Nanofluids as an innovative class of heat transfer fluids created by dispersing nanometre-sizedmetallic or non-metallic particles in conventional heat transfer fluids displayed the potential toimprove the thermophysical properties of the heat transfer fluids. The main purpose of this study is toinvestigate the influence of the use of nanofluids on two-phase heat transfer, particularly on thethermal performance of the heat pipes. In the first stage, the properties of the nanofluids were studied,then, these nanofluids were used as the working fluids of the heat pipes. The thermal performance ofthe heat pipes when using different nanofluids was investigated under different operating conditionsexperimentally and analytically. The influences of the concentration of the nanofluids, inclinationangles and heat loads on the thermal performance and maximum heat flux of the heat pipes wereinvestigated.This study shows that the thermal performance of the heat pipes depends not only on thermophysicalproperties of the nanofluids but also on the characteristics of the wick structure through forming aporous coated layer on the heated surface. Forming the porous layer on the surface of the wick at theevaporator section increases the wettability and capillarity and also the heat transfer area at theevaporator of the heat pipes.The thermal performance of the heat pipes increases with increasing particle concentration in all cases,except for the heat pipe using 10 wt.% water/Al2O3 nanofluid. For the inclined heat pipe, irrespectiveof the type of the fluid used as the working fluid, the thermal resistance of the inclined heat pipes waslower than that of the heat pipes in a horizontal state, and the best performance was observed at theinclination angle of 60o, which is in agreement with the results reported in the literature. Otheradvantages of the use of nanofluids as the working fluids of the heat pipes which were investigated inthis study were the increase of the maximum heat flux and also the reduction of the entropy generationof the heat pipes when using a nanofluid.These findings revealed the potential for nanofluids to be used instead of conventional fluids as theworking fluid of the heat pipes, but the commercialization of the heat pipes using nanofluids for largescale industrial applications is still a challenging question, as there are many parameters related to thenanofluids which are not well understood. / <p>QC 20170228</p>

Resumo: O objetivo deste trabalho é a análise numérica e experimental de escoamento viscoso, incompressível, permanente, com transferência de calor, em um canal estreito contendo um arranjo de obstáculos retangulares. A análise experimental envolveu determinação de coeficiente de transferência de calor médio bem como o número de Nusselt médio e medidas de temperatura em esteira térmica para comparação com os resultados obtidos por simulação numérica. Para a análise numérica usamos o programa comercial de mecânica dos fluidos e transferência de calor computacional ICEPAK®. Verificamos que quanto mais adentro o obstáculo estiver no arranjo maior é a transferência de calor por convecção forçada. Determinamos coeficientes de transferência de calor médio e número de Nusselt médio (com incerteza entre 6 e 15%) e verificamos que o efeito da posição diminui à medida que a velocidade aumenta. Concluímos também que ambos os modelos de turbulência utilizados, k-ε padrão e k-ε RNG, foram incapazes de predizer o efeito da posição apropriadamente. Entretanto, o modelo k-ε RNG apresentou melhor comportamento, pois o seu uso resultou em soluções com valores de temperatura intermediários aos experimentais / Abstract: The purpose of this work is the study of the numerical and experimental viscous incompressible steady flow with heat transfer into a narrow channel containing a rectangular array of obstacles. The experimental approach involves determining the coefficient of heat transfer and temperature measurements in thermal wake for comparison with the results obtained in numerical simulations. For the numerical analysis we use the commercial program of fluid mechanics and heat transfer computational ICEPAK™. We confirmed that in the last lines of the array the biggest is the heat transfer by forced convection. We determined the average heat transfer coefficients (with uncertainty between 6 and 15%) and found that the effect of the position decreases as flow speed increases. We use in the simulations the k-ε turbulence model and the k-ε RNG turbulence model. We conclude that both turbulence models used were unable to predict the effect of the position properly. However, the k-ε RNG model showed better behavior. The numerical temperatures with this model were consistent to the experimental temperature / Orientador: João Batista Campos Silva / Coorientador: Amarildo Tabone Paschoalini / Coorientador: Marcio Antonio Bazani / Banca: Ricardo Alan Verdú Ramos / Banca: Marcio Higa / Mestre

The growing demand for the development of efficient miniature cooling systems has led to stimulating numerous investigations on two-phase flow boiling in small to microscale tubes. Because of the variation in properties of synthetic cooling fluids, this causes an inaccuracy of existing flow boiling prediction models or correlations in the literature to interpolate or extrapolate the two-phase flow boiling heat transfer and pressure drop. The purpose of this investigation was to study experimentally the parametric aspects of flow boiling characteristics inside vertical stainless-steel tubes with four different internal diameters (1.1, 2.01, 2.88 and 4.26 mm). The R245fa (1,1,1,3,3-pentafluoropropane, HFC-245fa) was used as working fluid. The experiments were carried out under a system pressure range of 185 - 310 kPa (which correspond to a saturation temperature range of 31 - 46 °C), mass flux range of 200 - 500 kg/m²s, heat flux range of 3 - 188.5 kW/m², vapour quality up to the onset of dryout and 5 K inlet subcooling. Flow pattern visualisations, two-phase pressure drops and saturated flow boiling heat transfer coefficients were presented. The experimental data of R134a employed for comparison is acquired from the previous studies of Huo et al. (2007), Shiferaw et al. (2011) and Mahmoud et al. (2014a). These studies were carried out in the same experimental facility and under the similar operating conditions. The Two-phase flow regimes inside four tubes were visualised in a borosilicate glass tube located at the heated section outlet to capture the dominant flow patterns which assist to elucidate the heat transfer results. The flow boiling visualisation was recorded by a high-speed camera with experiments of increasing and decreasing heat flux. The four observed flow regimes are identified as bubbly flow, slug flow, churn flow and annular flow. In increasing heat flux experiments, the churn and annular flows were only the dominant patterns in all four tubes. The slug flow was often discerned at lower mass flux except for the tube of 1.1 mm where it was not observed at all. This is contrary to decreasing heat flux experiments where all flow patterns including the bubble flow were observed in all the tubes. This shows a strong impact of hysteresis, which is a result of nucleation sites remained active as the heat flux is reduced. The flow patterns and transition boundaries for R245fa are affected by mass flux, system pressure, and tube diameter. The vapour quality corresponding to flow pattern transition boundary tends to decrease with increasing mass flux and tends to increase with increasing system pressure and decreasing tube diameter. Except for the bubbly-slug boundary, its vapour quality decreases with decreasing tube diameter. The experimental flow pattern maps of R245fa were fairly predicted with the predictive models developed for mini- and micro-channels by Tibiriçá et al. (2017). The two-phase pressure drop of R245fa is affected by mass flux, heat flux, system pressure, tube diameter and surface topography. The two-phase pressure drop increases with increasing mass flux and heat flux (vapour quality) and decreases with increasing system pressure and tube diameter. The two-phase pressure drop of the coated tube is higher than that of the uncoated tube. This is attributed to the coated tube having a higher surface roughness compared to the uncoated tube. The comparison between R245fa and R134a shows that the measured two-phase pressure drop of R245fa is dramatically higher than that of R134a. This arises from the difference in physical properties of the two fluids. The experimental data of two-phase pressure drop for 4.26 mm tube were reasonably predicted by Müller-Steinhagen and Heck (1986) correlation. Further, the experimental data of 2.88 mm and 2.01 mm tubes were well predicted by Chisholm (1973a), and Kim and Mudawar (2013), respectively. The experimental data of 1.1 mm tube were not well predicted by any of the selected predictive methods. The local heat transfer coefficient of all tubes increases with increasing heat flux for low and intermediate vapour qualities. After this vapour qualities, the heat flux effect diminishes. Then, the local heat transfer coefficient increased slightly with vapour quality, especially for higher heat flux near the outlet of the tube. However, the dryout inception in the 1.1 mm tube occurs after the intermediate vapour quality value and expands along the high vapour quality region. The behaviour of the local heat transfer coefficients of 1.1 and 2.88 mm tube is slightly dependent on the mass flux and vapour quality. Contrarily, there is insignificant effect of mass flux along 2.01 and 4.26 mm tube. This gives an indication of the contribution of nucleate boiling in the heat transfer process at lower and medium heat fluxes and nucleate boiling plus convective evaporation at higher heat fluxes near the tube outlet. Further, the local heat transfer coefficient increases as the system pressure increases. The tube diameter has a strong influence on the enhancement of local heat transfer coefficient. The enhancement in average heat transfer coefficient approaches 83% when the tube diameter is reduced from 4.26 to 1.1 mm. The trend of the local heat transfer coefficient of R134a was almost similar to that of R245fa with the exception of local dryout. The average heat transfer coefficient of R134a is about 106-151% larger than that of R245fa for the operational range studied. The dominant heat transfer mechanism is also represented by nucleate boiling for both fluids, particularly for 4.26 mm tube tested in this study. Also, the average heat transfer coefficient was enhanced by 33% when the inner tube surface coated with a copper coating. Finally, the correlation of Fang et al. (2017) predicted all experimental data for the four tubes with fair and similar accuracy.

Submitted by Renan Luis Fragelli null (renan.fragelli@gmail.com) on 2017-03-28T15:54:09Z No. of bitstreams: 1 Dissertação de Mestrado - Renan Fragelli.pdf: 5490064 bytes, checksum: 80c3b38563331cc9ef7e88ff192c5c8b (MD5) / Approved for entry into archive by Luiz Galeffi (luizgaleffi@gmail.com) on 2017-03-29T20:46:29Z (GMT) No. of bitstreams: 1 fragelli_rl_me_bauru.pdf: 5490064 bytes, checksum: 80c3b38563331cc9ef7e88ff192c5c8b (MD5) / Made available in DSpace on 2017-03-29T20:46:29Z (GMT). No. of bitstreams: 1 fragelli_rl_me_bauru.pdf: 5490064 bytes, checksum: 80c3b38563331cc9ef7e88ff192c5c8b (MD5) Previous issue date: 2017-03-16 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Este trabalho surgiu a partir da necessidade de produzir avanços em projeto que trata do desenvolvimento de um porta-ferramentas refrigerado internamente através de um fluido em mudança de fase e, na tentativa de minimizar a alta temperatura na ferramenta de corte através desse sistema de circulação. A utilização de nanofluidos surgiu como uma alternativa para a otimização da transferência térmica entre fluido e ferramenta de corte. A pesquisa consiste em avaliar a influência da adição de nanopartículas de prata numa solução de etilenoglicol e água deionizada, e também, da adição de nanopartículas de hematita (Fe2O3) no fluido refrigerante R141b. Em ambos os casos, as nanopartículas possuíam formato esférico, diâmetro médio de 30nm e foram avaliadas em concentrações. Além disso, as duas soluções foram submetidas a um campo elétrico na região de transferência térmica para analisar a influência do efeito eletrohidrodinâmico e, por fim, considerando as propriedades magnéticas da hematita, este nanofluido foi testado sob influência de um campo magnético. Os testes mostraram que as nanopartículas realmente influenciaram as propriedades dos fluidos e, por consequência, a quantidade de calor transferido. O nanofluido Ag/ETG+H2O(l) (0,023 vol%) resultou num incremento de 11% no valor do coeficiente de transferência térmica convectivo (h) quando sujeito ao campo elétrico. Para o caso do nanofluido Fe2O3/R141b, o valor de h aumentou em 30,3%, porém, quando sob efeito do campo magnético ou elétrico, o coeficiente foi prejudicado, resultando num valor menor que o do controle. Ao final, tem-se a proposta de um possível modelo desse porta-ferramentas. / This work arose from the need to produce advances in design development of an internally cooled toolholder through a phase change fluid. In order to minimize the high temperature in the cutting tool by this circulation system, using nanofluids emerged as an alternative to optimize heat transfer between the fluid and the cutting tool. The research consists in evaluate the influence of addition of silver nanoparticles in an ethylene glycol and deionized water solution, and also the addition of hematite nanoparticles (Fe2O3) in the refrigerant R141b. In both cases, nanoparticles had spherical shape, diameter of 30nm, and they were evaluated in different concentrations. Moreover, both nanofluids were subjected to an electric field in the heat transfer region to evaluate the influence of electrohydrodynamic effect and, finally, considering the magnetic properties of hematite, this nanofluid was tested under the influence of a magnetic field. The tests have shown that the nanoparticles really influence the properties of the fluids and, therefore, the amount of heat transferred. The nanofluid Ag/ETG+H2O(l) also presented a positive influence of the electric field, further enhancing the value of the convective heat transfer coefficient (h) in 11% (0,039 vol%). In the case of Fe2O3/R141b nanofluid, the h value increased 30.3%. However, when the nanofluid was under magnetic or electric effect, the value of h was deteriorated, resulting in a lesser value than the control. As conclusion, a new toolholder prototype is presented.

Experimental data on SuperCritical-Water (SCW) cooled bundles are very limited. Major problems with performing such experiments are: 1) small number of operating SCW experimental setups and 2) difficulties in testing and experimental costs at very high pressures, temperatures and heat fluxes. However, SuperCritical Water-cooled nuclear Reactor (SCWRs) designs cannot be finalized without such data. Therefore, as a preliminary approach experiments in SCW-cooled bare tubes and in bundles cooled with SC modeling fluids can be used. One of the SC modeling fluids typically used is Freon-12 (R-12) where the critical pressure is 4.136 MPa and the critical temperature is 111.97ºC. These conditions correspond to a critical pressure of 22.064 MPa and critical temperature of 373.95ºC in water. A set of experimental data obtained in a Freon-12 cooled vertical bare bundle at the Institute of Physics and Power Engineering (IPPE, Obninsk, Russia) was analyzed. This set consisted of 20 cases of a vertically oriented 7-element bundle installed in a hexagonal flow channel. To secure the bundle in the flow channel 3 thin spacers were used. The dataset was obtained at equivalent parameters of the proposed SCWR concepts. Data was collected at pressures of about 4.65 MPa for several different combinations of wall and bulk-fluid temperatures that were below, at, or above the pseudocritical temperature. Heat fluxes ranged from 9 kW/m2 to 120 kW/m2 and mass fluxes ranged from 440 kg/m2s to 1320 kg/m2s. Also inlet temperatures ranged from 70ºC – 120ºC. The test section consisted of fuel elements that were 9.5 mm in diameter with the total heated length of 1 m. Bulk-fluid and wall temperature profiles were recorded using a combination of 8 different thermocouples.The data was analyzed with respect to its temperature profile and heat transfer coefficient along the heated length of the test section. In a previous study it was confirmed that there is the existence of three distinct regimes for forced convention with supercritical fluids. (1) Normal heat transfer; (2) Deteriorated heat transfer, characterized by higher than expected temperatures; and (3) Improved heat transfer, characterized by lower than expected temperatures. All three regions were observed for the 7 rod bundle experiments. This work compares the experimental data to predictions based upon current 1-D correlations for heat transfer in supercritical fluids. Results show that no current 1-D correlation was able to accurately predict heat transfer coefficients within ±50%. A parametric analysis of the data was also completed to determine if continuity in the experiment was present. Results of this study show that two distinct regions are present in the data. For cases with a mass flux below 1200 kg/m2s wall temperature profiles appear to be normal while in cases with mass flux above 1200 kg/m2s temperature given by the wall thermocouples were higher than normal. This phenomenon occurred regardless of heat flux-to-mass flux ratios. / UOIT

Phase-change heat transfer is an important process used in many engineering thermal designs. Boiling is an important phase change phenomena as it is a common heat transfer process in many thermal systems. Phase change processes are critical to thermodynamic cycles as most closed loop systems have an evaporator, in which the phase change process occurs. There are many applications/processes in which engineers employ the advantages of boiling heat transfer, as they seek to improve heat transfer performance. Recent research efforts have experimentally shown that nanofluids can have significantly better heat transfer properties than those of the pure base fluids, such as water. The objective of this study is to improve the boiling curve of de-ionized water by adding aluminum oxide nanopthesiss in 0.1%, 0.2%, 0.3% and 0.4% wt concentrations in a sub-cooled pool boiling apparatus. Enhancement to the boiling curve can be quantified in two ways: (i) the similar heat fluxes of de-ionized water at smaller excess temperature, indicating similar quantity of heat removal at lower temperatures and (ii) greater heat fluxes than de-ionized water at similar excess temperatures indicating better heat transfer at similar excess temperatures. In the same fashion, the secondary objective is to increase the convective heat transfer coefficient due to boiling by adding different concentrations of aluminum oxide nanopthesiss.

This thesis investigates the cooling behaviour of polymers during the microinjection moulding process. The work included bespoke experimental mould design and manufacturing, material characterisation, infra-red temperature measurements, cooling analysis and cooling prediction using commercial simulation software. To measure surface temperature of the polymers, compounding of polypropylene and polystyrene with carbon black masterbatch was performed to make materials opaque for the IR camera. The effects of addition of carbon black masterbatch were analysed using differential scanning calorimetry and Fourier transform infrared spectroscopy. Sapphire windows formed part of the mould wall and allowed thermal measurements using an IR camera. They were laser machined on their inside surfaces to generate a range of finishes and structures. Their topographies were analysed using laser confocal microscope. The surface energy of sapphire windows was measured and compared to typical mould steel, employing a contact angle measurement technique and calculated using Owens-Wendt theory. A heating chamber was designed and manufactured to study spreading of polymer melts on sapphire and steel substrates. A design of experiments approach was taken to investigate the influence of surface finish and the main processing parameters on polymer cooling during microinjection moulding. Cooling curves were obtained over an area of 1.92 by 1.92 mm of the sapphire window. These experiments were conducted on the Battenfeld Microsystem 50 microinjection moulding machine. A simulation study of polymer cooling during the microinjection moulding process was performed using Moldflow software. Particular interest was paid to the effect of the values of the interfacial heat transfer coefficient (HTC) on the simulated cooling predictions. Predicted temperature curves were compared to experimentally obtained temperature distributions, to obtain HTC values valid for the material and processing parameters.

Carbon dioxide (CO2) is a natural, low cost refrigerant with good thermo-physical properties. CO2 is a good alternative for replacing HFC refrigerants that possess high global warming potential and reducing the direct impacts of refrigeration systems on the environment. However, CO2 refrigeration systems operate at relatively high condenser/gas cooler pressures and this imposes special design and control considerations. The gas cooler is a very important part of the system and can have significant influence on its performance. In sub-critical operation, good gas cooler/condenser design can reduce the condenser pressure and delay switching to supercritical operation which increases system efficiency. In supercritical operation optimum design and control can enable the system to operate at pressures that maximise system efficiency. In air cooled systems, gas coolers/condensers are of the finned-tube type. This type of heat exchanger is well established in the HVAC and refrigeration industries. The large changes in the CO2 properties in the gas cooler, however, during supercritical operation impose special design and manufacturing considerations. This research project considered the influence of the unique heat transfer characteristics of CO2 on the design and performance of finned tube air cooled condensers/gas coolers for CO2 refrigeration applications. A combined experimental and modelling approach using Computational Fluid Dynamics (CFD) was employed. A CO2 condenser/gas cooler test facility was developed for the experimental investigations. The facility employs a ‘booster’ hot gas bypass CO2 refrigeration system, with associated condenser/gas cooler test rig and evaporator load simulation facility. A series of experimental tests were carried out with two gas coolers which incorporated horizontal and horizontal-vertical slit fins and was obtained adequate experimental data concerning gas cooler performance. CFD modelling was used to study the performance of the gas coolers. The model was validated against test results and was shown to predict the air outlet temperature and heat rejection of the gas cooler with an accuracy of within ±5%. The model was subsequently used to evaluate the effect of a fin slit between the 1st and 2nd row of tubes of the gas cooler as well as a vertical slit on the 1st row before the last tube of the section. The results showed a 6%-8% increase in the heat rejection rate of the gas cooler compared to the performance without the horizontal slit. The vertical slit in the fin of the last tube has resulted in an additional increase in heat rejection over and above that for the horizontal slit of 1%-2%. CFD modelling was also used to investigate the variation of the refrigerant side, air side and overall heat transfer coefficient along the heat exchanger. The results showed that the refrigerant heat transfer coefficient increases with the decreasing of bulk refrigerant temperature and reaches its maximum when the specific heat of the refrigerant is highest. Furthermore, increasing the refrigerant mass flux, increases the refrigerant side heat transfer coefficient and heat rejection. This can reduce the size of the gas cooler for a given capacity at the expense of higher pressure drop and compressor power consumption. Air side and overall heat transfer coefficient correlations were developed for the specific gas cooler designs which were investigated and showed the heat transfer coefficients increase with increasing Reynolds Number.

Orientador: Ana Maria Frattini Fileti / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-27T02:40:23Z (GMT). No. of bitstreams: 1 Camargo_StellaForganesdeGodoy_M.pdf: 2742507 bytes, checksum: a2cd6bf18b9859966ac846d9d5939a21 (MD5) Previous issue date: 2015 / Resumo: O processo de polimerização em emulsão é um processo industrialmente importante para a produção de polímeros com diversos tipos de aplicações. Existe um grande interesse industrial para a obtenção de teor de sólidos mais altos, pois assim otimiza-se o volume do reator para o mesmo tempo de reação, reduz-se espaço de armazenagem do produto acabado bem como custos com transporte ao consumidor final. Porém, para obtenção de polímeros com alta concentração de sólidos, a dificuldade de estabilização da emulsão, viscosidade mais alta e formação de resíduos (coágulos) geram limitações no processo, interferindo na segurança da reação. Para este trabalho foi escolhida a copolimerização em emulsão de estireno-butadieno devido à sua importância industrial bem como às propriedades relevantes para aspectos de segurança industrial. O objetivo foi estudar as influências do aumento de teor de sólidos nas propriedades da emulsão estireno-butadieno em processo semi-contínuo que afetam a segurança da reação. Primeiramente foi encontrado na literatura um modelo já validado para a copolimerização em emulsão estireno-butadieno em processo semi-contínuo como base para realizar as simulações nos software Aspen Polymers® para as análises das propriedades e comportamento exotérmico da emulsão. O teor de sólidos na emulsão estireno-butadieno foi aumentado, reduzindo gradativamente a água da formulação e mantendo a proporcionalidade entre as demais matérias-primas variando dos originais 48,4 % para 65,1 % em que toda a água da pré-emulsão foi eliminada. As propriedades finais da emulsão apresentaram resultados esperados conforme embasamento teórico abordado: a massa específica, a viscosidade, massa molar média e diâmetro de partícula aumentaram com o aumento do teor de sólidos e a polidispersidade, a temperatura de transição vítrea, o calor específico e a condutividade térmica diminuíram. A taxa de remoção de calor da reação e a temperatura da reação sob condições adiabáticas em possíveis cenários de descontrole de reação foram consideradas para a segurança do processo aumentando significativamente com o aumento do teor de sólidos e indicando presença de monômeros não reagidos ao final do tempo de reação de 10 horas. A análise de sensibilidade do modelo foi realizada variando a temperatura do processo em diferentes concentrações de produto final com o intuito de aumentar o rendimento da reação. Para cada alteração realizada, as variações das propriedades do produto foram analisadas em detalhe para verificar modificações no produto final. O melhor ponto de trabalho encontrado no estudo foi à concentração de 60 % à temperatura de reação de 78°C em que os resultados demonstraram que pequenas alterações no processo podem ser suficientes para garantir a segurança do processo, a qualidade do produto final com altos rendimentos / Abstract: The emulsion polymerization process is a very important process to the industry in the production of polymers with a wide range of applications. There is a large industrial interest to obtain higher solid content polymers in order to optimize the reactor capacity with the same time of reaction, reducing the storage area and transportation to the final costumer. However, to obtain polymers with high solid contents, the difficulties with the stabilization of the emulsion, the higher viscosity and formation of residues (clots) generate limitations in the process, interfering in the safety of reaction. To this paperwork was chosen the styrene-butadiene emulsion copolymerization because of their industrial importance as well as the relevant properties for industrial safety aspects. The objective was to study the influences of the increased solids content in the properties of the styrene butadiene emulsion in a semi-continuous process that affect the safety of the emulsion copolymerization reaction. First of all, was found in the literature a model already validated to the styrene butadiene emulsion copolymerization in a semi-continuous process. This model was used as a base to perform simulations in the Aspen Polymers® software in order to examine the exothermic properties and the behavior of the emulsion. The solid content in the styrene-butadiene emulsion was increased gradually reducing the water of the formulation and maintaining proportionality between the other raw materials ranged from the original 48.4 % to 65.1 % where all water from the pre-emulsion was removed. The final properties of the emulsion had expected results as discussed on theoretical basis: the specific mass, viscosity, molecular weight and particle diameter enlarged with the increasing of solid content and polidispersity, the glass transition temperature, the specific heat and the thermal conductivity decreased. The reaction heat removal rate and the reaction temperature under adiabatic conditions in scenarios of possible runaway reaction were considered for the safety of the process, increasing significantly with the rise of solid content and indicating the presence of unreacted monomers at the end of the reaction time of 10 hours. The analysis of the sensitivity of the model was performed by changing the processing temperature of the final product in different concentrations in order to increase the reaction yield. For each change made, variations of product properties were analyzed in detail to verify changes in the final product. The best working point found in this study was 60 % of solids content at 78°C reaction temperature. The results demonstrated that small changes in process may be sufficient to ensure the safety of the process and the quality of the final product with high yields / Mestrado / Sistemas de Processos Quimicos e Informatica / Mestra em Engenharia Química

Orientador: Elaine Maria Cardoso / Resumo: Dissipadores de calor compactos, baseados em microcanais, têm se mostrado um meio eficaz para o resfriamento de dispositivos de alta densidade de energia, tais como microprocessadores, além de proporcionarem redução de material utilizado para a fabri-cação e do inventário de fluido refrigerante necessário. Sistemas bifásicos que operam com fluidos refrigerantes proporcionam coeficientes de transferência de calor elevados para baixos valores de velocidade mássica e uma distribuição de temperatura mais uni-forme na superfície. O presente estudo teve por objetivo avaliar experimentalmente o desempenho de um dissipador de calor baseado em microcanais, em condições de ebuli-ção convectiva saturada do fluido HFE-7100. O dissipador, em cobre eletrolítico, possui 33 microcanais de seção retangular com dimensões de 10 mm de comprimento, 200 μm de largura, 500 μm de altura e espaçados 100 μm entre si. A eficiência térmica do dissi-pador foi avaliada utilizando como fluido de trabalho o HFE-7100 (fluido refrigerante com baixo ozone depleting potencial, ODP, e global warming potential, GWP). Dados experimentais para o coeficiente de transferência de calor (CTC) e perda de pressão fo-ram obtidos em condições de escoamento monofásico e bifásico saturados, para diferen-tes valores de velocidades mássicas. As condições testadas foram de fluxo de calor im-posto (footprint) variando de 50 a 700 kW/m², com velocidades mássicas do fluido entre 392 e 875 kg/m²s, obtendo coeficientes de transferên... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Microchannel-based heat sinks have been shown to be an effective way of cool-ing high-density energy devices such as microprocessors, as well as reducing the material used to manufacture the exchangers and the required refrigerant inventory. Two-phase flow systems that operate with refrigerant fluids provide high heat transfer coefficients with low mass flux values and more uniform temperature distribution on the surface. The present study aimed to evaluate experimentally the performance of a heat sink based on microchannels under saturated conditions of convective boiling of HFE-7100 fluid. The analyzed heat sink has 33 rectangular section microchannels measuring 10 mm length, 200 μm wide, 500 μm high and spaced 100 μm apart. The heat sink was evaluat-ed using HFE-7100 (low ozone-depleting potential, ODP, and global warming potential, GWP) as working fluid. Experimental data for the heat transfer coefficient and pressure drop were obtained under saturated single and two-phase flow conditions for different values of mass velocities. An experimental apparatus was assembled and validated for the accomplishment of testing. As experimental conditions, the heat flux was applied in a range from 50 to 700 kW/m², with mass flux from 392 and 875 kg/m²s, obtaining a heat transfer coefficient of 60 kW/m² and pressure drop up to 12 kPa. By decreasing the mass flux and the input of the subcooling the HTC increases; the pressure drop increases monotonically with the increase in the mass fl... (Complete abstract click electronic access below) / Mestre