224 results found
Chatzikyriakou D, Walker SP, Hale CP, et al., 2011, The measurement of heat transfer from hot surfaces to non-wetting droplets, INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER, Vol: 54, Pages: 1432-1440, ISSN: 0017-9310
Zeng YJ, Hale CP, Walker SP, et al., 2011, VISUAL AND THERMAL STUDIES OF SINGLE TUBE REFLOOD UNDER TYPICAL PWR LB-LOCA CONDITIONS, 18th International Conference on Nuclear Engineering (ICONE-18), Publisher: AMER SOC MECHANICAL ENGINEERS, Pages: 471-+
Ilyas M, Walker SP, Hewitt GF, 2011, MODELLING REWETTING OF HEATED SURFACES AS INTERMITTENTLY BURSTING LIQUID-METAL CONTACTS, 18th International Conference on Nuclear Engineering (ICONE-18), Publisher: AMER SOC MECHANICAL ENGINEERS, Pages: 1163-1169
Macchietto S, Hewitt GF, Coletti F, et al., 2011, Fouling in Crude Oil Preheat Trains: A Systematic Solution to an Old Problem, HEAT TRANSFER ENGINEERING, Vol: 32, Pages: 197-215, ISSN: 0145-7632
Ilyas M, Ahmad M, Hale CP, et al., 2011, REWETTING PROCESSES DURING TOP/BOTTOM REFLOODING OF HEATED VERTICAL SURFACES, 8th ASME/JSME Thermal Engineering Joint Conference, Publisher: AMER SOC MECHANICAL ENGINEERS, Pages: 1395-+
Walker SP, Ilyas M, Hewitt GF, 2011, The rewetting of PWR fuel cladding during post-LOCAreflood: a proposed physical explanation for themicro-scale high-frequency sputtering observed, Proceedings of the Institution of Mechanical Engineers Part A-Journal of Power and Energy
Following a loss of coolant accident in a light water reactor, reflooding of the core toquench overheating fuel is urgent. The process of quenching hot metal with liquid water has beenmuch studied, in large part because of its great importance in this context. There is good experimentalevidence such as quenching occurs via multiple micro-scale wettings of the surface,followed by vapour-driven ejection of liquid water. It is only after some tens of such wettingsthat permanent wetting seems to take place. In this article, we investigate this process, and putforward a physical mechanism that seems to explain this cyclical behaviour. The mechanisminvolves the need for some time to elapse following wetting of a hot body for heat to be conductedfrom within the depths of the body into the liquid water, such as to form a layer of water hot anddeep enough to accommodate a critically sized bubble and thus cause ejection of the water film.Simple one-dimensional calculations using this model produce results that are in broad accordwith experimental observations.
Dallas V, Vassilicos JC, Hewitt GF, 2010, Strong polymer-turbulence interactions in viscoelastic turbulent channel flow, PHYSICAL REVIEW E, Vol: 82, ISSN: 1539-3755
Zeng YJ, Hale CP, Hewitt GF, et al., 2010, Flow and heat transfer in pressurized water reactor reflood, Multiphase Science and Technology, Vol: 22, Pages: 279-370, ISSN: 0276-1459
In a pressurized water rector (PWR), following a postulated large break loss of coolant accident (LB-LOCA) an important stage in the recovery of the core is the reflood process in which the core is reflooded (rewetted) by water injected from the emergency core cooling system (ECCS). This review summarises the studies which have been carried out on the reflood process. Despite all the work that has been done, it is concluded that there is still a need for improved basic understanding of the detailed processes occurring, and in particular the nature of the fluid/hot solid interactions in the close vicinity of the rewetting front.
Coletti F, Hewitt GF, Dugwell DR, et al., 2010, Integrating crude oil fouling modelling and experiments on a new high pressure pilot-scale test rig, 10AIChE - 2010 AIChE Annual Meeting, Conference Proceedings
Crude oil fouling is a long-standing problem in oil refineries which causes major energy efficiency and economic losses, extra environmental emissions and disruption of operations, with related health and safety hazards. Because of the complex and interacting phenomena involved, the underlying mechanisms leading to fouling depositions are not well understood. Acquiring experimental data in a controlled laboratory environment representative of realistic refinery conditions, through very precise measurements, is a required step for gaining a better understanding of the fouling mechanisms and for testing mitigation strategies. This is important for improving refineries operational efficiency. Moreover, data on crude fouling behavior provide sensitive and important commercial information for oil companies which often base buying, pricing and allocation strategies on the quality of the crudes, including the ease with which they can be processed in specific refineries. A state-of-the-art high pressure oil rig (HIPOR) has been built at Imperial College London by a team under the lead of Prof. G. F. Hewitt. This facility is designed to process crude oil in two test sections (a tube and an annulus) up to 30 bars and 300 °C and to measure with accuracy key variables such as inlet and outlet temperatures, flowrates, heat fluxes and pressure drops. Moreover, temperature profiles across the length of the annular test section can be measured through a radiation equilibrium thermometer whilst the actual thickness of the foulant layer can be measured simultaneously using a novel dynamic gauging technique. The traditional experimental approach to crude oil fouling research focuses on the collection of fouling data which are typically interpreted through overall, lumped heat balances to yield overall fouling resistances. In this paper, an integrated approach is discussed which combines the detailed data from the above experimental apparatus with sophisticated thermo-hydraulic mod
Chatzikyriakou D, Walker SP, Belhouachi B, et al., 2010, Three Dimensional Modeling of the Hydrodynamics of Oblique Droplet-Hot Wall Interactions During the Reflood Phase After a LOCA, JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER-TRANSACTIONS OF THE ASME, Vol: 132, ISSN: 0742-4795
Chatzikyriakou D, Walker SP, Hewitt GF, 2010, The contribution of non-wetting droplets to direct cooling of the fuel during PWR post-LOCA reflood, 4th International Topical Meeting on High Temperature Reactor Technology, Publisher: ELSEVIER SCIENCE SA, Pages: 3108-3114, ISSN: 0029-5493
Chatzikyriakou D, Walker SP, Hale CP, et al., 2010, NUMERICAL AND EXPERIMENTAL INVESTIGATION OF THE BEHAVIOUR OF NON-CONTACTING DROPLETS DURING THE REFLOOD PHASE AFTER A LOCA, 14th International Heat Transfer Conference, Publisher: AMER SOC MECHANICAL ENGINEERS, Pages: 311-317
Dallas V, Vassilicos JC, Hewitt GF, 2010, The mean flow profile of wall-bounded turbulence and its relation to turbulent flow topology, Pages: 87-90, ISSN: 1382-4309
Dallas V, Vassilicos JC, Hewitt GF, 2010, The Mean Flow Profile of Wall-Bounded Turbulence and Its Relation to Turbulent Flow Topology, 7th International ERCOFTAC Workshop on Direct and Large-Eddy Simulation, Publisher: SPRINGER, Pages: 87-+, ISSN: 1382-4309
Ahmad M, Burlutskiy E, Walker SP, et al., 2010, EFFECT OF HEAT FLUX ON DROPLET ENTRAINMENT USING ANNULAR FLOW DRYOUT MODEL, 14th International Heat Transfer Conference, Publisher: AMER SOC MECHANICAL ENGINEERS, Pages: 547-552
Brown L, Hewitt GF, Hu B, et al., 2009, Predictions of droplet distribution in low liquid loading, stratified flow in a large diameter pipeline, 14th International Conference on Multiphase Production Technology, Pages: 157-181
In the pipeline transport of natural gas and condensates, large diameter (typically 38 inch. 0.9176 m) pipes are employed. In such systems, the two-phase flow is often in the stratifying annular regime in which there is a liquid layer on the wall with a dispersion of droplets in the gas core. A crucial issue in such systems is the distribution of the liquid phase around the tube periphery. It is vital (from the point of view of flow assurance risk) to understand the relationship between the continuous liquid film around the periphery and the thicker liquid pool at the bottom of the pipe. For large diameter pipes, the dominant mechanism for maintaining a liquid film at the top of the pipe is that of entrainment of liquid droplets from the thicker liquid layer at the bottom of the pipe and the deposition of these droplets in the upper part of the pipe. The project described here was commissioned and led by ConocoPhillips. with both analytical and computational modelling work being carried out. The two approaches gave broadly consistent results, allowing conclusions to be drawn about the likely liquid distribution and its implications for scale up of hydraulics to manage flow assurance risk in large diameter pipe. © 2009 BHR Group Multiphase Production Technology.
Mavromoustaki A, Lim B, Ng B, et al., 2009, An experimental study of wellbore phase redistribution effects in gas condensate reservoirs, 14th International Conference on Multiphase Production Technology, Pages: 245-263
This paper presents a series of experiments that were carried out at Imperial College to investigate Wellbore phase redistribution (WPR) phenomena. Results are being used to verify and calibrate a transient Wellbore multiphase simulator that will be used to predict the onset of WPR and design operating conditions to avoid or at least minimise it. The overall objective of the experimental study was to emulate two-phase flow in a gas condensate well-reservoir system. It was firstly aimed to investigate WPR effects independent of reservoir interaction and secondly as part of a gas condensate well-reservoir system in which the multiphase flow near the Wellbore and the single phase gas away from the well could be taken into account. The well was represented by a vertical tube of approximately 10.5 m in length, and gas and condensate by air and water, respectively. The reservoir was simulated with two pressurised vessels, one for water, the other for gas, feeding into the vertical tube. The effects of WPR on the isolated well were investigated by performing shut-in tests in which the bottom and top of the tube were closed off simultaneously. The reservoir impact on WPR effects was then investigated by creating steady state conditions and shutting in the vertical tube at the top to create a transient response. The resulting transient pressure data were analysed using well test interpretation methods. The steady state pressure and void fraction, measured along the tube, were used to validate GRAMP-2, a steady state Wellbore modelling code based on flow regime prediction developed at Imperial College. Good agreement was obtained with simulated and experimental results. © 2009 BHR Group Multiphase Production Technology.
Dallas V, Vassilicos JC, Hewitt GF, 2009, Stagnation point von Karman coefficient, PHYSICAL REVIEW E, Vol: 80, ISSN: 1539-3755
Chatzikyriakou D, Walker SP, Belhouachi B, et al., 2009, THREE DIMENSIONAL MODELLING OF THE HYDRODYNAMICS OF OBLIQUE DROPLET- HOT WALL INTERACTIONS DURING THE REFLOOD PHASE AFTER A LOCA, 17th International Conference on Nuclear Engineering, Publisher: AMER SOC MECHANICAL ENGINEERS, Pages: 561-568
Pugh SJ, Hewitt GF, Mueller-Steinhagen H, 2009, Fouling During the Use of Fresh Water as CoolantThe Development of a User Guide, HEAT TRANSFER ENGINEERING, Vol: 30, Pages: 851-858, ISSN: 0145-7632
Manley SS, Graeber N, Grof Z, et al., 2009, New insights into the relationship between internal phase level of emulsion templates and gas-liquid permeability of interconnected macroporous polymers, SOFT MATTER, Vol: 5, Pages: 4780-4787, ISSN: 1744-683X
Zeng YJ, Hale CP, Walker SP, et al., 2009, STUDIES OF FLOW DIVERSION DUE TO A BALLOONED PIN, 17th International Conference on Nuclear Engineering, Publisher: AMER SOC MECHANICAL ENGINEERS, Pages: 609-617
Chatzikyriakou D, Walker SP, Hewitt G, et al., 2009, Comparison of measured and modelled droplet–hot wall interactions, Applied Thermal Engineering, Vol: 29, Pages: 1398-1405
In this study CFD simulations of both sessile droplets resting upon a vapour cushion and droplets bouncing off a hot solid surface are presented. As a droplet approaches a hot surface the vapour layer formed by evaporation from the droplet acts like a cushion and can prevent contact between the liquid and the hot surface. Rather than hitting and wetting the surface, the droplet can rebound from the vapour film. For the tracking of the interface between the two fluids a one-fluid Level Set method is used, embodied in the TransAT© finite-volume two-phase flow computational code. Inter alia, this incorporates a full Navier–Stokes solution in the region of the thin film. The method is used to analyse the experiments conducted by Wachters et al. [L.H.J. Wachters, H. Bonne, H.J. Van Nouhuis, The heat transfer from a horizontal plate to sessile water drops in the spheroidal state, Chemical Engineering Science 21 (1966) 923–936] and Biance et al. [A.-L. Biance, F. Checy, C. Clanet, G. Lagubeau, D. Quere, On the elasticity of an inertial liquid shock, Journal of Fluid Mechanics 554 (2006) 47–66]. Good agreement with the experimental observations is obtained.
Costantini A, Falcone G, Hewitt GF, et al., 2008, Using Transient Inflow Performance Relationships to Model the Dynamic Interaction Between Reservoir and Wellbore During Pressure Testing, JOURNAL OF ENERGY RESOURCES TECHNOLOGY-TRANSACTIONS OF THE ASME, Vol: 130, ISSN: 0195-0738
Al-Darmaki S, Falcone G, Hale CP, et al., 2008, Experimental investigation and modeling of the effects of rising gas bubbles in a closed pipe, 2006 SPE Annual Technical Conference and Exhibition, Publisher: SOC PETROLEUM ENG, Pages: 354-365, ISSN: 1086-055X
Ujang PM, Pan L, Manfield PD, et al., 2008, Prediction of the translational velocity of liquid slugs in gas-liquid slug flow using computational fluid dynamics, Multiphase Science and Technology, Vol: 20, Pages: 25-79, ISSN: 0276-1459
This paper describes the application of computational fluid dynamics to address the following problems in gas-liquid slug flow: (i) Effect of mixture velocity on slug tail propagation velocity and tail shape in horizontal slug flow; (ii) effect of tube inclination on slug propagation velocity; (iii) "bubble turning" in slug flow in a downward inclined pipe; (iv) effect of liquid viscosity on propagation and tail shape; (v) effect of gravity on propagation velocity; and (vi) effect of slug length on tail propagation velocity. All of the simulations were carried out using the Ansys CFX code, with tracking of the gas-liquid interface achieved using the volume of fluid technique. The flow conditions considered were within the turbulent regime, and for this, the standard κ - ε model was used (although the influence of the turbulence model chosen was small). The calculated results compared favorably with experimental data, where such data is available.
Gao S, Leslie DC, Hewitt GF, 2008, Improvements to the modelling of in a transient nuclear two-phase flow and heat transfer reactor analysis code, APPLIED THERMAL ENGINEERING, Vol: 28, Pages: 915-922, ISSN: 1359-4311
Hewitt GF, 2008, Multiphase Flow in the Energy Industries, JOURNAL OF ENGINEERING THERMOPHYSICS, Vol: 17, Pages: 12-23, ISSN: 1810-2328
Hewitt GF, 2008, Multiphase flow in the energy industries, Journal of Engineering Thermophysics, Vol: 17, Pages: 12-23, ISSN: 1810-2328
Brinson C, 2008, Introduction, Ruth Borchard, "We are Strangers Here": An "Enemy Alien" in Prison in 1940, London, Publisher: Vallentine Mitchell, Pages: 1-15
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