Made available in DSpace on 2014-10-09T12:48:58Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:08:23Z (GMT). No. of bitstreams: 1 09626.pdf: 11035558 bytes, checksum: 15aa6dd9cdacdf9c6ea1b493f68aba84 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Made available in DSpace on 2014-10-09T12:47:39Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:08:47Z (GMT). No. of bitstreams: 1 08340.pdf: 14966348 bytes, checksum: aaa6cd8ca53387e367ec3e01876c6a48 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

The Advisory Council of Aeronautical Research in Europe (ACARE) has set record emission reduction targets for 2020, in response to increased awareness of global warming issues and the forecast high level of growth in global air traffic. In order to meet this legislation engine designers have to consider new and unconventional designs. An intercooled aero-engine with a heat exchanger (HX) positioned between the IP and HP compressors has the potential to reduce emissions and/or reduce specific fuel consumption relative to conventional engine cycles. In such an engine a coolant delivery system is required to bleed a proportion of the bypass flow, from behind the fan outlet guide vane (FOGV), rapidly diffuse the flow (to reduce pressure loss through the HX modules) and present it to the intercooler (i.e. heat exchanger) modules for cooling. This spent cooling air is then fed back into the bypass duct. To realise the benefits of the intercooled cycle the coolant delivery system must diffuse the flow, within the geometrical constraints, with minimal pressure loss and present it to the heat exchanger modules with suitable flow characteristics over a range of operating conditions. Therefore, a predominately experimental study, complemented with CFD predictions, was undertaken to investigate the design and performance of a coolant delivery system aimed at providing high pressure recovery in a relatively short length. For this to be achieved some pre-diffusion of the flow is required upstream of the offtake (i.e. by making the offtake larger than the captured streamtube), with a controlled diffuser or hybrid diffuser arrangement located downstream of the offtake. Although targeted at an intercooled aero-engine the concept of a system that produces a high pressure recovery in a limited length is applicable to a variety of applications. Experimental data were obtained on a modified existing low speed isothermal annular test facility operating at nominally atmospheric conditions. The offtake must operate aft of the FOGV in a highly complex flow field environment. Hence, a 1½ stage axial flow compressor (IGV, rotor and modified OGV) was used to simulate the unsteady blade wakes, secondary flows, loss cores and other turbo-machinery features that can significantly influence offtake performance. Preliminary numerical (CFD) studies enabled an offtake configuration to be determined and provided understanding of the governing fluid mechanic processes. A relatively small scale, low speed test facility was designed that had the capability to evaluate aerodynamic processes in isolation (i.e. pre-diffusion, controlled diffusion, hybrid diffusion) and full system modelling to enable the complex interaction between these flow processes to be assessed. Hence an optimal system could be characterised in terms of total pressure loss, static pressure recovery and flow profiles at HX inlet. Measurements and numerical predictions are initially presented for a baseline configuration with no offtake present. This enabled the OGV near field region to be characterised and provided a datum, relative to which the effects of introducing an offtake could be assessed. The results showed that in the near field region (i.e. within one chord downstream of the FOGV) the high velocity gradients in the circumferential direction, and associated turbulent shear stresses, dominate the profile mixing and loss production. There is little mixing out of profiles in the radial direction. Furthermore, the relatively large amount of kinetic energy associated with the compressor efflux and its subsequent mixing to a more uniform profile (i.e. reduced blockage) results in a significant static pressure recovery (Cp=5.5%). With the offtake present a variety of configurations were investigated including different levels of pre-diffusion, prior to the offtake, and different offtake positions. This enabled evaluation of the upstream pressure effects and interaction with the upstream FOGV. For very compact systems of short length, such that the gap between the OGV and offtake is relatively small, the amount of pre-diffusion achievable is limited by the offtake pressure field and its impact on the upstream OGV row. This pressure field is also influenced by parameters such as the non-dimensional offtake height and splitter thickness. For systems of increased length a significant amount of flow pre-diffusion can be achieved with little performance penalty (relative to the datum configuration). Hence, the loss associated with mixing blade wakes and secondary flows in an adverse pressure gradient is relatively small. However, the pre-diffusion level is eventually limited, to approximately 1.5, by the increased distortion and pressure losses associated with the captured streamtube. Further measurements were made with various controlled diffuser and hybrid diffusers (of varying area ratio) downstream of the offtake and various levels of pre-diffusion. The flow profile that is presented to the controlled diffuser is directly influenced by the upstream pre-diffusion process. Hence, in this case the upstream-downstream interaction is relatively strong. Conversely, the downstream-upstream interaction, between the controlled diffuser and pre-diffusion process, is relatively weak and thus has little effect on the upstream flow field. The data enabled an optimal system to be characterised (pre-diffusion/controlled diffusion split) in terms of total pressure loss, static pressure recovery and flow profiles at HX inlet. A total system diffusion of 1.8 was achievable with a pre-diffusion of 1.4 and controlled diffusion of 1.25, with further increases in either the pre-diffusion level or the controlled diffuser area ratio destabilising the system. This was achieved with an absolute mass weighted total pressure loss of 11% measured from FOGV inlet to the controlled diffuser exit plane. Utilising a hybrid bled diffuser, combined with the pre-diffusion, enabled a total system diffusion of 2.24 to be achieved. The system incorporated a 6% bleed from the hybrid diffuser and a system total pressure loss of 13%. Experimental and computational results obtained in the current research have provided an understanding of the governing flow mechanisms and quantified the geometric and aerodynamic interaction of the offtake with the FOGV and between the diffusion processes. This has enabled a design methodology to be outlined that provides approximate information on system geometry and performance (in terms of optimal diffusion split and total pressure loss) for future coolant delivery systems with minimal effort. Preliminary design maps have been developed to define the magnitude of the interaction between the offtake and FOGV in terms of the offtake height, pre-diffusion level, the splitter thickness and the axial distance between the fan OGV and offtake. In this way systems of optimal diffusion split, minimum pressure loss and minimal axial length can be determined.

Tento projekt se zabývá optimalizací chladicích kanálků nového vrtáku navrženého společností SECO Tools pro obrábění titanové slitiny Ti-6Al-4V. Cílem tohoto projektu je optimalizovat průměr a polohu chladicích kanálků na hřbetu tak, aby se snížila teplota vrtáku a tím i životnost nástroje. Nový vrták je použit pro provedení vrtacích zkoušek s použitím konvenční řezné kapaliny (emulze s 7% koncentrací) při tlaku 40 barů. Získané výsledky jsou porovnány s výsledky získanými pomocí dostupného standardního vrtáku od společnosti SECO Tools pro vrtání obrobku Ti-6Al-4V. Teplotní CFD model je vytvořen pro různé hodnoty vstupních tlaků kapaliny pomocí turbulentího modelu k- SST a tepelného zatížení vypočítaného na základě vrtacích zkoušek. Výsledky pro standardní a prototypové vrtáky jsou navzájem porovnávány, s ohledem na průtok, teplotu vrtáku, rychlost kapaliny a přenos tepla do MWF. Následně je model použit k ověření optimalizovaných návrhů.

The diploma thesis is aimed to the influence of the high-pressure and low-pressure coolant system according to the machining operation. The comparison was carried out with different types of materials and cutting tools using the main machining operations – turning, milling, and drilling. The study is focused on the chip and heat removal from the cutting zone, tools life and wear of the tools. A description of the basic principle of the high-pressure coolant system meant is described in this thesis. The economical analysis of the high-pressure compared to low-pressure system was determined in the last part of this work.

In der Reaktorsicherheitsforschung sind auftriebsgetriebene Strömungen von Relevanz für Störfall-szenarien mit Verdünnung der Borkonzentration und für thermische Schockbelastungen des Reak-tordruckbehälters. In der numerischen Simulation der Strömungen werden neben der Berücksichtigung der Auftriebskräfte Quell- und Korrekturterme in die Bilanzgleichungen für die turbulente Energie und die turbulente Dissipation eingeführt. Es wurden erweiterte Modelle entwickelt, in die zusätzliche Gleichungen für die Turbulenzgrößen turbulenter Massenstrom und Dichtevarianz eingehen. Die Modelle wurden in den CFD-Code ANSYS-CFX implementiert. Die Validierung der Modelle erfolgte an einem speziellen Versuchsaufbau (VeMix-Versuchsanlage), mit Einspeisung von Fluid höherer Dichte in eine Vorlage. Als Kriterien für die Validierung wurde der Umschlag zwischen impulsdominiertem Strömungsregime mit vertikalem Jet oder ein vertikales Absinken bei Dominanz von Dichteeffekten herangezogen sowie lokale Konzentrationsmessungen mit Hilfe eines speziell entwickelten Leitfähigkeits-Gittersensors. Eine Verbesserung der Simulation dichtedominierter Vermischungsprozesse mit den erweiterten Turbulenzmodellen konnte allerdings nicht nachgewiesen werden, da die Unterschiede zwischen den Rechnungen mit verschiedenen Turbulenzmodellen zu gering sind. Andererseits konnte jedoch die Simulation der Stratifikation von Fluiden unterschiedlicher Dichte im kalten Strang einer Reaktoranlage deutlich verbessert werden. Anhand der Nachrechnung von Ver-suchen am geometrisch ähnlichen Reaktor-Strömungsmodell ROCOM wurde gezeigt, dass diese Stratifikation von bedeutendem Einfluss auf die Vermischung und somit letztendlich auch auf die Temperatur- bzw. Borkonzentrationsverteilung innerhalb des Reaktordruckbehälters ist. Sie lässt sich nur korrekt simulieren, wenn ausreichend große Abschnitte des kalten Stranges mit modelliert werden. Somit konnte doch eine bessere Vorhersagegenauigkeit der Simulation der Vermischung erreicht werden. In reactor safety research, buoyancy driven flows are of relevance for boron dilution accidents or pressurised thermal shock scenarios. Concerning the numerical simulation of these flows, besides of the consideration of buoyancy forces, source and correction terms are introduced into the balance equations for the turbulent energy and its dissipation rate. Within the project, extended turbulence models have been developed by introducing additional balance equations for the turbulent quantities turbulent mass flow and density variance. The models have been implemented into the computati-onal fluid dynamics code ANSYS-CFX. The validation of the models was performed against tests at a special experimental set-up, the VeMix facility, were fluid of higher density was injected into a vertical test section filled with lighter fluid. As validation criteria the switching-over between a momentum controlled mixing pattern with a horizontal jet and buoyancy driven mixing with vertical sinking down of the heavier fluid was used. Additionally, measurement data gained from an especially developed conductivity wire mesh sensor were used. However, an improvement of the modelling of buoyancy driven mixing by use of the extended models could not be shown, because the differences between calculations with the different models were not relevant. On the other hand, the modelling of the stratification of fluids with different density in the cold leg of a reactor primary circuit could be significantly improved. It has been shown on calculations of experi-ments at the ROCOM mixing test facility, a scaled model of a real reactor plant, that this stratification is relevant as a boundary condition for the mixing process inside the reactor pressure vessel. It can be correctly simulated only if sufficient large parts of the cold legs are included in the modelling. On this way, an improvement of the accuracy of the prediction of mixing processes was achieved.

A parametrical study is performed of coolant dump gas ejectors for a sandwich rocket nozzle design. Five geometrical variations are simulated in four ambient conditions (static, subsonic, supersonic, vacuum) using an in-house CFD solver. The test cases are compared with a baseline case and the resulting thrust and ISP are evaluated on a local and global level. A longer dump wall is found to give the best performance in all ambient cases, with a second possibility of reducing the circumference of the nozzle end stiffener. The possibility of post-ejection coolant gas combustion is encountered for high ambient pressure, high subsonic velocity flight.

The Pressure Tube Super Critical Water Reactor (PT-SCWR) is a design with a light water coolant operating at 25 MPa above the thermodynamic critical pressure, with a separated low pressure and temperature moderator, facilitated by a High E ciency Channel consisting of a pressure tube and a porous ceramic insulator tube. The 2011 AECL reference design is considered along with a 2012 benchmark. In the 2011 reference design the coolant is permitted to ow through the insulator. The insulator region has a temperature gradient from 881 K at the inner liner tube to 478 K at the pressure tube wall. The density of light water varies by an order of magnitude depending on the local enthalpy of the uid. The lateral coolant density is estimated as a radial function at ve axial positions with the lattice physics codes WIMS-AECL and Serpent. The lateral coolant density variations in the insulator region of the PT-SCWR cause strong reactivity and CVR e ects which vary heavily on axial location due to the changes in the estimated mass of coolant and the physical relocation of the coolant closer to the moderator, as the coolant is estimated to be least dense closer to the fuel region of the coolant ow. The beta version of Serpent 2 is used to explore the lateral coolant densities in the subchannel region of the insulator in the 2012 version of the PT-SCWR. A more advanced coolant density analysis with FLUENT is used to estimate the subchannel coolant density variation, which is linked to SERPENT 2s multi-physics interface, allowing the lattice code to measure the sensitivity of the model to the analysis of the subchannels. This analysis increases the reactivity of the PT-SCWR through the displacement of the coolant. Serpent 2 is accepted as a valid lattice code for PT-SCWR analysis. / Thesis / Master of Applied Science (MASc)

Managing the thermal loads inside a non-airbreathing hypersonic vehicle is particularly difficult. The heat generated by the power electronics, avionics, etc. must be removed so that the components do not exceed their maximum temperatures. These vehicles cannot dump the waste heat into fuel or ram air because they carry no fuel and do not have provisions for ram air. This means that the thermal energy resulting from the heat generated must be dumped into an onboard heat sink. Existing solutions to this problem have been passive systems based on solid-liquid phase change materials (PCMs), which store thermal energy as they melt. Since space is at a premium, a heat sink must store a lot of energy per unit volume, while keeping components below their maximum temperature. In this project, three heat sink concepts are tested, i.e., one based on PCMs, a second on thermal to chemical (TTC) energy storage, and a third on a hybrid combination of the first two. For the first, three different PCMs are tested and for the second a single endothermic chemical reaction. The hybrid PCM/TTC concept consists of a single PCM which plays the dual role of PCM and reactant in the endothermic chemical reaction of the TTC energy storage. To enhance heat sink performance, the use of thermoelectric generators (TEGs) and a local coolant loop are investigated. The advantage of the former is that they transform waste heat into usable electricity, reducing the amount of thermal energy that needs to be stored by the heat sink. The advantage of the latter is that it results in a more uniform cooling of the heat source and more uniform heating of the heat sink. Prototypes of each of the heat sink concepts and the coolant loop are designed, built, and tested. Experimental results indicate that all the solutions tested in this project outperform widely used paraffin heat sink technologies on an energy per unit volume basis. Our experiments also show that a local coolant loop is indeed advantageous and that current off-the-shelf thermoelectric generators do not generate enough power to offset the power requirements of the coolant loop. Significant improvements in the ZT factor of the thermoelectric materials used by the TEG would be required. / Master of Science / All electronics produce waste heat and have a maximum operating temperature above which they fail due to overheating. Heat sinks absorb the waste heat and prevent overheating. Non-airbreathing hypersonic vehicles do not have natural heat sinks like intake air or liquid fuel which are commonly used as heat sinks in airbreathing vehicles. Heat cannot be transferred to the environment due to the high temperatures caused by the friction of hypersonic air travel. This means that all waste heat must absorbed by an onboard heat sink. Existing heat sinks in non-airbreathing hypersonic vehicles use paraffin based solid-liquid phase change materials (PCMs) which store thermal energy as they melt. Three novel heat sink options are evaluated in this project, hydrated salt PCMs which absorb energy as they melt, a chemical reaction which absorbs heat as it reacts, and a hybrid system which incorporates one of the hydrates salt PCM as a reactant in the chemical reaction. Because space is at a premium, these options are evaluated by the amount of energy they can absorb (kilojoules) per unit volume (in3) while keeping the electronics below their maximum temperature. To enhance heat sink performance, the use of thermoelectric generators (TEGs) and a local coolant loop are investigated. The advantage of the former is that they transform waste heat into usable electricity, reducing the amount of thermal energy that needs to be stored by the heat sink. The advantage of the latter is that it results in a more uniform cooling of the electronics and more uniform heating of the heat sink. Prototypes of each of the heat sink concepts and the coolant loop are designed, built, and tested. Experimental results indicate that all the solutions tested in this project outperform widely used paraffin heat sink technologies on an energy per unit volume basis. Our experiments also show that a local coolant loop is indeed advantageous and that current off-the-shelf thermoelectric generators do not generate enough power to offset the power requirements of the coolant loop. Significant improvements in the state of the art of thermoelectric materials would be required for TEGs to generate enough electricity from our waste heat load to power the local coolant loop.

No description available.