Flow Inside the Sidewall Gaps of Hydraulic Machines: A Review

The paper critically reviews the current state of the art in flow inside sidewall gaps of hydraulic pumps and turbines. It describes the consequences of the presence of this type of flow in turbomachinery and then relates it to other physical phenomena that determine the behavior, operating characteristics, and overall performance of the machine. Despite the small dimensions of the rotor-stator spaces, the flow in these regions can significantly affect the overall flow field and, consequently, efficiency. The circulation of the fluid inside the gaps and secondary flow that is caused by rotating elements influences the disk friction losses, which is of great importance, especially in the case of low specific speed pumps and turbines. The flow pattern affects the pressure distribution inside a machine and, thus, generates axial thrust. The presence of secondary flow also significantly changes the rotordynamics and can bring about undesirable vibrations and acoustics issues. This article aims to review and summarize the studies that were conducted on the mentioned phenomena. Experimental and numerical studies are both taken into consideration. It proposes some requirements for prospective research in order to fill current gaps in the literature and reveals the upcoming challenges in the design of hydraulic machine

Two Phase Flow, Phase Change and Numerical Modeling

The heat transfer and analysis on laser beam, evaporator coils, shell-and-tube condenser, two phase flow, nanofluids, complex fluids, and on phase change are significant issues in a design of wide range of industrial processes and devices. This book includes 25 advanced and revised contributions, and it covers mainly (1) numerical modeling of heat transfer, (2) two phase flow, (3) nanofluids, and (4) phase change. The first section introduces numerical modeling of heat transfer on particles in binary gas-solid fluidization bed, solidification phenomena, thermal approaches to laser damage, and temperature and velocity distribution. The second section covers density wave instability phenomena, gas and spray-water quenching, spray cooling, wettability effect, liquid film thickness, and thermosyphon loop. The third section includes nanofluids for heat transfer, nanofluids in minichannels, potential and engineering strategies on nanofluids, and heat transfer at nanoscale. The forth section presents time-dependent melting and deformation processes of phase change material (PCM), thermal energy storage tanks using PCM, phase change in deep CO2 injector, and thermal storage device of solar hot water system. The advanced idea and information described here will be fruitful for the readers to find a sustainable solution in an industrialized society

Fuel Injection

Fuel Injection is a key process characterizing the combustion development within Internal Combustion Engines (ICEs) and in many other industrial applications. State of the art in the research and development of modern fuel injection systems are presented in this book. It consists of 12 chapters focused on both numerical and experimental techniques, allowing its proper design and optimization

Manufacturing of high precision mechanical components

The main goal of the thesis is to analyze key aspects of Precision Manufacturing, aiming at optimizing critical manufacturing processes: innovative experimental methodologies and advanced modelling techniques will be applied to cases study of industrial interest which have been successfully optimized

Advanced Technologies in Hydropower Flow Systems

Hydropower is an essential part of the renewable energy sector. High efficiency, immediate availability, and safe operation of hydroelectric power plants are the three key issues in recent developments in the hydropower sector. This book brings together the latest achievements addressing these key factors. In addition, one contribution deals with the alternative harvesting of hydro energy from pivoted cylinders by generating flow-induced vibrations, which are unwanted phenomena in classical pump–turbine units

The MYRRHA reactor design and the primary heat exchanger (PHX) tube rupture event analysis

Tra tutti i differenti concetti di reattori nucleari proposti nell\u2019ambito della Generation IV, I reattori \u201cpool-type\u201d raffreddati a metallo liquido pesante rappresentano una delle opzioni pi\uf9 promettenti. Uno dei principali obbiettivi, dal punto di vista progettuale e della sicurezza, consiste nell\u2019ottenere un concetto efficiente e compatto. Tale requisito spesso implica l\u2019adozione di un numero inferiore di circuiti refrigeranti rispetto ad altri reattori simili. La rimozione del circuito intermedio pu\uf2 essere ottenuta tramite l\u2019adozione di un fluido secondario che entri direttamente nello scambiatore di calore (o generatore di vapore) situato nel vessel primario. Per quanto concerne il fluido secondario, una scelta comune \ue8 rappresentata dall\u2019acqua in pressione. Uno degli eventi pi\uf9 rilevanti dal punto di vista dell\u2019analisi di sicurezza applicata a reattori di questa tipologia \ue8 rappresentato dall\u2019ingresso accidentale di acqua nel vessel primario, che potrebbe scatenare una serie di conseguenze potenzialmente in grado di mettere a repentaglio la sicurezza del reattore. Lo studio di tale transitorio implica un\u2019analisi multifase dei flussi, caratterizzata da svariate fenomenologie su diverse scale spaziali e temporali. MYRRHA \ue8 un reattore di ricerca pool-type raffreddato da una lega eutettica di piombo e bismuto (LBE). Pur essendo un Accelerator Driven System (ADS), ha la capacit\ue0 di operare in modalit\ue0 critica. La potenza generata nel sistema di raffreddamento primario \ue8 trasferita, tramite lo Scambiatore di Calore Primario (PHX), nel sistema secondario, per il quale l\u2019acqua in pressione \ue8 stata selezionata come refrigerante. Le attivit\ue0 del Ph.D. si focalizzeranno sul progetto del reattore MYRRHA, con particolare riferimento al PHX. L\u2019incidente di rottura di un tubo dello scambiatore stesso (PHXTR), con le conseguenze sugli altri componenti del reattore, sar\ue0 analizzato in una configurazione realistica del reattore tramite specifici modelli di calcolo ed attivit\ue0 sperimentali dedicate. Le analisi teoriche sulle conseguenze del rilascio di una miscela bifase di acqua-vapore nel vessel primario devono essere eseguite in condizioni rappresentative del reattore MYRRHA: questo comporta una fedele modellazione, in termini geometrici e di processo, dello scambiatore e degli altri componenti, al fine di essere in grado di simulare l\u2019evoluzione dell\u2019incidente nel modo migliore possibile. L\u2019impatto sui componenti situati all\u2019interno del vessel ed i carichi meccanici generati dall\u2019incidente di rottura del tubo devono essere valutati in base alle reali condizioni d\u2019impianto, cos\uec come l\u2019incremento di pressione nel vessel e la conseguente apertura del disco di rottura. Numerose campagne sperimentali finalizzate all\u2019analisi della rottura di un tubo dello scambiatore primario sono previste nell\u2019ambito del progetto Europeo FP7-MAXSIMA. Tali esperimenti sono stati concepiti per simulare le condizioni operative del reattore MYRRHA nel migliore dei modi, allo scopo di validare i modelli di calcolo. Tali simulazioni numeriche saranno poi utilizzate per estendere le capacit\ue0 predittive degli esperimenti. Lo scopo finale del Ph.D. consiste dunque nella finalizzazione del progetto dello scambiatore di calore del reattore MYRRHA, rivolgendo particolare attenzione allo studio dell\u2019incidente di rottura di un tubo. La programmazione di specifici strumenti di calcolo \ue8 prevista al fine di essere in grado di simulare tutte le fasi dell\u2019incidente e le potenziali implicazioni per la sicurezza dell\u2019impianto.Among the different nuclear plant concepts proposed in the frame of Generation IV, the pool-type reactors cooled by Heavy Liquid Metal represent one of the most promising options. One of the most important challenges, form the point of view of design and safety, consists in optimizing an efficient and compact design. Such requirements often imply the adoption of a lower number of cooling loops in comparison with similar reactor concepts. The intermediate loop can be eliminated by adopting a secondary fluid entering in a heat exchanger (or steam generator) located in the primary vessel. Pressurized water represents a common choice as secondary cooling fluid. One of the most safety-relevant events for this reactor concept is indeed represented by the accidental water ingress in the primary vessel, which can trigger a series of consequences potentially jeopardizing the reactor safety functions. The study of this transient implies the analysis of multiphase flow, characterized by several phenomena on different time and spatial scales. The MYRRHA reactor is a pool-type Material Testing Accelerator Driven System (ADS), cooled by Lead-Bismuth Eutectic (LBE) with the ability to operate also as a critical reactor. Pressurized water is adopted as secondary coolant, removing the power generated in the primary system through the Primary Heat Exchangers (PHX). The Ph. D. activities should focus on the MYRRHA reactor design and the impact of a PHX Tube Rupture (PHXTR) event on its components: all the analyses foreseen and the experimental campaigns in support of calculations should be aimed at studying the transient in MYRRHA relevant configuration. The theoretical analysis on the consequences following the moisture release into the primary vessel must be performed in MYRRHA-like conditions, assuming the correct dimensions for the PHX and all the related systems and components in order to be able to predict in the best way the PHXTR accident evolution. The impact on the reactor internals and the mechanical loads determined by the pressure wave and potential steam explosion should be evaluated according to the real MYRRHA configuration, as well as the pressure build-up in the reactor cover gas and the consequent reactor cover rupture disk break. The experimental campaign foreseen for MYRRHA PHXTR event, mainly in the framework of EU FP7-MAXSIMA project, have been run in a set of conditions that closely resembles the MYRRHA environment. The purpose is to validate the theoretical models and the numerical simulations towards the experiments in order to obtain suitable calculation tools allowing correct predictions. The final purpose of the Ph.D. activities consists then in fully covering the evolution of the PHXTR accident in the MYRRHA reactor by the use of suitable and validated computational tools, taking thus into account all the evolution phases and predicting the potential implications caused by the event

Design and Application of Electrical Machines

Electrical machines are one of the most important components of the industrial world. They are at the heart of the new industrial revolution, brought forth by the development of electromobility and renewable energy systems. Electric motors must meet the most stringent requirements of reliability, availability, and high efficiency in order, among other things, to match the useful lifetime of power electronics in complex system applications and compete in the market under ever-increasing pressure to deliver the highest performance criteria. Today, thanks to the application of highly efficient numerical algorithms running on high-performance computers, it is possible to design electric machines and very complex drive systems faster and at a lower cost. At the same time, progress in the field of material science and technology enables the development of increasingly complex motor designs and topologies. The purpose of this Special Issue is to contribute to this development of electric machines. The publication of this collection of scientific articles, dedicated to the topic of electric machine design and application, contributes to the dissemination of the above information among professionals dealing with electrical machines

Development of HTS trapped field magnet using 2G HTS coated conductors

Compact High-Temperature Superconducting (HTS) trapped field magnets stand at the frontier of breakthroughs for advanced industrial equipment, medical devices, and transportation electrification, offering capabilities that conventional permanent magnets and electromagnets cannot achieve. While superconductors capitalize on zero resistance to uphold high currents, thus generating substantial fields, traditional HTS bulks and stacks have been limited by constraints such as geometry size and mechanical robustness. As second-generation (2G) commercial HTS coated conductors advance, there's a growing emphasis on utilizing these tapes to attain expansive and stable trapped field profiles. This thesis explores the innovative magnetization mechanisms and design optimizations of HTS trapped field magnets fabricated with 2G HTS tapes through a comprehensive analysis of HTS-stacked ring magnets, hybrid HTS-stacked ring design, their mechanical stress responses, and trapped field closed-loop HTS coil under field cooling magnetization. The research primarily investigated a novel hybrid HTS trapped field magnet, integrating HTS-stacked ring magnets with HTS bulks to surpass traditional size limitations and achieve a significant trapped field of 7.35 T. It further predicted their capability to generate a trapped field exceeding the applied field due to unique induced current distributions and flux redistribution. Additionally, the study addressed the mechanical challenges posed by Lorentz forces during magnetization, presenting 3D numerical models to analyze stress and strain in HTS-stacked ring magnets. A 90 % stress reduction was seen by proper impregnation and fixation methods. Lastly, a novel closed-loop HTS coil approach was introduced, achieving a compact high-field superconducting magnet that trapped a central field 4.59 T which was higher than the 4.5 T applied field, showcasing potential for diverse high-field applications. Above the inner edge of the HTS coil, the trapped field exceeded the applied field by 1.5 T. This thesis combines experimental findings and numerical modelling to advance the understanding of HTS magnetization processes, offering insights into designing more efficient and durable compact and portable HTS magnets for applications in nuclear magnetic resonance, Maglev transportation, and HTS machineryCompact High-Temperature Superconducting (HTS) trapped field magnets stand at the frontier of breakthroughs for advanced industrial equipment, medical devices, and transportation electrification, offering capabilities that conventional permanent magnets and electromagnets cannot achieve. While superconductors capitalize on zero resistance to uphold high currents, thus generating substantial fields, traditional HTS bulks and stacks have been limited by constraints such as geometry size and mechanical robustness. As second-generation (2G) commercial HTS coated conductors advance, there's a growing emphasis on utilizing these tapes to attain expansive and stable trapped field profiles. This thesis explores the innovative magnetization mechanisms and design optimizations of HTS trapped field magnets fabricated with 2G HTS tapes through a comprehensive analysis of HTS-stacked ring magnets, hybrid HTS-stacked ring design, their mechanical stress responses, and trapped field closed-loop HTS coil under field cooling magnetization. The research primarily investigated a novel hybrid HTS trapped field magnet, integrating HTS-stacked ring magnets with HTS bulks to surpass traditional size limitations and achieve a significant trapped field of 7.35 T. It further predicted their capability to generate a trapped field exceeding the applied field due to unique induced current distributions and flux redistribution. Additionally, the study addressed the mechanical challenges posed by Lorentz forces during magnetization, presenting 3D numerical models to analyze stress and strain in HTS-stacked ring magnets. A 90 % stress reduction was seen by proper impregnation and fixation methods. Lastly, a novel closed-loop HTS coil approach was introduced, achieving a compact high-field superconducting magnet that trapped a central field 4.59 T which was higher than the 4.5 T applied field, showcasing potential for diverse high-field applications. Above the inner edge of the HTS coil, the trapped field exceeded the applied field by 1.5 T. This thesis combines experimental findings and numerical modelling to advance the understanding of HTS magnetization processes, offering insights into designing more efficient and durable compact and portable HTS magnets for applications in nuclear magnetic resonance, Maglev transportation, and HTS machiner

Experimental and numerical modelling investigations into coal mine rockbursts and gas outbursts

Rockbursts and gas outbursts are a longstanding hazard in underground coal mining due to their sudden occurrences and high consequences. These hazards are becoming prominent due to the increase in mining depth, difficult mining conditions, and adverse gas pressure conditions. Several researchers have proposed different theories, mechanisms, and indices to determine the rockbursts and gas outbursts liability but most of them focus on only some aspects of the complex engineering system for the ease to represent them using partial differential equations. They have often ignored the dynamics of changing mining environment, coal seam heterogeneity and stochastic variations in the rock properties. Most of the indices proposed were empirical and their suitability to different mining conditions is largely debated. To overcome the limitations of previous theories, mechanisms and indices, a probabilistic risk assessment framework was developed in this research to mathematically represent the complex engineering phenomena of rockbursts and gas outbursts for a heterogeneous coal seam. An innovative object-based non-conditional simulation approach was used to distribute lithological heterogeneity occurring in the coal seam to respect their geological origin. The dynamically changing mining conditions during a longwall top coal caving mining (LTCC) was extracted from a coupled numerical model to provide statistically sufficient data for probabilistic analysis. The complex interdependencies among several parameters, their stochastic variations and uncertainty were realistically implemented in the GoldSim software, and 100,000 equally likely scenarios were simulated using the Monte Carlo method to determine the probability of rockbursts and gas outbursts. The results obtained from the probabilistic risk assessment analysis incorporate the variations occurring due to lithological heterogeneity and give a probability for the occurrence of rockbursts, coal and gas outbursts, and safe mining conditions. The framework realistically represents the complex mining environment, is resilient and results are reliable. The framework is generic and can be suitably modified to be used in different underground mining scenarios, overcoming the limitations of earlier empirical indices used.Open Acces