Transient vehicle thermal management simulations have the potential to be an important tool to ensure long component lifetimes in heavy-duty vehicles, as well as save development costs by reducing development time. Time-resolved computational fluid dynamics simulations of complete vehicles are however typically very computationally expensive, and approximation methods must be employed to keep computational costs and turn-around times at a reasonable level. In this thesis, two transient methods are used to simulate two important time-dependent scenarios for complete vehicles; hot shutdowns and long dynamic drive cycles. An approach using a time scaling between fluid solver and thermal solver is evaluated for a short drive cycle and heat soak. A quasi-transient method, utilizing limited steady-state computational fluid dynamics data repeatedly, is used for a long drive cycle. The simulation results are validated and compared with measurements from a climatic wind tunnel. The results indicate that the time-scaling approach is appropriate when boundary conditions are not changing rapidly. Heat-soak simulations show reasonable agreement between three cases with different thermal scale factors. The quasi-transient simulations suggest that complete vehicle simulations for durations of more than one hour are feasible. The quasi-transient results partly agree with measurements, although more component temperature measurements are required to fully validate the method.

Environmental concerns, resource depletion, energy security, technological advancements, and global policies are just a few of the variables influencing the global energy perspective. In the case of technological advancement, lithium batteries play a key role in the development of a more sustainable energy infrastructure. The high energy density and long lifespan of lithium batteries make them ideal for usage in a broad range of applications, such as portable electronics, electric vehicles, and grid-scale energy storage for renewable energy sources. However, there are certain possible concerns regarding the safe operation and performance of lithium batteries, most of which are associated with the temperature sensitivity of lithium batteries. Hence, battery thermal management systems are an essential component of a battery package for regulating the temperature level in lithium batteries to avoid the aging process, poor performance, and safety issues.   Many studies have been conducted to develop battery thermal management systems with improved cooling performance. Within this framework, Paper A in this licentiate thesis considers how the design of a lithium battery cell may be improved to reduce the thermal load on the thermal management system. An analytical model based on the integral transform technique is developed to accurately and efficiently predict the thermal behavior of a cylindrical lithium battery cell. Following model validation, the thermal behavior of cylindrical lithium-ion battery cells with different jelly-roll layers and can sizes are compared. The results demonstrate that 21700 cylindrical battery cells outperform other types of cylindrical battery cells in terms of thermal performance. Furthermore, the thermally optimal thicknesses for positive active material, negative active material, positive current collector, and negative current collector are 180, 34, 21, and 20 um, respectively. After learning about design considerations to reduce thermal issues in lithium-ion battery cells and developing a proper tool for further studies, the focus was set on the flow behavior surrounding a cylindrical battery cell in an air-based cooling system. The cooling system under consideration is a wall-bounded cross-flow heat exchanger, the most common air-based cooling system for battery applications. Despite the importance of the cooling system in battery safety, few studies have been conducted to investigate the thermo-flow characteristics of wall-bounded cross-flow heat exchangers. Hence, in the battery research field, it is common to estimate the performance of wall-bounded cross-flow heat exchangers using the thermal characteristics of free cross-flow heat exchangers due to their geometrical similarities. In Paper B, this assumption is scrutinized by comparing the thermo-fluid characteristics of free and wall-bounded cross-flow heat exchangers. According to the results, flow through both heat exchangers shows almost similar thermo-fluid behavior in areas sufficiently far from the bounding walls. A turbulence model study suggests that the k-kl-omega transition model is a time-efficient and reliable turbulence model for capturing thermo-fluid characteristics in such heat exchangers. Moreover, it is observed that the two different heat exchangers have an almost identical area-averaged heat transfer rate despite the local changes in Nusselt number along the height of cells. This finding shows that it is possible to do two-dimensional simulations for applications that only require an area-averaged heat transfer rate on the battery cells. The findings in Paper A and Paper B may be used to investigate the cooling performance of a battery thermal management system with a practical design. Hence, in Paper C, a comprehensive yet simplified model is developed that can be used to study the thermal field of lithium battery cells in a large-scale air-based battery thermal management system. The model consists of the CFD model derived in Paper B, which predicts the flow behavior around cells in the inner region of the battery package, and the analytical model described in Paper A, which determines the thermal field within the battery cells. The area-averaged heat transfer coefficient interconnects the models, and a system of equations is employed to estimate the row-to-row variation of the thermal field. The model is employed to assess the effect of transverse and longitudinal pitch ratios on the thermal performance of an air-based battery thermal management system used in a hybrid electric vehicle.

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<p>The present study investigates the capability of computational fluid dynamics (CFD) extensively to predict hydrodynamics and heat transfer characteristics of FC-72 flow boiling in a 2.5-mm ´ 5.0-mm rectangular channel and experimentally explores system instabilities: <em>density wave oscillation</em> (DWO), <em>pressure drop oscillation</em> (PDO) and <em>parallel channel instability</em> (PCI) in a micro-channel heat sink containing 38 parallel channels having a hydraulic diameter of 316-μm. </p> <p>The computational method performs transient analysis to model the entire flow field and bubble behavior for subcooled flow boiling in a rectangular channel heated on two opposite walls at high heat flux conditions of about 40% – 80% of <em>critical heat flux</em> (CHF).  The 3D CFD solver is constructed in ANSYS Fluent in which the <em>volume of fluid</em> (VOF) model is combined with a <em>shear stress transport</em> (SST) <em>k</em>-<em>ω</em> turbulent model, a surface tension model, and interfacial phase change model, along with a model for effects of shear-lift and bubble collision dispersion to overcome a fundamental weakness in modeling multiphase flows.  Detailed information about bubble distribution in the vicinity of the heated surface, thermal conduction inside the heating wall, local heat fluxes passing through the solid-fluid interface, and velocity and temperature profiles, which are not easily observed or measured by experiments, is carefully evaluated.  The simulation results are compared to experimental data to validate the solver’s ability to predict the flow configuration with single/double-side heating.  The added momentum by shear-lift is shown to govern primarily the dynamic behavior of tiny bubbles stuck on the heated bottom wall and therefore has a more significant impact on both heat transfer and heated wall temperature.  By including bubble collision dispersion force, coalescence of densely packed bubbles in the bulk region is significantly inhibited, with more giant bubbles even incurring additional breakup into smaller bubbles and culminating in far less vapor accumulation along the top wall.  Including these momentums is shown to yield better agreement with local interfacial behavior along the channel, overall flow pattern, and heat transfer parameters (wall temperature and heat transfer coefficient) observed and measured in experiments.  The computational approach is also shown to be highly effective at predicting local phenomena (velocity and temperature profiles) not easily determined through experiments.  Different flow regimes predicted along the heated length exhibit a number of dominant mechanisms, including bubble nucleation, bubble growth, coalescence, vapor blankets, interfacial waviness, and residual liquid sub-layer, all of which agree well with the experiment.  Vapor velocity is shown to increase appreciably along the heated length because of increased void fraction, while liquid velocity experiences large fluctuations.  Non-equilibrium effects are accentuated with increasing mass velocity, contributing minor deviations of fluid temperature from simulations compared to those predicted by the analytical method.  Predicted wall temperature is reasonably uniform in the middle of the heated length but increases in the entrance region due to sensible heat transfer in the subcooled liquid and decreases toward the exit, primarily because of flow acceleration resulting from increased void fraction.  When it comes to analyzing heat transfer mechanisms at extremely high heat flux via CFD, predicted flow pattern, bubble behavior, and heat transfer parameters (such as wall temperature excursion and thermal energy concentration) clearly represent phenomena of premature CHF, which take place slightly earlier than actual operating conditions.  But, despite these slight differences, the present computational work does demonstrate the ability to effectively predict the severe degradation in heat transfer performance commonly encountered at heat fluxes nearing CHF.  </p> <p>Much of the published literature addressing flow instabilities in thermal management systems employing micro-channel modules are focused on instability characteristics of the module alone, and far fewer studies have aimed at understanding the relationship between these characteristics and compressive volume in the flow loop external to the module.  From a practical point of view, developers of micro-channel thermal management systems for many modern applications are in pursuit of practical remedies that would significantly mitigate instabilities and their impact on cooling performance.  Experiments are executed using FC-72 as a working fluid with a wide range of mass velocities and a reasonably constant inlet subcooling of ~15°C.  The flow instabilities are reflected in pressure fluctuations detected mainly in the heat sink’s upstream plenum.  Both inlet pressure and pressure drop signals are analyzed in pursuit of amplitude and frequency characteristics for different mass velocities and over a range of heat fluxes.  The current experimental study also examines the effects of compressible volume location in a closed pump-driven flow loop designed to deliver FC-72 to a micro-channel test module having 38 channels with 315-μm hydraulic diameter.  Three accumulator locations are investigated: upstream of the test module, downstream of the test module, and between the condenser and pump.  Both high-frequency temporal parameter data and high-speed video records are analyzed for ranges of mass velocity and heat flux, with inlet subcooling held constant at ~15°C.  PDO is shown to dominate when the accumulator is situated upstream, whereas PCI is dominant for the other two locations.  Appreciable confinement of bubbles in individual channels is shown to promote rapid axial bubble growth.  The study shows significant variations in the amount of vapor generated and dominant flow patterns among channels, a clear manifestation of PCI, especially for low mass velocities and high heat fluxes.  It is also shown effects of the heat sink’s instabilities are felt in other components of the flow loop.  The parametric trends for PCI are investigated with the aid of three different types of stability maps which show different abilities at demarcating stable and unstable operations.  PDO shows severe pressure oscillations across the micro-channel heat sink, with rapid bubble growth and confinement, elongated bubble expansion in both directions, flow stagnation, and flow reversal (including vapor backflow to the inlet plenum) constituting the principal sequence of events characterizing the instability.  Spectral analysis of pressure signals is performed using Fast Fourier Transform, which shows PDO extending the inlet pressure fluctuations with the same dominant frequency to other upstream flow loop components, with higher amplitudes closer to the pump exit.  From a practical system operation point of view, throttling the flow upstream of the heat sink eliminates PDO but renders PCI dominant, and placing the accumulator in the liquid flow segment of the loop between the condenser and pump ensures the most stable operation.</p>

Effective heat management is essential for preserving performance and dependability as electronic equipment becomes increasingly powerful and smaller. This project presents the developed system, TeRMeS, which was created to test the thermal resistance of thermal interface materials (TIMs) essential for the thermal management of electronic devices, including battery systems. This work focuses on using steady-state techniques to evaluate TIMs under various operational forces and temperatures in real-world electronic packaging conditions. A noteworthy breakthrough is the creation of a user-friendly graphical user interface (GUI), which offers sophisticated options for real-time thickness measurement and enables researchers to alter parameters and dynamically display outcomes, thereby improving the measuring process. The results of the experiment highlight the importance of TIM thickness and applied force in lowering thermal resistance and increasing thermal conductivity. These elements are necessary to prevent battery packs and electrical parts from overheating. To improve heat management strategies in high-performance computing and electronics, the study provides accurate, reliable data by focusing on steady-state measurements.

Two computational fluid dynamics models are developed to predict the performance of a solid oxide fuel cell stack, a detailed and a simplified model. In the detailed model, the three dimensional momentum, heat, and species transport equations are coupled with electrochemistry. In the simplified model, the diffusion terms in the transport equations are selectively replaced by rate terms within the core region of the stack. This allows much coarser meshes to be employed at a fraction of the computational cost. Following the mathematical description of the problem, results for single-cell and multi-cell stacks are presented. Comparisons of local current density, temperature, and cell voltage indicate that good agreement is obtained between the detailed and simplified models, verifying the latter as a practical option in stack design. Then, the simplified model is used to determine the effects of utilization on the electrochemical performance and temperature distributions of a 10 cell stack. The results are presented in terms of fluid flow, pressure, species mass fraction, temperature, voltage and current density distributions. The effects of species and flow distributions on electrochemical performance and temperature are then analyzed for a 100 cell stack. The discussion highlights the importance of manifold design on performance and thermal management of large stacks. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2013-09-30 15:55:18.627

La gestion thermique est un des moyens de réduction de la consommation spécifique d’un véhicule. Avec le réchauffement climatique, les normes de dépollution deviennent de plus en plus sévères et les constructeurs automobiles cherchent à améliorer le rendement des véhicules. Le but de ces travaux de recherche est de valoriser, par simulation numérique, les nouveaux systèmes de gestion thermique en fonction du cycle d’homologation et de la température ambiante.Un modèle de simulation 1-D du moteur et de ses circuits de refroidissement et de lubrification ont été développés en utilisant le logiciel GT-Suite. Quatre cycles d’homologation ont été choisis : NEDC, WLTC, AH et AU. De plus, un nouveau cycle a été proposé durant cette étude. Le bilan d’énergie effectué pendant les différentes phases des cycles souligne l’importance du stockage et de la récupération d’énergie.Le stockage d’énergie dans un volume eau et/ou d’huile abouti à l’amélioration de la montée en température des deux fluides. Plusieurs configurations ont été proposées comme, par exemple, un carter d’huile multifonctionnel.Ainsi, une réduction importante de la consommation en carburant est obtenue.La récupération de chaleur au sein des gaz d’échappement est ensuite mise en oeuvre. L’échangeur est caractérisé sur un banc d’essais puis modélisé. Le réchauffement indirect et direct d’huile abouti à une réduction importante des frottements et de la consommation. Une configuration est proposée afin de contrôler la température maximale de l’huile.Finalement, différentes stratégies comme : le type d’huile, l’isolation du moteur, une température de régulation plus élevée etc… ont été étudiées et valorisées. / Thermal management proved itself in improving the fuel efficiency of the engine. Nowadays, automotive companies tend to apply different strategies to answer the greenhouse severe laws. The PhD aim is to valorize and analyze the different thermal management strategies with numerical simulations over different driving cycles and ambient conditions. A 1-D simulation code of the engine and its hydraulic circuits were built using GT-Suite. Four known driving cycles were chosen: NEDC, WLTC, AH and AU. In addition, an in-house developed driving cycle was introduced. An energy balance made over the different stages of the driving cycles underlines the importance of the heat storage and the exhaust heat recovery strategies.Heat recovery was applied over the coolant and the oil at ambient temperatures of -7°C and 20°C. Hot coolant storage and hot oil storage led to improve the coolant and lubricant initial temperatures respectively. Different configurations (total of 7) were proposed and studied. A multifunctional oil sump was introduced. Important fuel consumption savings were obtained. Exhaust heat recovery was then valorized. Heat exchanger was characterized over experimental setup then added to the engine model. Indirect and direct heating of the lubricant as well as both strategies back to back were tested. Remarkable friction reduction and fuel savings were obtained. Special configuration was proposed to control the lubricant high temperature instead of the bypass on the exhaust line. The study ended by valorizing minor strategies as the oil’s grade influence, the engine insulation, high temperature set point …

Preface: The research about product development of a prosthetic socket was conducted by two students from Mälardalen University, department of Innovation, Design, and Technology. Background: The most recent public survey shows that an estimated 5 million people in China are amputees, out of which a significantly large portion are below-elbow amputees. Sockets sold to below-elbow amputees are equipped with only two surface electromyography sensors, has low comfortability, has problems with perspiration, and a high weight. The current standard for socket manufacturing has not changed in decades. Research Questions: The following research questions have determined the direction of the research: (1) What measurable factors contribute to a convenient and ergonomic feature design in prosthetic socket from the end-user’s perspective? (2) How can the weight and functionality be improved to achieve a prosthetic socket more suited to the end-user, with respect to the existing prosthetic socket? (3) Which material and manufacturing method is suitable for producing cost-effective and customized prosthetic sockets? Research Method: The research was guided by the 5th edition of Product Design and Development by Ulrich &amp; Eppinger (2012) where the product development process described in five of the six phases from planning to test and refinement were utilized. The data collection and analysis techniques performed in this research was guided by Research Methods for Students, Academics and Professionals by Williamson &amp; Bow (2002). Interviews were conducted with five different stakeholders to find specifications of requirements and concretize subjectivism of what defines quality and ergonomics. Implementation: Currently, below-elbow amputees order sockets from orthopedic clinics. The socket was identified as a product of Ottobock. Investigations were made to find optimal solutions to the specification of requirements. Results: The development of a socket concept was designed for additive manufacturing using a multi-jet fusion printer. Analysis: This concept had significant improvements to parameters: higher grade of customizability, 30 % reduced weight, 48 % cost reduction, a new production workflow with 93,5 % automation, and a 69 % reduction in manual work hours. Conclusions: The data of the research strongly indicate existing potentials in enhancing socket design techniques and outputs by implementation of additive manufacturing processes. This can prove to be beneficial for achieving more competitive prosthetics and associated services. / Förord: Denna forskning om produktutvecklingsprocessen av en armprotes genomfördes av två studenter från Mälardalens universitet, avdelningen för innovation, design och teknik. Bakgrund: Den senaste offentliga undersökningen visar att cirka 5 miljoner människor i Kina är amputerade, varav en betydligt stor del är under-armbågsamputerade. Armproteser som säljs till underarmsamputerade individer är utrustade med endast två yt-elektromyografiska sensorer, har låg komfort, har problem med perspiration och hög vikt. Den nuvarande standarden för armproteser har inte förändrats under årtionden. Forskningsfrågor: Följande forskningsfrågor har bestämt riktningen för forskningen: (1) Vilka mätbara faktorer bidrar till en praktisk och ergonomisk funktionsdesign i underarmsproteser ur slutanvändarens perspektiv? (2) Hur kan vikten och funktionaliteten förbättras för att åstadkomma en underarmsprotes som är bättre anpassad för slutanvändaren med avseende på den befintliga underarmsprotesen? (3) Vilket material och tillverkningsmetod är lämpligt för att producera kostnadseffektiva och anpassade underarmsproteser? Forskningsmetod: Forskningsmetoden styrdes av den femte upplagan av Product Design and Development av Ulrich &amp; Eppinger (2012) där produktutvecklingsprocessen är uppdelad i sex faser. I denna forskning användes de fem första faserna från planering till testning och justering. Tekniker för datainsamling och analys som användes i denna forskning styrdes av Research Methods for Students, Academics and Professionals av Williamson &amp; Bow (2002). Intervjuer genomfördes med fem olika intressenter för att hitta kravspecifikationer och för att konkretisera subjektivitet för vad som definierar kvalitet och ergonomi. Implementering:  Underarmsamputerade individer beställer för närvarande armproteser från ortopediska kliniker. Armprotesen identifierades som en produkt av Ottobock. Undersökningar gjordes för att hitta optimala lösningar för kravspecifikationen. Resultat: Konceptutvecklingen av en armprotes utformades för additiv tillverkning med hjälp av en multi-jet-fusion-skrivare. Analys: Det här konceptet hade betydande förbättringar av parametrar: högre grad av anpassningsbarhet, 30 % minskad vikt, 48 % kostnadsreduktion, ett nytt produktionsflöde med 93,5 % automatisering och en 69 % minskning av manuella arbetstider. Slutsatser: Data från denna forskning indikerar att det finns starkt potential för att förbättra designtekniker och utgångar av underarmsproteser genom implementering av additiva tillverkningsprocesser. Detta kan visa sig vara fördelaktigt för att uppnå mer konkurrenskraftiga proteser och tillhörande tjänster.

The main goal of this thesis is to develop practical digital controller architectures for multi-phase dc-dc converters utilized in low power (up to few hundred watts) and cost-sensitive applications. The proposed controllers are suitable for on-chip integration while being capable of providing advanced features, such as dynamic efficiency optimization, inductor current estimation, converter component identification, as well as combined dynamic current sharing and fast transient response. The first part of this thesis addresses challenges related to the practical implementation of digital controllers for low-power multi-phase dc-dc converters. As a possible solution, a multi-use high-frequency digital PWM controller IC that can regulate up to four switching converters (either interleaved or standalone) is presented. Due to its configurability, low current consumption (90.25 μA/MHz per phase), fault-tolerant work, and ability to operate at high switching frequencies (programmable, up to 10 MHz), the IC is suitable to control various dc-dc converters. The applications range from dc-dc converters used in miniature battery-powered electronic devices consuming a fraction of watt to multi-phase dedicated supplies for communication systems, consuming hundreds of watts. A controller for multi-phase converters with unequal current sharing is introduced and an efficiency optimization method based on logarithmic current sharing is proposed in the second part. By forcing converters to operate at their peak efficiencies and dynamically adjusting the number of active converter phases based on the output load current, a significant improvement in efficiency over the full range of operation is obtained (up to 25%). The stability and inductor current transition problems related to this mode of operation are also resolved. At last, two reconfigurable digital controller architectures with multi-parameter estimation are introduced. Both controllers eliminate the need for external analog current/temperature sensing circuits by accurately estimating phase inductor currents and identifying critical phase parameters such as equivalent resistances, inductances and output capacitance. A sensorless non-linear, average current-mode controller is introduced to provide fast transient response (under 5 μs), small voltage deviation and dynamic current sharing with multi-phase converters. To equalize the thermal stress of phase components, a conduction loss-based current sharing scheme is proposed and implemented.