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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
51

Nekonvenční aplikace hybridních integrovaných obvodů / Non conventional applications of HIC´s

Klíma, Martin January 2011 (has links)
This thesis deals with non-conventional applications in the area of thick film technology, especially with indication of the temperature by thermodynamic sensors. The work summarizes thermodynamic sensors theory and also contains production data of the universal thermodynamic sensor realized on ceramic substrate, including measurement of its parameters and heat radiation.
52

Modellreduktion thermischer Felder unter Berücksichtigung der Wärmestrahlung

Rother, Stephan 15 November 2019 (has links)
Transiente Simulationen im Rahmen von Parameterstudien oder Optimierungsprozessen erfor-dern die Anwendung der Modellordnungsreduktion zur Minimierung der Berechnungs¬zeiten. Die aus der Wärmestrahlung resultierende Nichtlinearität bei der Analyse thermischer Felder wird hier als äußere Last betrachtet, wodurch die entkoppelte Ermittlung der strahlungs-beding¬ten Wärmeströme gelingt. Darüber hinaus ermöglichen die infolgedessen konstanten System¬matrizen die Reduktion des Temperaturvektors mit etablierten Verfahren für lineare Systeme, wie beispielsweise den Krylov-Unterraummethoden. Die aus der in der Regel großflächigen Verteilung der thermischen Lasten folgende hohe Anzahl von Systemeingängen limitiert allerdings die erzielbare reduzierte Dimension. Deshalb werden zustandsunabhängige, sich synchron verändernde Lasten zu einem Eingang zusammengefasst. Die aus der Strahlung resultierenden Wärmeströme sind im Gegensatz dazu durch die aktuelle Temperaturverteilung bestimmt und lassen sich nicht derart gruppieren. Vor diesem Hintergrund wird ein Ansatz basierend auf der Singulärwertzerlegung von aus Trai¬ningssimulationen gewonnenen Beispiellastvektoren vorgeschlagen. Auf diese Weise gelingt eine erhebliche Verringerung der Eingangsanzahl, sodass im reduzierten System ein sehr geringer Freiheitsgrad erreicht wird. Im Vergleich zur Proper Orthogonal Decomposition (POD) genügen dabei deutlich weniger Trainingsdaten, was den Rechenaufwand während der Offline-Phase erheblich vermindert. Darüber hinaus dehnt das entwickelte Verfahren die Gültigkeit des reduzierten Modells auf einen weiten Parameterbereich aus. Die Berechnung der strahlungsbedingten Wärmeströme in der Ausgangsdimension bestimmt dann den numerischen Aufwand. Mit der Discrete Empirical Interpolation Method (DEIM) wird die Auswertung der Nichtlinearität auf ausgewählte Modellknoten beschränkt. Schließlich erlaubt die Anwendung der POD auf die Wärmestrahlungsbilanz die schnelle Anpassung des Emissionsgrades. Somit hängt das reduzierte System nicht mehr vom ursprünglichen Freiheitsgrad ab und die Gesamt-simulationszeit verkürzt sich um mehrere Größenordnungen. / Transient simulations as part of parameter studies or optimization processes require the appli-cation of model order reduction to minimize computation times. Nonlinearity resulting from heat radiation in thermal analyses is considered here as an external load. Thereby, the determi-nation of the radiation-induced heat flows is decoupled from the temperature equation. Hence, the system matrices become invariant and established algorithms for linear systems, such as Krylov Subspace Methods, can be used for the reduction of the temperature vector. However, in general the achievable reduced dimension is limited as the thermal loads distributed over large parts of the surface lead to a high number of system inputs. Therefore, state-independent, synchronously changing loads are combined into one input. In contrast, the heat flows resulting from radiation are determined by the current temperature distribution and cannot be grouped in this way. Against this background, an approach based on the singular value decomposition of snapshots obtained from training simulations is proposed allowing a considerable decreased input number and a very low degree of freedom in the reduced system. Compared to Proper Orthogonal Decomposition (POD), significantly less training data is required reducing the computational costs during the offline phase. In addition, the developed method extends the validity of the reduced model to a wide parameter range. The computation of the radiation-induced heat flows, which is performed in the original dimension, then determines the numerical effort. The Discrete Empirical Interpolation Method (DEIM) restricts the evaluation of the nonlinearity to selected model nodes. Finally, the application of the POD to the heat radiation equation enables a rapid adjustment of the emissivity. Thus, the reduced system is no longer dependent on the original degree of freedom and the total simulation time is shortened by several orders of magnitude.
53

COMBINED BOILER WITH TPV

Björk, Magnus January 2013 (has links)
A TPV-system consists of a hot surface emitting heat radiation on a solar cell with a narrow bandgap.  A unit consisting of a boiler and a TPV-system has been constructed for testing of the performance of TPV cells. The emitter is heated by a fuel consisting of RME-oil. The radiation is collected and concentrated through two reflecting cones formed like a Faberge-egg, with an edge-type optical filter between the cones. The Faberge-egg is treated with electro-polishing in order to obtain a high reflectance of radiation. The edge filter transmits radiation of short wavelengths towards the solar cells and reflects long wavelengths back to the emitter. This increase the temperature of the emitter to prevent the TPV-cells to be overheated. The construction made was working as expected and can be used for further experiments. The performance of the TPV-cells were however very poor because of a low emitter temperature. The main problem was to obtain a good heat transport from the flame to the emitter. It is required that the emitter temperature is considerably increased for justifying a continued work on TPV-systems in combination with boilers.
54

Solblockerande textilier : Optimering av solskydd

Brobeck, Caroline, Westblom, Elin January 2018 (has links)
extilindustrin måste ständigt söka nya alternativ inom beläggningar och laminering för att minska den skadliga miljöpåverkan. En fråga som uppkommit är om beläggningar används i större utsträckning än vad som egentligen behövs. Denna kandidatuppsats har skrivits i samarbete med Artex AB och kretsar kring ett befintligt solskydd och solens ljusspektrum som består av strålar mellan 320–2500 nm. Material som bestrålas kan antingen absorbera, reflektera eller transmittera dessa strålar. Strålarnas alternativa vägar adderat med varandra blir alltid hundra procent, vilket innebär att genom att öka den reflekterande förmågan minskas de andra två tillstånden. I denna studie granskas den totala reflekterande förmågan av ljusspektrumet hos textila material som i sin tur beror på många olika faktorer. Det undersöks även om det är ett steg i fel riktning att använda sig av beläggningar för att nå ett bättre högreflekterande material. Detta även för att minska miljöbelastningen. Eftersom beläggningar generellt förstyvar material är detta kontraproduktivt när man vill bibehålla följsamheten hos en tygvara, vilket är avgörande för denna typ av produkt. Skrynkelheten går nämligen hand i hand med tygvarans då stumma yta. Detta projekt fokuserar på solskydd som ska användas inifrån en bil. Syftet med studien var alltså att undersöka om en obelagd vit och tät tygvara kan uppnå tillräcklig funktion för ett solskydd innanför en bil. I experimenten användes fyra olika tygvaror med olika strukturer i bindningarna för att göra en så omfattande studie som möjligt. Dessa fyra var: en satin, en varptrikå och två stycken tvåskaft, varav den ena glesare och mer matt än den andra. Respektive tygvara beströks med ett färgpigment för att analysera om kombinationen mellan reflektion och elastisk potential var möjlig. Tester som genomförts i denna undersökning var: bestämning av färghärdighet, total reflektion, ljustransmittansmätning och ett egenkomponerat skrynkeltest. Vidare granskades dess skillnader för att undersöka om ett vitt material kunde ge en bättre totalreflektion, men även för att bevisa att en tygvaras konstruktion kan erhålla följsamheten även om en beläggning är nödvändig. Mätvärdena granskades för att sedan jämföra, först med varandra och sedan mot ett referensprov som kommer från en befintlig produkt som författarna fick att tillgå från Artex AB. En trikåvaras elastiska förmåga visade sig kunna bibehållas trots ett belagt ytskikt, och visade även på bra totalreflektion. Denna varptrikå uppvisade, tillsammans med satinen, på bra totalreflektion då de var obelagda och hade god följsamhet. I test om totalreflektion visades det att en vit tät tygvara reflekterade större procent än en belagd tygvara i det synliga ljusets spektrum. För att kunna dra slutsatser om ett vitt obelagt tyg med dessa konstruktioner (satin och varptrikå) hade varit bättre för ett solskydd hade vidare undrsökningar behövts göras. Detta för att se hur mycket av den totala reaktionen som är diffus respektive spekulär / The textile industry must always find ways to reinvent itself and look for alternative options, as the coating and lamination industries are vital for a better environment. A question that needs answering is if coating on textiles are used more than needed. This bachelor thesis is written in cooperation with Artex AB and revolves around the suns light spectrum that consists of rays of 320 to 2500 nm. Materials that irradiate can either absorb, reflect or transmit these wavelengths. The rays alternative routes added with each other is always one hundred percent, which means that through increasing the reflecting capacity the other two will decrease. The most interesting part of this study, was to examine the ability of the light spectrum for material, and take in to consideration it’s construction, structure and color. Textile materials are often coated to add qualities and, in this case, to increase reflecting quality. This study is trying to prove, that it's a step in the wrong direction when it comes to the functionality of a sunshade product and for a reduced impact on the environment. As coating generally stiffens materials it’s contuerproductive with regards to keeping the resilience for the fabric, which is decisive for this type of product. The wrinkles go hand in hand with the fabrics coated surface. Since this project focuses on an existing sunshade product that will be used inside of a car, the heat radiation and the undulations within a certain wavelength that requires reflection will be focused on. The purpose with the study was to examine if an uncoated white fabric can achieve the same function in a sunshade as the current fabric in the product. In the experiments, four fabrics with different structures were used to complete such a comprehensive study as possible. These four fabrics were: one satin, one warp knitted and two plain weave, where one of them was more faint and sparse than the other. Each fabric was coated with a color pigment to analyze the possibilities of a high reflective material that still has elastic potential. The tests that were made was: determination of color fastness, total reflection, light transmit and a wrinkle test. Further on these differences were reviewed, and then concluded that the coating, in hope of increasing the reflection, is negligible. But also, to prove that a fabrics construction can keep its resilience even with a coated surface. These values have been reviewed and then compared with each other and against a reference fabric that the writers took part of from Artex AB. A warp knitted fabric was able to maintain its elastic ability regardless of a coated surface, and also shows good total reflection. This warp knitted fabric showed, together with the satin, good total reflection when they were uncoated and had good resilience. In this test for total reflection, it was proven that a white dense fabric reflects better than a coated fabric in the visible spectra of light. To be able to conclude if a white uncoated fabric with these constructions (satin and warp knitting) would be more useful for a sunshade, further studies had to be made, to see how much of the total reaction that is diffuse and specular.
55

The concept of Representative Crack Elements (RCE) for phase-field fracture: transient thermo-mechanics

Storm, J., Yin, B., Kaliske, M. 08 April 2024 (has links)
The phase-field formulation for fracture based on the framework of representative crack elements is extended to transient thermo-mechanics. The finite element formulation is derived starting from the variational principle of total virtual power. The intention of this manuscript is to demonstrate the potential of the framework for multi-physical fracture models and complex processes inside the crack. The present model at hand allows to predict realistic deformation kinematics and heat fluxes at cracks. At the application of fully coupled, transient thermo-elasticity to a pre-cracked plate, the opened crack yields thermal isolation between both parts of the plate. Inhomogeneous thermal strains result in a curved crack surface, inhomogeneous recontact and finally heat flow through the crack regions in contact. The novel phase-field framework further allows to study processes inside the crack, which is demonstrated by heat radiation between opened crack surfaces. Finally, numerically calculated crack paths at a disc subjected to thermal shock load are compared to experimental results from literature and a curved crack in a three-dimensional application are presented.
56

Spatiotemporal analysis of extreme heat events in Indianapolis and Philadelphia for the years 2010 and 2011

Beerval Ravichandra, Kavya Urs 12 March 2014 (has links)
Indiana University-Purdue University Indianapolis (IUPUI) / Over the past two decades, northern parts of the United States have experienced extreme heat conditions. Some of the notable heat wave impacts have occurred in Chicago in 1995 with over 600 reported deaths and in Philadelphia in 1993 with over 180 reported deaths. The distribution of extreme heat events in Indianapolis has varied since the year 2000. The Urban Heat Island effect has caused the temperatures to rise unusually high during the summer months. Although the number of reported deaths in Indianapolis is smaller when compared to Chicago and Philadelphia, the heat wave in the year 2010 affected primarily the vulnerable population comprised of the elderly and the lower socio-economic groups. Studying the spatial distribution of high temperatures in the vulnerable areas helps determine not only the extent of the heat affected areas, but also to devise strategies and methods to plan, mitigate, and tackle extreme heat. In addition, examining spatial patterns of vulnerability can aid in development of a heat warning system to alert the populations at risk during extreme heat events. This study focuses on the qualitative and quantitative methods used to measure extreme heat events. Land surface temperatures obtained from the Landsat TM images provide useful means by which the spatial distribution of temperatures can be studied in relation to the temporal changes and socioeconomic vulnerability. The percentile method used, helps to determine the vulnerable areas and their extents. The maximum temperatures measured using LST conversion of the original digital number values of the Landsat TM images is reliable in terms of identifying the heat-affected regions.

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