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Thermocapillary motion of droplets in complex fluid flows
Get PDFUnderstanding how the presence of thermal gradients affects the motion of bubbles and drops is a subject of great relevance both from a theoretical and a practical standpoint, particularly when gravitational effects are minimal or completely uninfluential. In the past half century, considerable progress has been made onthe investigation of the so-called thermocapillary phenomenon in an attempt to clarify the mechanisms at work in multiphase systems with liquid-liquid or liquid-gas interfaces.;Given the complexity of the problem, most of these investigations have been carried out under simplified conditions, assuming unbounded flows or considering relatively simple geometries in which the presence of solid boundaries was not explicitly taken into account. Additionally, even though non-Newtonian fluids are ubiquitous in engineering and science, the majority of these works have been carried out assuming Newtonian phases.;The aim of the present thesis is to study the thermocapillary migration of a droplet in systems exhibiting an added level of complexity, specifically in terms of wall effects, domain shape and rheological properties of the fluids. To accomplish these objectives, we rely on a concerted approach based on well-established numerical strategies and, where possible, we derive analytical solutions.;A thermocapillary solver based on a hybrid Level Set-Volume of Fluid method availablein OpenFOAM has been implemented and validated against previous analytical results, numerical solutions and experimental observations obtained in reduced gravity conditions (Sect. 3.5). In the first part of the study, we investigate the problem of a droplet interacting with the boundaries of a parallelepipedic domain.;The case study has been assessed by releasing the droplet in proximity to the lateral walls of the domain considering both adiabatic and purely conductive boundary conditions. The results showed that the droplet can experience a secondary motion perpendicular to the main direction of motion. In particular, it was observed that the droplet can either move away or towards the walls depending on the thermal boundary conditions at the wall (i.e., whether the wall is adiabatic or purely conductive) and on the extent of convective phenomena.;The investigation was then extended by adopting more complex geometries (converging and diverging channels), which were found to produce distortion of the thermal field distribution with direct consequences on the migration process (Sect. 4.2.1 and 4.2.2). In the second part of the thesis, non-Newtonian effects have been expressly considered. Specifically, the role played by the fluid's elasticity (while neglecting convective transport of energy and momentum) has been accounted for by modelling the continuous phase on the basis of constant-viscosity viscoelastic models, namely the Oldroyd-B model and FENE-CR model.;The numerical simulations were carried out for a specific value of the Capillary number and assuming thesame material properties for both phases. We investigated the effects of the various model parameters (i.e., polymer concentration and extensibility parameter) and Deborah number on the droplet motion. The results showed that the droplet speed, evaluated as a function of the Deborah number, initially decreases following a quadratic trend.;For larger Deborah number, the trend reverts its concavity and eventually reaches a plateau. In terms of shape, the results have shown that under the prescribed conditions the droplet deforms in a prolate manner and, for sufficiently large values of the Deborah number (having fixed the Capillary number), the viscoelastic stresses localised at the rear stagnation point are responsible for the formation of a pointed tail.;The viscoelastic problem was also tackled by means of perturbation techniques under the assumption of absence of confinement and weak viscoelastic effects, which allowed the derivation of corrective formulae for the droplet migration velocity and expressions describing the shape of the deformed drop. The results of the analytical solutions were found to be in fairly good agreement with the outcomes of the computations, both interms of drop shape and migration speed.Understanding how the presence of thermal gradients affects the motion of bubbles and drops is a subject of great relevance both from a theoretical and a practical standpoint, particularly when gravitational effects are minimal or completely uninfluential. In the past half century, considerable progress has been made onthe investigation of the so-called thermocapillary phenomenon in an attempt to clarify the mechanisms at work in multiphase systems with liquid-liquid or liquid-gas interfaces.;Given the complexity of the problem, most of these investigations have been carried out under simplified conditions, assuming unbounded flows or considering relatively simple geometries in which the presence of solid boundaries was not explicitly taken into account. Additionally, even though non-Newtonian fluids are ubiquitous in engineering and science, the majority of these works have been carried out assuming Newtonian phases.;The aim of the present thesis is to study the thermocapillary migration of a droplet in systems exhibiting an added level of complexity, specifically in terms of wall effects, domain shape and rheological properties of the fluids. To accomplish these objectives, we rely on a concerted approach based on well-established numerical strategies and, where possible, we derive analytical solutions.;A thermocapillary solver based on a hybrid Level Set-Volume of Fluid method availablein OpenFOAM has been implemented and validated against previous analytical results, numerical solutions and experimental observations obtained in reduced gravity conditions (Sect. 3.5). In the first part of the study, we investigate the problem of a droplet interacting with the boundaries of a parallelepipedic domain.;The case study has been assessed by releasing the droplet in proximity to the lateral walls of the domain considering both adiabatic and purely conductive boundary conditions. The results showed that the droplet can experience a secondary motion perpendicular to the main direction of motion. In particular, it was observed that the droplet can either move away or towards the walls depending on the thermal boundary conditions at the wall (i.e., whether the wall is adiabatic or purely conductive) and on the extent of convective phenomena.;The investigation was then extended by adopting more complex geometries (converging and diverging channels), which were found to produce distortion of the thermal field distribution with direct consequences on the migration process (Sect. 4.2.1 and 4.2.2). In the second part of the thesis, non-Newtonian effects have been expressly considered. Specifically, the role played by the fluid's elasticity (while neglecting convective transport of energy and momentum) has been accounted for by modelling the continuous phase on the basis of constant-viscosity viscoelastic models, namely the Oldroyd-B model and FENE-CR model.;The numerical simulations were carried out for a specific value of the Capillary number and assuming thesame material properties for both phases. We investigated the effects of the various model parameters (i.e., polymer concentration and extensibility parameter) and Deborah number on the droplet motion. The results showed that the droplet speed, evaluated as a function of the Deborah number, initially decreases following a quadratic trend.;For larger Deborah number, the trend reverts its concavity and eventually reaches a plateau. In terms of shape, the results have shown that under the prescribed conditions the droplet deforms in a prolate manner and, for sufficiently large values of the Deborah number (having fixed the Capillary number), the viscoelastic stresses localised at the rear stagnation point are responsible for the formation of a pointed tail.;The viscoelastic problem was also tackled by means of perturbation techniques under the assumption of absence of confinement and weak viscoelastic effects, which allowed the derivation of corrective formulae for the droplet migration velocity and expressions describing the shape of the deformed drop. The results of the analytical solutions were found to be in fairly good agreement with the outcomes of the computations, both interms of drop shape and migration speed
The identification of the effect of high rate deformation on the microstructure and properties of titanium alloys
Get PDFMaterial forming processes such as forming aerospace components, it is well known that are highly influenced by strain, strain rate and temperature. The effects of these parameters in flow stress and microstructure of titanium alloys are critical. The regime of strain rates where aerospace components such as aerofoil shapes for gas turbine engines are formed are between 1s-1 and 150 s-1. Conventional testing machines are unable to reach these strain rates and provide accurate information which the manufacturing community is currently interested. This project focused on the process optimization of a high strain rate forging simulator which is capable for strain rates up to 200s-1. An equipment bought bythe AFRC to deal with the lack of flow data. Data which will be used in the future for simulating high speed forging and extrusion. The experimental optimization was achieved through temperature optimization, sample relevant position to push rod and sample position to induction coil. Furthermore, the project investigates the high strain rate deformation of Ti6Al4V alloy with two distinct microstructures in terms of strain rate and temperature influence on the microstructure. The flow behaviour of the material were also investigated and modelled. The Hansel-Spittel (H&S) rheological law demonstrates good compliance with the high strain rate deformation of Ti6Al4V. Last but not least, the data obtained by the high strain rate deformation of the Ti6Al4V was used to create the process and instability maps for the Ti6Al4V. Forboth microstructures the stable and unstable deformation areas has been identified.Material forming processes such as forming aerospace components, it is well known that are highly influenced by strain, strain rate and temperature. The effects of these parameters in flow stress and microstructure of titanium alloys are critical. The regime of strain rates where aerospace components such as aerofoil shapes for gas turbine engines are formed are between 1s-1 and 150 s-1. Conventional testing machines are unable to reach these strain rates and provide accurate information which the manufacturing community is currently interested. This project focused on the process optimization of a high strain rate forging simulator which is capable for strain rates up to 200s-1. An equipment bought bythe AFRC to deal with the lack of flow data. Data which will be used in the future for simulating high speed forging and extrusion. The experimental optimization was achieved through temperature optimization, sample relevant position to push rod and sample position to induction coil. Furthermore, the project investigates the high strain rate deformation of Ti6Al4V alloy with two distinct microstructures in terms of strain rate and temperature influence on the microstructure. The flow behaviour of the material were also investigated and modelled. The Hansel-Spittel (H&S) rheological law demonstrates good compliance with the high strain rate deformation of Ti6Al4V. Last but not least, the data obtained by the high strain rate deformation of the Ti6Al4V was used to create the process and instability maps for the Ti6Al4V. Forboth microstructures the stable and unstable deformation areas has been identified
The nature and effectiveness of therapies provided in counselling centres at the Princess Nourah Bint Abdulrahman University
Get PDFInterest in counselling and guidance in Saudi Arabia has grown in recent years. Evidence about how it is delivered and by whom, as well as its effectiveness, is limited. What does psychotherapy/counselling look like in practical terms in Saudi Arabia? How have western mental health approaches and procedures fared in an Arabic/Islamic cultural milieu? What has been assimilated and what has been accommodated or adapted? In this research I aimed to explore the nature and effectiveness of the counselling services provided at Princess Nourah bint Abdulrahman University, Riyadh, Saudi Arabia. This dissertation presents two studies using complementary research methods, carried out within a pluralist, broadly critical-realistic framework. The first study was a constructivist/descriptive qualitative counselling service research study, which aimed to map the nature of the therapists' perceptions of the counselling services, asking three broad questions: First, what kinds of services do therapists see themselves as providing to their clients? This included kinds of 'therapies', 'techniques',and 'measures'. Second, what kinds of professional experiences have therapists report, including 'years of experience', 'personal development' and 'improvement in providing counselling'? Third, what kinds of practice difficulties and challenges do therapists perceive, including 'in-session challenges' and 'external difficulties'? The study sample consisted of thirteen (out of a total of sixteen) female therapists at the counselling centre in Princess Nourah bint Abdulrahman University, Riyadh, Saudi Arabia. A semi-structured interview was developed and piloted in order to collect the study data, which was then analysed from the viewpoints of both a version of grounded theory and Braun & Clarke's thematic analysis. The findings showed that therapists used different kinds of predominantly western forms of psychotherapy, both positivist-realist (e.g. CBT) and humanistic-phenomenological (Person-centred Therapy) as well as mostly positivist-realist therapeutic techniques (e.g.they most commonly used homework, behavioural therapy, and behavioural activation) and assessments/measures (e.g. the Beck Depression Inventory and Beck Anxiety Inventory).;Furthermore, therapists generally reported that they had improved in their performance and were interested in developing their skills and providing better services, although some complained of limited opportunities to do so. Finally, therapists indicated that they faced both external difficulties (e.g. lack of privacy and conflict with co-workers) and in-session challenges with their clients (e.g. lack of client commitment to counselling and client silence) that affected their performance and work satisfaction. The second study was a quantitative client practice-based outcome study, using what can be described as both a mental health services research design and a practice-based therapy effectiveness study of the outcomes of counselling practiced at Princess Nourah bint Abdulrahman University. It aimed to document amount of client-reported personality change in the counselling centre at the Princess Nourah bint Abdulrahman University over the course of therapy. To do this, I used a western psychotherapy outcome measure that had been developed to assess -in a non-pathologising manner- the outcome of humanist, phenomenological approaches to psychotherapy.;This assessment measure, the Strathclyde Inventory (developed by Elliott, Rodgers, Freire, & Stephen, 2016), was chosen to avoid cultural sensitivities that might have been activated by more commonly-used pathology distress measures such as the CORE-OM. Therefore, an Arabic translation of the Strathclyde Inventory was prepared, using standard practices including parallel and back translation. The result was the 20-item Arabic translation (the SI-20-A) that measures two factors based on Carl Rogers' theory of the fully functioning person, namely Congruence/Experiential Fluidity and Incongruence/Experiential Constriction, as these concepts were considered in Islam and Arab culture. The outcome measure was administered to the clients by their therapists at the beginning, the middle, and then at the end of a course of therapy. Data from thirty eight clients was used and analysed using descriptive, inferential statistical analyses (a repeated measure ANOVA) within a critical realist perspective; in addition, reliable and clinical significant changes were calculated to provide multiple ways of documenting reported client change or lack of it using the SI-20-A. The study results showed that there were medium to large differences between the three time points (pre-, mid- and post-tests) and that these were extremely unlikely to be due to chance (p < .001). Additionally, the study found that about 44% of the clients at the end of the therapy appeared to have made clinically significant and reliable changes, 50% of the clients showed no change in reported personality functioning, and one of the clients showed deterioration on this measure. However, cultural differences between Western and Saudi Arabia may have affected the study findings, a possibility that I explore in the Discussion chapter of this dissertation.;Overall, the research findings provide a multi-faceted view of counselling centre services within a Saudi university and their effectiveness, with possible benefits for these services, for the therapists, and for the university's students: The main potential benefit to the Counselling Centre is encouragement to continue to provide help and support to therapists who sometime struggle to deal with client's issues, and to consider the importance of supporting quality counselling services. The therapists involved could benefit from the knowledge that the services they provide are generally effective with many clients. And the university students could benefit from knowing what kind of services that counselling centre offers and the quality and effectiveness of these services. Beyond Princess Nourah bint Abdulrahman University, this dissertation contributes to knowledge about the counselling and psychotherapy field in Saudi Arabia by documenting the nature of university-based counselling services provided and quantifying client outcomes in the university counselling centre; these include the counselling services provided, therapists' their practice difficulties, and substantial amount of client pre-post change over the course of therapy. This dissertation may encourage counselling and guidance in education settings to set up a clear and fixed roles and requirements which would help therapists and counsellors to be more careful with client confidentiality and privacy, and, in addition, to provide a better work environment to carry out counselling sessions. Furthermore, it highlighted the usefulness of evaluating the performance of the counselling services. Further research is recommended in the field of counselling in higher education institutions in Saudi Arabia to replicate these findings and to provide a better understanding of counselling services at Saudi universities and their effectiveness.Interest in counselling and guidance in Saudi Arabia has grown in recent years. Evidence about how it is delivered and by whom, as well as its effectiveness, is limited. What does psychotherapy/counselling look like in practical terms in Saudi Arabia? How have western mental health approaches and procedures fared in an Arabic/Islamic cultural milieu? What has been assimilated and what has been accommodated or adapted? In this research I aimed to explore the nature and effectiveness of the counselling services provided at Princess Nourah bint Abdulrahman University, Riyadh, Saudi Arabia. This dissertation presents two studies using complementary research methods, carried out within a pluralist, broadly critical-realistic framework. The first study was a constructivist/descriptive qualitative counselling service research study, which aimed to map the nature of the therapists' perceptions of the counselling services, asking three broad questions: First, what kinds of services do therapists see themselves as providing to their clients? This included kinds of 'therapies', 'techniques',and 'measures'. Second, what kinds of professional experiences have therapists report, including 'years of experience', 'personal development' and 'improvement in providing counselling'? Third, what kinds of practice difficulties and challenges do therapists perceive, including 'in-session challenges' and 'external difficulties'? The study sample consisted of thirteen (out of a total of sixteen) female therapists at the counselling centre in Princess Nourah bint Abdulrahman University, Riyadh, Saudi Arabia. A semi-structured interview was developed and piloted in order to collect the study data, which was then analysed from the viewpoints of both a version of grounded theory and Braun & Clarke's thematic analysis. The findings showed that therapists used different kinds of predominantly western forms of psychotherapy, both positivist-realist (e.g. CBT) and humanistic-phenomenological (Person-centred Therapy) as well as mostly positivist-realist therapeutic techniques (e.g.they most commonly used homework, behavioural therapy, and behavioural activation) and assessments/measures (e.g. the Beck Depression Inventory and Beck Anxiety Inventory).;Furthermore, therapists generally reported that they had improved in their performance and were interested in developing their skills and providing better services, although some complained of limited opportunities to do so. Finally, therapists indicated that they faced both external difficulties (e.g. lack of privacy and conflict with co-workers) and in-session challenges with their clients (e.g. lack of client commitment to counselling and client silence) that affected their performance and work satisfaction. The second study was a quantitative client practice-based outcome study, using what can be described as both a mental health services research design and a practice-based therapy effectiveness study of the outcomes of counselling practiced at Princess Nourah bint Abdulrahman University. It aimed to document amount of client-reported personality change in the counselling centre at the Princess Nourah bint Abdulrahman University over the course of therapy. To do this, I used a western psychotherapy outcome measure that had been developed to assess -in a non-pathologising manner- the outcome of humanist, phenomenological approaches to psychotherapy.;This assessment measure, the Strathclyde Inventory (developed by Elliott, Rodgers, Freire, & Stephen, 2016), was chosen to avoid cultural sensitivities that might have been activated by more commonly-used pathology distress measures such as the CORE-OM. Therefore, an Arabic translation of the Strathclyde Inventory was prepared, using standard practices including parallel and back translation. The result was the 20-item Arabic translation (the SI-20-A) that measures two factors based on Carl Rogers' theory of the fully functioning person, namely Congruence/Experiential Fluidity and Incongruence/Experiential Constriction, as these concepts were considered in Islam and Arab culture. The outcome measure was administered to the clients by their therapists at the beginning, the middle, and then at the end of a course of therapy. Data from thirty eight clients was used and analysed using descriptive, inferential statistical analyses (a repeated measure ANOVA) within a critical realist perspective; in addition, reliable and clinical significant changes were calculated to provide multiple ways of documenting reported client change or lack of it using the SI-20-A. The study results showed that there were medium to large differences between the three time points (pre-, mid- and post-tests) and that these were extremely unlikely to be due to chance (p < .001). Additionally, the study found that about 44% of the clients at the end of the therapy appeared to have made clinically significant and reliable changes, 50% of the clients showed no change in reported personality functioning, and one of the clients showed deterioration on this measure. However, cultural differences between Western and Saudi Arabia may have affected the study findings, a possibility that I explore in the Discussion chapter of this dissertation.;Overall, the research findings provide a multi-faceted view of counselling centre services within a Saudi university and their effectiveness, with possible benefits for these services, for the therapists, and for the university's students: The main potential benefit to the Counselling Centre is encouragement to continue to provide help and support to therapists who sometime struggle to deal with client's issues, and to consider the importance of supporting quality counselling services. The therapists involved could benefit from the knowledge that the services they provide are generally effective with many clients. And the university students could benefit from knowing what kind of services that counselling centre offers and the quality and effectiveness of these services. Beyond Princess Nourah bint Abdulrahman University, this dissertation contributes to knowledge about the counselling and psychotherapy field in Saudi Arabia by documenting the nature of university-based counselling services provided and quantifying client outcomes in the university counselling centre; these include the counselling services provided, therapists' their practice difficulties, and substantial amount of client pre-post change over the course of therapy. This dissertation may encourage counselling and guidance in education settings to set up a clear and fixed roles and requirements which would help therapists and counsellors to be more careful with client confidentiality and privacy, and, in addition, to provide a better work environment to carry out counselling sessions. Furthermore, it highlighted the usefulness of evaluating the performance of the counselling services. Further research is recommended in the field of counselling in higher education institutions in Saudi Arabia to replicate these findings and to provide a better understanding of counselling services at Saudi universities and their effectiveness
Radiation generation and high-field physics phenomena in ultra-intense laser-solid interactions
Get PDFStrathcyde thesis - ask staff. Thesis no : T15435This thesis was previously held under moratorium from 3rd December 2019 till 1st April 2021.This thesis reports on experimental and numerical investigations of the radiation produced via ultra-intense laser-solid interactions. Laser intensities in the range 10exp18−10exp24 Wcm−2 are explored, enabling these interactions to be investigated at current laser facilities (at the lower end of this intensity range), and predictions to be made about the properties of the emitted radiation, which will be measured at upcoming multi-petawatt laser facilities (for which intensities exceeding 10exp23 Wcm−2 should be accessible). The associated laser fields have sufficiently strong magnitudes that quantum electrodynamics (QED) effects play a significant role in the interaction.;There are two key effects which will be considered within the context of this thesis. The first is prolific production of high energy radiation from electrons that are accelerated by the laser fields. This radiation emission is necessarily accompanied by a back-reaction, or radiation reaction(RR) force. The second key effect is the production of electron-positron pairs, from the interaction of the high energy radiation with the laser fields. These QED effects will, in turn, impact relativistic plasma physics processes, enabling insight to be gained into interactions in the QED-plasma regime.;Ion acceleration will be influenced, as well as the production of radiation, which may enable the realisation of ultra-bright radiation sources (with brightness ∼ 1024 ph·s−1·mm−2·mrad−2·(0.1% bandwidth)−1) from laser-solid interactions. Exploiting these QED effects will enable exotic states of matter, such as electron-positron pair-plasmas, to be produced in the laboratory enabling, for example, the study of fundamental astrophysical phenomena.;The results presented in this thesis form three distinct studies. The first investigates the process of relativistic self-induced transparency (RSIT) during the interaction of an ultra-intense laser pulse (10exp20 Wcm−2) with an ultra-thin foil target (which is tens of nanometers thick). RSIT is a plasma physics process which is predicted to be heavily influenced by QED effects. During this investigation of RSIT, it was found that the light detected at the rear of ultra-thin foil targets is converted into higher order spatial modes, at both the laser frequency and its second harmonic.;It is found that it is possible to produce a radially polarised mode, of high intensity (∼10exp18 Wcm−2). Such a mode has applications in the efficient acceleration of electrons and positrons, and in the generation of radiation sources which are optimised in terms of their average photon energy and beam divergence. It is highly difficult to generate these modes at high intensity, using conventional solid-state optics, given their damage thresholds.;The second study is a numerical and analytical investigation of the effects of RSIT and RR on the acceleration of thin foil targets (hundreds of nanometers thick) interacting with ultra-intense laser pulses (10exp23 Wcm−2). It is demonstrated that the magnitude of the RR force is sensitive to the target thickness, thus indicating that it may be possible to control the properties of the emitted radiation, and the partition of laser energy between the plasma species, at upcoming laser facilities. For targets in which the magnitude of the RR force is weak, the emitted radiation is nearly isotropic, whereas for strong RR, distinct peaks appear in the photon angular distribution.;Given that the magnitude of the RR force is also reduced by early onset RSIT, it will be possible to diagnose this process via changes in the radiation distribution, at upcoming laser facilities. In this study, an analytical model was developed which, for the first time, describes the target velocity in the light sail regime of radiation pressure acceleration,under the influence of the RR force. The predictions of this model, in terms of the target velocity and the photon conversion efficiency, are found to be in good agreement with numerical simulations.;The final study proposes a multi-stage scheme for the investigation of non-linear pair-production, utilising a laser-solid interaction. By employing numerical modelling,it is demonstrated that this set-up enables an enhancement in the number and energy of positrons produced during ultra-intense laser-solid interactions, compared to conventional experimental set-ups. The first stage is the generation and optimisation of aγ-ray beam (in terms of the average photon energy and divergence half-angle) from an ultra-intense (10exp23 Wcm−2) laser-solid interaction. In the second stage, this beam interacts with dual counter-propagating laser pulses, inducing non-linear pair-production. It is shown that a significant number of positrons are produced by employing this scheme, with an anisotropic energy-angle distribution. This study will assist in the design of future experiments aiming to generate QED plasmas in the laboratory.This thesis reports on experimental and numerical investigations of the radiation produced via ultra-intense laser-solid interactions. Laser intensities in the range 10exp18−10exp24 Wcm−2 are explored, enabling these interactions to be investigated at current laser facilities (at the lower end of this intensity range), and predictions to be made about the properties of the emitted radiation, which will be measured at upcoming multi-petawatt laser facilities (for which intensities exceeding 10exp23 Wcm−2 should be accessible). The associated laser fields have sufficiently strong magnitudes that quantum electrodynamics (QED) effects play a significant role in the interaction.;There are two key effects which will be considered within the context of this thesis. The first is prolific production of high energy radiation from electrons that are accelerated by the laser fields. This radiation emission is necessarily accompanied by a back-reaction, or radiation reaction(RR) force. The second key effect is the production of electron-positron pairs, from the interaction of the high energy radiation with the laser fields. These QED effects will, in turn, impact relativistic plasma physics processes, enabling insight to be gained into interactions in the QED-plasma regime.;Ion acceleration will be influenced, as well as the production of radiation, which may enable the realisation of ultra-bright radiation sources (with brightness ∼ 1024 ph·s−1·mm−2·mrad−2·(0.1% bandwidth)−1) from laser-solid interactions. Exploiting these QED effects will enable exotic states of matter, such as electron-positron pair-plasmas, to be produced in the laboratory enabling, for example, the study of fundamental astrophysical phenomena.;The results presented in this thesis form three distinct studies. The first investigates the process of relativistic self-induced transparency (RSIT) during the interaction of an ultra-intense laser pulse (10exp20 Wcm−2) with an ultra-thin foil target (which is tens of nanometers thick). RSIT is a plasma physics process which is predicted to be heavily influenced by QED effects. During this investigation of RSIT, it was found that the light detected at the rear of ultra-thin foil targets is converted into higher order spatial modes, at both the laser frequency and its second harmonic.;It is found that it is possible to produce a radially polarised mode, of high intensity (∼10exp18 Wcm−2). Such a mode has applications in the efficient acceleration of electrons and positrons, and in the generation of radiation sources which are optimised in terms of their average photon energy and beam divergence. It is highly difficult to generate these modes at high intensity, using conventional solid-state optics, given their damage thresholds.;The second study is a numerical and analytical investigation of the effects of RSIT and RR on the acceleration of thin foil targets (hundreds of nanometers thick) interacting with ultra-intense laser pulses (10exp23 Wcm−2). It is demonstrated that the magnitude of the RR force is sensitive to the target thickness, thus indicating that it may be possible to control the properties of the emitted radiation, and the partition of laser energy between the plasma species, at upcoming laser facilities. For targets in which the magnitude of the RR force is weak, the emitted radiation is nearly isotropic, whereas for strong RR, distinct peaks appear in the photon angular distribution.;Given that the magnitude of the RR force is also reduced by early onset RSIT, it will be possible to diagnose this process via changes in the radiation distribution, at upcoming laser facilities. In this study, an analytical model was developed which, for the first time, describes the target velocity in the light sail regime of radiation pressure acceleration,under the influence of the RR force. The predictions of this model, in terms of the target velocity and the photon conversion efficiency, are found to be in good agreement with numerical simulations.;The final study proposes a multi-stage scheme for the investigation of non-linear pair-production, utilising a laser-solid interaction. By employing numerical modelling,it is demonstrated that this set-up enables an enhancement in the number and energy of positrons produced during ultra-intense laser-solid interactions, compared to conventional experimental set-ups. The first stage is the generation and optimisation of aγ-ray beam (in terms of the average photon energy and divergence half-angle) from an ultra-intense (10exp23 Wcm−2) laser-solid interaction. In the second stage, this beam interacts with dual counter-propagating laser pulses, inducing non-linear pair-production. It is shown that a significant number of positrons are produced by employing this scheme, with an anisotropic energy-angle distribution. This study will assist in the design of future experiments aiming to generate QED plasmas in the laboratory
Orbital angular momentum and fully structured light in nonlinear media and cavities
No full textThe work in this thesis describes interesting phenomena that results from the interaction between high intensity laser light and nonlinear matter. By changing the structure of light's properties such as intensity and polarisation as well as the type of nonlinear action that occurs during propagation through the medium, we aim to describe how the properties of light are affected by the various interactions.;Considering down-conversion in a second order x(2) medium we first present a spatiotemporal mechanism for producing two dimensional optical rogue waves in a turbulent state driven by vortices with helical wavefronts. Self-organising hexagonal structures bound in phase lose stability and synchronised oscillations are unstable leading to phaseunbound vortex-mediated turbulence with high excursions in amplitude. Nonlinear amplification leads to rogue waves close to optical vortices, and probability density functions typical of rogue waves.;We then consider fully structured light (FSL) within a Kerr x(3) medium. In particular, we describe how the polarisation distribution of FSL beams is affected by propagation. In the linear case we derive an expression for the rotation of the polarisation and show the rotation is due to the difference in Gouy phase between the two eigenmodes in the beam. For nonlinear propagation we show the effect of the cross-phase modulation from self focusing results in additional rotation that can be controlled by changing various physical parameters of the FSL beam like the beam waist and magnitude of OAM.;Finally we consider the interaction with the Kerr medium in an optical cavity. Above Turing threshold we observe the formation of peaks upon the FSL structure. Where the beam carries a net orbital angular momentum we observe a rotation in the structure. We detail how the angular velocity of the Turing structure can be controlled by careful selection of the parameters of the FSL beams.The work in this thesis describes interesting phenomena that results from the interaction between high intensity laser light and nonlinear matter. By changing the structure of light's properties such as intensity and polarisation as well as the type of nonlinear action that occurs during propagation through the medium, we aim to describe how the properties of light are affected by the various interactions.;Considering down-conversion in a second order x(2) medium we first present a spatiotemporal mechanism for producing two dimensional optical rogue waves in a turbulent state driven by vortices with helical wavefronts. Self-organising hexagonal structures bound in phase lose stability and synchronised oscillations are unstable leading to phaseunbound vortex-mediated turbulence with high excursions in amplitude. Nonlinear amplification leads to rogue waves close to optical vortices, and probability density functions typical of rogue waves.;We then consider fully structured light (FSL) within a Kerr x(3) medium. In particular, we describe how the polarisation distribution of FSL beams is affected by propagation. In the linear case we derive an expression for the rotation of the polarisation and show the rotation is due to the difference in Gouy phase between the two eigenmodes in the beam. For nonlinear propagation we show the effect of the cross-phase modulation from self focusing results in additional rotation that can be controlled by changing various physical parameters of the FSL beam like the beam waist and magnitude of OAM.;Finally we consider the interaction with the Kerr medium in an optical cavity. Above Turing threshold we observe the formation of peaks upon the FSL structure. Where the beam carries a net orbital angular momentum we observe a rotation in the structure. We detail how the angular velocity of the Turing structure can be controlled by careful selection of the parameters of the FSL beams
Effect of water on copper electrodeposition from water-containing deep eutectic solvents
Get PDFMetal electrodeposition is mostly based on aqueous systems which sometimes require the addition of chemicals that can be hazardous for the environment. Due to growing environmental regulations, Ionic Liquids (ILs) have been investigated as an alternative electrochemical media for this process. Amongst a variety of ILs, deep eutectic solvents (DESs) formulated from choline chloride and hydrogen bond donors have exhibited the most promising characteristics to be exploitable at large scale. Some of these characteristics are the tolerance to water, low volatility and toxicity, and reasonable cost.;Despite these properties, DESs are viscous and the diffusivity of electroactive species is correspondingly low. This imposes mass transport constraints reflected in low deposition rates compared to either high-temperature ILs or aqueous systems. This study therefore examined if the use of water addition alleviated these problems and investigated the effect of water content on various aspects of metal electrodeposition from hydrated DES systems.;'Ethaline' was the DES focus of this study since it exhibits one of the highest conductivity and lowest viscosity amongst DESs. Cu electroplating had been particularly common as it is used extensively in the electronics and microelectronic industry. Since there is a large body of existing studies on Cu electrodeposition from both ILs and aqueous systems, it can be used to benchmark metal electrodeposition from hydrated DES systems. Thereby, the 'electrolyte' used in this work comprised of the cupric chloride salt (0.2 M CuCl2∙2H2O) dissolved in ethaline.;Since ethaline is a hygroscopic substance, the ability of the electrolyte to incorporate water from the atmosphere was quantified using Karl Fischer titration. It was found that the electrolyte could incorporate water from 3 to 15 wt% over a month. Using these water amounts, the speciation of Cu (II) complexes, viscosity and conductivity were investigated. The behaviour of Cu (II) reduction from ethaline and the electrochemical window of ethaline were examined as a function of water content.;Thereafter, Cu electrodeposition was performed from water-containing electrolytes using steel disks. The uniformity, morphology and microstructure features of Cu electrodeposits were assessed using SEM, EBSD and XRD techniques. One of the key technical issues to be resolved before practical DES-based plating systems can be deployed is the characterisation of the anode reaction. Therefore, the anodic reaction occurring at the soluble copper anode during the electrodeposition of Cu from the water-containing electrolytes was also studied.;The diffusion limiting currents for Cu (II) reduction from ethaline were found to increase three times as water content increased from 1 to 15 wt%, e.g. from 6 to 18.5 mA cm-2. This occurred with minimal influence on the speciation of Cu (II) complexes, electrochemical window and deposit characteristics. This finding could be mostly attributed to the improved diffusivity of electroactive species brought about by water.;This was therefore a beneficial effect since faster plating rates were achievable from hydrated DES systems than that of low water-containing ones. Cu electrodeposits were found to exhibit poor homogeneity despite the fact that increasing amounts of water increased the conductivity of the medium. Importantly, the addition of water was not detrimental to the current efficiency of the process, microstructure and purity of the Cu coatings.;The analysis of the anodic reaction using a Cu soluble anode showed that the dominant anodic species were the Cu (I) complexes whereas the solution was depleted of the higher valency species, Cu (II) complexes. In the electrolyte, the apparent dissolution valency (n') was typically less than unity, corresponding to an observed mass loss greater than that expected from Faraday's law. Moreover, n' showed a marked dependence on the electrode rotation rate, Cu (II) concentration, and water content.;These observations were consistent with a corrosion reaction occurring in parallel with the anodic dissolution. The most likely corrosion process was identified to be the comproportionation reaction: [CuCl4]2- + Cu 2[CuCl2]-.;This study therefore determined a simple model for the electro-dissolution of Cu from hydrated DES systems and showed that the influence of water content was not detrimental to the electrolyte properties, electrodeposition process, and electrodeposits. Hence, the addition of water content can be considered to be a simple way to improve the rate of electrodeposition from DES systems with no particular downside.Metal electrodeposition is mostly based on aqueous systems which sometimes require the addition of chemicals that can be hazardous for the environment. Due to growing environmental regulations, Ionic Liquids (ILs) have been investigated as an alternative electrochemical media for this process. Amongst a variety of ILs, deep eutectic solvents (DESs) formulated from choline chloride and hydrogen bond donors have exhibited the most promising characteristics to be exploitable at large scale. Some of these characteristics are the tolerance to water, low volatility and toxicity, and reasonable cost.;Despite these properties, DESs are viscous and the diffusivity of electroactive species is correspondingly low. This imposes mass transport constraints reflected in low deposition rates compared to either high-temperature ILs or aqueous systems. This study therefore examined if the use of water addition alleviated these problems and investigated the effect of water content on various aspects of metal electrodeposition from hydrated DES systems.;'Ethaline' was the DES focus of this study since it exhibits one of the highest conductivity and lowest viscosity amongst DESs. Cu electroplating had been particularly common as it is used extensively in the electronics and microelectronic industry. Since there is a large body of existing studies on Cu electrodeposition from both ILs and aqueous systems, it can be used to benchmark metal electrodeposition from hydrated DES systems. Thereby, the 'electrolyte' used in this work comprised of the cupric chloride salt (0.2 M CuCl2∙2H2O) dissolved in ethaline.;Since ethaline is a hygroscopic substance, the ability of the electrolyte to incorporate water from the atmosphere was quantified using Karl Fischer titration. It was found that the electrolyte could incorporate water from 3 to 15 wt% over a month. Using these water amounts, the speciation of Cu (II) complexes, viscosity and conductivity were investigated. The behaviour of Cu (II) reduction from ethaline and the electrochemical window of ethaline were examined as a function of water content.;Thereafter, Cu electrodeposition was performed from water-containing electrolytes using steel disks. The uniformity, morphology and microstructure features of Cu electrodeposits were assessed using SEM, EBSD and XRD techniques. One of the key technical issues to be resolved before practical DES-based plating systems can be deployed is the characterisation of the anode reaction. Therefore, the anodic reaction occurring at the soluble copper anode during the electrodeposition of Cu from the water-containing electrolytes was also studied.;The diffusion limiting currents for Cu (II) reduction from ethaline were found to increase three times as water content increased from 1 to 15 wt%, e.g. from 6 to 18.5 mA cm-2. This occurred with minimal influence on the speciation of Cu (II) complexes, electrochemical window and deposit characteristics. This finding could be mostly attributed to the improved diffusivity of electroactive species brought about by water.;This was therefore a beneficial effect since faster plating rates were achievable from hydrated DES systems than that of low water-containing ones. Cu electrodeposits were found to exhibit poor homogeneity despite the fact that increasing amounts of water increased the conductivity of the medium. Importantly, the addition of water was not detrimental to the current efficiency of the process, microstructure and purity of the Cu coatings.;The analysis of the anodic reaction using a Cu soluble anode showed that the dominant anodic species were the Cu (I) complexes whereas the solution was depleted of the higher valency species, Cu (II) complexes. In the electrolyte, the apparent dissolution valency (n') was typically less than unity, corresponding to an observed mass loss greater than that expected from Faraday's law. Moreover, n' showed a marked dependence on the electrode rotation rate, Cu (II) concentration, and water content.;These observations were consistent with a corrosion reaction occurring in parallel with the anodic dissolution. The most likely corrosion process was identified to be the comproportionation reaction: [CuCl4]2- + Cu 2[CuCl2]-.;This study therefore determined a simple model for the electro-dissolution of Cu from hydrated DES systems and showed that the influence of water content was not detrimental to the electrolyte properties, electrodeposition process, and electrodeposits. Hence, the addition of water content can be considered to be a simple way to improve the rate of electrodeposition from DES systems with no particular downside
Emotion in teaching : developing an understanding of the emotional side of teaching through the importance of context and role amongst teachers and classroom assistants in Scottish schools
Get PDFEmotion in organisation research has become an important aspect of work and employment research and has expanded from commercial interactive service work to include professionals and the public sector. However, teaching has received little focus from emotion in organisation research from this work and employment perspective, instead favouring a narrower education studies perspective. Resultantly, the significant modernisation of education in the UK has received a limited focus, while the unique Scottish context has also been largely overlooked. This paper brings a greater understanding of emotion in teaching for both teachers and classroom assistants working in Scotland, as well as bringing a more pronounced work and employment perspective to emotion in teaching. The research was exploratory and utilised a qualitative case study approach, with the school-based education system in Scotland chosen as the case study. The thesis reports on data from 69 semi-structured interviews, principally with teachers and classroom assistants in public sector primary, public sector secondary and private sector all-through schools, but also with other important stakeholders in Scottish education.The findings show that teachers and classroom assistants share a passion for their role and consider their relationship with pupils to be important, while support from colleagues is considered essential. Equally, there is concern around burnout and the level of training received for additional support needs, while teachers were critical of the Curriculum for Excellence and classroom assistants indicated that their role is vaguely defined and that they can be stretched into teaching. The research has also shown that all three emotion in organisation theories from a work and employment perspective can be used within a single piece of research and that such an approach is appropriate for studying emotion in teaching. Therefore, the research has made both an empirical and theoretical contribution to knowledge.Emotion in organisation research has become an important aspect of work and employment research and has expanded from commercial interactive service work to include professionals and the public sector. However, teaching has received little focus from emotion in organisation research from this work and employment perspective, instead favouring a narrower education studies perspective. Resultantly, the significant modernisation of education in the UK has received a limited focus, while the unique Scottish context has also been largely overlooked. This paper brings a greater understanding of emotion in teaching for both teachers and classroom assistants working in Scotland, as well as bringing a more pronounced work and employment perspective to emotion in teaching. The research was exploratory and utilised a qualitative case study approach, with the school-based education system in Scotland chosen as the case study. The thesis reports on data from 69 semi-structured interviews, principally with teachers and classroom assistants in public sector primary, public sector secondary and private sector all-through schools, but also with other important stakeholders in Scottish education.The findings show that teachers and classroom assistants share a passion for their role and consider their relationship with pupils to be important, while support from colleagues is considered essential. Equally, there is concern around burnout and the level of training received for additional support needs, while teachers were critical of the Curriculum for Excellence and classroom assistants indicated that their role is vaguely defined and that they can be stretched into teaching. The research has also shown that all three emotion in organisation theories from a work and employment perspective can be used within a single piece of research and that such an approach is appropriate for studying emotion in teaching. Therefore, the research has made both an empirical and theoretical contribution to knowledge
Establishing a biocatalytic platform for small molecule c-alkylation
No full textThe alkylation of aromatic small molecules is an essential synthetic process used throughout medicinal chemistry. Key limitations of synthetic methods such as the Friedel-Crafts reaction is its lack of chemoselectivity in complex organic scaffolds and stoichiometric amounts of metallic waste produced by this process. A potential solution to this issue could be the use of methyltransferase (MTase) enzymes as biocatalysts to carry out this process. In nature, Sadenosyl-L-methionine (SAM) dependent MTases carry out such reactions on a variety of substrates ranging from small molecules to DNA and proteins. SAM donates its methyl groupto the target substrate with S-adenosyl-L-homocysteine (SAH) generated as a stoichiometric byproduct.The MTase NovO regio specifically transfers alkyl groups from chemically synthesised SAM analogues to a coumarin scaffold which is a precursor to the naturally-occurring antibiotic novobiocin. Chemical synthesis of SAM analogues has the issue of producing a diastereomeric mixture with epimers generated at the sulfonium centre, and display limited stability. SAMcan be generated biosynthetically from the reaction of 5'-deoxy-5'-chloroadenosine (ClDA)with L-methionine (L-met), catalysed by an enzyme, SalL, from Salinospora tropica. Thismethod is particularly attractive as ClDA and L-met are cheap and produce only the biologically active (S,S) diastereomer.;This thesis is a study of both SalL and NovO and their use in tandem SAM generation/alkylation (Scheme). The crystal structure of SalL has been solved to guide Site-Directed Mutagenesis (SDM). This method has then been used to better understand key residues in substrate binding and enzyme activity. Further to this, rational mutations were made in an attempt to increase space in the binding pocket to allow L-met analogues bearing groups larger than methyl to be accommodated. To this end, a range of L-met analogues were synthesised. The crystal structure of SalL revealed a channel which leaves the 2-position of ClDA solvent exposed. This raises the possibility of accommodation of 2-modified ClDA analogues as substrates of SalL. A suite of 2-modified ClDA analogues were synthesised to test this hypothesis.The current substrate scope of NovO is narrow so it was desired to investigate coumarins which have not yet been investigated with NovO. A range of coumarins were synthesised including a precursor to a compound which has shown activity as an inhibitor of Heat ShockProtein 90 (Hsp90) which has been implicated in a number of cancers. To explore the use of NovO as a method for late-stage functionalisation of drug molecules methylation of 7-hydroxywarfarin, a metabolite of clinically approved drug warfarin, has been carried out.The alkylation of aromatic small molecules is an essential synthetic process used throughout medicinal chemistry. Key limitations of synthetic methods such as the Friedel-Crafts reaction is its lack of chemoselectivity in complex organic scaffolds and stoichiometric amounts of metallic waste produced by this process. A potential solution to this issue could be the use of methyltransferase (MTase) enzymes as biocatalysts to carry out this process. In nature, Sadenosyl-L-methionine (SAM) dependent MTases carry out such reactions on a variety of substrates ranging from small molecules to DNA and proteins. SAM donates its methyl groupto the target substrate with S-adenosyl-L-homocysteine (SAH) generated as a stoichiometric byproduct.The MTase NovO regio specifically transfers alkyl groups from chemically synthesised SAM analogues to a coumarin scaffold which is a precursor to the naturally-occurring antibiotic novobiocin. Chemical synthesis of SAM analogues has the issue of producing a diastereomeric mixture with epimers generated at the sulfonium centre, and display limited stability. SAMcan be generated biosynthetically from the reaction of 5'-deoxy-5'-chloroadenosine (ClDA)with L-methionine (L-met), catalysed by an enzyme, SalL, from Salinospora tropica. Thismethod is particularly attractive as ClDA and L-met are cheap and produce only the biologically active (S,S) diastereomer.;This thesis is a study of both SalL and NovO and their use in tandem SAM generation/alkylation (Scheme). The crystal structure of SalL has been solved to guide Site-Directed Mutagenesis (SDM). This method has then been used to better understand key residues in substrate binding and enzyme activity. Further to this, rational mutations were made in an attempt to increase space in the binding pocket to allow L-met analogues bearing groups larger than methyl to be accommodated. To this end, a range of L-met analogues were synthesised. The crystal structure of SalL revealed a channel which leaves the 2-position of ClDA solvent exposed. This raises the possibility of accommodation of 2-modified ClDA analogues as substrates of SalL. A suite of 2-modified ClDA analogues were synthesised to test this hypothesis.The current substrate scope of NovO is narrow so it was desired to investigate coumarins which have not yet been investigated with NovO. A range of coumarins were synthesised including a precursor to a compound which has shown activity as an inhibitor of Heat ShockProtein 90 (Hsp90) which has been implicated in a number of cancers. To explore the use of NovO as a method for late-stage functionalisation of drug molecules methylation of 7-hydroxywarfarin, a metabolite of clinically approved drug warfarin, has been carried out
The rise of Taylor bubbles in vertical and inclined pipes
Get PDFSlug flow is one of the key flow regimes encountered in multiphase flow systems. Through reviewing the literature, the researcher identified a research gap in performing a theoretical treatment to the problem, specifically using the dimensionless treatment and the order of magnitude analysis of equations of motions. To the best of the researcher's knowledge, an analysis of the literature identifies that there is a lack in the numerical studies on the drift of Taylor bubbles in inclined pipes with stagnant liquid.;This thesis focuses on studying the flow of the Taylor bubble in the stagnant liquid, which is considered an essential characteristic part of the slug flow regime in pipes by performing theoretical treatment of the problem. To achieve this, the following two steps are carried out (i) Performing a complete dimensionless analysis to the rise of Taylor bubble through stagnant liquid in a vertical and inclined pipe, covering inclination range of 0≤ɣ≤90° with respect to the vertical position,;(ii) Using the guideline of the order of magnitude analysis and the dimensionless group analysis, performing CFD study using the volume-of-fluid (VOF) methodology implemented in the commercial software ANSYS Fluent (Release 16.0) investigating the dynamics of single Taylor bubble drifting through stagnant Newtonian liquid in vertical and inclined pipe.;The dimensionless analysis shows that different governing parameters appear according to the range of pipe inclination angle. The adopted CFD model shows good results for the dynamics of the Taylor bubble covering three main regions the bubble nose, the bubble body and the bubble wake regions.;The simulation results show good agreement with the developed dimensionless treatment of the problem for all pipe inclination. No bubble propagates in a zero axial pressure gradient horizontal pipe, hence, a simplified model is suggested to solve the challenging problem of the three-dimensional Taylor bubble in the near horizontal and horizontal pipes.Slug flow is one of the key flow regimes encountered in multiphase flow systems. Through reviewing the literature, the researcher identified a research gap in performing a theoretical treatment to the problem, specifically using the dimensionless treatment and the order of magnitude analysis of equations of motions. To the best of the researcher's knowledge, an analysis of the literature identifies that there is a lack in the numerical studies on the drift of Taylor bubbles in inclined pipes with stagnant liquid.;This thesis focuses on studying the flow of the Taylor bubble in the stagnant liquid, which is considered an essential characteristic part of the slug flow regime in pipes by performing theoretical treatment of the problem. To achieve this, the following two steps are carried out (i) Performing a complete dimensionless analysis to the rise of Taylor bubble through stagnant liquid in a vertical and inclined pipe, covering inclination range of 0≤ɣ≤90° with respect to the vertical position,;(ii) Using the guideline of the order of magnitude analysis and the dimensionless group analysis, performing CFD study using the volume-of-fluid (VOF) methodology implemented in the commercial software ANSYS Fluent (Release 16.0) investigating the dynamics of single Taylor bubble drifting through stagnant Newtonian liquid in vertical and inclined pipe.;The dimensionless analysis shows that different governing parameters appear according to the range of pipe inclination angle. The adopted CFD model shows good results for the dynamics of the Taylor bubble covering three main regions the bubble nose, the bubble body and the bubble wake regions.;The simulation results show good agreement with the developed dimensionless treatment of the problem for all pipe inclination. No bubble propagates in a zero axial pressure gradient horizontal pipe, hence, a simplified model is suggested to solve the challenging problem of the three-dimensional Taylor bubble in the near horizontal and horizontal pipes
Investigation of sub-core scale fluid flow behaviour within heterogeneous sandstones : the role of deformation bands
Get PDFSmall-scale heterogeneities influence fluid flow at sub-core and reservoir scale. However, the influence of deformation bands, commonly found in high porosity sandstones, is poorly understood. Internal structure of small-scale heterogeneities is investigated with X-ray computed tomography (CT). To this aim, high-resolution, artefacts-free CT images are needed. Beam hardening artefact, in cylindrical-shaped samples, increases the X-ray attenuation values with increasing distance from the centre. A new beam hardening correction technique was developed using a post-processing linearization procedure on the beam hardening curve. The technique is implemented in an automated open-source ImageJ plug-in, and successfully applied on X-ray CT images of homogeneous and heterogeneous samples containing deformation bands. Petrophysical and multiphase properties of heterogeneous sandstones were investigated by performing core flooding experiments with positron emission tomography (PET) and/or X-ray CT imaging. Experiments were conducted on a Navajo sandstone core characterized by diagonal deformation bands and fine-grained laminae. PET images were used to derive the single phase hydrodynamic properties of the core. A drainage experiment (CO₂/water) was conducted in the water-saturated core and imaged with a medical X-ray CT scanner. Experimental results and numerical simulations indicate that deformation bands form stronger capillary barriers than laminae.A drainage core flooding experiment (N₂/water) was performed on a Navajo sandstone core containing conjugate deformation band clusters. Results show a high N₂ saturation in the host rock compartments upstream of a thick cluster of deformation bands, identified as an extreme capillary barrier. At the end of the experiment, host rock compartments show variable N₂ saturation. Simulation models demonstrate that the capillary end effect and discontinuities in bands impact fluid saturation. Clusters and individual cataclastic bands strongly affect fluid flow, minimizing crossflow between compartments and promoting fluid compartmentalization. Detailed characterization of deformation bands is necessary for accurate reservoir prediction, both for carbon storage and for enhanced oil recovery.Small-scale heterogeneities influence fluid flow at sub-core and reservoir scale. However, the influence of deformation bands, commonly found in high porosity sandstones, is poorly understood. Internal structure of small-scale heterogeneities is investigated with X-ray computed tomography (CT). To this aim, high-resolution, artefacts-free CT images are needed. Beam hardening artefact, in cylindrical-shaped samples, increases the X-ray attenuation values with increasing distance from the centre. A new beam hardening correction technique was developed using a post-processing linearization procedure on the beam hardening curve. The technique is implemented in an automated open-source ImageJ plug-in, and successfully applied on X-ray CT images of homogeneous and heterogeneous samples containing deformation bands. Petrophysical and multiphase properties of heterogeneous sandstones were investigated by performing core flooding experiments with positron emission tomography (PET) and/or X-ray CT imaging. Experiments were conducted on a Navajo sandstone core characterized by diagonal deformation bands and fine-grained laminae. PET images were used to derive the single phase hydrodynamic properties of the core. A drainage experiment (CO₂/water) was conducted in the water-saturated core and imaged with a medical X-ray CT scanner. Experimental results and numerical simulations indicate that deformation bands form stronger capillary barriers than laminae.A drainage core flooding experiment (N₂/water) was performed on a Navajo sandstone core containing conjugate deformation band clusters. Results show a high N₂ saturation in the host rock compartments upstream of a thick cluster of deformation bands, identified as an extreme capillary barrier. At the end of the experiment, host rock compartments show variable N₂ saturation. Simulation models demonstrate that the capillary end effect and discontinuities in bands impact fluid saturation. Clusters and individual cataclastic bands strongly affect fluid flow, minimizing crossflow between compartments and promoting fluid compartmentalization. Detailed characterization of deformation bands is necessary for accurate reservoir prediction, both for carbon storage and for enhanced oil recovery
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