Economical and environmental factors together with energy policies towards more efficient systemsare the driving force for the development of the vehicle industry. Significant changes have beenmade to fulfill new emissions legislation but the basic internal combustion vehicle architecture hasbeen kept. New emission treatment systems that increase the thermal loading of the cooling systemhad been added within the same package envelope as before, which means less space to place coolingfans and a greater need for airflow. Changes in the cooling system, namely the replacement of thehydraulic fan drive system by electrical fans is one of the energy efficient alternatives for severalcity buses under certain environments, like the ”typical red city buses”, well-known in the UnitedKingdom. In this thesis study, hydraulic fans are compared with electrical fans and a road-mapof the benefits and drawbacks of the two systems is developed, based on real traffic performanceperformance data and the results of existing simulations and tests. In addition, new simulations arepresented in order to find the most efficient design for the cooling system as well as a comparisonof these results with previous ones. This road map will be used later by Volvo-Buses Group as atool to better understand in which circumstances electrical fans can be beneficial, in terms of fuelconsumption, noise production, cooling performance, control of the fans and associated costs.

Thermo-elastic errors are one of the main drivers for reduced quality of workpieces in machining. Cooling systems can prevent these errors and improve quality. The paper describes a simulation method that takes into account both the temperature field of a machine tool frame and the fluid cooling system. Such simulations can help to improve the thermal stability of the machine tool frame.

Für Anwendungen mit niedrigen Drehzahlen und großen Drehmomentanforderungen wie z. B. Windenergiegeneratoren, Aufzugs-, Lüfter- und Radnabenmotoren werden häufig elektrische Direktantriebe in Außenläuferbauweise eingesetzt. Im Vergleich zur Innenläuferausführung ist die Abführung der Statorverluste aufgrund der schlechteren Konvektionsbedingungen im Luftspalt und an den Wicklungsköpfen sowie des geringen Wärmedurchganges in den Lagern erschwert. Die Anbindung des Stators an eine große Konvektionsoberfläche fehlt. Im Hinblick auf die maximal zulässige Wicklungstemperatur ist eine Einschränkung der elektromagnetischen Ausnutzung notwendig und bei Luftkühlung liegen erreichbare Ausnutzungsziffern meist im Bereich C < 2 kVA·min/m^3. Eine Alternative bietet die Methode der Statorrohrinnenkühlung, wobei ca. 80 % der Statorverluste über ein im innenliegenden Bauraum des Stators integriertes Kühlsystem abgeführt werden. Im Vergleich zur herkömmlichen Bauweise sind durch die intensivierte Luftkühlung Ausnutzungsziffern C > 3 kVA·min/m^3 realisierbar. Das Ziel der vorliegenden Dissertation ist die Ableitung von Auslegungskriterien für Außenläufermaschinen mit einer intensivierten Statorrohrinnenkühlung, wobei als Anwendungsbeispiel ein Kleinwindenergiegenerator, der eine geöffnete Rotornabe besitzt und durch die natürliche Windströmung gekühlt wird, dient. Aus der hochpoligen Ausführung der permanentmagneterregten Synchronmaschine ergeben sich geringere magnetische Flüsse pro Pol und der innere Bauraum kann aufgrund der geringeren Rückenhöhe zur Kühlung genutzt werden. Für die Festlegung der Abmessungen des Aktiv- und des Kühlsystemvolumens der Maschine ist eine gekoppelte Erwärmungsberechnung erforderlich. Diesbezüglich wird die Erstellung eines elektromagnetisch-strömungsmechanisch-thermisch gekoppelten Berechnungsmodells, das auf analytischen Ersatznetzwerken basiert und durch die Daten numerischer Teilmodelle gestützt wird, vorgestellt. Dabei sind die Schwerpunkte die Berechnungen des Arbeitspunktes des magnetischen Kreises, der Belastungskennlinien des Generators im Inselbetrieb, der lokalen Verlustverteilung, des Kühlluftvolumenstromes im Arbeitspunkt des Kühlsystems und der stationären Erwärmung der Maschine. Die Berechnung der Kühlsystemerwärmung erfolgt mit einem Subwärmequellennetz, wodurch der lokale konvektive Wärmeübergang und die Wärmeleitung im Kühlkörper berücksichtigt werden. Weitere Schwerpunkte der thermischen Modellierung sind u. a. die Berechnung der Wärmeübergänge im Luftspalt und in den Wicklungskopfbereichen, die Bestimmung der spezifischen Ersatzwärmeleitfähigkeiten der orthotropen Wärmeleitgebiete der Wicklung und des Elektroblechpaketes sowie die Berücksichtigung von Isolationsschichten, Füge- und Klebespalten. Experimentelle Untersuchungen in Form von Maschinenprüfungen an einem Prototyp des Kleinwindenergiegenerators sowie Windkanalmessungen an einem Strömungsmodell dienen der Verifikation der Berechnungen. Ausgehend von den Ergebnissen durchgeführter Parameterstudien zur Magnetkreis- und Wicklungsausführung in Kombination mit der Kühlsystemauslegung werden Schlussfolgerungen für die Projektierung der Außenläufermaschine mit intensivierter Statorrohrinnenkühlung zusammengefasst.:Kurzfassung Abstract Nomenklatur Verzeichnis der Formelzeichen und Indizes Abkürzungsverzeichnis 1 Einführung 1.1 Motivation 1.2 Aufgaben- und Zielstellung 1.3 Einordnung in der Fachliteratur 1.4 Struktur der Dissertation 2 Elektromagnetische und thermische Modellierung 2.1 Kopplung der physikalischen Modellebenen 2.2 Elektromagnetisches Modell und Betriebsverhalten 2.2.1 Experimentelle Prototypuntersuchung 2.2.2 Analytisches elektromagnetisches Modell 2.2.3 Ersatzschaltbildparameter, Zeigerbild und Belastungskennlinie 2.2.4 Numerisches elektromagnetisches Modell 2.3 Komponenten des Verlustmodells 2.3.1 Unterteilung der Verlustanteile 2.3.2 Verluste im Leerlaufbetrieb des Generators 2.3.3 Verluste im Belastungsbetrieb des Generators 2.4 Verifikation der Berechnungsergebnisse 2.5 Elektromagnetische Ausnutzung und Erwärmungsmodell 2.5.1 Analyse der elektromagnetischen Ausnutzung von Außenläufermaschinen 2.5.2 Stand der Technik in Bezug auf die Kühlung von Außenläufermaschinen 2.5.3 Erwärmungsmodell von Außenläufermaschinen mit Statorrohrinnenkühlung 2.5.4 Schlussfolgerungen für die Steigerung der elektromagnetischen Ausnutzung 3 Mechanismen des Wärmetransportes 3.1 Wärmeleitung 3.2 Wärmeübergang durch Konvektion 3.2.1 Beschreibung des konvektiven Wärmeüberganges 3.2.2 Stoffeigenschaften und Ähnlichkeitskennzahlen 3.2.3 Grundgleichungen der Strömungsmechanik 3.2.4 Turbulenzmodellierung 3.2.5 Wärmeübertragungsmodellierung 3.2.6 Wandeffekte und Berechnung der Grenzschicht 3.3 Wärmeübergang durch Strahlung 4 Wärmeübergang im Luftspalt 4.1 Analyse der Fachliteratur 4.1.1 Unterscheidung der Strömungsform 4.1.2 Untersuchung des Wärmeüberganges 4.2 Modellierung des glatten Luftspaltes 4.2.1 Modellerstellung und numerische Berechnung 4.2.2 Ergebnisauswertung und Ableitung empirischer Beziehungen 4.3 Modellierung des Luftspaltes mit Nutschlitzen oder Pollücken 4.3.1 Modellerstellung und numerische Berechnung 4.3.2 Ergebnisauswertung und Ableitung eines Korrekturfaktors 4.4 Modellierung des Luftspaltes mit Nutschlitzen und Pollücken 4.4.1 Modellerstellung und numerische Berechnung 4.4.2 Ergebnisauswertung und Ableitung eines Korrekturfaktors 4.4.3 Berechnung für ausgewählte Anwendungen 4.5 Schlussfolgerungen für die analytische Berechnung 5 Statorrohrinnenkühlung von Außenläufermaschinen 5.1 Beschreibung der Kühlsystemkonfigurationen 5.2 Strömungsmechanisches Berechnungsmodell des Kühlsystems 5.2.1 Berechnung des Kühlluftvolumenstromes im Gesamtmodell 5.2.2 Berechnung des Kühlluftvolumenstromes aus aktivem und passivem Modell 5.2.3 Experimentelle Untersuchung des strömungsmechanischen Verhaltens 5.2.4 Abhängigkeiten des Kühlluftvolumenstromes 5.3 Gekoppeltes thermisches Berechnungsmodell des Kühlsystems 5.3.1 Berechnung des Wärmeüberganges bei Rohrströmung 5.3.2 Berechnung der Kühlsystemerwärmung 5.3.3 Experimentelle Untersuchung des thermischen Verhaltens 5.3.4 Abhängigkeiten des Erwärmungsverhaltens 5.4 Schlussfolgerungen für die Projektierung des Kühlsystems 6 Erwärmungsberechnung und Auslegungskriterien statorrohrgekühlter Außenläufermaschinen 6.1 Analytisches thermisches Modell 6.1.1 Wärmeübergänge an den Wicklungsköpfen und der Innenseite der Lagerschilde 6.1.2 Wärmeübergänge am Rotorjoch und der Außenseite der Lagerschilde 6.1.3 Orthotrope Wärmeleitung in der Wicklung 6.1.4 Orthotrope Wärmeleitung im Blechpaket 6.1.5 Wärmedurchgang in den Lagern 6.1.6 Berücksichtigung von Isolationsschichten, Füge- und Klebespalten 6.2 Gekoppelte Erwärmungsberechnung 6.2.1 Analytische Berechnung der Temperaturverteilung und der Wärmeströme 6.2.2 Numerische Berechnung der stationären Enderwärmung des Stators 6.3 Elektromagnetische und kühltechnische Optimierung des KWEGs 6.3.1 Analytische Variantenrechnung zur elektromagnetischen Optimierung 6.3.2 Analytische Variantenrechnung zur kühltechnischen Optimierung 6.3.3 Numerische Nachrechnung der Neuauslegung des KWEGs 6.3.4 Anwendung des KWEGs in einer Kleinwindenergieanlage im Inselbetrieb 6.4 Schlussfolgerungen für die Projektierung einer Außenläufermaschine mit intensivierter Statorrohrinnenkühlung 7 Fazit und Ausblick 7.1 Zusammenfassung der wissenschaftlichen Ergebnisse 7.2 Ausblick auf weiterführende Entwicklungsarbeiten Anhang A Konvergenz- und Berechnungsgitteranalyse der numerischen Berechnungen am Beispiel des Luftspaltwärmeüberganges B Simulationsumfang des Luftspaltkonvektionswiderstandes von Außenläufern mit Nutschlitzen oder Pollücken C Experimentelle Prototypuntersuchung des KWEGs im Inselbetrieb bei Variation der Belastungsart D Auswahlkriterien zur Auslegung der Zweischicht-Zahnspulenwicklung E Schnittzeichnung des Kleinwindenergiegenerators Literaturverzeichnis / Electrical direct drives with outer rotor construction are often used for applications with low rotational speed and high torque requirements such as wind energy generators, elevators, fans and wheel hub motors. Compared to the internal rotor construction, it is more difficult to dissipate the stator losses due to the unfavorable convection conditions in the air gap and at the end windings and the low heat transfer in the bearings. The stator lacks contact to a large convection surface. The maximum permissible winding temperature necessitates reducing electromagnetic utilization, with air cooling the achievable utilization numbers are usually in the range C < 2 kVA∙min/m^3. An alternative method is stator tube inner cooling, whereby approx. 80 % of the stator losses are dissipated via a cooling system integrated in the internal volume of the stator. Compared to the conventional machine design, utilization numbers C > 3 kVA∙min/m^3 are feasible for the intensified air-cooling. This thesis aims to derive design criteria for outer rotor machines with intensified stator tube inner cooling. A small wind energy generator with an open rotor hub, cooled by the natural wind flow, serves as an application example. The high-pole design of the permanent magnet synchronous machine results in lower magnetic fluxes per pole, and the internal volume can be utilized for cooling due to the thinner back-iron. A coupled heating calculation is required to determine the dimensions of the active volume and the cooling system volume. The realization of an electromagnetic-fluid-mechanical-thermal coupled calculation model is presented. The model is based on analytical equivalent networks and is supported by the data of numerical sub-models. The key aspects are the calculations of the operating point of the magnetic circuit, the load characteristics of the generator in isolated operation mode, the local loss distribution, the cooling air volume flow in the operating point of the cooling system and the stationary heating of the machine. The cooling system heating is calculated with a sub-heat source network, whereby the local convective heat transfer and the heat conduction in the heat sink are considered. Additional key aspects of thermal modelling include calculating heat transfer in the air gap and in the end winding regions, determining the specific equivalent thermal conductivities of the orthotropic heat conduction areas of the winding and the laminated core and considering insulating layers, joint gaps and glue gaps. Experimental investigations in the form of machine testing on a prototype of the small wind turbine generator and wind tunnel measurements on a flow model verify the calculations. Based on the results of parameter studies on the magnetic circuit and winding design in combination with the cooling system configuration, conclusions for the design of the outer rotor machine with intensified stator tube inner cooling are summarized.:Kurzfassung Abstract Nomenklatur Verzeichnis der Formelzeichen und Indizes Abkürzungsverzeichnis 1 Einführung 1.1 Motivation 1.2 Aufgaben- und Zielstellung 1.3 Einordnung in der Fachliteratur 1.4 Struktur der Dissertation 2 Elektromagnetische und thermische Modellierung 2.1 Kopplung der physikalischen Modellebenen 2.2 Elektromagnetisches Modell und Betriebsverhalten 2.2.1 Experimentelle Prototypuntersuchung 2.2.2 Analytisches elektromagnetisches Modell 2.2.3 Ersatzschaltbildparameter, Zeigerbild und Belastungskennlinie 2.2.4 Numerisches elektromagnetisches Modell 2.3 Komponenten des Verlustmodells 2.3.1 Unterteilung der Verlustanteile 2.3.2 Verluste im Leerlaufbetrieb des Generators 2.3.3 Verluste im Belastungsbetrieb des Generators 2.4 Verifikation der Berechnungsergebnisse 2.5 Elektromagnetische Ausnutzung und Erwärmungsmodell 2.5.1 Analyse der elektromagnetischen Ausnutzung von Außenläufermaschinen 2.5.2 Stand der Technik in Bezug auf die Kühlung von Außenläufermaschinen 2.5.3 Erwärmungsmodell von Außenläufermaschinen mit Statorrohrinnenkühlung 2.5.4 Schlussfolgerungen für die Steigerung der elektromagnetischen Ausnutzung 3 Mechanismen des Wärmetransportes 3.1 Wärmeleitung 3.2 Wärmeübergang durch Konvektion 3.2.1 Beschreibung des konvektiven Wärmeüberganges 3.2.2 Stoffeigenschaften und Ähnlichkeitskennzahlen 3.2.3 Grundgleichungen der Strömungsmechanik 3.2.4 Turbulenzmodellierung 3.2.5 Wärmeübertragungsmodellierung 3.2.6 Wandeffekte und Berechnung der Grenzschicht 3.3 Wärmeübergang durch Strahlung 4 Wärmeübergang im Luftspalt 4.1 Analyse der Fachliteratur 4.1.1 Unterscheidung der Strömungsform 4.1.2 Untersuchung des Wärmeüberganges 4.2 Modellierung des glatten Luftspaltes 4.2.1 Modellerstellung und numerische Berechnung 4.2.2 Ergebnisauswertung und Ableitung empirischer Beziehungen 4.3 Modellierung des Luftspaltes mit Nutschlitzen oder Pollücken 4.3.1 Modellerstellung und numerische Berechnung 4.3.2 Ergebnisauswertung und Ableitung eines Korrekturfaktors 4.4 Modellierung des Luftspaltes mit Nutschlitzen und Pollücken 4.4.1 Modellerstellung und numerische Berechnung 4.4.2 Ergebnisauswertung und Ableitung eines Korrekturfaktors 4.4.3 Berechnung für ausgewählte Anwendungen 4.5 Schlussfolgerungen für die analytische Berechnung 5 Statorrohrinnenkühlung von Außenläufermaschinen 5.1 Beschreibung der Kühlsystemkonfigurationen 5.2 Strömungsmechanisches Berechnungsmodell des Kühlsystems 5.2.1 Berechnung des Kühlluftvolumenstromes im Gesamtmodell 5.2.2 Berechnung des Kühlluftvolumenstromes aus aktivem und passivem Modell 5.2.3 Experimentelle Untersuchung des strömungsmechanischen Verhaltens 5.2.4 Abhängigkeiten des Kühlluftvolumenstromes 5.3 Gekoppeltes thermisches Berechnungsmodell des Kühlsystems 5.3.1 Berechnung des Wärmeüberganges bei Rohrströmung 5.3.2 Berechnung der Kühlsystemerwärmung 5.3.3 Experimentelle Untersuchung des thermischen Verhaltens 5.3.4 Abhängigkeiten des Erwärmungsverhaltens 5.4 Schlussfolgerungen für die Projektierung des Kühlsystems 6 Erwärmungsberechnung und Auslegungskriterien statorrohrgekühlter Außenläufermaschinen 6.1 Analytisches thermisches Modell 6.1.1 Wärmeübergänge an den Wicklungsköpfen und der Innenseite der Lagerschilde 6.1.2 Wärmeübergänge am Rotorjoch und der Außenseite der Lagerschilde 6.1.3 Orthotrope Wärmeleitung in der Wicklung 6.1.4 Orthotrope Wärmeleitung im Blechpaket 6.1.5 Wärmedurchgang in den Lagern 6.1.6 Berücksichtigung von Isolationsschichten, Füge- und Klebespalten 6.2 Gekoppelte Erwärmungsberechnung 6.2.1 Analytische Berechnung der Temperaturverteilung und der Wärmeströme 6.2.2 Numerische Berechnung der stationären Enderwärmung des Stators 6.3 Elektromagnetische und kühltechnische Optimierung des KWEGs 6.3.1 Analytische Variantenrechnung zur elektromagnetischen Optimierung 6.3.2 Analytische Variantenrechnung zur kühltechnischen Optimierung 6.3.3 Numerische Nachrechnung der Neuauslegung des KWEGs 6.3.4 Anwendung des KWEGs in einer Kleinwindenergieanlage im Inselbetrieb 6.4 Schlussfolgerungen für die Projektierung einer Außenläufermaschine mit intensivierter Statorrohrinnenkühlung 7 Fazit und Ausblick 7.1 Zusammenfassung der wissenschaftlichen Ergebnisse 7.2 Ausblick auf weiterführende Entwicklungsarbeiten Anhang A Konvergenz- und Berechnungsgitteranalyse der numerischen Berechnungen am Beispiel des Luftspaltwärmeüberganges B Simulationsumfang des Luftspaltkonvektionswiderstandes von Außenläufern mit Nutschlitzen oder Pollücken C Experimentelle Prototypuntersuchung des KWEGs im Inselbetrieb bei Variation der Belastungsart D Auswahlkriterien zur Auslegung der Zweischicht-Zahnspulenwicklung E Schnittzeichnung des Kleinwindenergiegenerators Literaturverzeichnis

Indiana University-Purdue University Indianapolis (IUPUI) / The internal and external interactions between the complex structural and behavioral characteristics of the system of interest and the surrounding environment result in unpredictable emergent behaviors. These emergent behaviors are not well understood, especially when modeled using the traditional top-down systems engineering approach. The intrinsic nature of current complex systems has called for an elegant solution that provides an integrated framework in Model-Based Systems Engineering. A considerable gap exists to integrate system engineering activities and engineering analysis, which results in high risk and cost. This thesis presents a framework that incorporates indefinite and definite modeling aspects that are developed to determine the complexity that arises during the development phases of the system. This framework provides a workflow for modeling complex systems using Systems Modeling Language (SysML) that captures the system’s requirements, behavior, structure, and analytical aspects at both problem definition and solution levels. This research introduces a new level/dimension to the framework to support engineering analysis integrated with the system architecture model using FMI standards. A workflow is provided that provides the enabling methodological capabilities. It starts with a statement of need and ends with system requirement verification. Detailed traceability is established that glues system engineering and engineering analysis together. Besides, a method is proposed for predicting the system’s complexity by calculating the complexity index that can be used to assess the complexity of the existing system and guide the design and development of a new system. To test and demonstrate this framework, a case study consisting of a complex district cooling system is implemented. The case study shows the framework’s capabilities in enabling the successful modeling of a complex district cooling system. The system architecture model was developed using SysML and the engineering analysis model using Modelica. The proposed framework supports system requirements verification activity. The analysis results show that the district chiller model developed using Modelica produces chilled water below 6.6 degrees Celsius, which satisfies the system requirement for the district chiller system captured in the SysML tool. Similarly, many such requirement verification capabilities using dynamic simulation integration with the high-level model provides the ability to perform continuous analysis and simulation during the system development process. The systems architecture complexity index is measured for the district cooling case study from the black-box and white box-perspective. The measured complexity index showed that the system architecture’s behavioral aspect increases exponentially compared to the structural aspect. The systems architecture’s complexity index at black-box and white-box was 4.998 and 67.3927, respectively.

In a sustainable society, utilizing intermittent renewable power plants is an important building block for achieving green power production. However, the power production from these sources, e.g., wind farms and solar farms, are often located far away from the place of power consumption, and the electricity generation is affected by the weather conditions in the area. Therefore, there is a challenge in balancing power production and consumption with these sources. The HVDC (High-Voltage Direct Current) technology can be used to efficiently transport electricity over long distances and is a key concept in the utilization of renewable energy sources. However, the HVDC systems are sensitive to environmental effects such as elevated or dropping ambient temperatures, which can cause a forced stop in the system, e.g., when the remaining cooling capacity is low. Therefore, the HVDC systems are built to have a high redundancy to maintain a secure power transmission during seasonal changes.  This thesis aimed to create a forecasting model with applied machine learning that could trend the remaining cooling capacity in an HVDC system, to stay aware of how much remaining cooling capacity there is at different seasons. This can be used to optimize the power transmission during seasons when there is a surplus of cooling capacity. The machine learning pipelines were constructed in Python utilizing Hitachi Energy’s PGML (Power Grid Machine Learning) platform. Two different forecasting models were used: LSTM (Long Short-Term Memory) and XGBoost (eXtreme Gradient Boosting). The models were trained to make a five hour ahead multistep prediction and were validated with several evaluation metrics. The best performing model was the XGBoost model, therefore it was chosen as the final model and was tested on a hold-out data set to estimate the general performance. The final model performed well on the hold-out data set, based on the scores from evaluation metrics. Residual diagnostics were used to improve the models during training and to evaluate the final model. At the end of the discussion in Chapter 5 future improvements were suggested.

The growing industry of Information and Communication Technology requires higher computing capacity of data centers/technical sites. The air conditioning in data centers is the key to assure a sustainable computing environment. However, the traditional cooling systems cost are responsible for large environmental footprints especially on energy consumption and greenhouse gas emissions. As a result, a green innovation of data center cooling solutions is taking place. The telecommunication company Teliasonera is developing a high density data center cooling system - the “Green Room” and has been studying the environmental performance of this system using a Life Cycle approach. As an extension of the previous study, more aspects of the project i.e. the location, life span, alternative cooling solutions, energy recovery possibilities and uncertainty analysis is explored by using Life Cycle Assessment (LCA) methodology. The comparison of the locations of the Green Room indicates that the local temperature and electricity production sources are essential factors for the environmental performance of the Green Room. The analysis of the Green Room’s life span reveals that the utilization phase may not always cause the most significant impact during the whole life cycle of the Green Room. If the life span changes, the manufacture phase may predominate the life cycle of the Green Room. The comparative result of alternative cooling technologies addresses that utilizing “natural coolant” (e.g. geo cooling) is a key for sustainable cooling innovation as it would significantly reduce the environmental footprint of the cooling system. Besides, heating a single building (partly) by the waste heat generated from the Green Room could save 30% of cumulative energy input and could reduce more than half of the total environmental impact. Additionally, results uncertainties caused by the choice of different LCIA methods are discussed in the end of the study. / The Teliasonera Green Room Concept for high and mid density of ICT equipment

In this investigation, a single phase fluid is used to study the coupling between natural convection heat transfer within an enclosure and forced convection through computer covering case to cool the electronic chip. Two working fluids are used (water and air) within a rectangular enclosure and the air flow through the computer case is created by an exhaust fan installed at the back of the computer case. The optimum enclosure size configuration that keeps a maximum temperature of the heat source at a safe temperature level (85℃) is determined. The cooling system is tested for varying values of applied power in the range of 15−40𝑊. The study is based on both numerical models and experimental observations. The numerical work was developed using the commercial software (ANSYS-Icepak) to simulate the flow and temperature fields for the desktop computer and the cooling system. The numerical simulation has the same physical geometry as those used in the experimental investigations. The experimental work was aimed to gather the details for temperature field and use them in the validation of the numerical prediction. The results showed that, the cavity size variations influence both the heat transfer process and the maximum temperature. Furthermore, the experimental results ii compared favourably with those obtained numerically, where the maximum deviation in terms of the maximum system temperature, is within 3.5%. Moreover, it is seen that using water as the working fluid within the enclosure is capable of keeping the maximum temperature under 77℃ for a heat source of 40𝑊, which is below the recommended electronic chips temperature of not exceeding 85℃. As a result, the noise and vibration level is reduced. In addition, the proposed cooling system saved about 65% of the CPU fan power.

This master's thesis explores the role of bespoke air handling units in enhancing energy efficiency in existing buildings. The context for the study is set against the backdrop of global initiatives, including the United Nations' Sustainable Development Goals, specifically Goal 7, which emphasizes the need to improve energy efficiency to combat climate change. The significance of enhancing energy efficiency is well-established, evident both at the EU level and in national policies and regulations. Buildings represent a significant portion of the energy utilization puzzle, with substantial potential for enhancing energy efficiency, although it is often underutilized. One of the contributing factors to inefficiency is outdated ventilation systems, which lead to high thermal losses. This challenge can be addressed by retrofitting these systems with modern, efficient air handling units, thus contributing to energy conservation and cost savings. This study focuses on the adoption of bespoke air handling units adjusted to the site and capable of accommodating constraints related to factors such as space limitations in machine rooms, existing ductwork layouts, and the location of shafts. The primary goal is to empower engineers to move beyond conventional approaches, enabling them to optimize technology choices based on local conditions, specific system performance requirements, and the economic viability of each project. The aim of this study is twofold: first, to develop a methodology for designing bespoke air handling units; and second, to demonstrate the practical application of this methodology in the context of two distinct renovation projects. In line with the aim of the thesis, a design methodology for site-tailored units equipped with a two stage flat crossflow heat exchanger and an indirect evaporative cooling system was developed. The methodology delves into different aspects of data analysis, 3D modeling, and the conduct of performance calculations.The established methodology was applied in two reconstruction projects in central Stockholm, where bespoke air handling units were designed in compliance with provided technical specifications. In both scenarios, a viable option emerged for accommodating a tailored unit within the technical room situated on the first floor. For both units, the energy performance metrics signify a notable achievement in terms of heat recovery efficiency, coupled with relatively modest requirements for heating and cooling power capacity from the combined heating and cooling aircoil. However, the calculated maximum specific fan power for a single unit with heat recovery exceeded the stipulated value specified in the technical specifications, which was accepted by the client. The results of the study included air handling unit product drawings, ventilation blueprints of the technical room with the integrated air handling unit, component specifications, unit flowcharts, performance calculations, and control operating pictures. The results of this work indicate that the improvement of the building's energy efficiency is rendered feasible through the installation of bespoke air handling units in the studied reconstruction projects.

Yes / In order to improve the performance of the reverse osmosis (RO) desalination plant powered by photovoltaic (PV), two cooling systems were proposed in this study to cool the PV and preheating the RO feed water as well. In the cooling design (1), the cooling fluid flows in direct contact with the back surface of the PV through channels of half circular cross-sections. While in the design (2), it flows through channels of squar cross-sections fixed on the PV back surface. Two nano-fluids were also tested as cooling fluid: H2O/CuO and H2O/Al2O3, in addition to distilled water for the purpose of comparison. The effect of changing the weight concentration of the nano-fluid (0.05, 0.1, and 0.15%) on the PV performance was also investigated. The results showed that the PV integrated with the cooling design (1) achieves better performance compared to design (2) at all studied cooling fluids. The improvements in the electric efficiency of the PV integrated with design (1) reached 39.5, 34.8 and 27.3 % when CuO and Al2O3 nano-fluids and distilled water were used as cooling fluid, respectively, compared to the uncooled PV. Based on the obtained experimental results, the PV integrated with design (1) was selected to power the RO with H2O/CuO nano-fluid of weight concentration 0.15% and flow rate 0.15 kg/s being used as the coolant. The RO powered by the improved PV was tested at different salinities of brackish water when the preheating technique was implemented. The results showed that the proposed PV-RO desalination system produces 366 l/day when brackish water of salinity 3000 ppm was used.

<p dir="ltr">Improving launch vehicle and satellite propulsion system performance directly correlates to the delivery of more mass (or quantity) on orbit from launch vehicles, longer duration satellite missions, and longer ranges for missiles/interceptors. Alternative propulsion devices such as rotating detonation engines (RDEs) offer the potential for significant performance gains but their operability has only been demonstrated on “battle hardened” laboratory devices for rocket applications. The objective of this research was to demonstrate cooling and structural approaches that mature rotating detonation rocket engines (RDREs) to flight like maturation levels.</p><p dir="ltr">Multiple 1.6”/4.1 cm diameter RDE combustors were designed, fabricated, and tested. The RDE tested the most accumulated 309 seconds of hot fire testing and 118 starts/shutdowns. Long duration testing was completed to characterize heat flux and high cycle fatigue (HCF) loading. Large quantities of short duration tests were completed to evaluate thermal cycling impacts to the combustor structure and evaluate low cycle fatigue (LCF) loading. The hardware experienced 118 LCF loadings on the combustor cooling passages, equivalent to the amount of thermal cycle starts and shutdowns. An endurance test was completed at 60 seconds in duration, demonstrating operation well beyond thermal steady state. Additionally, ~3.7 million HCF loadings were placed on the combustor cooling passages, equivalent to the approximate amount of detonation wave passes present for all of the WC 2.0 testing.</p><p dir="ltr">Predicted operating pressures ranged from 5 to 15 atm. The highest-pressure conditions resulted in hot gas wall temperatures exceeding 1000°F on the outerbody of the combustor and injector face temperatures peaking at 350°F. Water calorimetry was used to compute heat fluxes, which were then compared to traditional rocket engine throat level heat fluxes calculated using Bartz equations under average operating conditions. The outerbody heat fluxes reached up to 3.7 kW/cm², while injector face heat fluxes reached a maximum of 1.6 kW/cm². When compared to Bartz throat level values, the outer-body heat fluxes varied from 0.9 to 1.6 times the throat level values, and injector heat fluxes ranged from 0.3 to 0.5 times the throat level values.</p><p dir="ltr">A combined thermal and pressure loading fatigue assessment was completed that took into consideration mean stresses and cumulative damage from the spectrum of loading events. Traditional rocket combustor life is typically limited by the thermal cycles that can be placed on the cooling channel hot wall. The fatigue analysis results highlight the reduction in available low cycle fatigue life as RDE's experience larger thermal loads when compared to traditional rocket combustors. Low cycle fatigue life will become especially challenging in higher chamber pressure combustors where thermal environments are more extreme, and the ability keep hot wall temperatures within acceptable levels is more challenging.</p><p dir="ltr">The study also highlights that the passing detonation wave provides a high cycle fatigue (HCF) failure mechanism that is not present in traditional rocket combustors. This failure mechanism is the result of the pressure pulse provided by the passing detonation wave causing a variable load on the hot wall. This variable load is applied at frequencies commonly in the 10's of kHz, resulting in large quantities of loading cycles when operated at rocket like durations (>60 sec). This HCF failure mechanism is most impactful at larger chamber pressures where the detonation pressure ratio causes peak pressures to be elevated, resulting in larger cyclic stresses and strains in the hot wall. The results indicate that high chamber pressure combustors may experience HCF life exceedances within seconds of operation.</p>