Auswahl der wissenschaftlichen Literatur zum Thema „Ansys Steady State Thermal“

Thesis (M.S.)--West Virginia University, 2005.<br>Title from document title page. Document formatted into pages; contains ix, 138 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 90-94).

The goal of this Master thesis is to design a power convertor for BLDC motor 48V/2kW. Emphasis is placed on the small dimensions of the final printed circuit board. Therefore, power SMD transistors STL135N8F7AG are used in small packages PowerFlat 5x6. To reduce area of the PCB, electrolytic capacitors are mounted on a separate board, which is located above the main PCB. Small high-capacity 22F/100V ceramic capacitors are used in the DC-LINK as well. They are located as close as possible to the power SMD tranzistors. Control logic will be provided by microprocesor STM32G474RE. High resolution timer HRTIM1 is used. The first part of this thesis is devoted to the brief description of BLDC motor construction and driving. Next parts are focused on the design itself.

Includes bibliographical references (p. 205-208).<br>Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2006.<br>(cont.) Since the results obtained in the main body of the analysis account only for thermal-hydraulic constraints, an estimate of the power reduction due to the application of neutronic constraints is also performed. This investigation, focused only on the "New Core" cases, is coupled with an increase of the thickness of the gap separating adjacent bundles from 2 to 5 mm. Under these more conservative conditions, the power gain percentages are lower, ranging between 24% and 43% (depending on the discharge burnup considered acceptable) for the upper pressure drop limit, and between 17% and 32% for the lower pressure drop limit.<br>(cont.) The benefits of the latter approach are evident since the space occupied by the bypass channel for cruciform control rod insertion becomes available for new fuel and a higher power can be achieved. The core power is constrained by applying thermal-hydraulic limits that, if exceeded, may induce failure mechanisms. These limits concern Minimum Critical Power Ratio (MCPR), core pressure drop, fuel average and centerline temperature, cladding outer temperature and flow-induced vibrations. To limit thermal-hydraulic instability phenomena, core power and coolant flow are constrained by fixing their ratio to a constant value. In particular, each BWR/5 core has been analyzed twice, each time with a different pressure drop limit: a lower limit corresponding to the pressure drop of the reference core and an upper limit 50% larger. It has been demonstrated that, in absence of neutronic constraints and with the maximum allowed pressure drop fixed at the upper limit, the implementation of the hydride fuel yields power gain percentages, with respect to oxide cores chosen as reference, of the order of 23% when its implementation is performed following the "Backfit" approach and even higher (50-70%) when greater design freedom is allowed in the core design, i.e. in the "New Core" approach. Should the maximum allowed pressure drop be fixed at the lower limit, the power gain percentage of the "Backfit" approach would decrease to 17%, while that of the "New Core" approach would remain unchanged, i.e. 50-70%.<br>This thesis contributes to the Hydride Fuel Project, a collaborative effort between UC Berkeley and MIT aimed at investigating the potential benefits of hydride fuel use in Light Water Reactors (LWRs). Considerable work has already been accomplished on hydride fueled Pressurized Water Reactor (PWR) cores. This thesis extends the techniques used in the PWR analysis to examine the potential power benefits resulting from the implementation of the hydride fuel in Boiling Water Reactors (BWRs). This work is the first step towards the achievement of a complete understanding of the economic implications that may derive from the use of this new fuel in BWR applications. It is a whole core steady-state analysis aimed at comparing the power performance of hydride fueled BWR cores with those of typical oxide-fueled cores, when only thermal-hydraulic constraints are applied. The integration of these results with those deriving from a transient analysis and separate neutronic and fuel performance studies will provide the data required to build a complete economic model, able to identify geometries offering the lowest cost of electricity and thus to provide a fair basis for comparing the performance of hydride and oxide fuels. Core design is accomplished for two types of reactors: one smaller, a BWR/5, which is representative of existing reactors, and one larger, the ESBWR, which represents the future generation of BWRs. For both, the core design is accomplished in two ways: a "Backfit" approach, in which the ex-bundle core structure is identical to that of the two reference oxide cores, and a "New Core" approach, in which the control rods are inserted into the bundles in the form of control fingers and the gap between adjacent bundles is fixed optimistically at 2 mm.<br>by Paolo Ferroni.<br>S.M.

A new methodology for the accurate and efficient determination of steady state thermal hydraulic parameters for prismatic high temperature gas reactors is developed. Two conceptual reactor designs under investigation by the nuclear industry include the General Atomics GT-MHR and the Department of Energy MHTGR-350. Both reactors use the same hexagonal prismatic block, TRISO fuel compact, and circular coolant channel array design. Steady state temperature, pressure, and mass flow distributions are determined for the base reference designs and also for a range of values of the important parameters. Core temperature distributions are obtained with reduced computational cost over more highly detailed computational fluid dynamics codes by using efficient, correlations and first-principles-based approaches for the relevant thermal fluid and thermal transport phenomena. Full core 3-D heat conduction calculations are performed at the individual fuel pin and lattice assembly block levels. The fuel compact is treated as a homogeneous medium with heat generation. A simplified 1-D fluid model is developed to predict convective heat removal rates from solid core nodes. Downstream fluid properties are determined by performing a channel energy balance down the axial node length. Channel exit pressures are then compared and inlet mass flows are adjusted until a uniform outlet pressure is reached. Bypass gaps between assembly blocks as well as coolant channels are modeled. Finite volume discretization of energy, and momentum conservation equations are then formed and explicitly integrated in time. Iterations are performed until all local core temperatures stabilize and global convective heat removal matches heat generation. Several important observations were made based on the steady state analyses for the MHTGR and GT-MHR. Slight temperature variation in the radial direction was observed for uniform radial powers. Bottom-peaked axial power distributions had slightly higher peak temperatures but lower core average temperatures compared to top and center-peaked power distributions. The same trend appeared for large bypass gap sizes cases compared to smaller gap widths. For all cases, peak temperatures were below expected normal operational limits for TRISO fuels. Bypass gap flow for a 3 mm gap width was predicted to be between 10 and 11% for both reactor designs. Single assembly hydrodynamic and temperature results compared favorably with those available in the literature for similar prismatic HTGR thermal hydraulic, computational fluid dynamics analyses. The method developed here enables detailed local and core wide thermal analysis with minimal computational effort, enabling advanced coupled analyses of high temperature reactors with thermal feedback. The steady state numerical scheme also offers a potential for select transient scenario modeling and a wide variety of design optimization studies.

Thesis (Ph.D.)--Case Western Reserve University, 2009<br>Title from PDF (viewed on 19 August 2009) Department of Biomedical Engineering Includes abstract Includes bibliographical references Available online via the OhioLINK ETD Center

Introduction One of the products made by SAAB Avionics Systems in Jönköping was in need of a better cooling solution. The product, a Head-Up Display, holds a LED that was overheating when run at desired input power. The purpose of this thesis was to identify the design weaknesses in the current solution regarding heat dissipation and produce new design proposals that fulfill the requirements. The parts analyzed consist of a LED light source, adjustment plates and a heat sink. The adjustment plates and heat sink where covered in a surface treatment. Theoretical framework A simulation of a finite element model was set up of the current solution in order to identify the influence of the different parts and their thermal properties. The simulation was set up as a steady state thermal model. The FEM and steady state equations used during this are mentioned and shortly explained. The state of modern research was found in order to find new innovative ways of solving the heat problem. Method In order to understand the current solution, experimentswere carried out. Interviews were used in order to get the correct information easily. A literature study was preformed to understand the different theories. Reverse engineering was applied to get a detailed understanding of the functionality both mechanically and thermally. Brainstorming was used to generate new solutions, which was followed by a feasibility evaluation and Pugh’s method to sort out the best concepts. Implementation and Result Based on the simulations it can be concluded that some of the developed solutions pass the requirements and can be implemented right away. Some need some more work in order to fully pass the demands. Conclusions The thermal flow was greatly affected by the properties of the aluminum in the adjustment plates and heat sink, though there was not much room for thickness reduction. However, the oxide layer and the surface roughness also had a great impact on the high junction temperature. The requirements where therefore met when adjustment plates and interfaces were removed, to lower the amount of oxide and air between the LED and the heat sink. But the oxide layers needed to be thinner and the surface roughness needed to be reduced in order to meet requirements. If the oxide layers need to stay at current thickness or the surface roughness cannot be changed, the heat sink needs to be redesigned. The recommended concepts were smaller than the current solution. If this space is utilized with a bigger heat sink, the goals can be met with greater ease. There is also room for improvement when it comes to heat sink heat spreader pattern. Discussion The discussion covers what knowledge which was needed to write this thesis and how different problems that occurred along its path were solved. Sustainability in different ways was also discussed.