, were utilised for the characterisation of these flowsover a wide range of gas and liquid superficial velocities (U_G = 0 – 34 m/s and U_L = 0.034 – 0.182 m/s),corresponding to Reynolds numbers Re_G = 0 – 84,600 and Re_L = 1,230 – 6,130. A flow regime map, whichcontains a previously unreported flow regime, is constructed based on the flow observations. The quantitativeanalysis of the liquid films allows the generation of film thickness, wave frequency, bubble size, bubblefrequency and velocity profile data. It was found that the different observed flow regimes posses a characteristiccombination of the investigated quantitative parameters. A model, based on modified mixing-length theory, wasused to predict the liquid film velocity profiles and good agreement was found with the experimental results.

Conference paper

Morgan RG, Markides CN, Hale CP, Hewitt GFet al., 2012, Horizontal liquid-liquid flow characteristics at low superficial velocities using laser-induced fluorescence, INTERNATIONAL JOURNAL OF MULTIPHASE FLOW, Vol: 43, Pages: 101-117, ISSN: 0301-9322

Journal article

Hewitt GF, 2012, Churn and Wispy Annular Flow Regimes in Vertical Gas-Liquid Flows, ENERGY & FUELS, Vol: 26, Pages: 4067-4077, ISSN: 0887-0624

Journal article

Hewitt GF, 2012, Horizons in Multiphase Flow, 12AIChE - 2012 AIChE Spring Meeting and 8th Global Congress on Process Safety, Conference Proceedings

The current situation on understanding and prediction of systems involving multiphase flow is described. Such systems are typified by hydrocarbon recovery systems, where the flows are commonly gas-liquid, liquid-liquid, and gas-liquid-liquid flows. Prediction of flow regime or flow pattern are considered as a first step. Once the flow pattern is established, the phenomenological models can be used for the specific regime. The principal regimes in both vertical and horizontal flows are examined. This is an abstract of a paper presented at the 2012 AIChE Spring National Meeting and 8th Global Congress on Process Safety (Houston, TX 4/1-5/2012).

Journal article

Breuil C, Paskumas V, 2012, Introduction, Publisher: AMER MATHEMATICAL SOC

Book

Zadrazil I, Bismarck A, Hewitt GF, Markides CNet al., 2012, Shear Layers in the Turbulent Pipe Flow of Drag Reducing Polymer Solutions, Chemical Engineering Science, Vol: 72, Pages: 142-154

A range of high molecular weight polymers (polyethylene oxide) was dissolved at very low concentrations – in the order of few wppm – in a solvent (water). The Newtonian character of the polymer solutions was confirmed by rheological measurements. The polymer solutions were then pumped through a long horizontal pipe section in fully developed turbulent conditions. The flow experienced a reduction in frictional drag when compared to the drag experienced by the equivalent flow of the pure solvent. Specifically, drag reduction was measured at Reynolds numbers ranging from 3.5×10^4 to 2.1×10^5 in a pressure driven flow facility with a circular tube section of internal diameter 25.3 mm. The turbulent flow was visualized by Particle Image Velocimetry and the resulting data were used to investigate the effect of the drag reducing additives on the turbulent pipe flow. Close attention was paid to the mean and instantaneous velocity fields, as well as the two-dimensional vorticity and streamwise shear strain rate. The results indicate that drag reduction is accompanied by the appearance of “shear layers” (i.e. thin filament-like regions of high spatial velocity gradients) that act as interfaces separating low-momentum flow regions near the pipe wall and high-momentum flow regions closer to the centerline. The shear layers are not stationary. They are continuously formed close to the wall at a random frequency and move towards the pipe centerline until they eventually disappear, thus occupying or existing within a “shear layer region”. It is found that the mean thickness of the shear layer region is correlated with the measured level of drag reduction. The shear layer region thickness is increased by the presence of polymer additives when compared to the pure solvent, in a similar way to the thickening of the buffer layer. The results provide valuable insights into the characteristics of the turbulent pipe flow of a solvent contai

Journal article

Myo Thant MM, Mohd Sallehud-Din MT, Hewitt GF, Hale CP, Quarini GLet al., 2011, Mitigating flow assurance challenges in deepwater fields using active heating methods, SPE Middle East Oil and Gas Show and Conference, MEOS, Proceedings, Vol: 1, Pages: 570-579

Flow assurance challenges, mainly of hydrates and wax depositions, are amongst the key issues that must be resolved and mitigated to ensure that hydrocarbons can be efficiently and economically transported from well to processing facilities. As wells step further away from shore into deeper water, the flow assurance challenges are increasing tremendously due to prevalence of higher pressure and lower temperature conditions. Thus, the development of cutting edge technologies to cater for the ever increasing demand in exploring the hostile and technologically challenging deepwater fields is a matter of great urgency. One of the effective solutions to prevent the formation of wax or hydrates is to use active heating methods. This paper describes an overview of the available active heating methods and mechanisms which are being implemented as thermal management systems for flowline in deepwater fields. It also discusses the thermal performance calculation models available to aid the design and modelling of such systems. Some comparative studies are carried out to determine the advantages and disadvantages of each of the methods to establish a general reference source on the technology that provides the most significant economic impact without compromising the reliability and efficiency of the overall system. Active heating systems have been used in several projects in the North Sea, Gulf of Mexico and Offshore West Africa. This paper also summarizes these projects and their operating experience from open literature. In general, due to their operational flexibility and high efficiency through control of the pipeline temperature above the hydrate formation and wax deposition temperatures, active heating seems to be the most practical, economical and viable solutions in managing flow assurance issues; especially for the development of deepwater fields. Copyright 2011, Society of Petroleum Engineers.

Journal article

Abdullahi MK, Pierre B, Hale CP, Hewitt GFet al., 2011, Experiments on gas entrainment in two-phase slug flows using a single entrapped gas bubble, BHR Group - 15th International Conference on Multiphase Production Technology, Pages: 359-370

Gas entrainment rates are measured using a new experiment where a single entrapped gas bubble is pushed in by pressurized liquid. The single bubble is created by draining liquid in between two ball valves or in the upper part of a dog leg. Experiments are carried out in horizontal and near horizontal pipelines, 32 mm in diameter, about 8.5 m in length. Gas entrainment rates are calculated using measurements (liquid holdup and slug front velocity) from conductance probes. Experimental results, though scattered, are in good agreement with data from Manolis (1995) where gas entrainment rates increase linearly with slug front velocity. © BHR Group 2011.

Journal article

Lecoeur N, Zeng YJ, Hale CP, Hewitt GFet al., 2011, Visualization and axial viewing techniques, Multiphase Science and Technology, Vol: 23, Pages: 29-55, ISSN: 0276-1459

Axial viewing techniques are advanced photographic methods that have been widely used to visualize two-phase flow systems. A review of the axial viewing techniques is presented, describing the development of axial view systems from their origin to diverse variants of the original device such as the parallel-light technique, the in-line axial viewer used on the Imperial College high pressure multiphase flow rig, and the high-temperature axial viewing system. With these techniques, it has been possible to visualize in detail the various flows and to identify previously unknown mechanisms. These techniques show great continuing potential in elucidating two-phase flow phenomena. © 2011 by Begell House, Inc.

Journal article

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