Spray cooling has proven to be efficient in managing thermal load in high power applications. Reliability of electronic products relies on the thermal management and understanding of heat transfer mechanisms including those related to spray cooling. However, to date, several of the key heat transfer mechanisms are still not well understood. An alternative approach for improving the heat transfer performance is to change the film dynamics through surface modification. The main goal of this study is to understand the effects of nano-scale features on flat heater surfaces subjected to spray cooling and to determine the major factors in droplet impingement cooling to estimate their effects in the spray cooling system. Single droplet stream and simultaneous triple droplet stream with two different stream spacings (500 μm and 2000 μm), experiments have been performed to understand the droplet-surface interactions relevant to spray cooling systems. Experiments have been conducted on nano-structured surfaces as well as on flat (smooth) surfaces. It is observed that nano-structured surfaces result in lower minimum wall temperatures, better heat transfer performance, and more uniform temperature distribution. A new variable, effective thermal diameter (de), was defined based on the radial temperature profiles inside the impact zone to quantify the effects of the nano-structured surface in droplet cooling. Results indicate that larger effective cooling area can be achieved using nano-structured surface in the single droplet stream experiments. In triple stream experiments, nano-structured surface also showed an enhanced heat transfer. In single stream experiments, larger outer ring structures (i.e. larger outer diameters) in the impact crater were observed on the nano-structured surfaces which can be used to explain enhanced heat transfer performance. Smaller stream spacing in triple stream experiments reveal that the outer ring structure is disrupted resulting in lower heat transfer. Lower static contact angle on the nano-structured surface has been observed, which implies that changes in surface properties result in enhanced film dynamics and better heat transfer behavior. The results and conclusions of this study should be useful for understanding the physics of spray cooling and in the design of better spray cooling systems.

Le marché du diagnostic connait un essor considérable depuis l’avènement de labiologie moléculaire. Plus précis et souvent plus rapide, le diagnostic moléculaire in vitro(DIV) est de plus en plus utilisé dans les laboratoires d’analyses médicales. L’ensemble destests dédiés au marché du DIV répond à des contraintes socio-économiques très précisescomme : la fiabilité du résultat, le délai de réponse court, le faible coût et la facilitéd’utilisation. Les indicateurs socio-économiques montrent que la technologie des biopuces estun potentiel bon candidat pour répondre aux attentes du marché. En effet, cet outil permetl’analyse simultanée de plusieurs dizaines voire centaines de séquences nucléiques et doncl’identification d’autant d’organismes en une seule analyse. Cette technologie s’inscrit encomplément de la PCR en apportant l’avantage de l’analyse multiplexée à moyen débit. Deplus, elle permet de donner une réponse globale de la multiplicité des espèces présentes dansl’échantillon sans avoir besoin de passer par une étape de culture. Néanmoins, cettetechnologie n’est pas optimisée pour le marché du DIV. En effet, son usage est complexe, peurobuste et trop cher pour concurrencer les méthodes actuelles (microbiologie pasteurienne,PCR, Elisa, etc..). Dans le but de réduire le coût de fabrication des biopuces à ADN, il estdonc nécessaire de développer des méthodes alternatives. Dans un premier temps, l’objectif de cette thèse Cifre a été de mettre au point unprototype nouveau de dépôt de biomolécules basé sur la lithographie douce, permettant dedéposer les oligonucléotides sondes de façon multiplexée et selon des motifs micrométriques.Cette nouvelle technologie a été évaluée par rapport aux technologies de références. Puis,nous avons développé un procédé innovant de double fonctionnalisation de surface. Ceprocédé simple et rapide a pour avantages de fonctionnaliser la biopuce avec la chimie desurface et les sondes en une seule étape et d’augmenter les signaux d’hybridation. La secondepartie de la thèse a été de coupler cette nouvelle technologie à la détection des événementsd’hybridation sans marquage en utilisant la diffraction de la lumière. La principale différenceavec la méthode de détection par fluorescence repose sur l’adressage des sondes. En effet, ledépôt doit être réalisé sous forme de réseaux de lignes nanométriques diffractants de façon àce que l'interaction entre les molécules déposées et les cibles qui interagissent soit trèssensible. Cette seconde phase du projet a été très ambitieuse et innovante. La faisabilité decette méthode de détection, démontrée par des simulations théoriques, a fait l’objet d’untravail d’optimisation très important et les résultats obtenus montrent que cette technologiesans marquage est possible. / The diagnosis market increased since the advent of molecular biology. More precise and often faster, the in vitro molecular diagnosis (DIV) is more and more used in medical analyses laboratories. DNA chips technology seems to be a good candidate to answer the market expectations. Indeed, this tool allows making several hundreds of analyses simultaneously. Furthermore, it allows giving a global answer of all the present species in the sample without the need of a culture step. Nevertheless, this technology is not optimized for the market of the DIV. Indeed, its use is complex and too expensive in comparison with the current methods (Pasteur microbiology, PCR, Elisa, etc.). So it is necessary to develop an alternative method to reduce the manufacturing cost and simplify the use of DNA chips. First, the goal of this industrial PhD Cifre supported by the Dendris Company was to complete a new prototype of biomolecules deposition based on soft lithography, allowing multiplexing the deposition of oligonucleotides probes along micro and nanometric patterns.This new technology was compared with the reference technologies. Then, we developed an innovative process of surface co-functionalization. This simple and fast process permits to functionalize the DNA chips with both surface chemistry and probes in a single step and to increase the hybridization signals. The second part of this PhD thesis was to couple this new technology with label-free detection using light diffraction. The main difference with fluorescence-based detection was about probes patterning. Indeed, we needed to generate molecular gratings of nanometric lines to diffract efficiently light from a laser beam. We showed that the absolute diffraction intensity increase with the gratings thickness, which is directly correlated with, probes and targets interactions. The second phase of the project was very ambitious and innovative because we demonstrated the feasibility of this label-free detection. And now we can think that this technology will appear as an alternative method for the diagnosis

Após a reunião de Kyoto ficou estabelecido o sistema de \"crédito carbono\" no qual as indústrias que reduzissem a emissão de gás carbônico para o ambiente aufeririam algumas vantagens. Neste sentido já há uma procura por parte de algumas empresas em reduzir esta emissão. Na maioria dos casos esta emissão é reduzida por meio da absorção do CO2 através de uma base, por exemplo, soda, amônia, cal, aminas, entre outras. O caso da amônia e da soda é interessante para empresas que possuem outros efluentes com estas bases em concentrações bem baixas, resultando assim soluções bem diluídas dos sais correspondentes. Soluções muito diluídas ou são descartadas no meio ambiente, que atualmente é proibido, ou são concentradas. A concentração, dessas soluções, usando vapor como meio de aquecimento torna-se um contra-senso por exigir a emissão de CO2 decorrente da queima de óleo combustível em caldeiras. Técnicas bem mais compatíveis com a preservação ambiental serão bem vindas daqui por diante, principalmente aquelas que não emitem CO2. Observando este fato este trabalho visa desenvolver um evaporador com promotor de película, em escala de laboratório para concentrar soluções diluídas, empregando energia solar como meio de aquecimento. O procedimento proposto não emite CO2, sendo mais compatível com a preservação ambiental. O equipamento construído consta de: coletor solar tipo placa plana com inclinação ajustável, promotor de película (aderido ao coletor),distribuidor de líquido, coletor de concentrado e acessórios. Foram estudadas as influências das variáveis: inclinação do coletor, vazão de alimentação e condições meteorológicas, na taxa de evaporação. As condições meteorológicas não podem ser controladas, mas foram constantemente monitoradas. Obtiveram-se maiores eficiências, quando a inclinação do coletor foi ajustada mensalmente, com valores até 36,4% maiores do que quando o coletor permanece fixo. / The system of Carbon Credits established by the 1997 Kyoto Protocol benefits companies that reduce their emissions of carbon into the environment with some advantages. Since the Protocol was signed, many companies have sought new ways to reduce their emissions. In most cases, these emissions are reduced through CO2 absorption by a base, e.g., soda, ammonia, lime and amines, among others. Ammonia and soda are interesting bases for companies that produce other effluents containing these products in much lower concentrations, resulting in highly diluted solutions of the corresponding salts. Highly diluted solutions are either discharged into the environment, which is forbidden today, or they are concentrated. Concentrating these solutions using vapor, as a means of heating is unfeasible since that would involve the emission of CO2 from burning oil in boilers. Therefore, from now on, attention will focus increasingly on more environmentally friendly techniques, especially techniques that do not cause CO2 emissions. A solar energy powered falling film evaporator with film promoter was developed for concentrating diluted solutions (industrial effluents). The procedure proposed here does not emit CO2, making it a viable alternative to the method of concentrating solutions. This novel device consists of the following components: a flat plate solar collector with adjustable inclination, a film promoter (adhering to the collector), a liquid distributor, a concentratecollector, and accessories. The evaporation rate of the device was found to be affected both by the inclination of the collector and by the feed flow. The meteorological variables cannot be controlled, but were monitored constantly to ascertain the behavior of the equipment in response to the variations occurring throughout the day. ) Higher efficiencies were attained when the inclination of the collector was adjusted monthly, showing up to 36.4% higher values than when the collector remained in a fixed position.

Após a reunião de Kyoto ficou estabelecido o sistema de \"crédito carbono\" no qual as indústrias que reduzissem a emissão de gás carbônico para o ambiente aufeririam algumas vantagens. Neste sentido já há uma procura por parte de algumas empresas em reduzir esta emissão. Na maioria dos casos esta emissão é reduzida por meio da absorção do CO2 através de uma base, por exemplo, soda, amônia, cal, aminas, entre outras. O caso da amônia e da soda é interessante para empresas que possuem outros efluentes com estas bases em concentrações bem baixas, resultando assim soluções bem diluídas dos sais correspondentes. Soluções muito diluídas ou são descartadas no meio ambiente, que atualmente é proibido, ou são concentradas. A concentração, dessas soluções, usando vapor como meio de aquecimento torna-se um contra-senso por exigir a emissão de CO2 decorrente da queima de óleo combustível em caldeiras. Técnicas bem mais compatíveis com a preservação ambiental serão bem vindas daqui por diante, principalmente aquelas que não emitem CO2. Observando este fato este trabalho visa desenvolver um evaporador com promotor de película, em escala de laboratório para concentrar soluções diluídas, empregando energia solar como meio de aquecimento. O procedimento proposto não emite CO2, sendo mais compatível com a preservação ambiental. O equipamento construído consta de: coletor solar tipo placa plana com inclinação ajustável, promotor de película (aderido ao coletor),distribuidor de líquido, coletor de concentrado e acessórios. Foram estudadas as influências das variáveis: inclinação do coletor, vazão de alimentação e condições meteorológicas, na taxa de evaporação. As condições meteorológicas não podem ser controladas, mas foram constantemente monitoradas. Obtiveram-se maiores eficiências, quando a inclinação do coletor foi ajustada mensalmente, com valores até 36,4% maiores do que quando o coletor permanece fixo. / The system of Carbon Credits established by the 1997 Kyoto Protocol benefits companies that reduce their emissions of carbon into the environment with some advantages. Since the Protocol was signed, many companies have sought new ways to reduce their emissions. In most cases, these emissions are reduced through CO2 absorption by a base, e.g., soda, ammonia, lime and amines, among others. Ammonia and soda are interesting bases for companies that produce other effluents containing these products in much lower concentrations, resulting in highly diluted solutions of the corresponding salts. Highly diluted solutions are either discharged into the environment, which is forbidden today, or they are concentrated. Concentrating these solutions using vapor, as a means of heating is unfeasible since that would involve the emission of CO2 from burning oil in boilers. Therefore, from now on, attention will focus increasingly on more environmentally friendly techniques, especially techniques that do not cause CO2 emissions. A solar energy powered falling film evaporator with film promoter was developed for concentrating diluted solutions (industrial effluents). The procedure proposed here does not emit CO2, making it a viable alternative to the method of concentrating solutions. This novel device consists of the following components: a flat plate solar collector with adjustable inclination, a film promoter (adhering to the collector), a liquid distributor, a concentratecollector, and accessories. The evaporation rate of the device was found to be affected both by the inclination of the collector and by the feed flow. The meteorological variables cannot be controlled, but were monitored constantly to ascertain the behavior of the equipment in response to the variations occurring throughout the day. ) Higher efficiencies were attained when the inclination of the collector was adjusted monthly, showing up to 36.4% higher values than when the collector remained in a fixed position.

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Die Effektivität keramischer Wärmeübertrager kann durch eine feinere Strukturierung der Oberflächen gesteigert werden. Dies kann durch die Integration textiler Urformen anstatt der konventionell im Schlickguss hergestellten gröberen Geometrien erfolgen. Für Strukturierungen in Form von wandgebundenen Halbbögen werden die Ergebnisse umfangreicher experimenteller und numerischer Untersuchungen zu den wärmetechnischen und strömungsmechanischen Eigenschaften vorgestellt. Basierend auf den Erkenntnissen der mittels numerischer Simulation durchgeführten Parameterstudie werden verschiedene Empfehlungen für eine optimierte Anordnung der Halbbögen gegeben, um das Verhältnis von Wärmeübergang zur Druckverlust zu verbessern. Die experimentellen Ergebnisse belegen die Richtigkeit der gewählten Randbedingungen und Vereinfachungen im numerischen Modell. Des Weiteren wurden die Strömungsstrukturen mit laserdiagnostischen Messmethoden umfangreich charakterisiert.

Die Effektivität keramischer Wärmeübertrager kann durch eine feinere Strukturierung der Oberflächen gesteigert werden. Dies kann durch die Integration textiler Urformen anstatt der konventionell im Schlickguss hergestellten gröberen Geometrien erfolgen. Für Strukturierungen in Form von wandgebundenen Halbbögen werden die Ergebnisse umfangreicher experimenteller und numerischer Untersuchungen zu den wärmetechnischen und strömungsmechanischen Eigenschaften vorgestellt. Basierend auf den Erkenntnissen der mittels numerischer Simulation durchgeführten Parameterstudie werden verschiedene Empfehlungen für eine optimierte Anordnung der Halbbögen gegeben, um das Verhältnis von Wärmeübergang zur Druckverlust zu verbessern. Die experimentellen Ergebnisse belegen die Richtigkeit der gewählten Randbedingungen und Vereinfachungen im numerischen Modell. Des Weiteren wurden die Strömungsstrukturen mit laserdiagnostischen Messmethoden umfangreich charakterisiert.:0 Verwendete Symbole und Formelzeichen IV 1 Einleitung 1 1.1 Motivation 1 1.2 Lösungsansatz 2 1.3 Zielstellung und Struktur der Arbeit 4 2 Stand der Technik 5 2.1 Vorwort 5 2.2 Kennzahlen zur Charakterisierung von Rekuperatoren und Wärmeüber-trageroberflächen 6 2.3 Strömungszustände und Strömungsprofile 13 2.3.1 Grenzschichten von Strömungen 13 2.3.2 Laminare Strömung zwischen zwei parallelen Platten und im Rechteckkanal 14 2.3.3 Turbulente Strömung zwischen zwei parallelen Platten 15 2.3.4 Kenngrößen, Längen- und Zeitmaße von turbulenten Strömungen 16 2.4 Umströmung von Zylindern und Wärmeübergang an Zylindern 19 2.4.1 Quer angeströmter Zylinder, Wirbelablösung und Kármánsche Wirbelstraße 19 2.4.2 Hufeisenwirbel um einen wandgebundenen Zylinder 25 2.4.3 Zylinder in Wechselwirkung miteinander und Zylinder in Tandempaarung 27 2.4.4 Quer angeströmter Zylinder parallel zu einer Wand 28 2.5 Weitere den Wärmeübergang steigernde Strukturen 29 2.5.1 Rohrbündel 30 2.5.2 Stabrippen – „pin fins“ 31 2.5.3 Zweidimensionale Rippengeometrien 33 2.5.4 Gedrehte Bleche und andere Einbauten in Rohrquerschnitten 36 2.5.5 Turbulatoren 38 2.5.6 Poröse Körper 39 2.5.7 Drähte als wärmeübergangsteigernde Struktur 40 2.6 Wärmeübertrager für Industriegasbrenner 41 3 Numerische und experimentelle Untersuchungen der neuentwickelten Wärmeübertragerstruktur 45 4 Numerische Untersuchungen bezüglich des Strömungsfelds um die Bogenstrukturen 49 4.1 Randbedingungen und Vernetzung der numerischen Simulation 49 4.2 Bemerkungen zum Turbulenzmodell 54 4.3 Validierung des numerischen Modells am leeren Kanal 59 4.4 Ergebnisse für die Grundgeometrie 63 4.5 Parameterstudie zur Anordnung und Anzahl der Bögen 70 4.5.1 Variation der Bogendichte 70 4.5.2 Variation der Anordnung der Bögen zueinander bei konstanter Bogendichte 75 4.5.3 Variation der Kanalhöhe bei konstanten Randbedingungen 78 4.5.4 Variation der Kanalhöhe bei umgekehrten Randbedingungen 80 4.5.5 Variation des Bogendurchmessers D 82 4.5.6 Bemerkung zum Anstellwinkel 83 5 Experimentelle Untersuchungen zum Wärmeübergangskoeffizienten 85 5.1 Versuchsaufbau 85 5.2 Versuchsdurchführung und Auswertung 88 5.3 Vergleich des Versuchsstandes mit Untersuchungen für Spaltströmungen 90 5.4 Referenzmessungen mit metallischen Wärmeübertragerstrukturen 93 5.4.1 Ergebnisse für die Grundgeometrie 93 5.4.2 Variation der Kanalhöhe 96 5.4.3 Variation der Kanalhöhe bei umgekehrten Randbedingungen 97 5.5 Messung mit keramischen Strukturen 98 6 Experimentelle Untersuchungen zum Strömungsverhalten 101 6.1 Versuchsaufbau 101 6.2 PIV-Messungen 104 6.2.1 Allgemeines zum Messprinzip 104 6.2.2 Messaufbau 105 6.2.3 Versuchsergebnisse 106 6.3 LDA-Messungen 111 6.3.1 Allgemeines zum Messprinzip und zur Versuchsdurchführung 111 6.3.2 Validierung des Versuchsstandes 114 6.3.3 Strömungsprofile aus der LDA-Messung 117 6.3.4 Wirbelablösung im Bogennachlauf 130 6.3.5 Skalen der Strömung 144 7 Anwendungsbeispiel: Rekuperatorbrenner 151 7.1 Brennerprototyp und Versuchsdurchführung 151 7.2 Versuchsergebnisse und Auswertung 153 8 Zusammenfassung und Ausblick 157 9 Literaturverzeichnis 161 10 Anhang 173 10.1 Messtechnik des Windkanals 173 10.2 PIV-Messtechnik 175 10.3 LDA-Messtechnik 176 10.4 Versuche mit dem Rekuperatorprototypen 177