Wilson Fermions in Lattice Quantum Chromodynamics

We have studied the Wilson fermion matrix in the lattice QCD in the quenched approximation. Having implemented the Lanczos algorithm to study Wilson fermion spectrum on finite volumes we have presented results to confirm the existence of a phase transition accompanied by a massless mode from a phase where parity is restored to a phase where this discrete symmetry is violated in accordance with Aoki's lattice QCD phase diagram. In an effort to set up the most suitable algorithm to investigate hadron spectrum for Wilson fermions, we have also studied different versions of the Lanczos and conjugate gradient algorithms and have found that the block Lanczos algorithm is really superior for inverting large sparse matrices. In particular we have shown that the rate of convergence of the block Lanczos algorithm becomes effectively independent of the details of the fermion matrix such as gauge coupling constant and hopping parameter. The application of the block Lanczos algorithm to investigate scalar and pseudoscalar meson propagators shows that the massless mode associated with the transition from parity-restoring to parity-violating phase in the above phase structure is indeed where the pion becomes massless

Development of a Multi-field Two-fluid Approach for Simulation of Boiling Flows

Safe and reliable operation of nuclear power plants is the basic requirement for the utilization of nuclear energy since accidents can release radioactivity and with that cause irreversible damage to human beings. Reliability and safety of nuclear reactors are highly dependent on the stability of thermal hydraulic processes occurring in them. Nucleate boiling occurs in Pressurized Water Reactors (PWRs) and Boiling Water Reactors (BWRs) as well as in their passive safety systems during an accident. Passive safety systems are solely driven by thermal gradients and gravitational force removing residual heat from the reactor core independent of any external power supply in the case of accidents. Instability of flow boiling in these passive circuits can cause flow oscillations. These oscillations may induce insufficient local cooling and mechanical loads, which threatens the reactors’ safety. Analysis of boiling two-phase flow and associated heat and mass transfer requires an accurate modeling of flow regime transitions and prediction of boiling parameters such as void fraction, steam bubble sizes, heat transfer coefficient, etc. Flow boiling has been intensively investigated through experiments, one-dimensional codes, and Computational Fluid Dynamics (CFD) methods. Costly hardware and no accessibility to all locations in complex geometries restrict the experimental investigation of flow boiling. Since one-dimensional codes such as ATHLET, RELAP and TRACE are ”lumped parameter” codes, they are unable to simulate complex flow boiling transition patterns. In the last decades, with the development of supercomputers, CFD has been considered as a useful tool to model heat and mass transfer occurring in flow boiling regimes. In many industrial applications and system designs, CFD codes and particularly the Eulerian-Eulerian (E-E) two-fluid model are quickly replacing the experimental and analytical methods. However, the application of this approach for flow boiling modelling poses a challenge for the development of bubble dynamics and wall boiling models to predict heat and mass transfer at the heating wall as well as phase-change mechanism. Many empirical and mechanistic models have been proposed for bubble dynamics modelling. Nevertheless, the validity of these models for only a narrow range of operating conditions and their uncertainties limit their applicability and consequently presently necessitate us to calibrate them for a given boundary condition via calibration factors. For that reason, the first aim of this thesis is the development of a bubble dynamics model for subcooled boiling flow, which needs no calibration factor to predict the bubble growth and detachment. This mechanistic model is formulated based on the force balance approach, physics of a single nucleated bubble and several well-developed models to cover the whole bubble life cycle including formation, growth and departure. This model considers dynamic inclination angle and contact angles between the bubble and the heating wall as well as the contribution of microlayer evaporation, thermal diffusion and condensation around the bubble cap. Validation against four experimental flow boiling data sets was conducted with no case-dependent recalibration and yielded good agreement. The second goal is the implementation of the developed bubble dynamics model in the E-E two-fluid model as a sub-model to improve the accuracy of boiling flow simulation and reduce the case dependency. This implementation requires an extension of the nucleation site activation and wall heat-partitioning models. The bubble dynamics and heat-partitioning models were coupled with the Population Balance Model (PBM) to handle bubble interactions and predict the Bubble Size Distribution (BSD). In addition, the contribution of bubble sliding to wall heat transfer, which has been rarely considered in other modelling approaches, is considered. Validation for model implementation in the E-E two-fluid model was made with ten experimental cases including R12 and R134a flow boiling in a pipe and an annulus. These test cases cover a wide range of operating parameters such as wall heat flux, fluid velocity, subcooling temperature and pressure. The validated parameters were the bubble diameter, void fraction, bubble velocity, Interfacial Area Density (IAD), bubble passing frequency, liquid and wall temperatures. Two-phase flow morphologies for an upward flow in a vertical heating pipe may change from bubbly to slug, plug, and annular flow. Since these flow patterns have a great impact on the heat and mass transfer rates, an accurate prediction of them is critical. The aim of this thesis is the implementation of the developed bubble dynamics and heat-partitioning models in the recently developed GENeralized TwO-Phase flow (GENTOP) framework for the modelling of these flow patterns transition as well. An adopted wall heat-partitioning model for high void fractions is presented and for a generic test case, flow boiling regimes of water in a vertical heating pipe were modelled using ANSYS CFX 18.2. Moreover, the impacts of wall superheat, subcooling temperature and fluid velocity on the flow boiling transition patterns and the effects of these patterns on the wall heat transfer coefficient were evaluated.:Nomenclature xi 1 Introduction 1 1.1 Background and motivation . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 1.3 Outline of the thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2 State-of-the-art in modelling of subcooled flow boiling 11 2.1 Physics of boiling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 2.2 Bubble growth modelling . . . . . . . . . . . . . . . . . . . . . . . . 15 2.3 CFD simulation of boiling flows . . . . . . . . . . . . . . . . . . . . . 21 2.3.1 The Eulerian-Eulerian two-fluid model . . . . . . . . . . . . . 21 2.3.2 The Population Balance Model (PBM) . . . . . . . . . . . . . 22 2.3.3 Governing equations of the two-fluid model . . . . . . . . . . 25 2.3.4 Closure models for adiabatic bubbly flow . . . . . . . . . . . . 28 2.3.5 Phase transfer models . . . . . . . . . . . . . . . . . . . . . . 37 2.3.6 The Rensselaer Polytechnic Institute (RPI) wall boiling model 37 2.4 Flow boiling transition patterns in vertical pipes . . . . . . . . . . . . 42 2.5 The GENeralized TwO-Phase flow (GENTOP) concept . . . . . . . . . 45 2.5.1 Treatment of the continuous gas . . . . . . . . . . . . . . . . 46 2.5.2 The Algebraic Interfacial Area Density (AIAD) model . . . . . 46 2.6 Interfacial transfers of continuous gas . . . . . . . . . . . . . . . . . 47 2.6.1 Drag and lift forces . . . . . . . . . . . . . . . . . . . . . . . . 48 2.6.2 Cluster and surface tension forces . . . . . . . . . . . . . . . . 49 2.6.3 Complete coalescence . . . . . . . . . . . . . . . . . . . . . . 50 2.6.4 Entrainment modelling . . . . . . . . . . . . . . . . . . . . . . 51 2.6.5 Turbulence modelling . . . . . . . . . . . . . . . . . . . . . . 51 2.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 3 An improved bubble dynamics model for flow boiling 55 3.1 Modelling of the bubble formation . . . . . . . . . . . . . . . . . . . 55 3.1.1 Bubble growth rate . . . . . . . . . . . . . . . . . . . . . . . . 57 3.1.2 Force balance . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 ix 3.1.3 Detachment criteria . . . . . . . . . . . . . . . . . . . . . . . 63 3.1.4 Wall heat flux model . . . . . . . . . . . . . . . . . . . . . . . 69 3.1.5 Heat transfer in the heating wall . . . . . . . . . . . . . . . . 70 3.2 Results and discussions . . . . . . . . . . . . . . . . . . . . . . . . . . 72 3.2.1 Discretization dependency study . . . . . . . . . . . . . . . . 72 3.2.2 Model validation . . . . . . . . . . . . . . . . . . . . . . . . . 72 3.2.3 Sensitivity analysis . . . . . . . . . . . . . . . . . . . . . . . . 79 3.3 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 4 An improved wall heat-partitioning model 85 4.1 The cavity group activation model . . . . . . . . . . . . . . . . . . . . 85 4.1.1 Bubble sliding length and influence area . . . . . . . . . . . . 88 4.1.2 Model implementation in the Eulerian-Eulerian framework . . 89 4.2 Results and discussions . . . . . . . . . . . . . . . . . . . . . . . . . . 90 4.2.1 DEBORA experiments . . . . . . . . . . . . . . . . . . . . . . 90 4.2.2 Subcooled flow boiling of R134a in an annulus . . . . . . . . 102 4.3 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114 5 Modelling of flow boiling patterns in vertical pipes 115 5.1 Adopted wall heat-partitioning model for high void fractions . . . . . 115 5.2 Results and discussions . . . . . . . . . . . . . . . . . . . . . . . . . . 118 5.2.1 Effect of wall superheat on the flow boiling transition patterns 118 5.2.2 Effect of flow morphologies on the wall heat transfer coefficient124 5.2.3 Comparison of GENTOP and Eulerian-Eulerian two-fluid models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 5.2.4 Effect of subcooling on the flow boiling transition patterns . . 129 5.2.5 Effect of inlet fluid velocity on the flow boiling transition patterns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 5.3 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 6 Conclusions and outlook 133 6.1 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 6.2 Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136 References 137 Declaration 15

The Effect of Proficiency and Task Type on the Use of Paraphrase Type in Writing among Iranian EFL University Students

Academic writers use paraphrasing as an important borrowing strategy when integrating source text into their writing. To have a better understanding of L2 university students’ paraphrasing strategies, the present study examines how language proficiency and the type of writing task (summary tasks vs. opinion tasks) affect students’ use of paraphrase type: near copy, minimal revision, moderate revision, and substantial revision. The participants of the study were 127 EFL learners at 3 different levels of proficiency (44 advanced, 42 high intermediate, and 41 low intermediate). They were given a text based on which they were asked to do a writing task. In each proficiency group, half of the participants were asked to summarize the source text (ie., to do a summary task) and the other half were required to write their opinions about the text (i.e., to do an opinion task). The assignment of the tasks to individuals was done randomly. The participants’ use of attempted paraphrases within the summary and opinion tasks was compared. It was found that the advanced group used more attempted paraphrases in their writing. In addition, the participants who did the summary task used more attempted paraphrases than those who did the opinion task. Furthermore, low and high intermediate groups used more near copies than the advanced group. Conversely, the advanced participants used more minimal, moderate, and substantial revisions than the other two groups. However, task type appeared to have no effect on the use of paraphrase type

Relationship between emotional intelligence and job satisfaction

These days, we have found out the ability of emotions in human life and we have found out role of emotions in human activities. In recent years, literatures gradually tend from logical intelligent to emotional intelligent. Since 90th, this concept has been used in management research. Thus, if managers and clerks have higher emotional intelligence, they can mix emotions and positive feelings, solve problems, by choosing suitable strategies, omit available conflicts, and rise job satisfaction. Consequently, this research tried to investigate relationship between emotional intelligent and job satisfaction. The sample study was clerks of water organization in Mashhad and included a random sample and sample determined based on Cochran formula of 80 people. All of analyses did by SPSS software and we used Excel software in order to draw the tables. We measured emotional intelligence and job satisfaction throughout using two standard questionnaires. Questionnaire of emotional intelligence had various questions which were based on 5-point Likert scale (from 1- strongly agree, to 5-strongly disagree). We tested normality by K-S test. Then, we used Pearson regression in order to investigate relationship between emotional intelligence and job satisfactions. Based on result of the research, significant relationship exists between self-confidence and job satisfaction. Moreover, as result of coefficient, regression is positive; the relationship is positive and significant. In other words, by increasing self-confidence of clerks, job satisfaction will increase. We concluded that for improving emotional intelligence of clerks it is necessary to pay attention to self-confidence and self-awareness more than to the other factors; on the other hand, two factors of self-awareness and self-confidence are related to individual behavior components. Thus, we concluded that it is important to emphasize on individual behavior of people in order to improve emotional intelligence for increasing job satisfaction. Meanwhile, among individual behavior should more emphasize on self-awareness and self-confidence

Electrical pulse formation during high temperature reaction between Ni and Al

An electric voltage pulse (duration of about 2ms) with an amplitude of up to 0.6V was generated during the reaction between nickel and aluminum powders by a high temperature moving reaction front. The electrical signal formed during the initial stages of the combustion was annihilated before the moving front attained its maximum temperature. The voltage amplitude and combustion temperature depended on the particle size of the reactants as well as the Al to Ni ratio in the reactant mixture, and their largest values were attained for a mixture containing 27–31.5wt% Al. The combustion temperature increased when smaller Al particles were used. The electric signals annihilated either due to the growth of the initially formed product layer and∕or as a result of the formation of a molten Al matrix as the reaction propagated. Oscillatory signals formed during unstable combustion in which the reaction front was perturbed. Unipolar and nonoscillating signals formed when the combustion front was planar. We conjecture that the electric field was generated by the different diffusion rates of charge carriers through a reaction generated thin exterior intermediate products shell of Al3Ni∕Al3Ni2

Relationship between emotional intelligence and job satisfaction

These days, we have found out the ability of emotions in human life and we have found out role of emotions in human activities. In recent years, literatures gradually tend from logical intelligent to emotional intelligent. Since 90th, this concept has been used in management research. Thus, if managers and clerks have higher emotional intelligence, they can mix emotions and positive feelings, solve problems, by choosing suitable strategies, omit available conflicts, and rise job satisfaction. Consequently, this research tried to investigate relationship between emotional intelligent and job satisfaction. The sample study was clerks of water organization in Mashhad and included a random sample and sample determined based on Cochran formula of 80 people. All of analyses did by SPSS software and we used Excel software in order to draw the tables. We measured emotional intelligence and job satisfaction throughout using two standard questionnaires. Questionnaire of emotional intelligence had various questions which were based on 5-point Likert scale (from 1- strongly agree, to 5-strongly disagree). We tested normality by K-S test. Then, we used Pearson regression in order to investigate relationship between emotional intelligence and job satisfactions. Based on result of the research, significant relationship exists between self-confidence and job satisfaction. Moreover, as result of coefficient, regression is positive; the relationship is positive and significant. In other words, by increasing self-confidence of clerks, job satisfaction will increase. We concluded that for improving emotional intelligence of clerks it is necessary to pay attention to self-confidence and self-awareness more than to the other factors; on the other hand, two factors of self-awareness and self-confidence are related to individual behavior components. Thus, we concluded that it is important to emphasize on individual behavior of people in order to improve emotional intelligence for increasing job satisfaction. Meanwhile, among individual behavior should more emphasize on self-awareness and self-confidence

Electric-Field Generated by the Combustion of Titanium in Nitrogen

A short temporal electrical impulse (duration of 30–150ms) was generated during the nitridation of mixtures of titanium and titanium nitride by a high temperature moving reaction front. The maximum voltage and current were generated in the combustion front region, in which the conversion of Ti to TiN was incomplete. The electric field (voltage up to 2V and current up to 60mA) decayed and vanished before the maximum combustion temperature was attained. The generation of an electric field during a rapid high-temperature nitridation is most probably due to the different diffusion velocities of charge carriers through the growing titanium nitride shell during the initial stage of the reaction. When the reactant mixture contained a high percentage of pure titanium (larger than 60wt%), partial melting led to irreproducibility in the amplitude and duration of the electrical signal