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The use of air assisted atomised water spray systems for controlled cooling of high temperature forgingsde Oliveira, Mónica Sandra Abrantes January 1999 (has links)
This thesis describes the work undertaken by the author in collaboration with Wyman-Gordon Forgings, USA, to assist in the development of a cooling system,based on air assisted atomised water sprays primarily for the quenching of aerospace components from high temperatures. The mechanical properties of forgings used in aircraft engines depend on the rate of cooling from the heat treatment solution temperature. It is well known that water quenching produces high cooling rate. Although, the severity of the quench can sometimes produce unacceptable distortion and high residual stresses in the component. For this reason water quenching is only used when a high cooling rate is definitely needed and it is often replaced by a less severe oil quench. However, over the last 10 years the trend to reduce manufacturing costs has led to the forging of parts that are closer to the net shape. In these cases even oil quenching can lead to residual stresses being developed that result in difficulties during the final machining of the engine component. Forced air cooling has been adopted in problem cases where the part is thin enough to attain the desired cooling rate. In many instances, however, the component is of intermediate size or varying in cross section and fan cooling cannot provide the cooling rate which is needed to obtain the desired mechanical properties, whilst oil quenching produces an unacceptable level of residual stresses. The use of air assisted atomised water sprays can provide heat transfer coefficients whose values lie between those for air cooling and oil quenching. Another advantage is that control of the air pressure enables the spray nozzle to operate with a much wider range of water flow rates so that the cooling rate can be readily controlled over the range. This study describes the investigation of the heat transfer characteristics of air assisted atomised water sprays to quench aeroengine components from temperatures of approximately 850°C. New data were obtained at high temperatures for air assisted atomised water sprays operating over a wide range of water mass fluxes, (8.01>w 0 >0kg/m2 .s). In practice the geometry of a component can be complex in shape. Therefore an investigation was also carried out into the application of spray cooling on recessed surfaces. It was found that the surface recess contributes significantly to the reduction in the rate of heat transfer at low and high water mass fluxes, but had little effect at intermediate flow rates. Pulsed sprays were investigated and proposed as a means of controlling heat transfer coefficients for both plane and recessed surfaces. The use of a pulsed spray makes it possible to control the amount of water impacting on a surface per second. It was found that "water off periods of 5 and 10 seconds resulted in a reduction in heat transfer coefficients at low temperatures and also reduced considerably the differences in cooling previously observed between plane and recessed surfaces. A finite element code was used to predict the residual stresses produced in a forged component for a range of spray parameters, and spray arrangements. The data were compared with cooling rates and stress patterns produced by both air and oil quenching. It was found that spray cooling resulted in cooling rates which met the mechanical property specification and provided residual stresses lower than those obtained during oil quenching. Furthermore, simulations of residual stress formation using two different spray arrangements in a typical forging indicated that spray non uniformities can substantially disturb the resultant residual stress patterns which could result in less predictable distortions during final machining. The study of spray cooling presented here suggests that the use of air assisted atomised water sprays has considerable potential and could provide the required cooling rate for individual forgings.
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ON HEAT TRANSFER MECHANISMS IN SECONDARY COOLING OF CONTINUOUS CASTING OF STEEL SLABHaibo Ma (11173431) 23 July 2021 (has links)
<p>Secondary cooling during continuous casting is a delicate
process because the cooling rate of water spray directly affects the slab
surface and internal quality. Undercooling may lead to slab surface bulging or
even breakout, whereas overcooling can cause deformation and crack of slabs due
to excessive thermal residual stresses and strains. Any slab which does not
meet the required quality will be downgraded or scrapped and remelted. In order to remain competitive and continuously
produce high-quality and high-strength steel at the maximum production rate,
the secondary cooling process must be carefully designed and controlled. Efficient
and uniform heat removal without deforming or crack the slab is a significant
challenge during secondary cooling. In the meantime, the on-site thermal
measurement techniques are limited due to the harsh environment. In contrast, experimental measurements
are only valid for the tested conditions, and the measurement process is not
only labor-intensive, but the result might be inapplicable when changes in the
process occur. On the other hand, the high-performance computing (HPC)-powered
computational fluid dynamics (CFD) approach has become a powerful tool to gain
insights into complex fluid flow and heat transfer problems. Yet, few
successful numerical models for heat transfer phenomena during secondary
cooling have been reported, primarily due to complex phenomena. </p>
<p> </p>
<p>Therefore, the current study has proposed two
three-dimensional continuum numerical models and a three-step coupling
procedure for the transport of mass, momentum, and energy during the secondary
cooling process. The first numerical model features the simulation of water
spray impingement heat and mass transfer on the surface of a moving slab considering
atomization, droplet dispersion, droplet-air interaction, droplet-droplet
interaction, droplet-wall impingement, the effect of vapor film, and droplet
boiling. The model has been validated against five benchmark experiments in
terms of droplet size prior to impingement, droplet impingement pressure, and
heat transfer coefficient (HTC) on the slab surface. The validated model has
been applied to a series of numerical simulations to investigate the effects of
spray nozzle type, spray flow rate, standoff distance, spray direction, casting
speed, nozzle-to-nozzle distance, row-to-row distance, arrangement of nozzles,
roll and roll pitch, spray angle, spray water temperature, slab surface
temperature, and spray cooling on the narrow face. Furthermore, the simulation
results have been used to generate a mathematically simple HTC correlation,
expressed as a function of nine essential operating parameters. A graphic user
interface (GUI) has been developed to facilitate the application of
correlations. The calculated two-dimensional HTC distribution is stored in the universal
comma-separated values (csv) format, and it can be directly applied as a boundary
condition to on-site off-line/on-line solidification calculation at steel mills.
The proposed numerical model and the generic methodology for HTC correlations should
benefit the steel industry by expediting the development process of HTC
correlations, achieving real-time dynamic spray cooling control, supporting
nozzle selection, troubleshooting malfunctioning nozzles, and can further
improve the accuracy of the existing casting control systems.</p>
<p> </p>
<p>In the second numerical model, the volume-averaged
Enthalpy-Porosity method has been extended to include the slurry effect at low
solid fractions through a switching function. With the HTC distribution on the
slab surface as the thermal boundary condition, the model has been used to
investigate the fluid flow, heat transfer, and solidification inside a slab
during the secondary cooling process. The model has been validated against the
analytical solution for a stationary thin solidifying body and the simulation
for a moving thin solidifying body. The effects of secondary dendrite arm
spacing, critical solid fraction, crystal constant, switching function
constant, cooling rate, rolls, nozzle-to-nozzle distance, and arrangement of
nozzles have been evaluated using the validated model. In addition, <a>the solidification model has been coupled with the
predictions from the HTC correlations, and the results have demonstrated the availability
of the correlations other than on-site continuous casting control. </a>Moreover,
the model, along with
the three-step coupling procedure, has been applied to simulate the initial
solidification process in continuous casting, where a sufficient cooling rate
is required to maintain a proper solidification rate. Otherwise, bulging or
breakout might occur. The prediction is in good agreement with the
measured shell thickness, which was obtained from a breakout incident. With the help of
HPC, such comprehensive simulations will continue to serve as a powerful tool
for troubleshooting and optimization.</p>
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High Heat Flux Spray Cooling With Ammonia On Enhanced SurfacesBostanci, Huseyin 01 January 2010 (has links)
Many critical applications today, in electronics, optics and aerospace fields, among others, demand advanced thermal management solutions for the acquisition of high heat loads they generate in order to operate reliably and efficiently. Current competing technologies for this challenging task include several single and two phase cooling options. When these cooling schemes are compared based on the high heat flux removal (100-1000 W/cm2) and isothermal operation (within several oC across the cooled device) aspects, as well as system mass, volume and power consumption, spray cooling appears to be the best choice. The current study focused on high heat flux spray cooling with ammonia on enhanced surfaces. Compared to some other commonly used coolants, ammonia possesses important advantages such as low saturation temperature, and high heat absorbing capability. Moreover, enhanced surfaces offer potential to greatly improve heat transfer performance. The main objectives of the study were to investigate the effect of surface enhancement on spray cooling performance, and contribute to the current understanding of spray cooling heat transfer mechanisms. These objectives were pursued through a two stage experimental study. While the first stage investigated enhanced surfaces for the highest heat transfer coefficient at heat fluxes of up to 500 W/cm2, the second stage investigated the optimized enhanced surfaces for critical heat flux (CHF). Surface modification techniques were utilized to obtain micro scale indentations and protrusions, and macro (mm) scale pyramidal, triangular, rectangular, and square pin fins. A third group, multi-scale structured surfaces, combined macro and micro scale structures. Experimental results indicated that micro- and macrostructured surfaces can provide heat transfer coefficients of up to 534,000 and 426,000 W/m2oC at 500 W/cm2, respectively. Multi-scale structured surfaces offered even a better performance, with heat transfer coefficients of up to 772,000 W/m2oC at 500 W/cm2, corresponding to a 161% increase over the reference smooth surface. In CHF tests, the optimized multi-scale structured surface helped increase maximum heat flux limit by 18%, to 910 W/cm2 at nominal liquid flow rate. During the additional CHF testing at higher flow rates, most heaters experienced failures before reaching CHF at heat fluxes above 950 W/cm2. However, the effect of flow rate was still characterized, suggesting that enhanced surfaces can achieve CHF values of up to 1,100 W/cm2 with 67% spray cooling efficiency. The results also helped shed some light on the current understanding of the spray cooling heat transfer mechanisms. Data clearly proved that in addition to fairly well established mechanisms of forced convection in the single phase regime, and free surface evaporation and boiling through secondary nucleation in the two phase regime, enhanced surfaces can substantially improve boiling through surface nucleation, which can also be supported by the concept of three phase contact lines, the regions where solid, liquid and vapor phases meet. Furthermore, enhanced surfaces are capable of retaining more liquid compared to a smooth surface, and efficiently spread the liquid film via capillary force within the structures. This unique advantage delays the occurrence of dry patches at high heat fluxes, and leads to higher CHF.
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The Effect of Variable Gravity on the Cooling Performance of a 16-Nozzle Spray ArrayElston, Levi J. 26 September 2008 (has links)
No description available.
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Refrigeração evaporativa por aspersão em telhas de fibrocimento: estudo teórico e experimentalRoriz, Victor Figueiredo 01 August 2007 (has links)
Made available in DSpace on 2016-06-02T20:09:08Z (GMT). No. of bitstreams: 1
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Previous issue date: 2007-08-01 / Financiadora de Estudos e Projetos / This research focuses the evaporative cooling by water aspersion on wavy
cement fiber tiles in the city of São Carlos, SP, seeking to use it to reduce the buildings heat
gains.
A theoretical model was developed, based on classic equations of fluids
mechanic, applied to iterative calculations of heat flows on the tile superior surface,
considered as control surface.
In the work development, this model was progressively adjusted to
experimental data obtained in a test cell, exposed to the local climatic conditions, with the
monitoring of superficial temperatures of both faces in two tiles, one maintained dry and other
under intermittent aspersion of water. The research results indicated that, despite of still being susceptible to
improvement, the theoretical model already presents quite satisfactory approach with the
measured data. Applying a statistical adjustment to the proposed model of iterative heat flows
calculation, it was obtained a correlation coefficient between measured and estimated
temperatures of 0,999 and a standard deviation of 0,35 ºC.
During the experiments, the average evaporative heat flow was 409 W/m2. Theaverage water volume evaporated was 0,7 l/(m².h), corresponding to an average difference of
temperatures among the compared tiles of 5,12 K, for the daylight period. Due to the growing need of energy consumption reduction, this procedure
seems to be a good option to reduce buildings thermal load, if compared to conventional air
conditioning systems / Esta pesquisa enfoca a refrigeração evaporativa por aspersão de água sobre
telhas onduladas de fibrocimento, na cidade de São Carlos, SP, visando sua utilização para
redução dos ganhos de calor em edificações.
Um modelo teórico foi desenvolvido, baseado em equações clássicas da
mecânica dos fluidos, aplicadas em cálculos iterativos dos fluxos de calor sobre a superfície
superior da telha, considerada como superfície de controle.
No desenvolvimento do trabalho, este modelo foi progressivamente ajustado a
dados experimentais obtidos em uma célula de teste, exposta às condições climáticas locais,
sendo monitoradas temperaturas superficiais de ambas as faces em duas telhas, uma mantida
seca e outra sob aspersão intermitente de água.
Os resultados da pesquisa indicaram que, apesar de ainda ser passível de
aprimoramento, o modelo teórico já apresenta aproximação bastante satisfatória com os dados
medidos. Aplicando-se um ajuste estatístico ao modelo proposto de cálculo iterativo dos
fluxos de calor, obteve-se um coeficiente de correlação entre temperaturas medidas e
estimadas de 0,999 e um desvio padrão de 0,35 ºC.
Durante os experimentos, o fluxo médio de calor por evaporação foi de 409 W/m2. O volume médio de água evaporado foi de 0,7 l/(m².h), correspondendo a uma diferença média de temperaturas entre as telhas comparadas, para o período diurno, de 5,12 K.
Frente à crescente necessidade de redução de consumo de energia, esta parece uma boa opção para redução da carga térmica dos edifícios, se comparada aos sistemas
convencionais de condicionamento de ar
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Preparação e caracterização de micro e nanopartículas lipídicas sólidas para aplicação em cosméticos / Preparation and caracterization of solid lipid micro and nanoparticles, for application in cosmeticsRossan, Marcos Roberto 18 August 2018 (has links)
Orientador: Maria Helena Andrade Santana / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-18T18:45:10Z (GMT). No. of bitstreams: 1
Rossan_MarcosRoberto_M.pdf: 4251170 bytes, checksum: f64611ade06535fb615dbd4f23afd20f (MD5)
Previous issue date: 2011 / Resumo: Neste trabalho, estudou-se o desenvolvimento tecnológico de micro/ nanopartículas lipídicas sólidas para aplicação cosmética capilar. As micropartículas foram produzidas por spray cooling, onde incorporou-se na matriz lipídica, composta por ceras naturais de origem vegetal (cera de carnaúba), mineral (microparafina) e sintética (cera de silicone), um ativo doador de brilho capilar, de nome comercial Activeshine Amazon, composto por uma mistura de triglicerídeos de murumuru e babaçú. As micropartículas foram obtidas a partir de misturas contendo 30% das ceras, porém a incorporação total do ativo na matriz lipídica ocorreu a partir de 70% de cera. A produção das micropartículas foi estudada através de um planejamento estatístico de experimentos e analise de superfície de resposta, onde determinou-se a influência da pressão do ar de atomização e concentração da cera, sobre o diâmetro médio. Os resultados mostraram que a pressão do ar de atomização foi a principal variável de significância estatística para os três tipos de ceras. Foram obtidas micropartículas esféricas, com diâmetro entre 30 - 320 ?m. As nanopartículas foram obtidas a partir da mistura lipídica composta por 50% de Activeshine Amazon e 50% de cera de carnaúba, além de sorbitol, óleo de mamona PEG-40 e quaternários de amônio (CTAC, BTAC e SDBAC), via nano-emulsificação de baixa energia, através do processo de inversão de fase por temperatura. Foram obtidas partículas com 0,08 a 0,35 de polidispersidade, 45 - 190 nm de diâmetro médio, e -20 A +70 mV de potencial zeta. Nestes estudos, verificou-se a influência destes componentes da formulação sobre o ponto de inversão de fase, comprovado por medidas de condutividade elétrica. Estes resultados mostram que os processos de spray cooling e nano-emulsificação utilizando ceras e triglicerídios produzem micro e nanopartículas que atendem aos requisitos de diâmetro médio, polidispersidade e potencial zeta para aplicação capilar. Essas partículas são também potencialmente úteis para a encapsulação de bioativos e desenvolvimento de formulações mais eficazes comparadas às que utilizam os compostos livres / Abstract: This work studied the technological development of solid lipid micro and nanopaparticles for cosmetic hair application. The microparticles were produced through spray cooling process, in which an active donator of hair brightness, commercially named Activeshine Amanzon was incorporated. The solid lipid matrix was composed by waxes from vegetal (carnauba), mineral (microparaffin) and synthetic (silicon) origin. The Activeshine Amazon is a mixture of triglycerides from murumuru butter and babassu oil. The microparticles were obtained from admixtures containing 30% of the waxes, but the total incorporation of the active in the lipid matrix occurred from 70% only. The production of microparticles was studied through a statistical experimental planning and surface response analysis from which it was determined the influence of the inlet atomization air pressure and wax concentration on the mean diameter of the particles. The results shown the air pressure was the statistically main significant variable for the three studied waxes. The mean diameter of the obtained spherical microparticles was in the range of 30 to 320 ?m. The nanoparticles were obtained through low-energy nano-emulsification process, known as temperature phase inversion. They were composed by a mixture of 50% Activeshine Amazon and 50% of carnauba wax, in which was also added sorbitol, castor oil PEG-40 and the ammonium quaternaries CTAC, BTAC and SDBAC. They presented 0.08 to 0.35 polydispersity, 45 to 190 nm mean diameter and -20 to + 70 mV zeta potential. The visual influence of the components of the formulation on the inversion phase temperature was comproved by electrical conductivity measurements. From these results we conclude that the spray cooling and nano-emulsification processes which use triglycerides as raw materials produce nano and microparticles which to meet the mean diameter, polydispersity and zeta potential requirements for hair care application. In addition to that, the particles are potentially useful for encapsulation of bioactives and also for the development of more efficient formulations than the free compounds ones / Mestrado / Desenvolvimento de Processos Biotecnologicos / Mestre em Engenharia Química
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Vliv vrstvy oxidů na chlazení ocelových povrchů / Influence of the oxide layer on the cooling of steel surfacesResl, Ondřej January 2018 (has links)
This thesis deals with the influence of the oxide layer on the spray cooling of steel surfaces. As part of the work steel samples with oxide layer are made and the thickness, porosity and surface roughness of this layer are characterized. The average thermal conductivity of porous oxide layer is determined for different regimes of oxidation. Further, the influence of the oxide layer on the heat transfer coefficient during the spray cooling is experimentally investigated on created samples and the basic numerical simulation of the cooling is done for selected experiment with oxide layer. The thesis also contains theoretical introduction to given issue.
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Two-Phase Spray Cooling with Water/2-Propanol Binary Mixtures for High Heat Flux Focal SourceObuladinne, Sai Sujith 12 1900 (has links)
Two-phase spray cooling has been an emerging thermal management technique offering high heat transfer coefficients and critical heat flux levels, near-uniform surface temperatures, and efficient coolant usage that enables to design of compact and lightweight systems. Due to these capabilities, spray cooling is a promising approach for high heat flux applications in computing, power electronics, and optics. Two-phase spray cooling inherently depends on saturation temperature-pressure relationships of the working fluid to take advantage of high heat transfer rates associated with liquid-vapor phase change. When a certain application requires strict temperature and/or pressure conditions, thermo-physical properties of the working fluid play a critical role in attaining proper efficiency, reliability, or packaging structure. However, some of the commonly used single-component working fluids have relatively poor properties and heat transfer performance. For example, water is the best coolant in terms of properties, yet in certain applications where the system operates at low temperature ambient, it cannot be implemented due to freezing risk. The common solution for this problem is to use the antifreeze mixtures (binary mixtures of water and alcohol) to reduce the freezing point. In such cases, utilizing binary mixtures to tune working fluid properties becomes an alternative approach.
This study has two main objectives; (1) to experimentally investigate the two-phase spray cooling performance of water/2-propanol binary mixture, and (2) to numerically investigate the performance of an advanced heat spreader featuring high and directional thermal conductivity materials for high heat flux focal sources. The first part of the study involves experimental characterization of heat transfer performance. Tests are conducted on a small-scale, closed loop spray cooling system featuring a pressure atomized spray nozzle. The test section, made of copper, measures 10 mm x 10 mm x 2 mm with a plain, smooth surface. A cylindrical copper block, with a matching size square protrusion attached onto the back side of the test section, generates heat using cartridge heaters and simulates high heat flux source. Embedded thermocouples are used to determine the spray surface temperature. The working fluid, water/alcohol mixture, has various concentration levels of 2-propanol by mass fraction 0.0 (pure water), 0.25, 0.50, 0.879 (azeotrope) and 1.0 (pure alcohol)), representing both non-azeotropic and azeotropic cases. Spray cooling tests are performed with a constant flow rate of 5.6 ml/cm².s at subcooled temperatures (~20oC) and atmospheric pressure. Experimental procedure involves controlling the heat flux in increasing steps, and recording the corresponding steady-state temperatures to obtain cooling curves in the form of surface superheat vs. heat flux. The second part of the study investigates an advanced heat spreader design for thermal management of a high heat flux focal source. The heat spreader comprises of three layers: a copper layer that interfaces with the heat source, a high and directional thermal conductivity material (such as CVD diamond and Pyrolytic graphite) layer, and another copper layer that is exposed to two-phase spray cooling. The analysis applies various heat fluxes on the heat source side and the experimentally obtained heat transfer coefficients on the spray side of the spreader design to determine the temperature and heat flux distributions, and examine the potential capabilities of this configuration.
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Thermal Management, Beam Control,and Packaging Designs For High PowerChung, Te-yuan 01 January 2004 (has links)
Several novel techniques for controlling, managing and utilizing high power diode lasers are described. Low pressure water spray cooling for a high heat flux system is developed and proven to be an ideal cooling method for high power diode laser arrays. In order to enable better thermal and optical performance of diode laser arrays, a new and simple optical element, the beam control prism, is invented. It provides the ability to accomplish beam shaping and beam tilting at the same time. Several low thermal resistance diode packaging designs using beam control prisms are proposed, studied and produced. Two pump cavity designs using a diode laser array to uniformly pump rod shape gain media are also investigated.
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NUMERICAL SIMULATION OF SOLIDIFICATION AND SEGREGATION BEHAVIOR DURING CONTINUOUS CASTINGDianzhi Meng (17635992) 14 December 2023 (has links)
<p dir="ltr">Approximately 95% of global steel production relies on continuous casting, there is a need for a practical, cost-effective, and accurate method to guide real-world production. A successful integration of three individual CFD models – spray cooling model, solidification model, and carbon segregation model – was accomplished. To understand the heat transfer behavior on a heated surface, a three-dimensional model was used to simulate the interaction of liquid droplets with a heated surface during the secondary cooling process, employing air-mist nozzles. The real nozzle layout, as employed in a full-scale continuous caster to provide HTC data on slab surface. For solidification model, enthalpy-porosity methods were applied to estimate the metallurgical length and surface temperatures. Carbon transport within the continuous caster was considered, revealing a phenomenon of positive segregation at the center of the slab. Building upon this foundation, further investigations were carried out to assess the implications of nozzle clogging. These effects encompass surface temperature, metallurgical length, and carbon concentration. Commercial software ANSYS Fluent 2021 R2 and Simcenter STAR-CCM+ 2302 are chosen for their exceptional computational performance. MATLAB and Python play key roles in both pre and post processing, including mapping HTC profiles, visualizing shell growth, and extracting temperature and cooling profiles.</p>
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