<p>U disertaciji je razvijena nova eksperimentalna postavka za merenje<br />graničnih uslova pri livenju u peščanim kalupima. Utvrđeno je da se<br />uvođenjem pojma prividne toplotne difuzivnosti materijala kalupa<br />može poništiti greška pozicioniranja termoparova i time smanjiti<br />greška procene graničnih uslova. Dodatno, pokazano je da proces<br />izdvajanja intermetalnih jedinjenja tokom procesa očvršćavanja<br />kalupa može uticati na vrednosti graničnih uslova. Razvijena je i<br />nova empirijska korelaciona funkcija kojom se može opisati promena<br />vrednosti koeficijenta prenosa toplote između kalupa i odlivka.</p> / <p>In this study a new experimental technique and apparatus for estimation of<br />boundary conditions in sand casting process were developed. It is shown<br />that thermocouple positioning errors can be nullified by introducing a concept<br />of apparent heat diffusivity of the mold material. In this way, total error of the<br />heat transfer estimation can be reduced. Additionally, it was found that the<br />process of precipitation of intermetallic compounds can influence the value of<br />achieved metal-mold heat transfer. A novel empirical correlation function is<br />proposed. This function has the ability to accurately describe the change in<br />interfacial heat transfer with the casting surface temperature.</p>

Submitted by JOSIANE SANTOS DE OLIVEIRA (josianeso) on 2017-08-09T15:47:57Z No. of bitstreams: 1 Jeferson Daniel Mathias_.pdf: 884742 bytes, checksum: c605c6232011e4df63e940eb350ced6c (MD5) / Made available in DSpace on 2017-08-09T15:47:57Z (GMT). No. of bitstreams: 1 Jeferson Daniel Mathias_.pdf: 884742 bytes, checksum: c605c6232011e4df63e940eb350ced6c (MD5) Previous issue date: 2017-03-22 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / PROSUP - Programa de Suporte à Pós-Gradução de Instituições de Ensino Particulares / A importância dos sistemas de refrigeração industrial é notória, destacando-se seu uso em grandes plantas químicas e petroquímicas e, principalmente, na indústria alimentícia, em frigoríficos, onde o consumo de energia tem impacto diretamente na qualidade e no valor final do produto. A modernização dos critérios de projeto de equipamentos de refrigeração visando à diminuição de custos de fabricação, manutenção, instalação, consumo de energia e de carga de refrigerante no sistema através do uso de novos materiais, diminuição do volume dos evaporadores e tanques separadores é uma necessidade atual e está sendo colocada em prática pela grande maioria das empresas fabricantes de equipamento. Desta forma, justifica-se a importância de avaliar a eficiência do sistema de refrigeração com evaporadores inundados conforme a variação do número de recirculação do refrigerante. A aplicação dos conceitos de evaporador inundado com recirculação através da refrigerante amônia tem intuito de ampliar os estudos em evaporadores industriais, visto a escassez de informações nessa área. Onde os resultados obtidos dos testes experimentais do evaporador inundado com recirculação de líquido possibilitam quantificar a influência no número de recirculação na capacidade do evaporador e na queda de pressão do escoamento do refrigerante no interior dos tubos comparados com os valores estimados por correlações utilizadas. Visto que, o evaporador apresentou um incremento de capacidade com o aumento do número de recirculação na ordem de 9,3%, variando de 108,6 a 118,7 kW, conforme dados coletados. Observa-se que no estudo das correlações estimadas e analisadas para o cálculo do coeficiente de transferência de calor no lado do ar, a correlação de Kim et al. (1999) para aletas planas e tubos, foi a que apresentou os menores erros relativos para o cálculo do coeficiente global de transferência de calor. A queda de pressão durante o escoamento da amônia no evaporador para cada número de recirculação, apresenta valores entre 15,2 a 35,7 kPa, representando um incremento de 134,8% e o título do refrigerante na saída do evaporador teve sua variação, em relação do número de recirculação de 0,67 até 0,248. / The importance of industrial refrigeration systems is notorious, highlighting their use in large chemical and petrochemical plants and, especially in food industry, in slaughterhouses, where the energy consumption impacts directly on quality and final value of the product. The modernization of project criteria for refrigeration equipment aiming at reducing the costs of manufacturing, maintenance, installation, energy consumption and refrigerant load in the system using new materials and decreasing the volume of evaporators and separator tanks is a current need and it is being implemented by the vast majority of equipment manufacturing companies. Therefore, it is justified the importance of evaluate the efficiency refrigeration system with Liquid Overfeed Evaporator according to the variation of refrigerant’s recirculation number. The application of the concepts of Liquid Overfeed Evaporator with recirculation through the ammonia refrigerant intends to expand the studies in industrial evaporators, given the scarcity of information in this area. The results obtained from the experimental tests of flooded evaporators with liquid recirculation make it possible to quantify the influence of the recirculation number in the capacity of the evaporator and in the pressure drop of the refrigerant flow inside the tubes compared with the values estimated through the used correlations. The evaporator presented an increment of capacity by increasing the recirculation number in the order of 9.3%, varying between 108.6 and 118.7 Kw, according to collected data. It is observed that in the study of estimated and analyzed correlations for the calculation of the coefficient of heat transfer on the air side, the correlation of Kim et al. (1999) to flat fins and tubes presented the smallest relative errors for the calculation of the global heat transfer coefficient. The pressure drop during the ammonia’s flow in the evaporator for each recirculation number showed values between 15.2 and 35.7 kPa, representing an increase of 134.8%, while the quality of the refrigerant at the output of the evaporator showed its variation, related to the number of recirculation, between 0.67 and 0.248.

This study numerically examines the heat transfer and pressure drop performance of finned tube heat exchangers with staggered and inline tube layout for a range of tube pitch. The first part of the thesis considers the case where the heat exchanger is placed in fully ducted airflow. The simulations indicate that the performance reduced considerably for the staggered tube layout with an increase in the tube pitch, but a minimal difference for the inline tube arrangement. The effects of other geometrical parameters like fin pitch and the number of tube rows are then presented. Finally, a correlation for fin and tube heat exchangers with inline tube layout is proposed based on 280 simulations for 70 different configurations. The proposed heat transfer correlation can describe the database within ±8% discrepancy while the friction factor correlation can correlate the dataset within a ±10% discrepancy. The mean deviations for heat transfer and friction factor correlations are 4.3% and 5.4%. An important factor that influences the performance of flat plate and finned tube heat exchangers is when there is bypass flow around the heat exchanger. The next section of this thesis numerically investigates the partially ducted inline fin and tube heat exchanger with side bypass. The effects of the side clearance and the Reynolds number on the heat transfer and the pressure drop performance of the heat exchanger are presented. The simulations indicate that the heat transfer performance depreciates by more than 25% for infinite side clearance. The study then compares the pressure difference observed for entry, exit and the friction pressure drop with the various correlations available in the literature. Finally, the heat transfer and pressure drop performance for staggered and inline tube layouts are compared. / Thesis / Master of Applied Science (MASc)

The subject of this diploma thesis is the creation of a spark ignition thermodynamics model using pressure data measured on the actual engine. The model made in Matlab programming language combines Wiebe function for fuel energy release and Woschni correlation for heat transfer between in-cylinder gasses and cylinder walls. The created model contains compression and expansion stroke only, that's why are conditions at the start of compression and total heat addition calculated by measured pressure data from Skoda 1.0 MPI engine. Creation of transparent model by Matlab scripts enables other users to understand the basics of „zero-dimensional“ thermodynamics models properly, which are used by number of commercial solvers such as GT-Power simulation software. First part of this thesis deals with fundamental laws of heat addition and heat transfer, description of equations for its modelling and application. The major section is devoted to Matlab model, where defined input parameters are mentioned, description of model operation and model parameters influence study. Next parts develops issues of combustion pressure measurement and creation of engine simulation by GT-Power software used for comparison with Matlab model. In the thesis conclusion are simulations and actual engine data differences discussed.

A breed-and-burn molten salt reactor (BBMSR) concept is proposed to address the Generation IV fuel cycle sustainability objective in a once-through cycle with low enrichment and no reprocessing. The BBMSR uses separate fuel and coolant molten salts, with the fuel contained in assemblies of individual tubes that can be shuffled and reclad periodically to enable high burnup. In this dual-salt configuration, the BBMSR may overcome several limitations of previous breed-and-burn (B$\&$B) designs to achieve high uranium utilisation with a simple, passively safe design. A central challenge in design of the BBMSR fuel is balancing the neutronic requirement of large fuel volume fraction for B$\&$B mode with the thermal-hydraulic requirements for safe and economically competitive reactor operation. Natural convection of liquid fuel within the tubes aids heat transfer to the coolant, and a systematic approach is developed to efficiently model this complex effect. Computational fluid dynamics modelling is performed to characterise the unique physics of the system and produce a new heat transfer correlation, which is used alongside established correlations in a numerical model. A design framework is built around this numerical model to iteratively search for the limiting power density of a given fuel and channel geometry, applying several defined temperature and operational constraints. It is found that the trade-offs between power density, core pressure drop, and pumping power are lessened by directing the flow of coolant downwards through the channel. Fuel configurations that satisfy both neutronic and thermal-hydraulic objectives are identified for natural, 5$\%$ enriched, and 20$\%$ enriched uranium feed fuel. B$\&$B operation is achievable in the natural and 5$\%$ enriched versions, with power densities of 73 W/cm$^3$ and 86 W/cm$^3$, and theoretical uranium utilisations of 300 $\mathrm{MWd/kgU_{NAT}}$ and 25.5 $\mathrm{MWd/kgU_{NAT}}$, respectively. Using 20$\%$ enriched feed fuel relaxes neutronic constraints so a wider range of fuel configurations can be considered, but there is a strong inverse correlation between power density and uranium utilisation. The fuel design study demonstrates the flexibility of the BBMSR concept to operate along a spectrum of modes ranging from high fuel utilisation at moderate power density using natural uranium feed fuel, to high power density and moderate utilisation using 20$\%$ uranium enrichment.