CERES :: Browsing by Author "Verdin, Patrick G."

Browsing by Author "Verdin, Patrick G."

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Open Access
Analytical and numerical predictions of the thermal performance of multi-layered lattice structures
(Elsevier, 2019-10-04) Ernot, Jean; Verdin, Patrick G.; Ahmad, Hayder; Indge, Philip
The recent development of additive manufacturing has allowed complex geometries such as multi-layered lattice structures to be designed for different applications, including heat transfer. Performing Computational Fluid Dynamics (CFD) analyses on each new design iteration of lattice structures would require high computational time and cost. An analytical model has therefore been developed, able to rapidly and cost-effectively predict the heat transfer of complex lattice structures. The numerical code has been written for a given multi-layered lattice sample and a two-step approach with fin analogy has been applied to determine the mean outlet fluid temperature and the total heat dissipation for air as the working fluid. CFD simulations have also been performed and results compared to the analytical ones. A very good agreement is obtained between numerical and analytical results under the defined industrial operating conditions of the complex lattice structures, showing that such analytical model can be quickly and efficiently applied to evaluate the thermal performance of multi-layered lattice structures.
Open Access
Application of foam assisted water-alternating-gas flooding and quantification of resistivity and water saturation by experiment and simulation to determine foam propagation in sandstone
(Elsevier, 2024-02-01) Khan, Javed Akbar; Kim, Jong; Irawan, Sonny; Permatasar, Karina Aryanti; Verdin, Patrick G.; Cai, Baoping; Yekeen, Nurudeen
Foam flooding by Foam Assisted Water-Alternating-Gas (FAWAG) is an important enhanced oil recovery method that has proven successful in experimental and pilot studies. The present study is carried out to monitor the movement of the foam front once injected into the porous medium. This study aims to investigate applications of resistivity waves to monitor foam propagation in a sandstone formation. In the present lab-scale experiments and simulations, resistivity measurements were carried out to monitor the progression of foam in a sand pack, and the relationships between foam injection time and resistivity, as well as brine saturation, were studied. The brine saturation from foam simulation using CMG STAR is exported to COMSOL and calculated true formation resistivity. A diagram was produced summarizing the progression of foam through the sand pack in the function of time, which enabled us to establish how foam progressed through a porous medium. A surfactant and brine mixture was injected into the sand pack, followed by nitrogen gas to generate the foam in situ. As foam progressed through the sand pack, resistance measurements were taken in three zones of the sand pack. The resistance was then converted into resistivity and finally into brine saturation. As foam travels through the sand pack, it is predicted to displace the brine initially in place. This gradually increases each zone's resistivity (decreases the brine saturation) by displacing the brine. Also, an increase in the surfactant concentration results in higher resistivity. Finally, a comparison of three different surfactant concentrations was evaluated in terms of resistivity results, water saturation, and foam propagation monitoring to obtain the optimum surfactant concentration involved in foam flooding.
Open Access
An automatic multi-stepping approach to aircraft ice prediction
(Cranfield University, 2007-10) Verdin, Patrick G.; Charpin, J. P. F.
Flying an aircraft in icing conditions may seriously degrade its aerodynamical performance and threaten the flight safety. Over the years, new technologies and improved procedures have limited the potential risks caused by aircraft icing. Experimental studies being very expensive, numerous computer codes have been developed to simulate ice shapes and tackle the problem. Typically in these codes, a flow solution and key icing parameters are evaluated around a clean un-iced geometry and their values remain constant during the entire simulation. This approach may be acceptable for short exposure times or when the ice shape only slightly deforms the initial geometry. However, in other cases, the values of the icing parameters may vary and the simulation will loose its accuracy: for large shapes, the presence of the ice influences the surrounding airflow significantly, altering the value of icing parameters and ultimately the ice accretion. Calculating more accurate ice shapes therefore requires to periodically recompute the flow field around the body during the simulation and determine updated values for icing parameters. This procedure, known as multi-stepping, is investigated in this thesis and adapted to the new threedimensional icing code ICECREMO2. Several multi-step algorithms are presented and tested on cylinders and airfoils. When possible, the ice shapes simulated are compared with experimental results. The first multi-step calculations were generally performed manually. The user had to perform a rather tedious work and inappropriate instructions could lead to severe inaccuracies in the simulations. To avoid these difficulties, a fully automated procedure will be developed including all stages of a multi-step computation. This significantly reduces user interaction and the overall computing time. The present research work forms part of the ICECREMO2 project. ICECREMO2 is a three-dimensional ice accretion and water flow code developed collaboratively by Airbus UK, BAe Systems, Dunlop Aerospace, Rolls-Royce, GKN Westland Helicopters, QinetiQ and Cranfield University under the auspices of the UK Department of Trade and Industry. i
Open Access
CFD and experimental study of heat dissipation from an anti-coning, pin vented, inboard mounted brake disc
(Sage, 2022-09-29) Mingozzi, Filippo; Verdin, Patrick G.; Gucci, Lorenzo; Tirovic, Marko
Anti-coning brake discs are known for their superior NVH characteristics when compared to other disc designs, but also for poorer heat dissipation. Cooling characteristics of such a disc design are studied numerically and experimentally on a specially developed Thermal Spin Rig. The disc is installed inboard on a high-performance off-road vehicle, with portal axles and wheel drives, resulting in nearly fourfold higher disc rotational speeds in comparison to the wheel speeds. Being exposed to the free-flowing air and rotating much faster makes this application well worth the attention and deeper study in terms of disc cooling. Computational Fluid Dynamics (CFD) analyses show a detailed distribution of air velocities and pathlines, temperatures, pressures, and convective heat transfer coefficients. The results are all very coherent, conveying very useful information, both qualitatively and quantitatively. Their cumulative effect has been successfully validated by comparing the CFD predicted average convective heat transfer coefficients (hconv) with the experimental results obtained on the Thermal Spin Rig, in a controlled environment. CFD results show to be very close to average hconv values calculated from measured cooling curves. The agreement is very good for the wide temperature and speed range. The overall relative differences are under 5%, and in most cases under 3%, except for the low disc rotation speeds, which show a maximum relative difference of 12.5% calculated at 200 rpm, for the disc heated to 300◦ C. Such outcomes give confidence in the CFD results for future work in both disc design and vehicle installations.
Open Access
CFD modeling of a high enthalpy geothermal context
(2018-02-28) Renaud, Théo; Stebel, Michal; Verdin, Patrick G.; Falcone, Gioia
The promising development of highly energetic geothermal resources could considerably enhance geothermal power production worldwide. The first attempt at tapping supercritical/heated fluids was made by the Iceland Deep Drilling project (IDDP), but unfortunately a magma layer at a depth of 2,100m was encountered, and the drilling was abandoned. Yet, this drilling operation failure generated new opportunities for assessing the potential power generation close to shallow magmatic intrusions. Detailed numerical methods are required to assess the heat transfer and fluid thermodynamics at wellbore and reservoir scale at near supercritical conditions to provide production scenarios and forecasts as accurate as possible. A primary steady-state study of reservoir and wellbore heat extraction from a geothermal well near a magmatic chamber has been performed with Computational Fluid Dynamics (CFD) techniques. Using simplified geological assumptions based on the IDDP-1 well description, a 2D axisymmetric single phase flow model was developed and its results were compared to those obtained with a full 3D CFD model. The simulated output power simulations reached 25 MW at 350°C and a wellhead pressure of 140 bars. Methodology and results from this study show that CFD techniques can be successfully used to assess geothermal energy outputs for unconventional geothermal wells and can provide details of a vapor superheated flow structure at wellbore-reservoir scale.
Open Access
CFD study of the characteristics of a single elongated gas bubble in liquid in a moderately inclined pipe
(Elsevier, 2021-03-23) Livinus, Aniefiok; Verdin, Patrick G.
In recent years, Computational Fluid Dynamics (CFD) modelling methods have been applied to study the behavior of a single elongated bubble in stagnant and flowing liquid. To date, only very few studies have been performed for slightly upwardly inclined pipes. This work presents mostly 2D numerical simulations based on the Volume of Fluid approach, dealing with the characteristics of a single elongated bubble injected into a liquid in a slightly upwardly inclined pipe. CFD-based results were compared with experimental results. In general, except the numerical bubble length, drift velocity, bubble fraction and bubble shape, agreed fairly with the experimental outcomes.
Open Access
CFD-based j-shaped blade design improvement for vertical axis wind turbines
(MDPI, 2022-11-15) García Auyanet, Antonio; Santoso, Rangga E.; Mohan, Hrishikesh; Rathore, Sanvay S.; Chakraborty, Debapriya; Verdin, Patrick G.
The need for an increase in energy harvesting has led to novel ideas and designs to extract more power from wind. One innovative solution is through the use of J-shaped blades for Darrieus vertical axis wind turbines (VAWTs), which is based on the removal of a portion of a conventional blade, either on the pressure or suction side. Although improvements in the self-starting capabilities of VAWTs have been reported when using such blades, the literature only studied hollow blades, showing a hair-like structure. This work numerically investigates six different J-shaped designs. A turbine comprising NACA0015-based blades forms the base case and is used to evaluate the 2D numerical models. Results show that blades with an external cut systematically outperform those designed with an internal cut. In addition, all proposed cut-based designs are shown to improve the starting torque of the turbine, reaching a 135% increase compared to the base model.
Open Access
Computational fluid dynamics simulations of water flow on a studded upstream eel pass
(Wiley, 2021-07-19) Syihab, Abu B. M. Ibnu; Verdin, Patrick G.; Wright, Rosalind M.; Piper, Adam T.; Rivas Casado, Monica
The European eel population has undergone a significant decline in recruitment over the last 3–4 decades. Anthropogenic riverine barriers that disrupt the eel's life cycle when migrating upstream are contributory factors in this decline. The development of eel passage facilities is one of many attempts to mitigate this problem. In upstream passes, eels rely on a substrate in the base of the pass to assist their ascent by climbing and/or swimming. This study numerically evaluates, using computational fluid dynamics, the hydrodynamic characteristics of water flow on a studded substrate, under a range of installation angles and water flowrates. To assess and predict the efficiency of the pass, simulated flow field data were used to create pass-ability maps by comparing simulated velocity data with eel swimming capabilities. An 11° installation angle with a ramp flowrate of 1.12 × 10−3 m3/s per metre width was shown to be likely most suitable for 70 mm long eels, and could be used by eels with sizes up to 150 mm. The numerical study has also shown that under specific water flowrates, installation angles of 30° or more can make the water level fluctuate and splash out of the eel pass, resulting in potential inefficiency in ramp water supply, while posing additional challenges for eels ascending the pass.
Open Access
Design and optimisation of a 20 MW offshore wind turbine blade
(Elsevier, 2024-04-24) Koragappa, Pavana; Verdin, Patrick G.
In the global pursuit of Net Zero emissions by 2050, wind turbines have become a leading solution. These renewable energy generators offer a trifecta of benefits, significantly reducing CO2 emissions, minimizing environmental impact, and delivering cost-competitive clean power. However, the key to maximizing their potential lies in the aerodynamic design of the turbine blades. By improving the blade performance, researchers and engineers can significantly increase wind energy capture, propelling wind turbines to the forefront of the global transition to a sustainable future. Higher power generating wind turbines are needed to reach the Net Zero target. By upscaling the “DTU 10 MW Reference Wind Turbine”, this research has achieved an aerodynamically stable 20 MW offshore wind turbine blade design. Variable rotation speed and variable pitch angle configurations have been considered to achieve an ideal power curve. The aerodynamic performance has been evaluated and quantified for a length optimised blade design, wherein the power and thrust have been increased by 80.84% and 88.67%, respectively, at a rated wind velocity of 12 m/s.
Open Access
Examination of non-traditional wax management techniques for flow assurance in petroleum production
(Society of Petroleum Engineers (SPE), 2022-12-01) Bassey, Bassey O.; Verdin, Patrick G.; Lao, Liyun
Wax deposition and build-up in reservoirs, wells and pipelines negatively impact asset productivity, integrity and economics. Several flow assurance techniques have been developed to mitigate or remediate waxing problems. Prominent among these are controlling operating conditions, chemical, thermal and mechanical methods. Their major drawbacks have remained exorbitant costs over life-of-field, no single method being sufficient, risk of costly mistakes due to overdesign or underdesign, etc. Some innovative, unconventional solutions were also developed over the past 2 decades, with promising results, though mostly yet to be commercialised. This paper highlights and reflects upon these hitherto standalone technologies given the largely sparse treatise they have received in the literature. The aim is to explore alternative wax management techniques as a means of improving the science of wax deposition and dissolution. Non-traditional methods were critically examined during a 12-month extensive literature survey. In-depth study of the rationale, principle of operation, results obtained, advantages and limitations of each method was performed. Independent studies using variants of the same method were juxtaposed to ascertain similarities and differences in applicability, with meeting points established to pave the way for future research collaboration. Reflections upon their merits, limitations, areas for improvement, and a case for scale-up are presented. Some non-traditional techniques have overcome certain perennial constraints of conventional techniques widely used in industry. The wax inhibition tool, for example, has low energy requirements, causes minimal environmental impacts and has relatively low costs. The precious metals and quartz used in making the tool are available locally, the alloys were mixed in the university's materials laboratory using in-house manpower and the flow loop was locally designed and fabricated. Having developed expertise on this project through repeat and improved experiments, preparing and implementing a cost-effective work program for its commercialization is doable by the research group with industry partnership. Adapting oscillatory motion based on Avrami theory to understand mechanism and kinetics of wax crystallization by experiments on North Sea crude had yielded two opposite effects that are interesting to note. Repeat experiments a decade later using synthetic oils from Southeast Asia yielded improved results and better understanding of wax deposition kinetics; an indication that this topic holds promise to unravel some mysteries in the subject, if its deliverables are embraced and implemented. The expose provided by this paper will hopefully contribute towards available knowledge on wax management. It is expected that conscious follow up on these technologies, some of which are related and could be hybridized, would inform future research directions for both the academia and industry in the field of flow assurance.
Open Access
Experimental study of a single elongated bubble in liquid in under 10-degree upwardly inclined pipes
(Elsevier, 2020-09-12) Livinus, Aniefiok; Verdin, Patrick G.
Two phase flow is of great interest in chemical and petroleum industries, and multiphase pipe flow models with closure relationships require experimental data for their development and validation. However, only little experimental information is available for slightly upward inclined pipes. Experimental investigations of single elongated bubble in marginally upwardly inclined pipes less than 10° have therefore been performed. Observations of the bubble drift velocity along the pipe has been highlighted. The drift velocity data presented here can contribute to improve knowledge of pipe inclination and viscosity dependency in drift velocity correlations. The new data on the bubble characteristics - shape, length, fraction and drift velocity may also provide useful information for the development and validation of numerical models. The measured drift velocity data have therefore been compared with some recently developed bubble velocity correlations.
Open Access
An experimental study on oil-water slug flow in export pipelines with shallow inclined elevations.
(Cranfield University, 2022-08) Akarcay, Mehmet; Lao, Liyun; Verdin, Patrick G.
The present study aims to better understand liquid-liquid intermittent flow regimes under different operational and flow conditions, such as flowrates of fluids, pipe inclination and fluid properties, with a focus on the pipe inclination alternating between 0° and +5°. A 0.0254m diameter pipe loop multiphase flow rig was utilised to conduct the experimental study. The fluids used for tests were tap water (pw = 997kg/m ³ and μw = 1mPa.s under the normal temperature and pressure (i.e. NTP, 15°C and 1atm) with an oil. Two different oils, EDM250 (p₀ = 811kg/m ³ and μw = 7mPa.s under the NTP) and H100 (p₀ = 878kg/m ³ and μw = 423mPa.s under the NTP) were used for tests to cover the variations in density and viscosity. It was found that less dense and viscous oils are less likely to develop intermittent flow regimes than heavier oils. In addition, regardless of the oil type present, intermittent flows are more likely to develop in a pipe with a higher degree of upwards inclination. This is particularly more effective for lighter oils because the inclination factor alters the angle between multiphase flow direction and gravity. This, in turn, aids the oil phases to intrude into the water phase region to have a greater prospect of developing and widening the relevant flow regimes envelopes such as slug and plug flows. Additionally, this thesis also proposes a modified liquid-liquid flow regime grouping method based on the modified Froude numbers. The proposed dimensionless parameter takes water hold-up variables into consideration by defining the hydraulic diameter to coincide with each phase's gravitational and inertial forces. Furthermore, correlations of pressure gradient and hold-up are also developed and presented. The developed models are then implemented with a dimensionless scale-up protocol to demonstrate scaling across laboratory experimental data generated from systems with different pipe diameter sizes. Overall, the models developed show improved performance for grouping flow patterns consistently, hence allowing for better prediction of liquid-liquid flow regimes that transition between intermittent flows. The significant outcomes of this project are the following: (1) evidence of intermittent flow regimes existing across a wide range of dual-incompressible multiphase flow conditions, (2) the development of design charts for pipelines that consider the prevention of intermittent flow regimes and (3) utilising the proposed hold-up and pressure gradient correlations with a scale-up protocol to predict larger pipeline behaviours.
Open Access
Heat transfer and fluid flow characteristics investigation using detached ribs in an axisymmetric impinging jet flow
(Springer, 2022-10-15) Rasheed, Adnan; Allauddin, Usman; Ali, Hafiz Muhammad; Uzair, Muhammad; Verdin, Patrick G.; Siddiqui, Yasir H.
This research work is directly concerned with the heat transfer involved in a single jet flow covering a heated surface having detached ribs present above the surface. A computational study has been conducted to check the effect due to the presence of such detached ribs. The generalized k−ω (GEKO) turbulence model with Reynolds-averaged Navier–Stokes equations formulation has been adopted after validation with the relevant experimental data from the literature. A rectangular rib design was selected for which rib width, height, clearance, pitch and first rib radial distance were varied to study their effect on heat transfer. Local heat transfer distributions were investigated over the target surface, especially focusing on the ribs-based region for different nozzle positions. The thermal performance with and without ribs is compared. A maximum increase in heat transfer of 64% was observed for a normalized nozzle to plate spacing z/d = 0.5.
Open Access
Heat transfer enhancement investigation in jet impingement system of a single and array of square jets using numerical tools
(Begell House, 2023-06-04) Allauddin, Usman; Sohail, Muhammad U.; Sohaib, Muhammad; Siddiqui, Muhammad A.; Khan, Muhammad H. U.; Khan, Kashif; Verdin, Patrick G.
Computational Fluid Dynamics (CFD) techniques can predict complex fluid flow structures and the thermal performance of jet impingement systems. Numerical studies can complement extensive and time-consuming experimental studies, where local parameter measurements are difficult and costly to obtain. In the current work, a single and an array of four and nine square jets impingements were numerically investigated with CFD, for mass flow rate (m) ranging from 2.71x10-4to 7.40x10-4kg/s. The effects of the jet’s outlet-to-target plate distance (Z) were assessed as a function of the width of a single square nozzle (B). The flow field features of different nozzle configurations were also studied. It was shown that the Nusselt number increases as the mass flow rate increases, but increases inversely as the dimensionless jet’s outlet-to-target plate spacing Z/B increases. The numerical investigation also demonstrated that when increasing the number of nozzles under a constant mass flow rate, the Nusselt number significantly increases. The effect of nozzle configuration is not that significant at Z/B > 7. The present impinging jet system offers about 63% enhancement in thermal efficiency was found while the pumping power increased by 3.7 times. All simulations were successfully validated with experimental data.
Open Access
The hydrodynamics of two-phase flows in the injection part of a conventional ejector
(Elsevier, 2018-10-10) Mifsud, Darren; Cao, Y.; Verdin, Patrick G.; Lao, Liyun
The characteristics of two-phase flow through a ‘conventional’ convergent-nozzle in an entrainment chamber of an ejector apparatus are described in this paper. A unique data set comprising 350 data points was generated in an air-water horizontal test-rig. Two sets of flow conditions were established, the first one including high liquid - low gas fluids with void fractions less than 0.55, and the second one involving high gas - low liquid fluids with void fractions greater than 0.75. All considered flow-rates lied within the sub-critical flow region. Two-phase flow pressure drop multiplier based empirical correlations were developed to estimate the total mass flow-rates. In the high liquid region, Morris (1985) correlation was modified, resulting in less than 10% error. In the high gas region, two new correlations were proposed, showing less than 10% and 15% of errors, respectively. The established empirical correlations were related to other available multipliers for different geometric configurations including a Venturi, an orifice plate, a gate valve, and a globe valve and were compared to 20 other void fraction correlations. The Chisholm (1983b) and Huq and Loth (1992) correlations showed the highest similarities to the ones proposed for the high liquid and high gas regions, respectively.
Open Access
Investigation towards a coupling between population balance and solidification models
(Cranfield University, 2016-08) Bourdillon, Arnaud; Verdin, Patrick G.
Due to the current oil consumption increase, deposits have decreased drastically. Engineers are constantly pushing the limits in order to drill deeper, convey oil further or build more efficient and sturdy pipelines. In an e.ort to obtain this rare ressource, companies are sometimes forced to install pipelines in extreme conditions and isolated terrains to exploit untouched oil deposits. If the structural designs of these devices have come to an agreement, internal phenomena occuring during the oil transport, are, currently not fully understood. In particular, droplets distribution evolution along with freezing events are the two main mechanisms responsible for efficiency loss of pipelines under extreme conditions. The aim of this work is to improve the current knowledge on these phenomena. For many years, oil industry has focused on expensive experiments to better apprehend complex flow phenomena. A promising alternative, computational fluid dynamic (CFD), has been used in this PhD to fill the gap of knowledge in this field of study. Two new single-fluid solidification solvers, an improved population balance model and a novel multi-fluid solidification model have been developed. These solvers have been implemented in an open-source CFD environment (OpenFOAM) to ensure universal acces and a potential extension to this work. It is shown that both single-fluid solidification solvers provide very good results when compared to experimental data. The maximum local discrepancies are evaluated below 20% for the worst case. The population balance model study performed in this PhD has identified important parameters, often under-looked. These findings have led to an improvement of the previous model close to 30% for the best case when compared to experimental results. The multi-fluid solidification model provides accurate ice formation rates (10% of maximal local discrepancies) when compared to experiments. The work presented in this thesis, describes, within the same CFD environment, solvers able to compute both droplet size and distribution evolution and solidification processes. They can be used separately or conjointly to perform the numerical analysis of the flow behavior under extreme conditions, improving the way such problems are currently tackled. They can also be enhanced further to deal with sligthtly di.erent research areas such as hydrates formations and corrosion events.
Embargo
Modeling of dual‐factor drag correction model for bubbly flow under elevated pressure
(Wiley, 2024-08) Gao, Yibo; Geng, Linlin; Verdin, Patrick G.; Fall, Ibra; Zhang, Ruijie; Tian, Zhongjie; Zhang, Desheng
A pressure correction method is proposed considering the influence of a dual factor. The applicability of a pressure correction method coupled with a drag model is discussed along with the accuracy of the simulation results obtained by such a pressure correction method. It is found that the present pressure correction method combined with the DBS (dual bubble size) drag model can accurately reflect the changing trend of gas holdup distribution with pressure. It is also established that results from this model applied to a bubble column match well with the experimental data. Finally, when compared with other pressure correction models, the proposed model shows better robustness in three‐dimensional simulations and can predict radial gas holdup distributions with better accuracy.
Open Access
Modelling an unconventional closed-loop deep borehole heat exchanger (DBHE): sensitivity analysis on the Newberry volcanic setting
(Springer, 2021-02-15) Doran, Hannah R.; Renaud, Théo; Falcone, Gioia; Pan, Lehua; Verdin, Patrick G.
Alternative (unconventional) deep geothermal designs are needed to provide a secure and efficient geothermal energy supply. An in-depth sensitivity analysis was investigated considering a deep borehole closed-loop heat exchanger (DBHE) to overcome the current limitations of deep EGS. A T2Well/EOS1 model previously calibrated on an experimental DBHE in Hawaii was adapted to the current NWG 55-29 well at the Newberry volcano site in Central Oregon. A sensitivity analysis was carried out, including parameters such as the working fluid mass flow rate, the casing and cement thermal properties, and the wellbore radii dimensions. The results conclude the highest energy flow rate to be 1.5 MW, after an annulus radii increase and an imposed mass flow rate of 5 kg/s. At 3 kg/s, the DBHE yielded an energy flow rate a factor of 3.5 lower than the NWG 55-29 conventional design. Despite this loss, the sensitivity analysis allows an assessment of the key thermodynamics within the wellbore and provides a valuable insight into how heat is lost/gained throughout the system. This analysis was performed under the assumption of subcritical conditions, and could aid the development of unconventional designs within future EGS work like the Newberry Deep Drilling Project (NDDP). Requirements for further software development are briefly discussed, which would facilitate the modelling of unconventional geothermal wells in supercritical systems to support EGS projects that could extend to deeper depths
Open Access
Nature and magnitude of operating forces in a horizontal bend conveying gas-liquid slug flows
(Elsevier, 2020-02-18) Gourma, Mustapha; Verdin, Patrick G.
Operating forces and magnitude of loads from gas-liquid slug flows exerted on a horizontally orientated 90o bend are investigated. The distributed forces are either Newtonian, associated with the fluids motion or Configurational, inherent to the internal distributions of the phases. The forces are derived through the conventional balances of mass and linear momentum arising from the volume of fluid (VOF) description of gas-liquid flows. The study uses the integral form of the momentum balance to estimate the operating forces budget. Invoking dynamical time scales separation discloses the connection of the Lamb vector (vortex-force) to the local time rate of momentum. An interesting outcome being an explicit expression for Favre-Reynolds stress that reveals the contribution of void fraction fluctuations in the redistribution of the stress across the interface. Numerical simulations are performed to determine the magnitude of Newtonian loads on bend using a segmented domain technique to represent the fully established slug flow regime. The time-dependent traces of the relevant flow variables such as liquid hold-up, flow rates and resultant forces on the bend are recorded and analysed. Compared to the isotropic component, the deviatoric stresses are shown to have a marginal contribution to the total forces. It is also shown that loading cycles on bends are much higher than slugging cycles; this is an important feature for the structural integrity assessment of pipelines with bends.
Open Access
Numerical analysis of enhanced conductive deep borehole heat exchangers
(MDPI, 2021-06-19) Renaud, Théo; Pan, Lehua; Doran, Hannah R.; Falcone, Gioia; Verdin, Patrick G.
Geothermal energy is a reliable and mature energy source, but it represents less than 1% of the total renewable energy mix. While the enhanced geothermal system (EGS) concept faces technical validation challenges and suffers from public acceptance issues, the development of unconventional deep-well designs can help to improve their efficiency and reliability. Modelling single-EGS-well designs is key to assessing their long-term thermal performances, particularly in unconventional geological settings. Numerical results obtained with the T2WELL/EOS1 code have been validated with available experimental data from a deep borehole heat exchanger (DBHE), where a temperature of 358 ∘" role="presentation" style="max-height: none; display: inline; line-height: normal; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; min-width: 0px; min-height: 0px; border-width: 0px; border-style: initial; position: relative;">∘C has been measured at a depth of 1962 m. Based on a calibrated model, the thermal performances of two enhanced thermal conductive DBHEs with graphite were compared for high geothermal gradients. The analysis highlights the potential recovery of a variable fraction of vapour. Graphite used along the well appears to be the most suitable solution to enhance the thermal output by 5 to 8% when compared to conventional wells. The theoretical implementation of such well in the Newberry volcano field was investigated with a single and doublet DBHE. The findings provide a robust methodology to assess alternative engineering solutions to current geothermal practices.