CERES :: Browsing by Author "Yeung, Hoi"

Browsing by Author "Yeung, Hoi"

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Open Access
Behaviour of Water in Aviation Fuels at Low Temperature
(2011-12-07T00:00:00Z) Carpenter, Mark D.; Hetherington, Janice I.; Lao, Liyun; Ramshaw, C.; Yeung, Hoi; Lam, Joseph K.-W.; Masters, Simon; Barley, Sarah; Morris, R. E.
Open Access
CFD simulation of horizontal oil-water flow with matched density and medium viscosity ratio in different flow regimes
(Elsevier, 2017-01-10) Shi, Jing; Gourma, Mustapha; Yeung, Hoi
Simulation of horizontal oil-water flow with matched density and medium viscosity ratio (μo/μw=18.8) in several different flow regimes (core annular flow, oil plugs/bubbles in water and dispersed flow) was performed with the CFD package FLUENT in this study. The volume of fluid (VOF) multiphase flow modeling method in conjunction with the SST k-ω scheme was applied to simulate the oil-water flow. The influences of the turbulence schemes and wall contact angles on the simulation results were investigated for a core annular flow (CAF) case. The SST k-ω turbulence scheme with turbulence damping at the interface gives better predictions than the standard k-ε and RNG k-ε models for the case under consideration. The flow regime of density-matched oil-water flow with medium viscosity ratio, or more generally speaking, the flow regime of fluids where the surface tension is playing a prevailing role is sensitive to the wall contact angle. Simulation results were compared with experimental counterparts. Satisfactory agreement in the prediction of flow patterns were obtained for CAF and oil plugs/bubbles in water. The simulation results also demonstrated some detailed flow characteristics of CAF with relatively low-viscosity oil (oil viscosity one order higher than the water viscosity in the present study compared to the extensively studied CAF with oil viscosity being two to three orders higher than the water viscosity). Different from the velocity profiles of high-viscosity oil CAF where there is sharp change in the velocity gradient at the phase interface with velocity across the oil core being roughly flat, there is no sharp change in the velocity gradient at the phase interface for CAF with relatively low-viscosity oil.
Open Access
Characterization of liquid-liquid flows in horizontal pipes
(Wiley, 2016-08-26) Shi, Jing; Yeung, Hoi
Diverse flow regimes have been encountered in liquid-liquid flows. Some degree of consistency in the observed flow patterns is shown in reported studies, while inconsistency exits when physical properties of the two phases concerned are wide enough. An attempt was made in this study to investigate the mechanisms behind flow patterns of liquid-liquid flows in horizontal pipes. A literature review on flow patterns of liquid-liquid flows in horizontal pipes was conducted. The ratio of the gravitational force to viscous force was proposed to characterize liquid-liquid flows in horizontal pipes into gravitational force dominant, viscous force dominant and gravitational force and viscous force comparable flow featured with different basic flow regimes. Comparisons of the proposed characterization criterion with the literature data show good agreement.
Open Access
Comparative analysis of riser base and flowline gas injection on vertical gas-liquid two-phase flow
(MDPI, 2022-10-10) Brini Ahmed, Salem K.; Aliyu, Aliyu M.; Baba, Yahaya D.; Abdulkadir, Mukhtar; Abdulhadi, Rahil Omar; Lao, Liyun; Yeung, Hoi
Gas injection is a frequently used method for artificial lift and flow regime rectification in offshore production and transportation flowlines. The flow behaviour in such flowlines is complex and a better understanding of flow characteristics, such as flow patterns, void fraction/hold up distributions and pressure gradient is always required for efficient and optimal design of downstream handling facilities. Injection method and location have been shown to strongly affect downstream fluid behaviour that can have important implications for pumping and downstream facility design, especially if the development length between pipeline and downstream facility is less than L/D = 50 as reported by many investigators. In this article, we provide the results of an experimental investigation into the effects of the gas injection position on the characteristics of the downstream upwards vertical gas flow using a vertical riser with an internal diameter of 52 mm and a length of 10.5 m. A horizontal 40-m-long section connected at the bottom provides options for riser base or horizontal flow line injection of gas. The flowline gas injection is performed 40 m upstream of the riser base. A 16 by 16 capacitance wire mesh sensor and a gamma densitometer were used to measure the gas-liquid phase cross-sectional distribution at the riser top. A detailed analysis of the flow characteristics is carried out based on the measurements. These include flow regimes, cross-sectional liquid holdup distributions and peaking patterns as well as analysis of the time series data. Our findings show that flow behaviours differences due to different gas injection locations were persisting after a development length of 180D in the riser. More specifically, core-peaking liquid holdup occurred at the lower gas injection rates through the flowline, while wall-peaking holdup profiles were established at the same flow conditions for riser base injection. Wall peaking was associated with dispersed bubbly flows and hence non-pulsating as against core-peaking was associated with Taylor bubbles and slug flows. Furthermore, it was found that the riser base injection generally produced lower holdups. It was noted that the circumferential injector used at the riser base promoted high void fraction and hence low liquid holdups. Due to the bubbly flow structure, the slip velocity is smaller than for larger cap bubbles and hence the void fraction is higher. The measurements and observations presented in the paper provides valuable knowledge on riser base/flowline gas introduction that can directly feed into the design of downstream facilities such as storage tanks, slug catchers and separators.
Open Access
Development of a cascaded latent heat storage system for parabolic trough solar thermal power generation
(Cranfield University, 2014-09) Muhammad, Mubarak Danladi; Badr, Ossama; Yeung, Hoi
Concentrated solar power (CSP) has the potential of fulfilling the world’s electricity needs. Parabolic-trough system using synthetic oil as the HTF with operating temperature between 300 and 400o C, is the most matured CSP technology. A thermal storage system is required for the stable and cost effective operation of CSP plants. The current storage technology is the indirect two-tank system which is expensive and has high energy consumption due to the need to prevent the storage material from freezing. Latent heat storage (LHS) systems offer higher storage density translating into smaller storage size and higher performance but suitable phase change materials (PCMs) have low thermal conductivity, thus hindering the realization of their potential. The low thermal conductivity can be solved by heat transfer enhancement in the PCM. There is also lack of suitable commercially-available PCMs to cover the operating temperature range. In this study, a hybrid cascaded storage system (HCSS) consisting of a cascaded finned LHS and a high temperature sensible or concrete tube register (CTR) stages was proposed and analysed via modelling and simulation. Fluent CFD code and the Dymola simulation environment were employed. A validated CFD phase change model was used in determining the heat transfer characteristics during charging and discharging of a finned and unfinned LHS shell-and-tube storage element. The effects of various fin configurations were investigated and heat transfer coefficients that can be used for predicting the performance of the system were obtained. A model of the HCSS was then developed in the Dymola simulation environment. Simulations were conducted considering the required boundary conditions of the system to develop the best design of a system having a capacity of 875 MWhth, equivalent to 6 hours of full load operation of a 50 MWe power plant. The cascaded finned LHS section provided ~46% of the entire HCSS capacity. The HCSS and cascaded finned LHS section have volumetric specific capacities 9.3% and 54% greater than that of the two-tank system, respectively. It has been estimated that the capital cost of the system is ~12% greater than that of the two-tank system. Considering that the passive HCSS has lower operational and maintenance costs it will be more cost effective than the twotank system considering the life cycle of the system. There is no requirement of keeping the storage material above its melting temperature always. The HCSS has also the potential of even lower capital cost at higher capacities (>6 hours of full load operation).
Open Access
Development of process system for treatment of oil contaminated soils & sludges in the Niger Delta
(Cranfield University, 2005-10) Chukwuogo, C. E. B.; Yeung, Hoi; Shang, Z.
One of the major problems with process equipment/systems set up in Nigeria is the lack of sustained productivity, arising from the basic inappropriateness of such equipment/system to the technological level of the country. The pollutions arising from the Oil & Gas exploitation activities in the Niger Delta were highlighted. In this project, the development of a unique processing system capable of advantageously treating oil contaminated soils and sludges in the Niger Delta was undertaken. The specific constraints in that terrain are outlined. The treatment systems that are currently available worldwide which are applicable to the Niger Delta have various limitations. The system designed had to be able to overcome all those limitations. Design superiority and success in the market place being two desirable aspects of a product, the project focused on the possibility of processing the contaminated materials at a higher rate without compromising quality. The need to generate its own fuel for firing burners and diesel for firing the electricity generators was one of the main drivers for the project. The system developed was tested at pilot level for effectiveness in those key areas. A totally energy-independent process has thus been created, which generates energy for the material being treated. This will guaranty the success in the market place in treating the contaminated sites of the Niger Delta, at commercial rates that are about a third of the current rates in the region. It is also estimated that capital and operating costs will be less than half of foreign built units, which ensure faster attainment of breakeven point. The future work that could be undertaken in this area include the field trials of a mini-sized processing unit and the eventual translation of processing parameters and information into a life size, commercial system able treat materials as required.
Open Access
Dynamic modeling and simulation of CO2 chemical absorption process for coal- fired power plants
(2009-10-04) Lawal, Adekola; Wang, Meihong; Yeung, Hoi; Stephenson, Peter; de Brito Alves, RM, Oller do Nascimento, CA, Biscaia Jr, EC
Post combustion capture via chemical absorption is viewed as the most mature CO capture technique. The effects of the addition of CO chemical absorption process on power plant performance have been studied using various steady-state models. However, there are several gaps in the understanding of the impact of post combustion capture on the operability of the power plant. These questions could be addressed by studying the dynamic behavior of such plants. In this study, dynamic models of the CO chemical absorption process were developed and validated. Dynamic analyses of the process reveal that absorber performance is sensitive to L/G ratio and that changes in reboiler duty significantly affect the regenerator performance.
Open Access
Dynamic modelling and analysis of post-combustion CO2 chemical absorption process for coal-fired power plants
(Elsevier Science B.V., Amsterdam., 2011-12-06) Lawal, Adekola; Wang, Meihong; Stephenson, Peter; Koumpouras, G.; Yeung, Hoi
Post-combustion capture by chemical absorption using MEA solvent remains the only commercial technology for large scale CO2 capture for coal-fired power plants. This paper presents a study of the dynamic responses of a post- combustion CO2 capture plant by modelling and simulation. Such a plant consists mainly of the absorber (where CO2 is chemically absorbed) and the regenerator (where the chemical solvent is regenerated). Model development and validation are described followed by dynamic analysis of the absorber and regenerator columns linked together with recycle. The gPROMS (Process Systems Enterprise Ltd.) advanced process modelling environment has been used to implement the proposed work. The study gives insights into the operation of the absorber- regenerator combination with possible disturbances arising from integrated operation with a power generation plant. It is shown that the performance of the absorber is more sensitive to the molar L/G ratio than the actual flow rates of the liquid solvent and flue gas. In addition, the importance of appropriate water balance in the absorber column is shown. A step change of the reboiler duty indicates a slow response. A case involving the combination of two fundamental CO2 capture technologies (the partial oxyfuel mode in the furnace and the post-combustion solvent scrubbing) is studied. The flue gas composition was altered to mimic that observed with the combination. There was an initial sharp decrease in CO2 absorption level which may not be observed in steady-state simulations. (C) 2010 Elsevier Ltd. All rights reserved.
Open Access
Dynamic modelling of CO2 absorption for post combustion capture in coal-fired power plants
(Elsevier Science B.V., Amsterdam., 2009-12-01T00:00:00Z) Lawal, Adekola; Wang, Meihong; Stephenson, Peter; Yeung, Hoi
Power generation from fossil fuel-fired power plants is the largest single source of CO2 emissions. Post combustion capture via chemical absorption is viewed as the most mature CO2 capture technique. This paper presents a study of the post combustion CO2 capture with monoethanolamine (MEA) based on dynamic modelling of the process. The aims of the project were to compare two different approaches (the equilibrium-based approach versus the rate-based approach) in modelling the absorber dynamically and to understand the dynamic behaviour of the absorber during part load operation and with disturbances from the stripper. A powerful modelling and simulation tool gPROMS was chosen to implement the proposed work. The study indicates that the rate-based model gives a better prediction of the chemical absorption process than the equilibrium-based model. The dynamic simulation of the absorber indicates normal absorber column operation could be maintained during part load operation by maintaining the ratio of the flow rates of the lean solvent and flue gas to the absorber. Disturbances in the CO2 loading of the lean solvent to the absorber significantly affect absorber performance. Further work will extend the dynamic modelling to the stripper for whole plant analysis.
Open Access
Effect of particle size on sand deposition in single-phase and multi-phase pipelines.
(Cranfield University, 2016-11) Fajemidupe, Olawale T.; Yeung, Hoi
Sand production in the life of oil and gas reservoirs is inevitable, as it is co- produced with oil and gas from the reservoirs. Sand deposition in petroleum pipelines poses considerable risk to the production of oil and gas. This study investigates the effect both of sand particle diameter and concentration on minimum transport conditions in single phase and multiphase horizontal pipelines through experimental methods. This study defines the minimum transport condition (MTC) for sand grains under stratified two-phase flow regimes, as the combined minimum gas and liquid velocities at which all sand particles have sufficient energy to keep them moving in the liquid phase along the pipe. In this study, careful analyses based on experimental observations were made producing several conclusions. Based on the analysis, it was found that sand of different particle diameters and concentrations exhibits similar behaviours in single phase flow and stratified two-phase flow in horizontal pipes. Furthermore, in stratified two-phase flow, sand particles were transported within the liquid film and never observed crossing into the gas phase or transported across the gas- liquid interface; however, an increase in gas velocity tends to cause an increase in liquid velocity which in turn increases the velocity of the sand particles in stratified two-phase flow. Studies carried out on the effect of particle diameter and concentration on MTCs in both single phase (water) and stratified two-phase flows (air-water) in horizontal pipes showed that MTC increases with increases in particle diameter for the same concentration and also increases as the concentration increases for the same particle diameter. Sand sensors were used in this study for the purpose of sand monitoring and detection in single phase (water) and stratified two-phase flow in horizontal pipes. The sensors were flush-mounted at the bottom of the pipe. These sensors are commonly used to measure the thickness of a film in multiphase flow but have not been used before for monitoring and detecting sand both in single phase and multiphase flows. In this work the sensors were applied in monitoring and detecting sand in single phase and multiphase flows; they were found to be capable of monitoring and detecting sand in a conducting liquid in both single phase and stratified two-phase flows. Measured pressure gradients for sand-water flow at MTC were compared with measured pressure gradients for sand-air-water flow for the same particle diameter and concentration; it was found that there was a difference between the two pressure gradients. The pressure gradient of sand-water flow at MTC was higher than the pressure gradient of sand-air-water flow at MTC. For this reason, King et al.’s (2001) pressure gradient approach cannot be used to design wet gas pipelines. Modified concentration (v/v) correction correlation is proposed to predict sand transport at MTC in air-water. The correlation accounts for low concentration of sand (5.39E-05 to 4.90E-04v/v) in air-water flow. The proposed correlation predicted fairly when compared with the experimental results at MTC.
Open Access
Effects of pipe orientation on sand transportation
(Cranfield University, 2013-11) Osho, Adeyemi Joseph; Yeung, Hoi
Sand transport in hilly terrain geometry is different and complex to understand compared to horizontal pipeline, due to the influence of the geometry that greatly affect multiphase flow and sand behaviour at the dip. The overall aim of this research work is to use experimental method to investigate the effects of multiphase flow behaviour on sand transport in a dip configuration. Experimental work was carried out to understand the complex dynamic mechanisms that exist during sand multiphase flow using 2” inch dip test facility with different inclination angles of ±24° and ±12° configurations. In order determine the multiphase flow parameters and sand flow regimes, extensive data were collected and analysed from continuous local measurement of instantaneous liquid hold up and sand hold up using conductivity rings. Significant observations were made during this study from which several conclusions were made. In the air–water test, three slug behaviours were observed at the dip: complete stratified flow downhill with slug initiation at dip; stratified flow (with energetic ripple) downhill with slug initiation and slug growth upward dip; and aerated slug downhill and slug growth at the dip. These behaviours are different from published work on this subject with low angle of inclination. The data analysis revealed that the two types of slug initiation mechanisms (wave growth and wave coalescence) observed are geometry specifics. The slug translational velocities (at the dip and uphill section) were used as criterion to determine the flow condition for each slug initiation mechanism at the dip. Significant observations were made during this study from which several conclusions were made. In the air–water test, three slug behaviours were observed at the dip: complete stratified flow downhill with slug initiation at dip; stratified flow (with energetic ripple) downhill with slug initiation and slug growth upward dip; and aerated slug downhill and slug growth at the dip. These behaviours are different from published work on this subject with low angle of inclination. The data analysis revealed that the two types of slug initiation mechanisms (wave growth and wave coalescence) observed are geometry specifics. The slug translational velocities (at the dip and uphill section) were used as criterion to determine the flow condition for each slug initiation mechanism at the dip. Five sand-water flow regimes (full suspension, streak, saltation, sand dune, and sand bed) were established by physical observation and data analysis. It was also observed that sand streaks were denser towards the central line of pipe bottom in the downhill pipe than that in uphill pipe. At downhill pipe section, there were sand gathering toward the central line of the pipe bottom. The characteristics of sand transportation at the dip section were found slightly different from downhill and uphill pipe for higher sand concentrations. When dense streak occurred at the downhill, the sand particles become dispersed at the dip. The minimum transport conditions (MTC) were determined at different sand concentration. The sand minimum transport condition in the dip section was found to be slightly lower than those in the downhill and uphill section. The minimum transport condition for a single phase water flow for the 24˚ dip. test section was slightly higher (with difference of about 0.1m/s) than that of the 12˚ at the downward and upward of the dip section at low sand concentration. In addition, local sand measurements using conductivity time series results at the downhill and uphill section showed the influence of sand concentration and flow condition on sand flow patterns. The air-water-sand results showed that sand deposits occurred in uphill section after sand transport at the downhill and dip sections. This was due to different flow regimes exhibited at the different pipe sections. The stratified (wavy) flow was the dominant flow in downhill pipe; therefore sand was observed transporting within the liquid film as thin streak for most of test conditions. The slug initiation at the dip section was observed to be a major factor that influences the sand behaviour. Sand particles in the slug unit (at the dip and uphill of the pipe) were observed to be entrained in the slug body once slug is initiated, thereby changing the force vector generating turbulence flow at the front of slug body. Once the sand particles entered the film zone of the slug unit, they immediately stopped moving forward due to the film velocity significantly lower than the slug body coupled with gravity effect. . Sand particles were found to be falling back while travelling with the water film at some conditions, until they were picked up by the next slug body. The results of this work provide a better understanding to the study of multiphase flow for pipeline design and most especially sand behaviour at the dip. The sand dune regime is identified distinctively using conductivity ring technique which would assist in determining the operating conditions that allow sand dune formation. The knowledge of flow condition at full suspension of sand is an important parameter to determine the erosion rate over the life span of the pipeline. Also, the quantity of sand bed and flow condition of sand settling at the dip is useful information for production chemist in order to determine the effectiveness of corrosion inhibitor at the bottom of the pipe. In conclusion, sand transport characteristics and MTC were strongly dependent on the gas-liquid flow regime and pipe geometry; and cannot be generalised on the superficial liquid and gas velocities of the transport fluid.
Open Access
Experimental and numerical investigation of high viscosity oil-based multiphase flows
(Cranfield University, 2013-05) Alagbe, Solomon Oluyemi; Yeung, Hoi
Multiphase flows are of great interest to a large variety of industries because flows of two or more immiscible liquids are encountered in a diverse range of processes and equipment. However, the advent of high viscosity oil requires more investigations to enhance good design of transportation system and forestall its inherent production difficulties. Experimental and numerical studies were conducted on water-sand, oil-water and oilwater- sand respectively in 1-in ID 5m long horizontal pipe. The densities of CYL680 and CYL1000 oils employed are 917 and 916.2kg/m3 while their viscosities are 1.830 and 3.149Pa.s @ 25oC respectively. The solid-phase concentration ranged from 2.15e-04 to 10%v/v with mean diameter of 150micron and material density of 2650kg/m3. Experimentally, the observed flow patterns are Water Assist Annular (WA-ANN), Dispersed Oil in Water (DOW/OF), Oil Plug in Water (OPW/OF) with oil film on the wall and Water Plug in Oil (WPO). These configurations were obtained through visualisation, trend and the probability density function (PDF) of pressure signals along with the statistical moments. Injection of water to assist high viscosity oil transport reduced the pressure gradient by an order of magnitude. No significant differences were found between the gradients of oil-water and oil-water-sand, however, increase in sand concentration led to increase in the pressure losses in oil-water-sand flow. Numerically, Water Assist Annular (WA-ANN), Dispersed Oil in Water (DOW/OF), Oil Plug in Water (OPW/OF) with oil film on the wall, and Water Plug in Oil (WPO) flow pattern were successfully obtained by imposing a concentric inlet condition at the inlet of the horizontal pipe coupled with a newly developed turbulent kinetic energy budget equation coded as user defined function which was hooked up to the turbulence models. These modifications aided satisfactory predictions.
Open Access
Experimental investigation of high viscous multiphase flow in horizontal pipelines
(2016) Baba, Yahaya D.; Yeung, Hoi
Diminishing reserves of “conventional” light crude oil, increased production costs amidst increased world energy demand over the last decade has spurred industrial interest in the production of the significantly and more abundant “unconventional” heavy crude oil. Recent findings have shown that unconventional oil being a veritable energy source accounts for over two-thirds of the world total oil reserve. The exploration of this vast resource for easy production and transportation requires a good understanding of multiphase system for which the knowledge of the effect of fluid viscosity is of great importance. Heavy oils are known for their high liquid viscosities which make them even more difficult and expensive to produce and transport in pipelines at ambient temperatures. In the light of this, it has become imperative to investigate the rheology of high viscosity oils and ways of enhancing its production and transportation since a critical understanding of multiphase flow characteristics are vital to aid engineering design. It is clear from experimental investigation reported so far in literatures and in Cranfield University that the behaviour of high viscosity oil-gas flows differs significantly from that of low viscosity oils. This means that most of the existing prediction models in the literature which were developed from observations of low viscosity liquid-gas flow will not perform accurately when compared to oil-gas flow data for high viscosity oil. Therefore, this research work seek to extend databank and provide a clearer understanding of the physics of high viscous multiphase flows. Experimental investigation have been conducted using 3-inch and 1-inch ID horizontal test facilities for oil-gas and oil-water respectively using different oil viscosities. The effects of liquid viscosities on oil-gas two phase flow parameters (i.e. pressure gradient, mean liquid holdup, slug frequency, slug translational velocity and slug body length) have been discussed. Assessment of existing prediction models and correlations in the literature are also carried out and their performance highlighted. New/improved prediction correlations for high viscosity oil-gas flow slug frequency, slug translational velocity and slug body have been proposed with their performance evaluated against the results obtained for this study and in literature. As for high viscosity oil-water flows, a new flow pattern maps have been established for high viscous oil-water two-phase flow in horizontal pipe with ID = 0.0254 m for which four flow patterns were observed namely; rivulet, core annular, plug and dispersed flows were observed. Generally, it was observed that increase in oil viscosity favoured the Core Annular Flow pattern, similar behaviour was also observed for increased oil holdup. Comparatively analysis of results obtained here with low viscous kerosene and water flow study obtained under similar flow geometry and conditions shows significant difference in flow patterns under similar flow conditions.
Open Access
Experimental investigations of two-phase flow measurement using ultrasonic sensors
(Cranfield University, 2016-05) Abbagoni, Baba Musa; Yeung, Hoi
This thesis presents the investigations conducted in the use of ultrasonic technology to measure two-phase flow in both horizontal and vertical pipe flows which is important for the petroleum industry. However, there are still key challenges to measure parameters of the multiphase flow accurately. Four methods of ultrasonic technologies were explored. The Hilbert-Huang transform (HHT) was first applied to the ultrasound signals of air-water flow on horizontal flow for measurement of the parameters of the two- phase slug flow. The use of the HHT technique is sensitive enough to detect the hydrodynamics of the slug flow. The results of the experiments are compared with correlations in the literature and are in good agreement. Next, experimental data of air-water two-phase flow under slug, elongated bubble, stratified-wavy and stratified flow regimes were used to develop an objective flow regime classification of two-phase flow using the ultrasonic Doppler sensor and artificial neural network (ANN). The classifications using the power spectral density (PSD) and discrete wavelet transform (DWT) features have accuracies of 87% and 95.6% respectively. This is considerably more promising as it uses non-invasive and non-radioactive sensors. Moreover, ultrasonic pulse wave transducers with centre frequencies of 1MHz and 7.5MHz were used to measure two-phase flow both in horizontal and vertical flow pipes. The liquid level measurement was compared with the conductivity probes technique and agreed qualitatively. However, in the vertical with a gas volume fraction (GVF) higher than 20%, the ultrasound signals were attenuated. Furthermore, gas-liquid and oil-water two-phase flow rates in a vertical upward flow were measured using a combination of an ultrasound Doppler sensor and gamma densitometer. The results showed that the flow gas and liquid flow rates measured are within ±10% for low void fraction tests, water-cut measurements are within ±10%, densities within ±5%, and void fractions within ±10%. These findings are good results for a relatively fast flowing multiphase flow.
Open Access
Experimental study on severe slugging mitigation by applying wavy pipes
(Elsevier Science B.V., Amsterdam, 2013-01-31T00:00:00Z) Xing, Lanchang; Yeung, Hoi; Shen, Joseph; Cao, Yi
Wavy pipes were installed in the pipeline for mitigating severe slugging in pipeline/riser systems. Experimental results have revealed that: with a wavy pipe applied, the operating region of severe slugging is reduced; the severity of severe slugging and oscillation flow is mitigated; the wavy pipe performs better with its outlet located upstream of the riser base. The wavy pipe is essentially reducing the slug length. For severe slugging the wavy pipe works by accelerating the movement of the gas in the pipeline to the riser base; for the oscillation flow it works by mixing the gas/liquid two phases.
Open Access
Flow measurement and monitoring using orifice plates
(1996-03) Papadopoulos, Christos E.; Yeung, Hoi
The orifice meter is still commonly used for natural gas measurement despite its many limitations. Considerable efforts in recent years have resulted in improved knowledge of factors such as installation effects and the value of discharge coefficient but a serious problem still remains with the measurement of differential pressure since, when line static pressures are as high as 200 bar, differential pressures of 500mbar have to be measured. Furthermore, the flow is never absolutely steady and the performance of the pressure transducers under such conditions is not yet fully understood. This thesis demonstrates the need to apply modern signal processing and analysis techniques to enhance the performance of process instrumentation systems. The use of two static pressure transducers of resonance type upstream and downstream the orifice meter, with a high frequency response, can offer the ability, by using spectral analysis and spectrum estimation methods, to extract additional information regarding the meter’s performance as well as diagnostic information about the whole process plant. It also demonstrates a method to check and, at the same time, to safeguard the flow information obtained from an orifice meter with the use of a third pressure transducer upstream of a Mitsubishi flow conditioner. Furthemore, information about the performance of the package orifice - conditioner using the discharge coefficient (Cd) and the amplitude spectrum from the three pressure transducers can be obtained.
Open Access
Gamma radiation methods for clamp-on multiphase flow metering
(Cranfield University, 2008-02) Blaney, S.; Yeung, Hoi
The development of a cost-effective multiphase flow meter to determine the individual phase flow rates of oil, water and gas was investigated through the exploitation of a single clamp-on gamma densitometer and signal processing techniques. A fast-sampling (250 Hz) gamma densitometer was installed at the top of the 10.5 m high, 108.2 mm internal diameter, stainless steel catenary riser in the Cranfield University multiphase flow test facility. Gamma radiation attenuation data was collected for two photon energy ranges of the caesium-137 radioisotope based densitometer for a range of air, water and oil flow mixtures, spanning the facility’s delivery range. Signal analysis of the gamma densitometer data revealed the presence of quasi-periodic waveforms in the time-varying multiphase flow densities and discriminatory correlations between statistical features of the gamma count data and key multiphase flow parameters. The development of a mechanistic approach to infer the multiphase flow rates from the gamma attenuation information was investigated. A model for the determination of the individual phase flow rates was proposed based on the gamma attenuation levels; while quasi-periodic waveforms identified in the multiphase fluid density were observed to exhibit a strong correlation with the gas and liquid superficial phase velocity parameters at fixed water cuts. Analysis of the use of pattern recognition techniques to correlate the gamma densitometer data with the individual phase superficial velocities and the water cut was undertaken. Two neural network models were developed for comparison: a single multilayer-perceptron and a multilayer hierarchical flow regime dependent model. The pattern recognition systems were trained to map the temporal fluctuations in the multiphase mixture density with the individual phase flow rates using statistical features extracted from the gamma count signals as their inputs. Initial results yielded individual phase flow rate predictions to within ±10% based on flow regime specific correlations.
Open Access
Gas-Liquid Two-Phase Flow in Up and Down Vertical Pipes
(Cranfield University, 2013-10) Almabrok, Almabrok Abushanaf; Yeung, Hoi
Multiphase flows occurring in pipelines with a serpentine configuration is an important phenomenon, which can be encountered in heat exchangers used in a variety of industrial processes. More specifically, in many industrial units such as a large cracking furnace in a refinery, the tubes are arranged in a serpentine manner and are relatively short. As flow negotiates round the 180o bend at the ends of the tubes, the generated centrifugal force could cause flow maldistribution creating local dry spots, where no steady liquid film is formed on the adjacent straight sections of the pipe. As a result, events including coking, cracking and overheating of heat transfer surfaces may occur and lead to frequent shutdown of the facilities. Consequently, this could increase operating costs and reduce production revenue. Thus, it is desirable to know the effect that the bends exert on the flow in the straight part of the pipe. Apart from this, knowledge of the bend effects on the flows in the pipeline could also be important for the design of other pipelines for gas/liquid transport, e.g. offshore gas and oil pipelines. Quite a large number of studies have been found in the literature. The majority of them were for two-phase flow with small diameter pipes (i.d. ≤ 50 mm). However, studies with large diameter pipes (i.d. ≥ 100 mm), have increasingly been considered in recent years as problems related to large diameter vertical pipes are being encountered more and more often in industrial situations. This thesis studies the effect of 180o bends on the characteristics and development of gas-liquid two-phase flows in large diameter downward and upward pipes. The study particularly focuses on the influence of serpentine configuration on flow structure, cross-sectional void distribution and circumferential liquid film profiles and their development along the downward and upward sections. It was found that both the top and bottom bends have considerable impacts on flow behaviour, although to varying degrees. These impacts were highly dependent on the air and water flow rates. For sufficient flow rates, the bends were observed to create flow maldistribution in the adjacent straight section, due to the effects of centrifugal force. The air moved towards the inner zone of the bend and the water towards the outer zone, while a lesser quantity of water was identified on the other surfaces of the pipe. Investigation of the film thickness development in the downward and upward sections showed that, the liquid film behaviour close to the bends was significantly different from those located further away. This can be attributed to the centrifugal force of the bends. Examination of the power spectral density (PSD) along the downward and upward sections showed that, the shape of PSD located in the adjacent section to the bends, was substantially different from those located further away. Furthermore, several flow regime maps were generated which showed that, in addition to bubbly, intermittent and annular flows, unstable flows existed along the upward section, particularly for low gas and water flow rates. In this study it was found that, the lower bend was periodically blocked by the liquid and then blown through by the accumulated air. The data obtained from this study were compared with different theoretical correlations found in the existing literature. Some discrepancy between the results of the current study and those of previous published materials was noted. Updated correlations were presented which provided well results when they applied for the data obtained from the current study and previous studies.
Open Access
Gas/liquid flow behaviours in a downward section of large diameter vertical serpentine pipes
(Elsevier, 2015-10-09) Almabrok, Almabrok Abushanaf; Aliyu, A. M.; Lao, Liyun; Yeung, Hoi
An experimental study on air/water flow behaviours in a 101.6 mm i.d. vertical pipe with a serpentine configuration is presented. The experiments are conducted for superficial gas and liquid velocities ranging from 0.15 to 30 m/s and 0.07 to 1.5 m/s, respectively. The bend effects on the flow behaviours are significantly reduced when the flow reaches an axial distance of 30 pipe diameters or more from the upstream bend. The mean film thickness data from this study has been used to compare with the predicted data using several falling film correlations and theoretical models. It was observed that the large pipe data exhibits different tendencies and this manifests in the difference in slope when the dimensionless film thickness is plotted as a power law function of the liquid film Reynolds number.
Open Access
Hydraulic optimisation of service reservoirs to maintain water quality in distribution systems
(Cranfield University, 2001-10) O'Neill, S.; Yeung, Hoi
Water supply utilities worldwide are under pressure to meet stringent water quality and supply demands Service reservoirs (SRs) or treated water storage reservoirs have been built for the dual function of maintaining pressure and providing a buffer of supply. A balance must be sought between operational objectives in order to ensure adequate supply in the event of unforeseen incidents whilst limiting the maximum time between abstraction and the point of use. Existing reservoirs can have storage times between a couple of hours and several tens of days. The resulting degradation in water quality ensures that it is no longer feasible to focus on point of abstraction treatment as a means of assuring that all customer and legislator expectations are continuously met. This thesis aims to evaluate the hydraulic design and operation of service reservoirs in the UK and evaluate methods to improve performance. A generic study of mixing in service reservoirs has been conducted using physical modelling techniques. The segregation of generic groups of reservoirs for modelling was defined after a comprehensive survey of 166 operational full-scale reservoirs was completed. Reservoir groups are defined in terms of shape and aspect ratio. Steady state, transient tests and intermittent flow — "fill and draw" tracer tests were conducted. Step and pulse trace injection techniques were used. Dye tests were conducted for flow visualisation and the results recorded with photographic stills and a digital video recorder. Water age is quantified in terms of cumulative percentage of injected trace recovery. Flow fractions in terms of dead space, plug flow and mixed flow are quantified for each series of tests using a multiparameter model. Alternative methods of quantification. dead areas are evaluated and discussed. Key reservoir performance indicators are defined and linked to water quality issues. The results presented have been compiled into a design guide document to enable water utility managers to simply evaluate existing reservoir designs and evaluate potential operational and retrofit options for optimisation. Case studies of full-scale reservoirs applications are presented.