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1
Meana, Melvin Bernabe. „Forced-air cooling of strawberries in reusable plastic containers“. [Gainesville, Fla.] : University of Florida, 2005. http://purl.fcla.edu/fcla/etd/UFE0011867.
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2
Diette, Christophe. „Measurement and analysis of forced convection phenomena in blade cooling channels“. Valenciennes, 2003. http://ged.univ-valenciennes.fr/nuxeo/site/esupversions/c76547a4-820c-48f8-9717-ced740f0cb38.
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Dealing with gas turbine aircraft engines, the Turbine Entry Temperature (TET) is generally targeted as high as possible. Increasing this parameter leads to higher thermodynamic efficiency and power output and reduces the weight-to-thrust ratio and the Specific Fuel Consumption (SFC). Since the maximum permissible TET is determined by the temperature limitations of the turbine assembly, the choice of turbine material and the design of cooling systems applied to turbine blades are essential. This work reports both an experimental and numerical investigation on internal blade cooling cavities. Various cross sections are examined depending on the region of the blade to cool down. Numerous parameters regarding the promoters of turbulence and the flow conditions are varied to find an optimum solution in terms of both heat transfer and pressure losses. Numerical simulations are performed to support the analysis of the flow behaviour. A good agreement is found between the simulations and the aerodynamic measurements. Theoretical diagrams to interpret the flow field are finally proposed. This study provides a better understanding of flow features occuring in cooling channels together with a very detailed database. The later is useful for further numerical validations and the optimisation of cooling cavitiesEn matière de moteurs d'avion à turbine à gaz, une Température d'Entrée de Turbine (TET) aussi élevée que possible est souhaitée. Augmenter sa valeur permet en effet d'obtenir un rendement thermodynamique plus élevé tout en réduisant le rapport poids-poussée et la consommation spécifique (SFC). Parce que la TET maximum permise est liée aux limites de température supportées par les composants de la turbine, le choix des matériaux et la conception des circuits de refroidissement d'aubes sont cruciaux. Cette recherche rend compte d'une étude expérimentale et numérique sur les cavités internes de refroidissement d'aubes. Des sections de passage différentes sont examinées, en fonction de la région de l'aube à refroidir. Plusieurs paramètres en ce qui concerne les promoteurs de turbulence et les conditions de l'écoulement, sont variés pour définir une solution optimale en termes de transfert de chaleur et pertes de charges. Des simulations numériques sont réalisées pour appuyer l'analyse de l'écoulement. La comparaison de ces résultats avec les mesures aérodynamiques se révèle très satisfaisante. Enfin, des diagrammes sont proposés, pour décrire l'écoulement dans chaque cavité étudiée. De cette étude, il ressort une meilleure compréhension des phénomènes mis en jeu dans les cavités de refroidissement, ainsi qu'une base de données détaillée. Cette dernière est utile pour la validation de codes de calcul et l'optimisation des systèmes de refroidissement
3
Racine, Evan Michael. „Experimental Study - High Altitude Forced Convective Cooling of Electromechanical Actuation Systems“. University of Dayton / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1450286609.
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4
Faust, Adriane (Adriane Jean) 1976. „Forced convective heat transfer to supercritical water in micro-rocket cooling passages“. Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/9296.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2000.Includes bibliographical references (p. 101-102).
An investigation of heat transfer to supercritical fluids in micro-channels was completed to assess the cooling characteristics of the MIT micro-rocket engine. Previous results from supercritical ethanol heat transfer tests were compared to water tests to establish a baseline for future fuel testing. Existing literature on supercritical heat transfer was also consulted to corroborate the water test results. It was found that the characteristics of the water tests matched those observed in the literature, as well as those of ethanol tests run at similar conditions.
by Adriane Faust.
S.M.
5
Arani, Sassan Abedi. „Experimental and computational investigation of forced convection cooling of rectangular blocks in a duct“. Thesis, University of Bath, 1992. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305056.
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6
Wright, Lesley Mae. „Experimental investigation of turbine blade platform film cooling and rotational effect on trailing edge internal cooling“. [College Station, Tex. : Texas A&M University, 2006. http://hdl.handle.net/1969.1/ETD-TAMU-1826.
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7
Dietz, Carter Reynolds. „Single-phase forced convection in a microchannel with carbon nanotubes for electronic cooling applications“. Thesis, Available online, Georgia Institute of Technology, 2007, 2007. http://etd.gatech.edu/theses/available/etd-07052007-155623/.
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Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2008.Dr. David Gerlach, Committee Member ; Dr. Samuel Graham, Committee Member ; Dr. Minami Yoda, Committee Member ; Dr. Yogendra Joshi, Committee Chair.
8
Jonsson, Hans. „Turbulent forced convection air cooling of electronics with heat sinks under flow bypass conditions /“. Stockholm : Tekn. högsk, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3127.
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9
Ratts, Eric B. (Eric Bradley) 1963. „Cooling enhancement of forced convection air cooled chip array through active and passive flow modulation“. Thesis, Massachusetts Institute of Technology, 1986. http://hdl.handle.net/1721.1/15072.
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10
Dehghannya, Jalal. „Mathematical modeling of airflow, heat and mass transfer during forced convection cooling of produce in ventilated packages“. Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=115663.
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Forced convection cooling process is the most widely used method of cooling to extend shelf life of horticultural produce after harvest. However, heterogeneous cooling of produce inside different parts of ventilated packages is a serious problem. Therefore, it is essential to design packages that facilitate air circulation throughout the entire package to provide uniform cooling. Selection of appropriate combinations of air temperature and velocity for a given vent design is currently done largely by experimental trial and error approach. A more logical approach in designing new packages, to provide uniform cooling, is to develop mathematical models that would be able to predict package performance without requiring costly experiments.In this study, mathematical models of simultaneous airflow, heat and mass transfer during forced convection cooling process were developed and validated with experimental data. The study showed that produce cooling is strongly influenced by different ventilated package designs. Generally, cooling uniformity was increased by increasing number of vents from 1 (2.4% vent area) to 5 (12.1% vent area). More uniform produce cooling was obtained at less cooling time when vents were uniformly distributed on package walls with at least 4.8% opening areas. Aerodynamic studies showed that heterogeneity of airflow distribution during the process is strongly influenced by different package vent configurations. The highest cooling heterogeneity index (108%) was recorded at 2.4% vent area whereas lowest heterogeneity index (0%) was detected in a package with 12.1% vent area.
The magnitudes of produce evaporative cooling (EC) and heat generation by respiration (HG) as well as the interactive effects of EC, HG and package vent design on produce cooling time were also investigated. Considerable differences in cooling times were obtained with regard to independent and simultaneous effects of EC and HG in different package vent configurations. Cooling time was increased to about 47% in a package with 1 vent compared to packages with 3 and 5 vents considering simultaneous effects of EC and HG. Therefore, the effects of EC and HG can be influential in designing the forced-air precooling system and consequently, in the accurate determination of cooling time and the corresponding refrigeration load.
11
Tan, Seng Sing. „Optimization study for forced-convective cooling of an augmented printed-circuit-board surface with minimum pumping power“. Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/11252.
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12
Sage, Martin Glenn. „A Flownex uncertainty analysis of a depressurised loss of forced cooling event for the PBMR / Martin Glenn Sage“. Thesis, North-West University, 2006. http://hdl.handle.net/10394/1262.
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The world is currently experiencing an energy crisis. To cope with the rising demand in
South Africa, nuclear power was identified as a clean, safe and reliable source of electricity.
The Pebble Bed Modular Reactor (PBMR) is an inherently safe, next-generation nuclear
power plant that uses pebble fuel. In the event of a depressurized loss of coolant (DLOFC)
accident, the reactor will passively cool itself, and remain within safe limits.
The main purpose of this dissertation was to perform an uncertainty study on the PBMR
reactor during a DLOFC accident to demonstrate this safety feature. An extensive literature
survey was carried out to research the concept of uncertainty, methods for addressing
uncertainty and to gather the required input data to set up a model of the PBMR reactor.
The model requirements were established by use of a systematic PIRT process. A detailed
model of the reactor was set up in Flownex after making the necessary assumptions and
simplifications. A sensitivity and Monte Carlo sampling platform was set up in conjunction
with Flownex in order to perform the uncertainty study.
During the DLOFC transient, the best-estimate maximum fuel, core-barrel and RPV
temperatures reached 1529, 621 and 490’C respectively. Sensitivity studies showed that
the parameters that most strongly influence the results are the power profile, decay heat,
pebble bed effective conductivity and the properties of the graphite reflector. Variations in
fluid properties had a negligible influence on the DLOFC results.
Statistical processing of the Monte Carlo simulation results provided uncertainty bands for
each output. The conclusion was that with 95% confidence, there is a 5% probability of
exceeding maximum fuel, core-barrel and RPV temperatures of 1582, 638 and 503 CC
respectively. All three of these temperatures are below the maximum allowable temperature
for each respective component. Thus all three components will stay within their code cases
during the unlikely event of a DLOFC.
The final effort in this study went to verification and validation (V&V) of the results. This
process included V&V of the input data, software, the calculation and the model
development. These processes included: a detailed internal review; comparison with
analytical solutions; comparison with alternative independent calculations; and comparison
with experiment. The effective pebble bed thermal conductivity is currently being validated
via construction of the Heat Transfer Test Facility (HTTF). The large extent of V&V activities
that have been carried out provides a high level of confidence that the results produced in
this dissertation are satisfactory, if not slightly conservative.Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2007.
13
Van, der Spuy Sybrand Johannes. „Perimeter fan performance in forced draught air-cooled steam condensers“. Thesis, Stellenbosch : Stellenbosch University, 2011. http://hdl.handle.net/10019.1/17858.
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Thesis (PhD)--Stellenbosch University, 2011.ENGLISH ABSTRACT: Axial flow fan arrays form part of air-cooled steam condensers in direct drycooled power plants. This dissertation investigates the performance of axial flow fans when located at the perimeter of a fan array. The perimeter (or edge) fans may experience a reduction in air flow through the fan due to the prevalence of distorted inlet conditions upstream of the fan. The reduction in air flow leads to a reduction in the heat transfer capability of the steam condenser and a consequent reduction in the electricity output of the power plant. Due to the physical size of an air-cooled condenser, full-scale experiments are often impractical and computational fluid dynamics (CFD) is used to model its performance under various conditions. To limit the size of the CFD model the axial flow fans in the CFD analysis are represented by means of simplified methods. Three different simplified methods are presented and applied to a CFD model of a single axial flow fan, namely the pressure jump method (PJM), actuator disc method (ADM) and extended actuator disc method (EADM). The results are compared to experimental values. The comparison highlights the limitations of the models: The ADM fails to model fan performance correctly at low flow rates, while the PJM ignores the variation in fan blade properties at different locations within the fan rotor. The EADM is presented as an improvement on both the other two models. A multiple fan test facility is constructed, consisting of three 630 mm diameter fans extracting air from a common inlet chamber. The inlet chamber is constructed in such a way that one of the three fans act as the perimeter (edge) fan. The floor of the inlet chamber can be adjusted to increase or reduce the inlet flow distortion experienced by the edge fan. Six different fan configurations are tested in the position of the edge fan and an empirical method is derived by which the volumetric effectiveness of an edge fan can be predicted. The experimental results are compared to CFD results for the same facility using the three different simplified simulation methods investigated previously. Particle image velocimetry (PIV) measurements are also performed upstream of the edge fan and the velocity profiles at the inlet of the fan are compared to the profiles obtained numerically. The comparisons show that the EADM predicts the performance of the edge fan more accurately than the ADM en PJM. The effect of adding a walkway and removing the bell mouth upstream of the edge fan was investigated using the EADM. The results are used to show the location of the loss mechanisms upstream of the edge fan. The addition of a walkway moves the location of the pressure loss away from the edge fan bell mouth towards the edge of the walkway. Consequently the distortion directly upstream of the edge fan is reduced and its volumetric effectiveness increased. The effect of removing the edge fan’s bell mouth is similar to the effect of adding a walkway upstream of the edge fan.
AFRIKAANSE OPSOMMING: Aksiaalwaaiermatrikse vorm deel van lugverkoelde kondensors in direk droëverkoelde kragstasies. Hierdie verhandeling ondersoek die werkverrigting van aksiaalwaaiers wat geleë is op die rand van ‘n groot waaiermatriks. Die randwaaiers kan ’n vermindering in deurvloei ondervind as gevolg van versteurde inlaattoestande stroom-op vanaf die waaier. Die vermindering in lugvloei lei tot ’n vermindering in die warmetoordagvermoë van die stoomkondensor en ’n gepaardgaande afname in die elektrisiteitslewering van die kragstasie. As gevolg van die fisiese grootte van die lugverkoelde kondensor is volskaalse eksperimente gewoonlik onprakties en word berekeningsvloeimeganika (BVM) gebruik om die werking van die aanleg onder verskeie toestande te modelleer. Ten einde die grootte van die BVM model te beperk, word die aksiaalwaaiers in so ‘n BVM analiese voorgestel met behulp van vereenvoudigde metodes. Drie verskillende vereenvoudigde metodes word aangebied en toegepas op ‘n BVM model van ‘n enkelwaaier, naamlik die druksprongmetode, die aksieskyfmetode en die verlengde aksieskyfmetode. Die resultate word vergelyk met eksperimentele waardes. Die vergelyking benadruk die beperkings van die modelle: Die aksieskyfmetode kan nie die werking van die waaier akkuraat voorspel by lae vloeie nie en die druksprongmetode ignoreer die variasie in lemeienskappe op verskillende liggings binne-in die waaierrotor. Die verlengde aksieskyfmetode word voorgestel as ‘n verbetering op die ander twee metodes. ‘n Veelvuldige waaiertoetsfasiliteit is saamgestel, bestaande uit drie 630 mm deursnee waaiers wat lug uit ’n gemeenskaplike inlaatkamer suig. Die inlaatkamer is so saamgestel dat een van die waaiers in die fasiliteit ‘n randwaaier verteenwoordig. Die vloerhoogte van die inlaatkamer kan aangepas word om die inlaatversteuring wat deur die raandwaaier ondervind word te vermeerder of te verminder. Ses verskillende waaierkonfigurasies is getoets in die randwaaierposisie. ‘n Empiriese metode waarmee die volumetriese effektiwiteit van ‘n randwaaier voorspel kan word is afgelei. Die eksperimentele resultate word vergelyk met ooreenstemmende BVM resultate vir dieselfde fasiliteit deur gebruik te maak van die drie verskillende vereenvoudigde metodes wat vroeër ondersoek is. Partikelbeeld snelheidsmetings word ook stroom-op vanaf die randwaaier uitgevoer en die snelheidsprofiele by die inlaat van die waaier word vergelyk met profiele wat numeries bereken word. Die vergelykings wys dat die verlengde aksieskyfmetode die werkverrigting van ’n aksiaalwaaier meer akkuraat voorspel as die aksieskyf- of druksprongmetodes. Die effek van die installering van ‘n loopvlak en die verwydering van die randwaaier se inlaatmondstuk word ondersoek met behulp van BVM deur gebruik te maak van die verlengde aksieskyfmetode. Die resultate word spesifiek gebruik om die ligging van die verliesmeganismes stroom-op vanaf die randwaaier aan te dui. Die resultate wys dat die installering van ‘n loopvlak die ligging van die drukverlies wegneem vanaf die rand van die waaierinlaat na die rand van die loopvlak. Dit verminder die inlaatversteuring stroom-op vanaf die randwaaier en die volumetriese effektiwiteit word verhoog. Die verwydering van die randwaaier se inlaatmondstuk het ‘n soortgelyke effek as die installering van ‘n loopvlak stroom-op vanaf die randwaaier.
14
Ozturk, Emre. „Cfd Analyses Of Heat Sinks For Cpu Cooling With Fluent“. Master's thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/12605700/index.pdf.
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In this study, forced cooling of heat sinks mounted on CPU&rsquos was investigated. Heat sink effectiveness, effect of turbulence models, effect of radiation heat transfer and different heat sink geometries were numerically analyzed by commercially available computational fluid dynamics softwares Icepak and Fluent. The numerical results were compared with the experimental data and they were in good agreement. Conjugate heat transfer is simulated for all the electronic cards and packages by solving Navier-Stokes equations. Grid independent, well converged and well posed models were run and the results were compared. The best heat sink geometry is selected and it is modified in order to have lower maximum temperature distribution in the heat sink.
15
Berry, Tarl Michael. „Resistance to airflow and the effects on cooling efficiency of multi-scale ventilated pome fruit packaging“. Stellenbosch : Stellenbosch University, 2013. http://hdl.handle.net/10019.1/85685.
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Thesis (MScAgric)--Stellenbosch University, 2013.ENGLISH ABSTRACT: Inadequate cooling of produce after it has been packed into ventilated packaging can result in inconsistent fruit quality. Misalignment of ventilation holes during stacking as well as the use of internal packaging, such as trays, polyliner bags and thrift bags reduces airflow distribution through the packaging. Consequently, the complex needs of maintaining the cold chain of perishable produce and the considerable variations in packaging designs have made it challenging to find an optimal ventilated package and stacking arrangement. The aims of this study were, therefore, to assess the status of ventilated packaging in the South African pome fruit industry, and to characterize the effects of package design and multi-scale packaging components on the resistance to airflow and cooling performance of apples under forced-air cooling conditions. A survey of the pome fruit industry identified over twenty packaging designs which were grouped into eleven unique designs and further categorised into either ‘display’ or ‘telescopic’ designs. Although South African fruit industry standards recommend ventilation areas of at least 5%, the ventilation areas of package designs identified from the survey varied considerably between <1 and 11%. Furthermore, the study showed that use of stacking renders many of the ventilation holes ineffective, due to blockages from adjacent cartons. The contribution of each component of the multi-scale packages used for handling apples was determined by analysis of pressure drop during forced-air cooling. The results showed when utilising a combination of cartons, fruit trays and plastic liner bags, the total pressure drop contribution of the cartons (8%) and fruit trays (3%) was minimal, while the use of plastic liner bags contributed 89%. However, in a carton and thrift bag packaging combination, the thrift bags contributed 66% to the pressure drop while the carton contributed 34%. The cooling results indicated a negative correlation between the total stack ventilation area and the cooling heterogeneity. In addition, the airflow velocity was correlated positively with fruit cooling rate and negatively with total moisture loss. Fruit packed inside polyliner bags had cooling rates four times slower than fruit on trays and three times slower in thrift bags. The use of liner bags blocked the ventilation holes, thereby reducing the airflow velocity. As a result of the longer cooling times in the polyliner bags, fruit remained at higher temperatures for longer periods, resulting in up to three times more moisture loss during forced-air cooling. In addition, a temperature gradient formed due to a progressive increase in air temperature through the stack, thereby resulting in a similar gradient of moisture loss. This research showed that airflow velocity and distribution were the most important factors contributing to the effectiveness of fruit cooling in multi-scale packaging. From a cold chain perspective, future packaging designs should therefore focus on optimising ventilation characteristics and alignment during stacking to ensure adequate airflow. Given the contribution of internal packaging to high resistance to airflow, such packaging components should be used with caution and only when necessary to meet physiological and market requirements.
AFRIKAANSE OPSOMMING: Onvoldoende verkoeling van vars produkte nadat hulle verpak is kan lei tot wisselende vruggehalte. Wanbelyning van ventilasiegate tydens stapeling sowel as die gebruik van interne verpakking soos rakkies (eng. “trays”), poli-etileensakke en drasakkies (eng. “thrift bag”) verminder die lugverspreiding deur die verpakking. Komplekse behoeftes om bederfbare produkte in die koue ketting te behou en die aansienlike verskille in verpakkingsontwerpe het dit 'n uitdaging gemaak om 'n optimale geventileerde verpakking en stapelskikking of -rangskikking te vind. Die doelwitte van hierdie studie was dus om die status van geventileerde verpakking in die Suid-Afrikaanse kernvrugbedryf te asseseer, en die gevolge van die verpakkingsontwerp en multi-skaal verpakkingskomponente op die weerstand teen lugvloei en verkoeling van appels onder geforseerde lugverkoeling te bepaal. ‘n Opname van die kernvrugbedryf het meer as twintig verpakkingsontwerpe geïdentifiseer, wat in elf unieke ontwerpe gegroepeer is en verder getipeer word in ‘vertoon’ en ‘teleskopiese’ kartonontwerpe. Alhoewel die Suid-Afrikaanse vrugindustrie-standaarde ventilasie areas van ten minste 5% aanbeveel, het die ventilasie areas van die verpakkingsontwerpe geïdentifiseer uit die opname aansienlik gewissel tussen <1 en 11%. Verder het die studie getoon dat gebruik van stapeling baie van die ventilasiegate ondoeltreffend laat weens blokkasies veroorsaak deur aangrensende kartonne. Die bydrae van elke komponent van die multi-skaal verpakkingskombinasies gebruik vir die hantering van appels was bepaal deur analise van die afname in lugdruk tydens geforseerde lugverkoelingskondisies. Die resultate het getoon dat wanneer ‘n kombinasie van kartonne, polietileensakke en vrugte plus rakkies gebruik word, die bydrae van die kartonne (8%) en vrugte plus rakkies (3%) tot die totale afname in lugdruk minimaal was, terwyl die gebruik van polietileensakke ‘n 89% bydrae gemaak het. In ‘n karton en drasakkie kombinasie het die drasakkies 66% bygedra tot die afname in lugdruk, terwyl die karton 34% bygedra het. Die verkoelingsresultate het 'n negatiewe korrelasie getoon tussen die totale stapelventilasie-area en die verkoelingsheterogeniteit. Daarbenewens was die lugvloeisnelheid positief gekorreleer met vrugverkoelingstempo en negatief gekorreleer met totale vogverlies. Die verkoelingstydperk van vrugte in die poli-etileensakke was vier keer langer as die rakkie met vrugte kombinasie en drie keer langer in die drasakkies. Die poli-etileensakke het die ventilasiegate versper en dus die lugvloeisnelheid verlaag. Weens die langer verkoelingstye in die poli-etileensakke was vrugte veel langer aan hoër temperature blootgestel, wat uiteindelik gelei het tot drie keer meer massaverlies gedurende geforseerde lugverkoeling. Daarby het ‘n temperatuurgradiënt gevorm as gevolg van ‘n progressiewe verhoging in lugtemperatuur deur die stapel wat gelei het tot ‘n gelykstaande gradiënt van vogverlies. Hierdie navorsing het getoon dat die lugvloeisnelheid en -verspreiding die belangrikste faktore was wat die doeltreffendheid van vrugverkoeling in multi-skaal verpakking geaffekteer het. Uit 'n koelketting perspektief moet die toekomstige verpakkingsontwerpe dus fokus op die optimalisering van ventilasie eienskappe en belyning (eng. “alignment”) tydens stapeling om voldoende lugvloei te verseker. Gegewe die bydrae van die interne verpakking tot hoë weerstand teen lugvloei, moet sulke verpakkingskomponente met omsigtigheid gebruik word en slegs wanneer dit nodig is om aan markvereistes te voldoen.
16
Colpa, Bekir Onur. „Correlation Based Thermal Design Of Air Transport Rack Chassis“. Master's thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613517/index.pdf.
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In this thesis, a Thermal Model Tool (TMT) is developed for standard Avionic
Transport Rack (ATR) chassis and thermal design of a standard ATR chassis is done
using developed TMT. This ATR chassis is a Digital Moving Map (DMAP) of a
helicopter and the tool is used to determine the cooling channel details of DMAP.
TMT decreases design process steps and eliminates the complexity of the design.
Experimental studies are conducted on one of the existing chassis produced in
Aselsan Inc. for different operating conditions. There are two different operating
conditions for the chassis as 25 ºC and 55 º
C, which are given, in military standard MIL-STD-810F. Critical temperature values are measured, which are used in analytical calculations, and results are represented. At the first step, outputs of the experimental studies are used in analytical calculation in order to develop TMT. Secondly, heat dissipation rate of two different chassis are v calculated easily by using the TMT, and without making effort for CFD analysis, the necessary number of plate fins of the chassis are assessed considering given geometrical constraints and heat loads. Finally, cooling channels are generated using the results of TMT. In the next step the chassis, which are designed using the results of TMT, are analyzed numerically by using Icepak Computational Fluid Dynamics (CFD) tool and results of TMT are verified. The cooling capacities of the decided plate fins, which are obtained by TMT, are checked whether or not the required heat dissipation rates are ensured. Consequently, TMT is tested under for two different operating conditions on two different chassis. Analytical and numerical studies for both conditions are compared and discussed in detail. Comparisons show that, developed TMT results are meaningful and close to numerical results, therefore TMT can be used in forthcoming ATR chassis designs.
17
Kapalla, Alexej. „Simulace oteplení rozváděčů VN“. Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2021. http://www.nusl.cz/ntk/nusl-442798.
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This thesis focuses on the issue of heating of medium-voltage switchgears. The paper contains descriptions of the individual devices which the switchgear consists of. Furthermore, the paper examine the theoretical relations which describe the heating of the conductor. It also present the normative regulations regarding the heading of MV switchgears as well as specific impacts which influence the final temperature-rise. This is followed by chapters that describe the refining of a 3D model of specific switchgear for purposes of simulating temperature-rise, further followed by chapters that look at the actual simulation environment. The thesis further focuses on the actual simulation of MV switchgear temperature-rise and it will compare the results of the simulation with measurements taken under real conditions. The thesis also includes results of simulated temperature-rise while taking into consideration the forced cooling of the switchgear. In the last part, it focuses on the creation of an excel file, which enables the prediction of final results for the temperature-rise of disconnector based on its contact resistance.
18
Watel, Barbara. „Etude des échanges convectifs sur un cylindre aileté en rotation, soumis a un courant d'air parallèle aux ailettes“. Valenciennes, 1997. https://ged.uphf.fr/nuxeo/site/esupversions/29267151-660f-45b9-af69-34482a8dce42.
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L'évaluation expérimentale des échanges convectifs avec l'air est faite sur des ailettes circulaires d'un arbre en rotation à vitesse uniforme et soumises ou non à un courant d'air parallèle à leurs faces. Un banc d'essais a été conçu pour mesurer, par thermographie infrarouge, l'évolution temporelle des températures suivant un rayon d'une ailette durant son refroidissement, cette dernière ayant été préalablement chauffée. Une analyse théorique des phénomènes thermiques se produisant dans une ailette, en régime transitoire, permet de déterminer le coefficient d'échange moyen de celle-ci avec l'air. L’étude bibliographique de la structure d'écoulement entre les ailettes en fonction de leur espacement, de leur vitesse de rotation et de la vitesse du courant d'air a été réalisée. Cette étude sert de base à l'analyse physique de la variation du coefficient d'échange en fonction des différents paramètres. Les essais avec les ailettes en rotation, soumises ou non à un courant d'air parallèle, ont permis de mettre en évidence les domaines d'influence de la convection forcée due à la rotation, de la convection forcée due au courant d'air et de la convection naturelle. Les résultats obtenus sur le coefficient d'échange en convection forcée sont justifiés par la représentation du champ des vitesses de l'écoulement entre les ailettes par vélocimétrie par images de particules. L’ensemble des essais réalisés peuvent être corrélés avec un écart relatif inférieur à 5% par une équation générale.
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Olakoyejo, O. T. (Olabode Thomas). „Geometric optimisation of conjugate heat transfer in cooling channels with different cross-sectional shapes“. Thesis, University of Pretoria, 2012. http://hdl.handle.net/2263/25484.
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In modern heat transfer, shape and geometric optimisation are new considerations in the evaluation of thermal performance. In this research, we employed constructal theory and design to present three-dimensional theoretical and numerical solutions of conjugate forced convection heat transfer in heat generating devices with cooling channels of different cross-sectional shapes. In recent times, geometric configurations of cooling channel have been found to play an important role in thermal performance. Therefore, an efficient ways of optimally designing these cooling channels shapes is required. Experimentation has been extensively used in the past to understand the behaviour of heat removals from devices. In this research, the shapes of the cooling channels and the configurations of heat-generating devices were analytically and numerically studied to minimise thermal resistance and thus illustrate cooling performance under various design conditions. The cooling channels of five different cross-sectional shapes were studied: Circular, square, rectangular, isosceles right triangular and equilateral triangular. They were uniformly packed and arranged to form larger constructs. The theoretical analysis is presented and developed using the intersection of asymptotes method. This proves the existence of an optimal geometry of parallel channels of different cross-sectional shapes that penetrate and cool a volume with uniformly distributed internal heat generation and heat flux, thus minimising the global thermal resistance. A three-dimensional finite volume-based numerical model was used to analyse the heat transfer characteristics of the cross-sectional shapes of various cooling channels. The numerical computational fluid dynamics (CFD) package recently provided a more cost-effective and less time-consuming means of achieving the same objective. However, in order to achieve optimal design solutions using CFD, the thermal designers have to be well experienced and carry out a number of trial-and-error simulations. Unfortunately, this can not always guarantee an accurate optimal design solution. In this thesis a mathematical optimisation algorithm (a leapfrog optimisation program and DYNAMIC-Q algorithm) coupled with numerical CFD was employed and incorporated into the finite volume solver, –FLUENT, and grid (geometry and mesh) generation package, – GAMBIT to search and identify the optimal design variables at which the system would perform optimally for greater efficiency and better accuracy. The algorithm was also specifically designed to handle constraint problems where the objective and constraint functions were expensive to evaluate. The automated process was applied to different design cases of cooling channels shapes. These cooling channels were embedded in a highly conductive solid and the peak temperature was minimised. The trend and performance of all the cooling channel shapes cases studied were compared analytically and numerically. It was concluded that an optimal design can be achieved with a combination of CFD and mathematical optimisation. Furthermore, a geometric optimisation of cooling channels in the forced convection of a vascularised material (with a localised self-cooling property subjected to a heat flux) was also considered. A square configuration was studied with different porosities. Analytical and numerical solutions were provided. This gradient-based optimisation algorithm coupled with CFD was used to determine numerically the optimal geometry that gave the lowest thermal resistance. This optimiser adequately handled the numerical objective function obtained from numerical simulations of the fluid flow and heat transfer. The numerical results obtained were in good agreement with results obtained in the approximate solutions based on scale analyses at optimal geometry dimensions. The approximate dimensionless global thermal resistance predicted the trend obtained in the numerical results. This shows that there were unique optimal design variables (geometries) for a given applied dimensionless pressure number for fixed porosity. The results also showed that the material property had a significant influence on the performance of the cooling channel. Therefore, when designing the cooling structure of vascularised material, the internal and external geometries of the structure, material properties and pump power requirements would be very important parameters to be considered in achieving efficient and optimal designs for the best performance. Finally, this research investigated a three-dimensional geometric optimisation of conjugate cooling channels in forced convection with an internal heat generation within the solid for an array of cooling channels. Three different flow orientations based on constructal theory were studied numerically- firstly, an array of channels with parallel flow; secondly, an array of channels in which flow of every second row was in a counter direction and finally, an array of channels in which the flow direction in every channel was opposite to that of previous channel. The geometric configurations and flow orientations were optimised in such a way that the peak temperature was minimised subject to the constraint of fixed global volume of solid material. The optimisation algorithm coupled with CFD was also used to determine numerically the optimal geometry that gave the lowest thermal resistance. The use of the optimisation algorithm coupled with the computational fluid dynamics package; render the numerical results more robust with respect to the selection of optimal structure geometries, internal configurations of the flow channels and dimensionless pressure difference.Thesis (PhD(Eng))--University of Pretoria, 2012.
Mechanical and Aeronautical Engineering
unrestricted
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Gupta, Abhishek. „Experimental and theoretical analysis of single-phase convective heat transfer in channel with resistive heater and thermoelectric modules for hydronic cooling and heating device“. Cincinnati, Ohio : University of Cincinnati, 2009. http://www.ohiolink.edu/etd/view.cgi?acc_num=ucin1236202446.
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Thesis (M.S.)--University of Cincinnati, 2009.Advisors: Dr. Michael Kazmierczak PhD (Committee Chair), Dr. Milind A. Jog PhD (Committee Member), Dr. Sang Y. Son PhD (Committee Member). Title from electronic thesis title page (viewed April 26, 2009). Includes abstract. Keywords: Peltier cooling; developing internal turbulent forced convection; heat pump and coefficient-of-performance. Includes bibliographical references.
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Castro, Larissa Rodrigues de. „Analise dos parametros relacionados ao resfriamento a ar forçado em embalagens para produtos horticolas“. [s.n.], 2004. http://repositorio.unicamp.br/jspui/handle/REPOSIP/257530.
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Orientadores: Luis Augusto Barbosa Cortez, Clement VigneaultTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Agrícola
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Resumo: Esta pesquisa teve como objetivo desenvolver uma metodologia para o projeto dos orifícios de embalagens para frutas e hortaliças submetidas ao processo de resfriamento rápido a ar forçado. Tendo em vista as altas perdas registradas anualmente sobretudo devido à falta de embalagens adequadas e armazenagem frigorificada, tal metodologia poderá auxiliar de forma prática e precisa a escolha da configuração dos orifícios da embalagem para maximização da eficiência do resfriamento rápido de produtos hortícolas. Esta ferramenta deverá ser utilizada em combinação com demais tecnologias existentes para o projeto de uma embalagem suficientemente atrativa ao consumidor e que atenda não apenas às necessidades do produto submetido a tratamentos pós-colheita, como também à resistência estrutural da caixa, possibilitando inclusive sua higienização, reutilização e desmontagem, visando reduzir custos de confecção e transporte. Para atingir a meta da pesquisa, os produtos hortícolas acondicionados em embalagens foram representados por produtos-modelo nos experimentos laboratoriais. Vários materiais e arranjos experimentais foram testados até se chegar à simulação de uma embalagem com um grupo de esferas plásticas sólidas instrumentadas. Estas simularam com maior precisão a distribuição do ar através de um leito de produtos hortícolas durante o resfriamento rápido a ar forçado. A partir dos resultados obtidos para o coeficiente de resfriamento das esferas, foram desenvolvidas correlações para determinação indireta da velocidade de aproximação do ar ao redor de cada uma delas, considerando sua posição na embalagem relativa ao ar de entrada. Estas correlações foram posteriormente aprimoradas através do refinamento da pesquisa na faixa de regime de fluxo transiente. A precisão das correlações estabelecidas foi verificada através de análises de balanço de massa nas camadas de produto ao longo da direção do fluxo de ar. A metodologia foi aplicada para a investigação do efeito de diferentes configurações de abertura de embalagem na distribuição do ar através do produto submetido ao resfriamento. Tais configurações incluíram orifícios centrais, periféricos, diagonais e uniformemente distribuídos, além das aberturas tipo ¿alça¿ para manuseio. Também foi realizada uma análise energética envolvendo o calor adicionado ao sistema devido à taxa respiratória do produto e ao funcionamento do ventilador usado no resfriamento rápido. Através da ferramenta desenvolvida, foram definidos certos valores de operação do sistema para maximizar a eficiência do processo de resfriamento, em termos de velocidade e uniformidade de resfriamento e energia requerida, que afetarão a qualidade e preço finais do produto. Assim, recomenda-se o projeto de orifícios uniformemente distribuídos na superfície da embalagem com área total aberta entre 8 e 16% . A porcentagem a ser escolhida nesta faixa dependerá dos limites de resistência estrutural do material, fluxo de ar fornecido pelo ventilador e taxa respiratória do produto. Por exemplo, hortícolas com atividade metabólica muito elevada, como brócolis, acondicionados em caixas mais abertas exigirão um maior fluxo de ar para otimização do processo de resfriamento rápido
Abstract: The aim of this research was to develop a methodology for designing container openings for fruits and vegetables submitted to a forced-air precooling process. Due to significant annual losses of fruits and vegetables, especially because of inappropriate packaging and storage, this tool could allow practical and accurate selection of the best package opening configuration to maximize the precooling efficiency of horticultural produce. The tool should be combined with other technologies currently in market use to design a container sufficiently attractive to consumers. This container must not only meet the produce requirements when submitted to postharvest operations, but also the material structural constraints. Furthermore, reusable and foldable containers could be desirable for manufacture and transport cost reductions. To this end, packed horticultural produce were represented by produce simulators in the trials. Several materials and experimental set-ups were tested before selecting an arrangement of instrumented solid plastic spheres in a container. These spheres simulated the air distribution through a horticultural produce stack during forced-air precooling with more accuracy. Correlations were established by measuring the cooling rate of the instrumented simulators for indirect determination of the surrounding air velocity, as a function of the simulator locations in reference to the inlet air. These correlations were further improved by refining the airflow range studied in laminar, transient, and turbulent phases. Their applicability was verified by performing a mass balance through the produce layers perpendicular to the main airflow direction. The methodology was applied to investigate the container opening design on air distribution through horticultural produce submitted to precooling. The configurations tested included central, peripheral, diagonal, and uniformly distributed openings, besides the container handle openings. Furthermore, an energy analysis was performed involving heat added to the system due to produce respiratory rate and fan functioning during precooling. The research tool developed here allowed defining some optimum values for system operation to maximize the cooling efficiency regarding the process rate and uniformity and required energy, which affect produce final quality and cost. Therefore, it is recommended that design openings be uniformly distributed on package surface with total vented area between 8 and 16%. The exact percentage to be selected in this range will depend on the material structural resistance, airflow and produce respiratory rates. For instance, horticultural produce with very high respiratory activity, such as broccoli, require higher airflow rate when submitted to larger venting package to optimize precooling process
Doutorado
Tecnologia Pós-Colheita
Doutor em Engenharia Agrícola
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Novak, Vladimir. „Experimental and Numerical Studies of Mist Cooling with Thin Evaporating Subcooled Liquid Films“. Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/10528.
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An experimental and numerical investigation has been conducted to examine steady, internal, nozzle-generated, gas/liquid mist cooling in vertical channels with ultra-thin, evaporating subcooled liquid films. Interest in this research has been motivated by the need for a highly efficient cooling mechanism in high-power lasers for inertial fusion reactor applications. The aim is to quantify the effects of various operating and design parameters, viz. liquid atomization nozzle design (i.e. spray geometry, droplet size distribution, etc.), heat flux, liquid mass fraction, film thickness, carrier gas velocity, temperature, and humidity, injected liquid temperature, gas/liquid combinations, channel geometry, length, and wettability, and flow direction, on mist cooling effectiveness.
A fully-instrumented experimental test facility has been designed and constructed. The facility includes three cylindrical and two rectangular electrically-heated test sections with different unheated entry lengths. Water is used as the mist liquid with air, or helium, as the carrier gas. Three types of mist generating nozzles with significantly different spray characteristics are used. Numerous experiments have been conducted; local heat transfer coefficients along the channels are obtained for a wide range of operating conditions. The data indicate that mist cooling can increase the heat transfer coefficient by more than an order of magnitude compared to forced convection using only the carrier gas. The data obtained in this investigation will allow designers of mist-cooled high heat flux engineering systems to predict their performance over a wide range of design and operating parameters.
Comparison has been made between the data and predictions of a modified version of the KIVA-3V code, a mechanistic, three-dimensional computer program for internal, transient, dispersed two-phase flow applications. Good agreement has been obtained for downward mist flow at moderate heat fluxes; at high heat fluxes, the code underpredicts the local heat transfer coefficients and does not predict the onset of film rupture. For upward mist flow, the code underpredicts the local heat transfer coefficients and, contrary to experimental observations, predicts early dryout at the test section exit.
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Joska, Jakub. „Charakteristiky ventilátorových chladicích věží“. Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2021. http://www.nusl.cz/ntk/nusl-443198.
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This diploma thesis deals with the problematics of fan cooling towers. The very first part of the text is research, focusing mainly on the theory of cooling and the function of fan cooling towers in general. The following chapter deals with the water resource management of the Dukovany nuclear power plant and the specification of its objects of forced draft cooling towers. The second part describes a computational model created to determine the cooling performance of these towers under the given input conditions. In the following chapters, the results from the computational model are compared with the available data from warranty measurements and with the provided characteristics. The final pages deal with the study of the influence of changes in input parameters on the cooling performance and the research of the behavior of the cooling towers under extreme weather conditions.
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Susna, David. „Návrh chladícího okruhu pro odvod tepla z kondenzátoru parní turbíny“. Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2018. http://www.nusl.cz/ntk/nusl-378737.
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This thesis deals with the problems of wounding of low potential transferred from steam turbine condenser. First, in the theoretical part variations of steam condenser design are described. Then there is a description of variations of cooling cycles and possibilities of their operation range. In second part of the thesis there are two common cooler options chosen. Those are wet cooling tower with natural draft and dry chiller with forced draft. Two types of cooling liquid are chosen to be used for dry cooling. These are water and the other one is 50 % mixture of water and propylene glycol. Based on the calculation results of both cooling cycle variations appropriate pumps are chosen, fan for forced convection respectively. Parts of the thesis are also projection drawings for both calculated variations.
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Sousa, Reginaldo Ribeiro de. „Análise numérica e experimental na determinação da potência térmica dissipada em componentes eletrônicos /“. Ilha Solteira : [s.n.], 2008. http://hdl.handle.net/11449/94552.
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Orientador: Amarildo Tabone PaschoaliniBanca: Luiz de Paula do Nascimento
Banca: Marcelo Moreira Ganzarolli
Resumo: Os objetivos deste trabalho são determinar a potência térmica dissipada dos componentes eletrônicos de forma experimental e verificar a eficácia do método através de simulações numéricas computacionais utilizando o software comercial ANSYS. O Software ANSYS foi usado como ferramenta de Dinâmica de Fluidos Computacional neste trabalho. Para a realização deste trabalho um ensaio experimental foi executado a fim de obter alguns dados para o cálculo da potência térmica dissipada, outros foram fornecidos pelo CPqD e Trópico. Foi montado um Laboratório Computacional com o apoio da Trópico e do CPqD na UNESP, campus de Ilha Solteira para a simulações numéricas. O método de cálculo de potência apresentou-se eficaz, de modo na melhor situação os resultados apresentaram um erro relativo médio de 1,94%.
Abstract: The purpose of this study is to determine the thermal power dissipation of electronic components through an experimental test and verify the effectiveness of the method through numerical simulations using the computational software ANSYS commercial. Software ANSYS was used as a tool for Computational Fluid Dynamics for this work. For this work an experimental test was done to obtain some data to calculate the thermal power dissipation, others were supplied by CPqD, Nilko and Trópico. It was dubbed a Computer Laboratory with the support of the Trópico, CPqD and at UNESP, campus de Ilha Solteira for the numerical simulations. The method of calculation of power proved to be effective, that the better the results showed a mean relative error is 1.94%.
Mestre
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Cherief, Wahid. „Etude des ferrofluides et de leurs applications à l'intensification des transferts de chaleur par convection forcée“. Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAT102/document.
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Cette thèse a pour objectif d’étudier les performances thermiques et rhéologiques des ferrofluides sous champ magnétique pour des applications de refroidissement. L’approche adoptée dans cette thèse est de nature macroscopique, et est basée sur plusieurs études expérimentales. Cette caractérisation des performances des ferrofluides est focalisée sur trois aspects : i) étude de la rhéologie ii) étude de la convection forcée iii) étude la conductivité thermique. Différents outils de caractérisation correspondant à chaque domaine d’étude ont été développés. Dans le domaine de la rhéologie, une cellule magnétique a été construite et adaptée à un rhéomètre afin d’étudier le comportement rhéologique du ferrofluide sous un champ magnétique allant jusqu’à 0,8 T. Cette démarche met en évidence l’influence du champ magnétique et de son intensité sur les forces de cisaillement. Dans le domaine des transferts de chaleur, une boucle thermohydraulique pour l’étude de l’échange de chaleur en convection forcée avec une paroi à flux imposée sous champ magnétique a été mise au point. Ce type de dispositif permet l’étude de plusieurs paramètres liés à la configuration spatiale du champ magnétique appliqué, à l’effet de l’uniformité du champ sur l’intensification des échanges de chaleur. La compréhension et l’analyse de ces résultats sont consolidées par l’étude de la conductivité thermique du ferrofluide sous champ magnétique. Un banc a été mis en place et a permis de mettre en évidence l’influence de la température ainsi que de l’intensité du champ magnétique sur cette grandeur. Á l’issue de ces caractérisations, l’application des ferrofluides pour le refroidissement de composants électroniques de puissance est discutée par une mise en œuvre expérimentale. Ces essais ouvrent la voie pour de nouvelles recherches et permettent de mener des réflexions relatives aux domaines d’application des ferrofluidesThis thesis aims to study the thermal and rheological performances of ferrofluids under magnetic field for an application in cooling systems. The approach consists on macroscopic analysis based on experimental studies. Our approach is focused on three aspects: i) rheology ii) internal forced convection iii) thermal conductivity. We developed different characterization benches. For rheological studies, a magnetic circuit is developed and integrated into rheometer to create magnetic fields reaching 0,8 T. This approach demonstrates the influence of magnetic flux density on the shear forces. Concerning heat transfers, we carried out experimental tests based on the use of a closed loop flow system to study forced convection of ferrofluids with imposed wall flux under magnetic field. This test bench allows us to understand the impact of several parameters related to the configuration of the applied magnetic field on the enhancement of convective heat transfers. To analyze why convective heat transfers are better under magnetic field, we carried out a system for measuring the thermal conductivity. This bench tests allows us to show the effect of temperature and magnetic flux density on this physical property. All these tests are paving the way for new research activities and to the ferrofluids applications in cooling systems
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Xuereb, Andre. „Optical cooling using the dipole force“. Thesis, University of Southampton, 2011. https://eprints.soton.ac.uk/205463/.
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The term `laser cooling' is applied to the use of optical means to cool the motional energies of either atoms and molecules, or micromirrors. In the literature, these two strands are kept largely separate; both, however suffer from severe limitations. Laser cooling of atoms and molecules largely relies on the internal level structure of the species being cooled. As a result, only a small number of elements and a tiny number of molecules can be cooled this way. In the case of micromirrors, the problem lies in the engineering of micromirrors that need to satisfy a large number of constraints|these include a high mechanical Q-factor, high re ectivity and very good optical quality, weak coupling to the substrate, etc.|in order to enable efficient cooling. During the course of this thesis, I will draw these two sides of laser cooling closer together by means of a single, generically applicable scattering theory that can be used to explain the interaction between light and matter at a very general level. I use this `transfer matrix' formalism to explore the use of the retarded dipole{dipole interaction as a means of both enhancing the efficiency of micromirror cooling systems and rendering the laser cooling of atoms and molecules less species selective. In particular, I identify the `external cavity cooling' mechanism, whereby the use of an optical memory in the form of a resonant element (such as a cavity), outside which the object to be cooled sits, can potentially lead to the construction of fully integrated optomechanical systems and even two-dimensional arrays of translationally cold atoms, molecules or even micromirrors. The concept of an optical memory is a very general one, and use it to link together mechanisms that would otherwise appear disparate, including the cavity cooling of atoms and cooling mechanisms based on the non-adiabatic following of atomic populations. A fully vectorial three-dimensional scattering theory including the effects of such a memory is also presented and used to explore several different experimentally-realisable cooling configurations
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Sousa, Reginaldo Ribeiro de [UNESP]. „Análise numérica e experimental na determinação da potência térmica dissipada em componentes eletrônicos“. Universidade Estadual Paulista (UNESP), 2008. http://hdl.handle.net/11449/94552.
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Os objetivos deste trabalho são determinar a potência térmica dissipada dos componentes eletrônicos de forma experimental e verificar a eficácia do método através de simulações numéricas computacionais utilizando o software comercial ANSYS. O Software ANSYS foi usado como ferramenta de Dinâmica de Fluidos Computacional neste trabalho. Para a realização deste trabalho um ensaio experimental foi executado a fim de obter alguns dados para o cálculo da potência térmica dissipada, outros foram fornecidos pelo CPqD e Trópico. Foi montado um Laboratório Computacional com o apoio da Trópico e do CPqD na UNESP, campus de Ilha Solteira para a simulações numéricas. O método de cálculo de potência apresentou-se eficaz, de modo na melhor situação os resultados apresentaram um erro relativo médio de 1,94%.
The purpose of this study is to determine the thermal power dissipation of electronic components through an experimental test and verify the effectiveness of the method through numerical simulations using the computational software ANSYS commercial. Software ANSYS was used as a tool for Computational Fluid Dynamics for this work. For this work an experimental test was done to obtain some data to calculate the thermal power dissipation, others were supplied by CPqD, Nilko and Trópico. It was dubbed a Computer Laboratory with the support of the Trópico, CPqD and at UNESP, campus de Ilha Solteira for the numerical simulations. The method of calculation of power proved to be effective, that the better the results showed a mean relative error is 1.94%.
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Ates, Ahmet Muaz. „Experimental Comparison Of Fluid And Thermal Characteristics Of Microchannel And Metal Foam Heat Sinks“. Master's thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613577/index.pdf.
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Doubling transistor count for every two years in a computer chip, transmitter and receiver (T/R) module of a phased-array antenna that demands higher power with smaller dimensions are all results of miniaturization in electronics packaging. These technologies nowadays depend on improvement of reliable high performance heat sink to perform in narrower volumes. Employing microchannels or open cell metal foam heat sinks are two recently developing promising methods of cooling high heat fluxes. Although recent studies especially on microchannels can give a rough estimate on performances of these two methods, since using metal foams as heat sinks is still needed further studies, a direct experimental comparison of heat exchanger performances of these two techniques is still needed especially for thermal design engineers to decide the method of cooling.
For this study, microchannels with channel widths of 300 µm, 420 µ
m, 500 µ
m and 900 µ
m were produced. Also, 92% porous 10, 20 and 40 ppi 6101-T6 open cell aluminum metal foams with compression factors 1,2, and 3 that have the same finned volume of microchannels with exactly same dimensions were used to manufacture heat sinks with method of vacuum brazing. They all have tested under same conditions with volumetric flow rate ranging from 0,167 l/min to 1,33 l/min and 60 W of heat power. Channel height was 4 mm for all heat sinks and distilled water used as cooling fluid. After experiments, pressure drops and thermal resistances were compared with tabulated and graphical forms. Also, the use of metal foam and microchannel heat sinks were highlighted with their advantages and disadvantages for future projects.
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Glaspell, Shannon Lynnette. „Effects of the electric Kelvin force on spray cooling performance“. Morgantown, W. Va. : [West Virginia University Libraries], 2006. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=4762.
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Thesis (M.S.)--West Virginia University, 2006.Title from document title page. Document formatted into pages; contains xiii, 246 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 131-133).
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Vacenovský, Jan. „Návrh zařízení pro úpravu mikroklimatu v rekonstruovaném rodinném domě“. Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2018. http://www.nusl.cz/ntk/nusl-378499.
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This work is devoted to the design of a microclimate facility in a family house. The first part contains analysis of thermal losses before and after using thermal insulation. Based on this analysis, a heating system is proposed, including the necessary technical calculations for the operation of the system. As a heat source, a condensing boiler is selected. At the next point, the thesis focuses on the calculation of the heat gains in selected rooms in order to design a cooling device. A multisplit system is selected for cooling the rooms. In the next part the thesis deals with the design of forced ventilation of selected rooms. The ventilation system provides the necessary air exchange and covers heat losses through ventilation. At the end of the thesis is outlined the concept of regulation of individual systems and also the requirements for individual professions are described.
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Prins, Cilliers. „Through spindle cooling : a study of the feasibility of split tool titanium machining“. Thesis, Stellenbosch : Stellenbosch University, 2015. http://hdl.handle.net/10019.1/97118.
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Thesis (MEng)--Stellenbosch University, 2015.ENGLISH ABSTRACT: Efficient face milling of titanium alloys provides a global challenge. Difficult-to-cut super alloys such as Ti-6Al-4V is considered the “workhorse” material for aerospace components. During the machining of aerospace components, 80% – 90% of the material is removed. This requirement drives the innovation for machines and tooling to become more efficient, while driving down costs. In South Africa, this requirement is no different. Due to the historic practice of exporting valuable minerals such as Ilmenite, leucoxene and rutile, South Africa does not enjoy many of financial benefits of producing value added titanium alloy products. The Titanium Centre of Competence (TiCoC) is aimed at creating a South African titanium manufacturing industry by the year 2020. More specifically, the roughing of Ti-6Al-4V aerospace components has been identified as an area for improvement. The thermal conductivity of Ti-6Al-4V is significantly lower than that of other “workhorse” metals such as steel or aluminium. Therefore, heat rapidly builds up in the tool tip during high speed machining resulting in shortened tool life and increased machining costs. Hence the ongoing developments in the field of cooling methods for high speed machining. The latest development in high pressure cooling (HPC) is split tools that deliver coolant into the cutting interface via flat nozzles in the rake face of the insert. Although it has been released recently and limited to a single supplier, this cooling method is commercially available, yet little is known about its performance or application conditions. The operational characteristics of split tools are studied by answering set research questions. A dynamometer was used to measure the tangential cutting forces during 11 cutting experiments that follow a three-factor factorial design at two levels and with three centre points. A second-order model for predicting the tangential cutting force during face milling of Ti-6Al-4V with split tools was fit to the data at 95% confidence level. A predictive cutting force model was developed in terms of the cutting parameters: (1) Axial depth of cut (ADOC), (2) feed per tooth and, (3) cutting speed. The effect of cutting parameters on cutting force including their interactions are investigated. Data for chip evacuation, surface finish and tool wear are examined and discussed. Practical work was done at a selected industry partner to determine: (1) impact of an analytical approach to perform process development for aerospace component roughing, (2) determine the feasibility of implementing split tools to an existing process. A substantial time saving in the roughing time of the selected aerospace component was achieved through analytical improvement methods. Furthermore it was found that the split tools were not a suitable replacement for current tooling. It was established that certain critical operational requirements of the split tools are not met by the existing milling machine at the industry partner.
AFRIKAANSE OPSOMMING: Doeltreffende masjinering van titaan allooie bied `n wêreldwye uitdaging. Moeilik-om-te-sny super allooie soos Ti-6Al-4V word as die “werksesel” materiaal vir lugvaart komponente beskou. Gedurende die masjinering van lugvaart komponente word 80% - 90% van die materiaal verwyder. Dit is hiérdie behoefte wat die innovering van masjien -en snygereedskap dryf om dit meer doeltreffend en finansieël vatbaar te maak. Die Suid Arikaanse behoefte vir doeltreffende snygereedskap vir Ti-6Al-4V masjinering stem ooreen met hierdie internationale behoefte. Die geskiedkundige Suid Afrikaanse praktyk om onverwerkte, waardevolle minerale soos Ilmeniet, rutiel en leucoxene uit te voer, kniehalter die land se kans om winste uit verwerkte titaan allooi produkte te geniet. Die “Titanium Centre of Competence” (TiCoC) se mikpunt is om `n Suid Afrikaanse titaanproduk vervaardigingsmark op die been te bring teen 2020. Stellenbosch Universiteit se funksie, binne hierdie strategiese raamwerk, fokus op hoë spoed masjinering van Ti-6Al-4V lugvaart komponente. Die hitte geleidingsvermoë van Ti-6Al-4V is noemenswaardig laer as die van ander “werksesel” materiale soos byvoorbeeld staal of alumium. Om hierdie rede word hitte in die freesbeitelpunt gedurende hoë spoed masjinering opgeberg. Dit verkort gereedskap leeftyd en verhoog masjinerings kostes. Daarvandaan deurlopende ontwikkelinge in verkoelingsmetodes vir hoë spoed masjinering. Die mees onlangse ontwikkeling in hoë druk verkoeling is “split tools” wat koelmiddel na die snyoppervlak deur middel van langwerpige gleufies in die hark gesig van die beitelpunt lewer. Hierdie tegnologie is op die mark beskikbaar, maar slegs deur `n enkele verskaffer. Daar is ook geen akademiese publikasies wat oor Ti-6Al-4V masjinering met “split tools” handel nie. Die verrigtings vermoë en toepassings gebied vir die gereedskap is steeds onbekend. 'n Dinamometer is gebruik om die tangensiale snykragte tydens 11 sny eksperimente te meet. Die eksperiment ontwerp is faktoriaal van aard en bevat drie faktore en drie middelpunte oor twee vlakke. `n Kwadratiese model is geskik om die data op 95% vertroue vlak voor te stel en voorspellings mee te maak. Die voorspellingsmodel is ontwikkel in terme van: (1) Diepte van snit, (2) voertempo, en (3) Snyspoed. Die invloed van die drie parameters op die tangentiale snykrag, asook invloed met mekaar word ondersoek. Verdere data in verband met materiaal verwydering, oppervlak afwerking en beitel slytasie word ook bespreek. Praktiese werk is met behulp van `n bedryfsvennoot gedoen om vas te stel: (1) die impak van 'n analitiese benadering en ontwikkelings proses op die uitrof van lugvaart komponente, (2) en om die lewensvatbaarheid van implementering van “split tools“ aan 'n bestaande proses te bepaal. `n Noemenswaardige besparing is sodoende behaal. Dit is verder bevind dat “split tools” nie `n geskikte plaasvervanger vir die huidige snygereedskap is nie. Die rede daarvoor is gedeeltelik omdat die huidige freesmasjien by die bedryfsvennoot nie aan die kritiese operasionele vereistes van die gereedskap vervaardiger voldoen nie.
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Baummer, Thomas Buchanan. „A self-contained cold plate utilizing force-fed evaporation for cooling of high-flux electronics“. College Park, Md.: University of Maryland, 2007. http://hdl.handle.net/1903/7795.
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Thesis (M.S.) -- University of Maryland, College Park, 2007.Thesis research directed by: Dept. of Mechanical Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Brumbaugh, Scott J. „Development of a Methodology to Measure Aerodynamic Forces on Pin Fins in Channel Flow“. Thesis, Virginia Tech, 2006. http://hdl.handle.net/10919/30871.
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The desire for smaller, faster, and more efficient products places a strain on thermal management in components ranging from gas turbine blades to computers. Heat exchangers that utilize internal cooling flows have shown promise in both of these industries. Although pin fins are often placed in the cooling channels to augment heat transfer, their addition comes at the expense of increased pressure drop. Consequently, the pin fin geometry must be judiciously chosen to achieve the desired heat transfer rate while minimizing the pressure drop and accompanying pumping requirements.
This project culminates in the construction of a new test facility and the development of a unique force measurement methodology. Direct force measurement is achieved with a cantilever beam force sensor that uses sensitive piezoresistive strain gauges to simultaneously measure aerodynamic lift and drag forces on a pin fin. After eliminating the detrimental environmental influences, forces as small as one-tenth the weight of a paper clip are successfully measured.
Although the drag of an infinitely long cylinder in uniform cross flow is well documented, the literature does not discuss the aerodynamic forces on a cylinder with an aspect ratio of unity in channel flow. Measured results indicate that the drag coefficient of a cylindrical pin in a single row array is greater than the drag coefficient of an infinite cylinder in cross flow. This phenomenon is believed to be caused by an augmentation of viscous drag on the pin fin induced by the increased viscous effects inherent in channel flow.Master of Science
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Thrift, Alan Albright. „Aerodynamic Force and Pressure Loss Measurements on Low Aspect Ratio Pin Fin Arrays“. Thesis, Virginia Tech, 2007. http://hdl.handle.net/10919/31189.
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The desire to achieve higher heat transfer augmentation for turbine blades is fueled by the increased power output and efficiency that is achievable with high turbine inlet temperatures. The use of internal cooling channels fitted with pin fin arrays serves as one method of accomplishing this goal. Consequently, the addition of pin fin arrays comes at the expense of increased pressure drop. Therefore the pin fin geometry must be judiciously chosen to achieve the required heat transfer rate while minimizing the associated pressure drop.
This project culminates in the measurement of both pin fin force and array pressure drop as they related to changes in the array geometry. Specifically, the effects of Reynolds number, spanwise pin spacing, streamwise pin spacing, pin aspect ratio, and flow incidence angle. Direct two-component force measurement is achieved with a cantilever beam force sensor that uses highly sensitive piezoresistive strain gauges, relating the strain at the base of the beam to the applied force. With proper characterization, forces as small as one-tenth the weight of a paper clip are successfully measured. Additionally, array pressure drop measurements are achieved using static pressure taps.
Experiments were conducted over a range of Reynolds numbers between 7,500 and 35,000. Changes in the spanwise pin spacing were shown to substantially alter the pin fin drag and array pressure drop, while changes in the streamwise pin spacing were less influential. The experimental results also showed a dramatic reduction in the pin fin drag and array pressure drop for an inline flow incidence angle. Finally, changes in the pin aspect ratio were shown to have little effect on the array pressure drop.
Master of Science
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Sleiti, Ahmad Khalaf. „EFFECT OF CORIOLIS AND CENTRIFUGAL FORCES ON TURBULENCE AND TRANSPORT AT HIGH ROTATION AND BUOYANCY NUMBERS“. Doctoral diss., University of Central Florida, 2004. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4408.
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This study attempts to understand one of the most fundamental and challenging problems in fluid flow and heat transfer for rotating machines. The study focuses on gas turbines and electric generators for high temperature and high energy density applications, respectively, both which employ rotating cooling channels so that materials do not fail under high temperature and high stress environment. Prediction of fluid flow and heat transfer inside internal cooling channels that rotate at high rotation number and high density ratio similar to those that are existing in turbine blades and generator rotors is the main focus of this study. Both smooth-wall and rib-roughened channels are considered here. Rotation, buoyancy, bends, ribs and boundary conditions affect the flow inside theses channels. Ribs are introduced inside internal cooling channel in order to enhance the heat transfer rate. The use of ribs causes rapid increase in the supply pressure, which is already limited in a turbine or a generator and requires high cost for manufacturing. Hence careful optimization is needed to justify the use of ribs. Increasing rotation number (Ro) is another approach to increase heat transfer rate to values that are comparable to those achieved by introduction of ribs. One objective of this research is to study and compare theses two approaches in order to decide the optimum range of application and a possible replacement of the high-cost and complex ribs by increasing Ro. A fully computational approach is employed in this study. On the basis of comparison between two-equation (k-[epsilon] and k-[omega]) and RSM turbulence models, against limited available experimental data, it is concluded that the two-equation turbulence models cannot predict the anisotropic turbulent flow field and heat transfer correctly, while RSM showed improved prediction. For the near wall region, two approaches with standard wall functions and enhanced near wall treatment were investigated. The enhanced near wall approach showed superior results to the standard wall functions approach. Thus RSM with enhanced near wall treatment is validated against available experimental data (which are primarily at low rotation and buoyancy numbers). The model was then used for cases with high Ro (as much as 1.29) and high-density ratios (DR) (up to 0.4). Particular attention is given to how turbulence intensity, Reynolds stresses and transport are affected by Coriolis and buoyancy/centrifugal forces caused by high levels of Ro and DR. Variations of flow total pressure along the rotating channel are also predicted. The results obtained are explained in view of physical interpretation of Coriolis and centrifugal forces. Investigation of channels with smooth and with rib-roughened walls that are rotating about an orthogonal axis showed that increasing Ro always enhances turbulence and the heat transfer rate, while at high Ro, increasing DR although causes higher turbulence activity but does not necessarily increase Nu and in some locations even decreases Nu. The increasing thermal boundary layer thickness near walls is the possible reason for this behavior of Nu. The heat transfer enhancement for smooth-wall cases correlates linearly with Ro (with other parameters are kept constant) and hence it is possible to derive linear correlation for the increase in Nu as a function of Ro. Investigation of channels with rib-roughened walls that rotate about orthogonal axis showed that 4-side-average Nur correlates with Ro linearly, where a linear correlation for Nur/Nus as a function of Ro is derived. It is also observed that the heat transfer rate on smooth-wall channel can be enhanced rapidly by increasing Ro to values that are comparable to the enhancement due to the introduction of ribs inside internal cooling channels. This observation suggests that ribs may be unnecessary in high-speed machines, and has tremendous implications for possible cost savings in these machines. In square channels that rotate about parallel axis, the heat transfer rate enhances with Ro on three surfaces of the square channel and decreases on the inner surface (that is the one closest to the axis of rotation). However, the four-sides average Nu increases with Ro. Increasing wall heat flux at high Ro does not necessarily increase Nu on walls although higher turbulence activity is observed. This study examines the rich interplay of physics under the simultaneous actions of Coriolis and centrifugal/buoyancy forces in one of the most challenging internal flow configurations. Several important conclusions are reached from this computational study that may have far-reaching implications on how turbine blades and generator rotors are currently designed. Since the computation study in not validated for high Ro cases, these important results call for a experimental investigation.Ph.D.
Department of Mechanical, Materials and Aerospace Engineering
Engineering and Computer Science
Mechanical, Materials and Aerospace Engineering
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Viswanathan, Aroon Kumar. „Detached Eddy Simulation of Turbulent Flow and Heat Transfer in Turbine Blade Internal Cooling Ducts“. Diss., Virginia Tech, 2006. http://hdl.handle.net/10919/28518.
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Detached Eddy Simulations (DES) is a hybrid URANS-LES technique that was proposed to obtain computationally feasible solutions of high Reynolds number flows undergoing massive separation with reliable accuracy. Since its inception, DES has been applied to a wide variety of flow fields, but mostly limited to unbounded external aerodynamic flows. This is the first study to apply and validate DES to predict the internal flow and heat transfer in non-canonical flows of industrial relevance. The prediction capabilities of DES in capturing the effects of Coriolis forces, which are induced by rotation, and centrifugal buoyancy forces, which are induced by thermal gradients, are also authenticated.
The accurate prediction of turbulent flows is sensitive to the level of turbulence predicted by the turbulence scheme. By treating the regions of interest in LES mode, DES allows the unsteadiness in these regions to develop and hence predicts the turbulence levels accurately. Additionally, this permits DES to capture the effects of system rotation and buoyancy. Computations on a rotating system (a sudden expansion duct) and a system subjected to thermal gradients (cavity with a heated wall) validate the prediction capability of DES.
The application of DES is further extended to a non-canonical, internal flow which is of relevance in internal cooling of gas turbine blades. Computations of the fully developed flow and heat transfer shows that DES surpasses several shortcomings of the RANS model on which it is based. DES accurately predicts the primary and secondary flow features, the turbulence characteristics and the heat transfer in stationary ducts and in rotating ducts, where the effects of Coriolis forces and centrifugal buoyancy forces are dominant. DES computations are carried out at a computational cost that is almost an order of magnitude less than the LES with little compromise on the accuracy.
However, the capabilities of DES in predicting the transition to turbulence are inadequate, as highlighted by the flow features and the heat transfer in the developing region of the duct. But once the flow becomes fully turbulent, DES predicts the flow physics and shows good quantitative agreement with the experiments and LES.Ph. D.
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Mayo, Yague Ignacio. „Flow field and heat transfer in a rotating rib-roughened cooling passage“. Phd thesis, Toulouse, INPT, 2017. http://oatao.univ-toulouse.fr/19529/1/MayoYague_Ignacio.pdf.
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A great effort has been carried out over the recent years in the understanding of the flow field and heat transfer in the internal cooling channels present in turbine blades. Indeed, advanced cooling schemes have not only lead to the increase of the gas turbine efficiency by increasing the Turbine Inlet Temperature above the material melting temperature, but also the increase of the turbine lifespan. To allow such progresses, modern experimental and numerical techniques have been widely applied in order to interpret and optimize the aerodynamics and heat transfer in internal cooling channels. However, the available data is limited in the case of internal cooling channels in turbine rotor blades. Rotation and temperature gradients introduce Coriolis and centripetal buoyancy forces in the rotating frame of reference, modifying significantly the aerothermodynamics from that of the stationary passages. In the case of turbine rotor blades, most of the investigations are either based on point-wise measurements or are constraint to low rotational regimes. The main objective of this work is to study the detailed flow and heat transfer of an internal cooling channel at representative engine dimensionless operating conditions. This work introduces a laboratory test section that operates ribbed channels over a wide range of Reynolds, Rotation and Buoyancy numbers. In the present work, the Reynolds number ranges from 15,000 to 55,000, the maximum Rotation number is equal to 0.77, and the maximum Buoyancy number is equal to 0.77. The new experimental facility consists in a versatile design that allows the interchangeability of the tested geometry, so that channels of different aspect ratios and rib geometries can be easily fitted. Particle Image Velocimetry and Liquid Crystal Thermography are performed to provide accurate velocity and heat transfer measurements under the same operating conditions, which lead to a unique experimental data set. Moreover, Large Eddy Simulations are carried out to give a picture of the entire flow field and complement the experimental observations. Additionally, the numerical approach intends to provide a robust methodology that is able to provide high fidelity predictions of the performance of internal cooling channels.
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Dowd, Cody Stewart. „A Study of Centrifugal Buoyancy and Particulate Deposition in a Two Pass Ribbed Duct for the Internal Cooling Passages of a Turbine Blade“. Thesis, Virginia Tech, 2016. http://hdl.handle.net/10919/81181.
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In this thesis, the ribbed ducts of the internal cooling passage in turbine blading are investigated to demonstrate the effects of high speed rotation. Rotation coupled with high temperature operating conditions alters the mean flow, turbulence, and heat transfer augmentation due to Coriolis and centrifugal buoyancy forces that arises from density stratification in the domain. Gas turbine engines operate in particle laden environments (sand, volcanic ash), and particulate matter ingested by the engine can make their way into the blade internal cooling passages over thousands of operating hours. These particulates can deposit on the walls of these cooling passages and degrade performance of the turbine blade. Large-Eddy Simulations (LES) with temperature dependent properties is used for turbulent flow and heat transfer in the ribbed cooling passages and Lagrangian tracking is used to calculate the particle trajectories together with a wall deposition model. The conditions used are Re=100,000, Rotation number, Ro = 0.0 and 0.2, and centrifugal Buoyancy parameters of Bo=0, 0.5, and 1.0.
First, the independent effects of Coriolis and centrifugal buoyancy forces are investigated, with a focus on the additional augmentation obtained in heat transfer with the addition of centrifugal buoyancy. Coriolis forces are known to augment heat transfer at the trailing wall and attenuate the same at the leading wall. Phenomenological arguments stated that centrifugal buoyancy augments the effects of Coriolis forces in outward flow in the first pass while opposing the effect of Coriolis forces during inward flow in the second pass. In this study, it was found that in the first pass, centrifugal buoyancy had a greater effect in augmenting heat transfer at the trailing wall than in attenuating heat transfer at the leading wall. On the contrary, it aided heat transfer in the second half of the first pass at the leading wall by energizing the flow near the wall. Also, contrary to phenomenological arguments, inclusion of centrifugal buoyancy augmented heat transfer over Coriolis forces alone on both the leading and trailing walls of the second pass.
Sand ingestion is then investigated, by injecting 200,000 particles in the size range of 0.5-175μm with 65% of the particles below 10 μm. Three duct wall temperatures are investigated, 950, 1000 and 1050 °C with an inlet temperature of flow and particles at 527 °C . The impingement, deposition levels, and impact characteristics are recorded as the particles move through the domain. It was found that the Coriolis force greatly increases deposition. This was made prevalent in the first pass, as 84% of the deposits in the domain occurred in the first pass for the rotating case, whereas only 27% of deposits occurred in the first pass for the stationary case with the majority of deposits occurring in the bend region. This was due to an increased interaction with the trailing wall in the rotating case whereas particles in the stationary case were allowed to remain in the mean flow and gain momentum, making rebounding from a wall during collision more likely than deposition. In contrast, the variation of wall temperatures caused little to no change in deposition levels. This was concluded to be a result of the high Reynolds number used in the flow. At high Reynolds numbers, the particles have a short residence times in the internal cooling circuit not allowing the flow and particles to heat up to the wall temperature. Overall, 87% of the injected particles deposited in the rotating duct whereas 58% deposited in the stationary duct.Master of Science
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Vaibar, Roman, Thomas Höhne und Ulrich Rohde. „CFD-Modellierung von Vermischungsvorgängen in Druckwasserreaktoren in Anwesenheit von Dichtegradienten“. Forschungszentrum Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-27933.
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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.
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Vaibar, Roman, Thomas Höhne und Ulrich Rohde. „CFD-Modellierung von Vermischungsvorgängen in Druckwasserreaktoren in Anwesenheit von Dichtegradienten“. Forschungszentrum Dresden-Rossendorf, 2008. https://hzdr.qucosa.de/id/qucosa%3A21620.
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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.
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Cavalheiro, Júnior Milton César [UNESP]. „Controle de válvulas de sucção de compressores de refrigeração usando limitador de abertura“. Universidade Estadual Paulista (UNESP), 2017. http://hdl.handle.net/11449/151661.
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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
A maioria dos sistemas de refrigeração por compressão de vapor utiliza compressores alternativos, considerados mecanismos importantes na era moderna. O ciclo de operação de um compressor alternativo é descrito por uma série de fenômenos complexos ocorrendo em um curto período de tempo. Dentre os fatores considerados importantes para e ciência termodinâmica dos compressores, destacam-se as válvulas que controlam os processos de sucção e de descarga, que são responsáveis por grandes perdas termodinâmicas no ciclo. Parte das perdas ocorre no sistema de válvulas, particularmente na válvula de sucção, onde as instabilidades do seu movimento reduzem a e ciência do processo de sucção. Como uma forma de reduzir os problemas gerados pelas instabilidades no funcionamento da válvula de sucção, propomos a utilização de um esbarro para limitar a abertura máxima da válvula, reduzindo sua instabilidade e aumentando a e ciência do compressor. Mostramos experimentalmente que existe uma posição de equilíbrio que mantém a válvula aberta sem instabilidades e que esta posição varia, aproximadamente, linearmente com o número de Reynolds.
Most of the vapor refrigeration systems use reciprocating compressors, which are considered important mechanisms in the modern era. The cycle of operation of a reciprocating compressor is described by a series of complex phenomena ocurring in a short period of time. Among the factors considered important for the thermodynamic efficiency of compressors are the valves that control the suction and discharge processes, which are responsible for large cycle thermodynamic losses. Part of that losses occurs in the valves system, particularly in the suction valve, where the movement instabilities reduce the efficiency of the suction process. In order to reduce the instabilities of the suction valve, we propose the use of a stop to limit the maximum aperture of the valve, reducing its instabilities and increasing the compressor efficiency. We show experimentally that does exist an static equilibrium position in which the valve remains opened without oscillation and that position varies almost linearly through the Reynolds number.
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Cavalheiro, Júnior Milton Cesar. „Controle de válvulas de sucção de compressores de refrigeração usando limitador de abertura /“. Ilha Solteira, 2017. http://hdl.handle.net/11449/151661.
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Orientador: José Luiz GascheResumo: A maioria dos sistemas de refrigeração por compressão de vapor utiliza compressores alternativos, considerados mecanismos importantes na era moderna. O ciclo de operação de um compressor alternativo é descrito por uma série de fenômenos complexos ocorrendo em um curto período de tempo. Dentre os fatores considerados importantes para e ciência termodinâmica dos compressores, destacam-se as válvulas que controlam os processos de sucção e de descarga, que são responsáveis por grandes perdas termodinâmicas no ciclo. Parte das perdas ocorre no sistema de válvulas, particularmente na válvula de sucção, onde as instabilidades do seu movimento reduzem a e ciência do processo de sucção. Como uma forma de reduzir os problemas gerados pelas instabilidades no funcionamento da válvula de sucção, propomos a utilização de um esbarro para limitar a abertura máxima da válvula, reduzindo sua instabilidade e aumentando a e ciência do compressor. Mostramos experimentalmente que existe uma posição de equilíbrio que mantém a válvula aberta sem instabilidades e que esta posição varia, aproximadamente, linearmente com o número de Reynolds.
Mestre
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Boháček, Jan. „EFFECT OF FLOW PARAMETERS OF WATER AND AIR ATOMIZED SPRAYS ON COOLING INTENSITY OF HOT SURFACES“. Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2011. http://www.nusl.cz/ntk/nusl-233959.
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Práce komplexně popisuje vodní a vodovzdušné chlazení pomocí metod CFD (Computational Fluid Dynamics) konkrétně s využitím software ANSYS FLUENT. Skládá se ze dvou hlavních částí, z nichž první se zabývá numerickým popisem jediné vodní kapky a druhá popisem směsí kapek představující paprsek válcové a ploché trysky. Je založena převážně na vícefázových modelech proudění a vlastních uživatelsky definovaných funkcí (User Defined Functions, UDF) představujících stěžejní část práce. Uvedené výpočtové modely jsou ve většině případů verifikovány pomocí experimentálních dat nebo jiných numerických modelů. V první části práce jsou teoreticky postupně rozebrány všechny tři použité vícefázové modely proudění. První z nich, Volume Of Fluid model (VOF), byl použit pro modelování jediné kapky (mikromodel). Zatímco zbývající dva, Euler-Euler model a Euler-Lagrange model, byly aplikovány v modelu celého paprsku trysky (makromodel). Mikromodel popisuje dynamiku volného pádu vodní kapky. Pro malé průměry kapek (~100µm) standardní model povrchového napětí (Continuum Surface Force, CSF) způsoboval tzv. parazitní proudy. Z toho důvodu je v práci rozebrána problematika výpočtu normál, křivostí volných povrchů a povrchového napětí jako zdroje objemových sil v pohybových rovnicích. Makromodel se zabývá studiem dynamiky celého paprsku tj. oblastí od ústí trysky po dopad na horký povrch, bere v úvahu kompletní geometrii, tzn. např. podpůrné válečky, bramu, spodní část krystalizátoru apod. V práci je rozebrána 2D simulace dopadu paprsku válcové trysky pomocí VOF modelu Euler-Lagrange modelu na horký povrch. Pro případ s VOF modelem byl navržen model blánového varu. Euler-Euler model a Euler-Lagrange model byly využity pro simulaci paprsku ploché trysky horizontálně ostřikující horkou bramu přímo pod krystalizátorem nad první řadou válečků. Pro Euler-Euler model byl navržen model sekundárního rozpadu paprsku založený na teorii nejstabilnější vlnové délky (Blob jet model). Jelikož diskrétní Lagrangeovy částice tvořily v určitých místech spíše kontinuální fázi, byl navržen a otestován model pro konverzi těchto částic do VOF.
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Sewall, Evan Andrew. „Large Eddy Simulations of Flow and Heat Transfer in the Developing and 180° Bend Regions of Ribbed Gas Turbine Blade Internal Cooling Ducts with Rotation - Effect of Coriolis and Centrifugal Buoyancy Forces“. Diss., Virginia Tech, 2005. http://hdl.handle.net/10919/29858.
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Increasing the turbine inlet temperature of gas turbine engines significantly increases their power output and efficiency, but it also increases the likelihood of thermal failure. Internal passages with tiny ribs are typically cast into turbine blades to cool them, and the ability to accurately predict the flow and heat transfer within these channels leads to higher design reliability and prevention of blade failure resulting from local thermal loading. Prediction of the flow through these channels is challenging, however, because the flow is highly turbulent and anisotropic, and the presence of rotational body forces further complicates the flow. Large Eddy Simulations are used to study these flows because of their ability to predict the unsteady flow effects and anisotropic turbulence more reliably than traditional RANS closure models.
Calculations in a stationary duct are validated with experiments in the developing flow, fully developed, and 180° bend regions to establish the accuracy and prediction capability of the LES calculations and to aid in understanding the major flow structures encountered in a ribbed duct. It is found that most flow and heat transfer calculations come to within 10-15% of the measurements, typically showing excellent agreement in all comparisons.
In the developing flow region, Coriolis effects are found to destabilize turbulence and increase heat transfer along the trailing wall (pressure side), while decreasing leading wall heat transfer by stabilizing turbulence. Coriolis forces improve flow turning in the 180° bend by shifting the shape of the separated recirculation zone at the tip of the dividing wall and increasing the mainstream flow area. In addition, turbulence is attenuated near the leading wall throughout the bend, while Coriolis forces have little effect on trailing wall turbulence in the bend.
Introducing and increasing centrifugal buoyancy in the developing flow region increases trailing wall heat transfer monotonically. Along the leading wall, buoyancy increases the size of the recirculation zones, shifting the peak heat transfer to a region upstream of the rib, which decreases heat transfer at low buoyancy parameters but increases it as the buoyancy parameter is increased beyond a value of 0.3. Centrifugal buoyancy in the 180° bend initially decreases the size of the recirculation zone at the tip of the dividing wall, increasing flow area and decreasing flow impingement. At high buoyancy, however, the recirculation zone shifts to the middle of the bend, increasing flow resistance and causing strong flow impingement on the back wall.
The Boussinesq approximation is used in the buoyancy calculations, but the accuracy of the approximation comes into question in the presence of large temperature differences. A variable property algorithm is developed to calculate unsteady low speed flows with large density variations resulting from large temperature differences. The algorithm is validated against two test cases: Rayleigh-Bénard convection and Poiseuille-Bénard flow.
Finally, design issues in rotating ribbed ducts are considered. The fully developed assumption is discussed with regard to the developing flow region, and controlling the recirculation zone in the 180° bend is considered as a way to determine the blade tip heat transfer and pressure drop across the bend.Ph. D.
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Grunwald, G., S. Kliem, T. Höhne, U. Rohde, H. M. Prasser, K. H. Richter und F. P. Weiß. „Versuchsanlage ROCOM zur Untersuchung der Kühlmittelvermischung in Druckwasserreaktoren - Ergebnisse quasistationärer Vermischungsexperimente“. Forschungszentrum Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-29348.
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The test facility ROCOM (Rossendorf Coolant Mixing Model) has been built for the investigation of coolant mixing processes in the reactor pressure vessel of pressurised water reactors (PWR). ROCOM is a 1:5 model of the German PWR KONVOI and has been designed for a wide range of different mixing scenarios. ROCOM disposes of four loops with fully controllable coolant pumps. The test facility is operated with demineralised water. For the investigation of mixing, tracer solution (water labelled with salt) is injected into the facility. The transient distribution of the electrical conductivity is is measured at different positions of the flow path by means of wire-mesh sensor technique with high resolution in space and time. The measured conductivity is transformed into a dimensionless mixing scalar. The mixing at quasi-stationary conditions (constant loop mass flow rates) has been investigated in the presented experiments. That concerned nominal operation conditions, the operation with a reduced number of loops and the investigation of cold-water transients with running pumps and conditions of developed natural circulation. In special experimental series, the reproducibility of the results at identicla boundary conditions within the confidence intervalls has been shown. Further, the influence of various factors on the mixing has been investigated. This included the pressure losses at the core bottom plate, the global coolant flow level and the influence of the loop flow rate on the perturbed sector at the core inlet. An analysis of the measurement error of the used measurement technique completes the report.
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Grunwald, G., S. Kliem, T. Höhne, U. Rohde, H. M. Prasser, K. H. Richter und F. P. Weiß. „Versuchsanlage ROCOM zur Untersuchung der Kühlmittelvermischung in Druckwasserreaktoren - Ergebnisse quasistationärer Vermischungsexperimente“. Forschungszentrum Rossendorf, 2002. https://hzdr.qucosa.de/id/qucosa%3A21761.
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The test facility ROCOM (Rossendorf Coolant Mixing Model) has been built for the investigation of coolant mixing processes in the reactor pressure vessel of pressurised water reactors (PWR). ROCOM is a 1:5 model of the German PWR KONVOI and has been designed for a wide range of different mixing scenarios. ROCOM disposes of four loops with fully controllable coolant pumps. The test facility is operated with demineralised water. For the investigation of mixing, tracer solution (water labelled with salt) is injected into the facility. The transient distribution of the electrical conductivity is is measured at different positions of the flow path by means of wire-mesh sensor technique with high resolution in space and time. The measured conductivity is transformed into a dimensionless mixing scalar. The mixing at quasi-stationary conditions (constant loop mass flow rates) has been investigated in the presented experiments. That concerned nominal operation conditions, the operation with a reduced number of loops and the investigation of cold-water transients with running pumps and conditions of developed natural circulation. In special experimental series, the reproducibility of the results at identicla boundary conditions within the confidence intervalls has been shown. Further, the influence of various factors on the mixing has been investigated. This included the pressure losses at the core bottom plate, the global coolant flow level and the influence of the loop flow rate on the perturbed sector at the core inlet. An analysis of the measurement error of the used measurement technique completes the report.
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Deng, Lu. „Molecular Dynamics Simulations of the Structure and Properties of Boron Containing Oxide Glasses: Empirical Potential Development and Applications“. Thesis, University of North Texas, 2017. https://digital.library.unt.edu/ark:/67531/metadc1062909/.
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Potential parameters that can handle multi-component oxide glass systems especially boron oxide are very limited in literature. One of the main goals of my dissertation is to develop empirical potentials to simulate multi-component oxide glass systems with boron oxide. Two approaches, both by introducing the composition dependent parameter feature, were taken and both led to successful potentials for boron containing glass systems after extensive testing and fitting. Both potential sets can produce reasonable glass structures of the multi-component oxide glass systems, with structure and properties in good agreement with experimental data. Furthermore, we have tested the simulation settings such as system size and cooling rate effects on the results of structures and properties of MD simulated borosilicate glasses. It was found that increase four-coordinated boron with decreasing cooling rate and system size above 1000 atoms is necessary to produce converged structure. Another application of the potentials is to simulate a six-component nuclear waste glass, international simple glass (ISG), which was for first time simulated using the newly developed parameters. Structural features obtained from simulations agree well with the experimental results. In addition, two series of sodium borosilicate and boroaluminosilicate glasses were simulated with the two sets of potentials to compare and evaluate their applicability and deficiency. Various analyses on the structures and properties such as pair distribution function, total correlation function, coordination number analysis, Qn distribution function, ring size distribution function, vibrational density of states and mechanical properties were performed. This work highlights the challenge of MD simulations of boron containing glasses and the capability of the new potential parameters that enable simulations of wide range of mixed former glasses to investigate new structure features and design of new glass compositions for various applications.
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Al, Sofyani Sharaf. „Analytical Modeling and Experimental Analysis of Metalworking Fluids in theMilling Process“. University of Toledo / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1494853268000644.
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Bonin, Aurélie. „Relations entre les variations climatiques, les perturbations du cycle du carbone et les crises de la production carbonatée : application au Crétacé inférieur“. Phd thesis, Université de Bourgogne, 2011. http://tel.archives-ouvertes.fr/tel-00705496.
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Le Crétacé inférieur est ponctué de perturbations du cycle du carbone associées à des épisodes de préservation de matière organique et à des crises de la production carbonatée néritique et pélagique. Ces évènements coïncident également avec des refroidissements à très court terme (<1Ma) dont l'origine et les conséquences sont encore imprécises en raison de la faible résolution des courbes de températures dans les eaux de surface. Les études récentes réalisées à partir de modèles climatiques couplés à des modèles géochimiques laissent penser qu'une crise de la production carbonatée pourrait engendrer un refroidissement climatique sur une échelle de temps inférieure à 1 Ma (Donnadieu et al., accepté). Basées sur les dépôts d'âge Valanginien des coupes de La Charce-Vergol et d'Ollioules (Sud-est de la France) et sur les sédiments de l'Aptien du sous-Bassin de Galvé (Nord-est de l'Espagne), des études stratigraphiques, paléoécologiques et géochimiques ont été menées pour établir les relations entre la production carbonatée et le climat au cours du Valanginien et de l'Aptien. Pour cela, des courbes de température à haute résolution pour les eaux de surface ont été établies et mises en regard des évolutions des producteurs néritiques et pélagiques de carbonate. Le Valanginien et l'Aptien présentent tous deux des arrêts polyphasés de la production carbonatée néritique. Certains arrêts précèdent des refroidissements à court terme, dont ceux datés du Valanginien supérieur, du début et de la fin de l'Aptien inférieur. Cette succession suggérerait un lien de cause à effet entre les crises de la production et les fluctuations climatiques. Toutefois, les refroidissements du Valanginien supérieur et de la fin de l'Aptien inférieur sont respectivement précédés par un enfouissement de matière organique continentale et océanique, qui est un processus pouvant également générer une diminution de CO2 et un refroidissement. Ce travail a permis de mettre en évidence les répercutions des changements climatiques sur la production carbonatée par l'intermédiaire de changements de producteurs dans les domaines néritiques et pélagiques. Dans un premier temps, la mise en place de conditions froides au Valanginien supérieur et à la fin de l'Aptien inférieur est suivie de remplacements floro-fauniques caractérisés par l'évolution de communautés hétérozoaires à photozoaires. Les bouleversements observés suggèrent un changement drastique des conditions trophiques sous le développement de conditions arides relatives au refroidissement. Dans un second temps, l'évolution des communautés pélagiques au Valanginien répondraient également aux changements climatiques : ces communautés marquées d'un déclin depuis la fin du Valanginien inférieur présentent une courte reprise du début au milieu du Valanginien supérieur. Cette reprise coïncide avec le développement de conditions froides et plus arides occasionnant des conditions trophiques plus faibles