O processamento térmico contínuo usando trocadores de calor é uma forma muito comum de industrialização de alimentos líquidos. Atrelada à inativação de micro-organismos e enzimas pela alta temperatura, está a perda de qualidade do produto; portanto, o estudo e avaliação deste tipo de processo é fundamental para garantir a inocuidade e a melhora da qualidade do produto. Neste trabalho foi desenvolvida a modelagem matemática de um processo térmico contínuo em trocadores bitubulares para determinação da distribuição da temperatura média do produto e da letalidade sobre um atributo de segurança ou qualidade. No modelo, foram considerados os trocadores de aquecimento e de resfriamento, bem como o tubo de retenção. Admitiu-se regime permanente, escoamento pistonado e leva-se em conta a troca de energia com o ambiente. Para a aplicação do modelo, foi adotado um sistema em escala de laboratório com vazão de processamento entre 10 e 50 L/h, trocadores com quatro módulos de troca térmica e área total de 0,13 m² e sistema de indicação e aquisição de dados de temperatura. Como fluidos de trabalho foram usados: mistura de glicerina/água 80 % (Newtoniano) e solução 1 % de carboxi-metil-celulose (CMC, não-Newtoniano). Fluidos e utilidade foram água quente pressurizada e água gelada. Os parâmetros de troca térmica do modelo foram ajustados com sucesso através de ensaios experimentais. Foram ajustados: 1) coeficientes de convecção natural do ar sobre as seções de aquecimento e de resfriamento; 2) parâmetros da correlação de Nusselt x Reynolds para o coeficiente de convecção dos fluidos de trabalho; 3) coeficiente global de troca térmica com o ambiente no tubo de retenção. A validação do modelo ajustado foi realizada através da comparação das distribuições de temperatura experimental com a predição do modelo. A letalidade, levando em conta o tempo espacial no percurso do produto foi calculada e avaliada, indicando importante contribuição da seção de aquecimento e forte influência da elevação de temperatura na entrada do tubo de retenção para compensar as perdas para o ambiente. O modelo proposto mostra-se útil para a avaliação de processos térmicos em sistemas tubulares. / The continuous thermal processing using heat exchangers is a very usual form of industrialization of liquid foods. Linked to the inactivation of microorganisms and enzymes by high temperature is the loss of product quality; thus, the study and evaluation of this type of process is critical to ensure the safety and improve product quality. In this work, it was developed a mathematical model of a continuous process with tubular heat exchangers to determine the distribution of the average temperature of the product and the lethality considering a safety or quality attribute. In the model, are considered the exchangers for heating and cooling and the holding tube. It was assumed steady state plug-flow and it was taken into account the energy exchange with the ambient air. For the application of the model, it was adopted a laboratory system with processing flow rate between 10 and 50 L/h, exchangers with four heat transfer modules and total area of 0.13 m² and a temperature indication and acquisition system. The working fluids used were: a mixture of glycerol/water 80 % (Newtonian) and a 1 % solution of carboxymethylcellulose (CMC, non-Newtonian). Utility fluids were pressurized hot water and cold water. The heat transfer parameters of the model were adjusted successfully using the experimental data. Were adjusted: 1) the coefficients of natural convection of the air over the heating and cooling sections; 2) the parameters of the Nusselt x Reynolds correlation for the convective coefficient of the working fluid; 3) the overall heat exchange coefficient between the product and the ambient air in the holding tube. The validation of the fitted model was performed by comparing the experimental temperature distributions with the prediction from the model. Lethality, taking into account the space-time in the path of the product was calculated and evaluated, indicating a significant contribution of the heating section and a strong influence on the temperature rise in the entrance of the holding tube to compensate for losses to the surroundings. The model proves useful for the evaluation of thermal processes in tubular systems.

Em sistemas frigoríficos de compressão a vapor, o evaporador é o equipamento responsável direto pela retirada de calor de ambientes refrigerados. Por esta razão, este componente é a fonte de investigação do presente estudo, o qual teve por objetivo principal a busca por alternativas para a melhoria de desempenho térmico em sistema frigoríficos. Isto posto, o trabalho foi desenvolvido em três frentes de estudo, as quais encontram-se interligadas entre si: desenvolvimento de programa de simulação de serpentinas resfriadoras; realização de ensaios para determinação das capacidades de trocadores de calor; e revisão bibliográfica circunstanciada do coeficiente de transferência de calor do lado do ar. O programa de simulação desenvolvido, o qual tomou como base o modelo proposto por Rich, mostrou-se ser uma ótima ferramenta de trabalho, tanto no meio acadêmico como no industrial. Como conseqüência da elaboração do programa, fez-se uso de correlações já existentes para determinação dos coeficientes de transferência de calor do lado do refrigerante, Bo Pierre, e do lado do ar, McQuiston, sendo esta última escolhida a partir de um sumário de correlações levantadas quando no estudo dos coeficientes de transferência de calor descritos acima. Para que o programa fosse validado como ferramenta de trabalho, foram realizadas simulações dos ensaios das serpentinas testadas e seus resultados confrontados. Tais resultados apresentam uma adequada concordância,possibilitando validar o programa. Os ensaios foram realizados segundo recomendações da norma ASHRAE 25/1992. Dos dados obtidos nos testes, também foi proposto uma correlação para o fator j-Colburn para superfícies secas; no entanto, tratou-se apenas de especular acerca de seu comportamento com as demais correlações, as quais obtiveram boa concordância. / In refrigerating systems of compression to vapour, the evaporator is the direct responsible equipment for remove of heat of cooling environments. In this way, the component is the source of investigation of the present study, which had for main objective the search for alternatives to improvement the performance thermal in refrigeration systems. The research was developed in three studies fronts, that are connected each other: development of program of simulation of cooling coils; tests to find the performance of heat exchange; and revision bibliographical of the coefficient of heat transfer of air. The developed simulation program, based in the Rich\'s model, it showed to be a good work tool, as in the academic, as in the industrial behaviour. As consequence of the elaboration the program, it was used existents correlations to calculation the coefficients of refrigerant heat transfer, Bo Pierre, and to air, McQuiston, the last one was choose from a correlation\'s summary. Same simulations were made to validated the program of the tested serpentines and the results were confronted. Such results presented an appropriate agreement that contributed to validate the program. The tests were accomplished according to recommendations of the norm ASHRAE 25/1992. One correlation was proposed for the factor j-Colburn for dry surfaces in base of the testes results; however, the purpose was to speculated its behaviour with the other correlations, which obtained good agreement.

A presente pesquisa teve por objetivo o estudo da ebulição convectiva dos novos refrigerantes halogenados no interior de tubos horizontais de cobre. Uma busca na literatura pertinente ao assunto mostrou que a determinação do coeficiente de transferência de calor pode ser determinado por correlações que, aqui, foram classificadas como: 1- Estritamente Convectivas, 2- Superposição de Efeitos e 3- Estritamente Empíricas. Essas correlações mostraram-se inadequadas a generalizações. Uma bancada experimental foi concebida e construída, o que permitiu a obtenção de dados experimentais envolvendo uma ampla faixa de condições operacionais. Efeitos de parâmetros físicos como a velocidade mássica, fluxo de calor, temperatura de saturação e título, foram investigados. Os dados experimentais obtidos foram utilizados no desenvolvimento de uma correlação para o coeficiente de transferência de calor na ebulição convectiva que satisfizesse adequadamente esses dados obtidos para condições operacionais típicas de aplicações frigoríficas. A partir da análise efetuada foi proposto um modelo no qual foram introduzidos os adimensionais que envolvem os principais efeitos relacionados à mudança de fase. O modelo proposto apresentou resultados bastante adequados não apenas na correlação dos resultados experimentais obtidos na presente pesquisa como também em dados encontrados na literatura. / Present research has aimed at the study of convective boiling of recently introduced halocarbon refrigerants inside horizontal copper tubes. A comprehensive literature survey has revealed that the correlations for the convective boiling heat transfer coefficient can be divided into three main categories: (1) strictly convective; (2) superposition of effects; (3) strictly empirical. As a general rule these correlations are not fitted for generalizations. An experimental set up has been developed and constructed in order to raise data involving a relatively wide range of operational conditions. These data have been used to investigate effects of such parameters as heat flux, mass velocity, quality and evaporating temperature. In addition gathered data have been used in the development of a correlation for the heat transfer coefficient under convective boiling conditions typical of refrigeration applications. The model has been developed in terms of the main intervening non dimensional groups. The proposed equation correlated very well not only experimental data from present investigation but data obtained else where.

An experimental investigation has been undertaken to study operating temperatures and heat fluxes in the cylinder walls and cylinder head of a modern diesel engine. Temperatures were measured under a wide range of speed and torque at more than one hundred locations in the block and cylinder head of the engine employing conventional thermocouples arranged to obtain one-dimensional metal thermal gradients and subsequently deduce the corresponding heat fluxes and surface temperatures. Results observed in the cylinder bores revealed that in addition to heat transferred by convection and radiation from combustion gases, the temperature and heat flux distributions are considerably affected by heat conduction from piston rings and skirt through the oil film, and by frictional heat generated at these components. The heat fluxes and surface temperatures obtained in the cylinder head combined with gas pressure measurements were used to evaluate existing formulae to predict heat transfer coefficients from combustion gases to the chamber walls. The evaluation confirmed the significant variation previously observed between the various methods. As a consequence, a modified correlation has been proposed to estimate the gas-side heat transfer coefficient. This new correlation is considered to be an improved tool for estimating the heat transfer coefficients from combustion gases in modern diesel engines. Additionally, the results observed in the cylinder bores were used to develop a simple model from first principles to estimate the heat transferred from piston rings and skirt to the cylinder wall.

This thesis investigates, both theoretically and experimentally, the phenomenon of ingress through gas turbine rim seals. The work presented focuses on modelling and measuring the required sealing flow levels to purge the wheelspace against combined ingress and the effect of externally-induced ingress on the surface temperature and heat transfer to the rotor. Combined ingress is driven by a pressure difference between the mainstream annulus and wheelspace cavity resulting from the combination of the asymmetric external pressure profile in the annulus and the rotation of fluid in the rotor-stator wheelspace cavity. Ingress can be prevented by pressurising the wheelspace through the supply of sealant flow. The Owen (2011b) combined ingress orifice model was solved to predict the required levels of sealant flow to prevent ingress into the wheelspace. The model was validated using prepublished data and data collected experimentally over the course of this research. Gas concentration measurements were made on the stator of the Bath single-stage gas turbine test rig to determine the variation of sealing effectiveness with sealant flow rate for an axial clearance seal geometry at design and off-design operational conditions. The measured variation of the required sealant flow rate with the ratio of the external and rotational Reynolds numbers, ReW / Reϕ, was consistent with the findings of other workers: at low values of ReW / Reϕ, ingress levels were influenced by the combined effects of the disc rotation and the annulus pressure profile and were therefore considered to fall into the combined ingress region; the influence of rotation diminished as ReW / Reϕ increased and the ingress levels were dominated by the annulus pressure field (externally-induced ingress). The orifice model was in good agreement with the experimental measurements and the prepublished experimental data. Thermochromic liquid crystal (TLC) was used to determine effect of ingress on the heat transfer coefficient, h, and adiabatic wall temperature, Tad, on the rotor of the Bath gas turbine rig. Concurrent gas concentration measurements were made on the stator to compare the effects of ingress on the two discs. Data was collected at the design condition, where ReW / Reϕ = 0.538 and at an overspeed off-design condition, where ReW / Reϕ = 0.326. The comparison between a newly defined adiabatic effectiveness, εad, on the rotor and the concentration effectiveness, εc, on the stator, showed that the rotor was protected against the effects of ingress relative to the stator. The sealing air, which is drawn into the rotor boundary layer from the source region, thermally buffers the rotor against the ingested fluid in the core. A thermal buffer ratio, η, was defined as the ratio of the minimum sealant flow required to purge the stator against ingress to the minimum sealant flow required to purge the rotor against ingress. The thermal buffer is dependent upon the flow structure in the wheelspace, which itself is governed the turbulent flow parameter, λT. A hypothesis relating η to λT was developed and shown to be in good agreement with the experimental data. The local Nusselt numbers, Nur, on the rotor were shown to be fairly constant with radius and increased as λT was increased. The latter finding can be explained by the flow structure in the wheelspace: as λT is raised, the swirl in the fluid core reduces, which results in an increase in the moment coefficient and Nur on the rotor. Difficulties in measuring Tad during the experiments suggested a new technique from which to solve for h and Tad using TLC surface temperature measurements. The solution Fourier’s equation for a step-change in the temperature of a fluid flowing over a solid of semi-infinite thickness (the ‘semi-infinite solution’) is limited to relatively low Fourier numbers if Tad is to be calculated accurately. A two-layer composite substrate made from, for example, polycarbonate and Rohacell, could be used to achieve accurate estimates of h and Tad over a larger range of Biot numbers than for a single material substrate. TLC could be used to measure the surface temperature history of the composite substrate during an experiment; this would allow h and Tad to be solved from the numerical solution of Fourier’s equation or from a combination of the semi-infinite and steady-state solutions. The work presented in this thesis has uncovered some interesting findings in areas where research was limited. The measurements of the minimum sealant flow required to purge the wheelspace at off-design operation for a rotor-stator system with blades and vanes and the measurements of the adiabatic effectiveness on a rotating disc affected by ingress are unique and provide a platform for further experimental studies and validation of CFD models.

"Asphalt pavements are made up of several layers of materials and different types of materials are being used as base courses in these pavements. The properties of these pavement layers are affected significantly by temperature, and all of the layers are made up of heterogeneous mixtures of a wide variety of materials whose thermal properties are not readily available. Therefore, laboratory experiments were carried out with samples of pavements with different base course materials to determine temperature profiles along the depth, and finite element analysis was used to backcalculate thermal properties of the materials in the different layers of the different samples. The concept of extracting heat energy from asphalt pavements was evaluated by finite element modelling and testing small and large scale asphalt pavement samples. Water flowing through copper tubes inserted within asphalt pavements samples were used as heat exchangers in the experiments. The rise in temperature of water as a result of flow through the asphalt pavement was used as the indicator of efficiency of heat capture. The results of small scale testing show that the use of aggregates with high conductivity can significantly enhance the efficiency of heat capture. The efficiency can also be improved by using a reflectivity reducing and absorptivity increasing top layer over the pavement. Tests carried out with large scale slabs show that a larger surface area results in a higher amount of heat capture, and that the depth of heat exchanger is critical Heat-Islands are formed as a result of construction that replaces vegetation with absorptive surfaces (asphalt pavement). One suggested method to reduce the emitted heat from asphalt pavement surfaces is to reduce the temperature of the surface by flowing a suitable fluid through the pavement. Laboratory experiments were carried out using hand-compacted hot mix asphalt samples with quartzite and metagranodiorite aggregates. Pipes with different surface area were used to flow water through the samples, and the processes were modeled using finite element method. The results clearly show the feasibility of the proposed method, and indicate the beneficial effects of higher thermal conductivity of aggregates and larger surface area of pipes. "

Aluminum and steel components are usually quenched in forced gas, oil or water flow to improve mechanical properties and improve product life. During the quenching process, heat is transferred rapidly from the hot metal component to the quenchant and the rapid temperature drop introduces phase transformation and deformation in the hot metal component. As a result, quenching problems arise such as distortion, cracking and high tensile residual stresses. To avoid or minimize these problems while improving mechanical properties, process optimization is needed for both part geometry and quenching process design. A series of methods, including four existing methods and two new methods developed in this dissertation, were applied to obtain accurate thermal boundary conditions, i.e., the heat transfer coefficient (HTC) distribution. The commercially available material model DANTE was applied with finite element software ABAQUS to model the phase transformations and constitutive behavior of steel parts during quenching. A user material subroutine was developed for aluminum alloys based on a constitute model and tensile test data. The predicted residual stresses in the quenched parts agreed with those measured using the improved resistance strain gauge hole-drilling method and other methods, which validates the numerical models.

An experimental investigation has been conducted on CHTE quench probes and IVF quench probes to determine the influence of flow rate, spray distance and concentration of AQ251 polymer quenchant on the cooling rate and heat transfer coefficient during spray quenching. Time-temperature data has been collected for each spraying condition using the CHTE spray quenching system. Heat transfer coefficients as a function of temperature have been estimated and compared by using lumped thermal capacity model and an inverse heat conduction model. The results revealed that the maximum cooling rate increases with increasing in the flow rate in varying concentration of polymer quenchant in both probes. It was also found that the cooling rate decreases with the increase of the concentration of polymer quenchant.

"The performance of a series of mineral oil based quenchants has been investigated using the CHTE Quench Probe System and probe tips of 4140 steel to determine the cooling rate, heat transfer coefficient, Hardening Power (HP) and Tamura’s V indices in terms of the physical properties of quenchants; e.g. viscosity and oil start temperature. The Quench Factor, Q, was also calculated in terms of the hardness of the quenched parts. The lumped parameter approximation was used to calculate the heat transfer coefficient as a function of temperature during quenching. The results revealed that the maximum cooling rate increases with decrease in quenchant viscosity. As viscosity increases, Tamura’s V is nearly constant, while the HP decreases. For the selected oils, cooling ability of quenching oil increases with the increase in oil operating temperature, reaches a maximum and then decreases. The heat transfer coefficient increases with the increase in hardening power and maximum cooling rate. As the viscosity increases, the quench factor increases, which indicates the cooling ability of the oil decreases since the higher quench factor means the lower cooling ability of the oil. The hardness decreases with the increase in quench factor. Also the effect of surface oxides during quenching in commercial oils is studied. It was found that for 4140 steel probes the formation of oxide in air increases the cooling rate and heat transfer coefficient, the cooling rate curve of 4140 steel probe heated in argon shows clear Leidenfrost temperature, the oxide layer may require a significant thickness to cause the decrease in heat transfer coefficient. For 304 stainless steel probes the cooling rate and heat transfer coefficient are quite similar in air and in argon."

Computational Fluid Dynamics (CFD) is one of the fields that has strongly developed since the recent development of faster computers and numerical modeling. CFD is also finding its way into chemical engineering on several levels. We have used CFD for detailed modeling of heat and mass transfer in a packed bed. One of the major questions in CFD modeling is whether the computer model describes reality well enough to consider it a reasonable alternative to data collection. For this assumption a validation of CFD data against experimental data is desired. We have developed a low tube to particle, structured model for this purpose. Data was gathered both with an experimental setup and with an identical CFD model. These data sets were then compared to validate the CFD results. Several aspects in creating the model and acquiring the data were emphasized. The final result in the simulation is dependent on mesh density (model detail) and iteration parameters. The iteration parameters were kept constant so they would not influence the method of solution. The model detail was investigated and optimized, too much detail delays the simulation unnecessarily and too little detail will distort the solution. The amount of data produced by the CFD simulations is enormous and needs to be reduced for interpretation. The method of data reduction was largely influenced by the experimental method. Data from the CFD simulations was compared to experimental data through radial temperature profiles in the gas phase collected directly above the packed bed. It was found that the CFD data and the experimental data show quantitatively as well as qualitatively comparable temperature profiles, with the used model detail. With several systematic variances explained CFD has shown to be an ample modeling tool for heat and mass transfer in low tube to particle (N) packed beds.