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<p> Experiments were performed to investigate the effect that a gap between a heated fin and a porous plate has on the heat transfer performance of a simulated capillary evaporator. The heat transfer performance was examined for two porous plates with average pore radii of 50 and 200 μm respectively. Tests were performed for gap distances between 0 and 900 μm and heat fluxes ranging from 17 to 260 kW/m^2. The heat transfer performance of the simulated capillary evaporator initially increased as the gap distance was increased. However, a further increase in the gap distance caused a decrease in performance. The maximum heat transfer performance occurred at a smaller gap distance for the plate with the smaller pore radius. For small gap distances, persistent high temperature regions were observed on the surface of the heated foil that grew and became more frequent at higher heat fluxes. For larger gap distances, saturated regions that appeared on the foil at moderate heat fluxes suggest that microlayer evaporation may be taking place within the gap. At high heat fluxes, these saturated regions are no longer present, but the temperature of the heated foil remained stable.</p> <p> The heat transfer process in the porous media was examined using thermocouples embedded within the porous plates. These temperature measurements indicate that a two phase region forms within the porous plate for a pore radius of 200 μm. Little evidence of vapour was observed within the plate with a pore radius of 50 μm. In that case, there was more evidence of vapour present at the surface of the porous plate. There was less evidence of vapour at the surface of the porous plate for the larger gap distances, suggesting that the vapour escapes more easily through the gap at larger gap distances.</p> / Thesis / Master of Applied Science (MASc)

Industrial and mining sectors are amongst the largest single energy consumers in South Africa, making them a primary focus for implementing energy saving initiatives. Refrigeration systems on mines are responsible for consuming up to25 % of the electrical energy consumption on a typical South African deep level mine. Ample opportunities to reduce the energy consumption of these systems exists, as many of the current systems rely on old technology and function under partial or inadequate control management. In compiling this thesis, various energy saving strategies on deep level mines were investigated. In specific, the effects of controlling and improving the cooling auxiliaries. Scenarios were investigated and simulated, where after an optimum solution was implemented. Implementations, such as the ones covered in this dissertation, form part of the IDM (Integrated Demand Management) energy efficiency incentive introduced by Eskom, where funding is made available based on actual power saving; ensuring that the projects will be financially viable to the clients. Reduced electrical energy consumption realised from the abovementioned projects were measured, captured and compared to the consumption before project implementation to determine the achieved savings. Savings of up to 30 % of the plant installed capacity were realised, providing average savings of up to 2.3 MW per day. / Thesis (MIng (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2013

Industrial and mining sectors are amongst the largest single energy consumers in South Africa, making them a primary focus for implementing energy saving initiatives. Refrigeration systems on mines are responsible for consuming up to25 % of the electrical energy consumption on a typical South African deep level mine. Ample opportunities to reduce the energy consumption of these systems exists, as many of the current systems rely on old technology and function under partial or inadequate control management. In compiling this thesis, various energy saving strategies on deep level mines were investigated. In specific, the effects of controlling and improving the cooling auxiliaries. Scenarios were investigated and simulated, where after an optimum solution was implemented. Implementations, such as the ones covered in this dissertation, form part of the IDM (Integrated Demand Management) energy efficiency incentive introduced by Eskom, where funding is made available based on actual power saving; ensuring that the projects will be financially viable to the clients. Reduced electrical energy consumption realised from the abovementioned projects were measured, captured and compared to the consumption before project implementation to determine the achieved savings. Savings of up to 30 % of the plant installed capacity were realised, providing average savings of up to 2.3 MW per day. / Thesis (MIng (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2013

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>

Made available in DSpace on 2017-07-21T20:42:41Z (GMT). No. of bitstreams: 1 ADRIANO BORGES MARTINS DA SILVA.pdf: 3121513 bytes, checksum: 07dee82c52a009778c436836023d7495 (MD5) Previous issue date: 2013-08-30 / The Kraft pulping process responsible for producing more than 130 million tons / year of all pulp produced in the world, is widely spread due to recycling of the chemicals used in pulping, NaOH and Na2S and co-generation of energy and steam for the chemical recovery process, where the residual weak black liquor from the wood cooking, is transformed into heavy black liquor by water evaporation and concentration of the liquor. Evaluating the chemical composition and the difference in solids caused by the water evaporation liquor has been proposed to study the corrosion process caused by the presence of black liquor in different types of metals used in evaporation plant, evaluating the physico-chemical properties of the black liquor in two distinct points of the evaporation plant, the impact caused by the effect of the presence of black liquor in 1020 alloy steel, stainless steel 304L and SAF 2205 duplex and compare the corrosion rate and polarization resistance experienced by the 1020 steel, stainless steel 304L and SAF 2205 duplex at two different concentrations. For verification of corrosion rate, electrochemical concepts were used according to the method ASTM G59-97, where electrodes were fabricated with three types of steels to be studied, the latter being immersed in the solution of black liquor, and evaluated their respective corrosion rates. In all conditions studied the 1020 alloy steel showed the worst corrosion rate and polarization resistance among the studied metals. For the 304L stainless steel and SAF 2205 duplex stainless steel both have acceptable corrosion rates for use with small additions between certain situations between 304L and SAF 2205 duplex steels, but as corrosion rates remained near the various situations studied so it is necessary to evaluate the financial viability of the application of one of the two leagues in the process. / O processo de polpação KRAFT responsável pela produção de mais de 130 milhões de toneladas/ano de toda celulose produzida no mundo, é amplamente difundido devido à reciclagem dos produtos químicos utilizados na polpação, NaOH e Na2S e a co-geração de energia e vapor durante o processo de recuperação química, onde o licor negro fraco residual do cozimento da madeira é transformado em licor negro forte, pela evaporação da água e concentração deste licor. Avaliando a composição química e a diferença no teor de sólidos ocasionado pela evaporação da água do licor foi proposto estudar o processo corrosivo causado pela presença de licor negro em diferentes tipos de metais utilizados em planta de evaporação, avaliando as propriedades físico-químicas do licor negro em dois pontos distintos da planta de evaporação, o impacto causado pelo efeito da presença de licor negro em ligas de aço 1020, aços inoxidáveis 304L e duplex SAF 2205 e comparar a taxa de corrosão e a resistência de polarização sofrida pelo aço 1020, aços inoxidáveis 304L e duplex SAF 2205 em duas concentrações diferentes. Para verificação da taxa de corrosão, foram utilizados conceitos eletroquímicos conforme a metodologia ASTM G59-97, onde foram confeccionados eletrodos com os três tipos de aços a serem estudados, sendo estes imersos na solução de licor negro, e avaliados suas respectivas taxas de corrosão e resistência de polarização. Em todas as condições estudadas o aço 1020 apresentou a pior taxa de corrosão entre os metais estudados. Para os aços inoxidáveis 304L e duplex SAF 2205, os dois apresentam taxas de corrosão aceitáveis para sua utilização, com pequenas vantagens entre determinadas situações entre os aços 304L e o duplex SAF 2205, porém como as taxas de corrosão se mantiveram próxima nas várias situações estudadas assim é necessário avaliar a viabilidade financeira da aplicação de uma das duas ligas em processo.

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.

Submitted by Nara Lays Domingues Viana Oliveira (naradv) on 2015-06-23T18:20:38Z No. of bitstreams: 1 DANIELDEITOS.pdf: 2301580 bytes, checksum: 0e88198dccb50c04a43cba524f61d255 (MD5) / Made available in DSpace on 2015-06-23T18:20:38Z (GMT). No. of bitstreams: 1 DANIELDEITOS.pdf: 2301580 bytes, checksum: 0e88198dccb50c04a43cba524f61d255 (MD5) Previous issue date: 2012-06 / Banco Santander / Banespa / Este trabalho apresenta uma análise do desempenho hidráulico do lado do escoamento do ar de uma nova geometria de tubos para evaporadores de túneis de congelamento. Estes evaporadores são trocadores de calor de tubo-aletados e fluxo cruzado. A nova geometria dos tubos consiste em um perfil tipo gota, que é testada e comparada com tubos circulares, já estudados e com resultados disponíveis na literatura. O objetivo do trabalho é determinar experimentalmente valores para perda de carga para as duas geometrias, comparar os resultados e apontar a geometria que apresenta as melhores características de perda de carga. É apresentada uma ampla revisão feita na literatura disponível sobre estudos realizados com relação ao efeito de diversos parâmetros no desempenho destes trocadores de calor, entre eles a geometria dos tubos, e os resultados indicam que tubos elípticos e achatados apresentam melhor desempenho térmico e menor perda de carga quando comparados com os tradicionais tubos circulares. O procedimento de cálculo para perda de carga para trocadores de calor tubo-aletados, também é apresentado. Para os evaporadores testados, foram mantidos constante o espaçamento entre tubos e o espaçamento entre aletas, variando apenas a geometria do tubo. As aletas usadas foram do tipo plana. Os testes foram realizados em túnel de vento construído em conformidade com a norma ANSI/ASHRAE 51-1999. Um ventilador gera um fluxo de ar que passa pela serpentina aletada e uma placa de bocais. Para diferentes velocidades de ar são obtidas a perda de carga no trocador de calor, as temperaturas médias de entrada e saída para o ar, a velocidade e a vazão de ar. Os resultados da perda de carga em função da velocidade do ar mostram que os tubos tipo gota tem desempenho hidráulico superior aos tubos circulares. Foi obtida uma redução média da perda de carga de 26% e do fator de atrito de 16%, comparando o tubo tipo gota com o tubo circular, para os ensaios realizados com regimes de escoamento que vão do laminar ao de transição. Uma análise da potência de ventilação mostrou novamente uma vantagem dos tubos tipo gota e na análise de uma situação real para um modelo de túnel de congelamento, os tubos tipo gota apresentaram uma redução da potência de ventilação total de 12,87%, quando comparado com os tubos circulares. Os modelos são ferramentas importantes para o projeto de trocadores de calor, assim foram analisadas diferentes correlações para predição do coeficiente de atrito do escoamento do ar através das aletas e comparadas com os dados experimentais. Verificou-se que a correlação de Gray e Webb (1986) foi a que melhor se ajustou, com um erro médio de 15% e a dispersão entre os valores medidos e calculados de 31% para tubos circulares e de 50% para o tipo gota. / This study presents an analysis of hydraulic performance of the air side for a new tube geometry of evaporators used in freezing tunnel. These evaporators are heat exchangers with finned tubes and air in cross flow. The new geometry consists in a wing profile tube that is tested and compared to circular tubes, which are already studied and with available results in literature. The objective of this work is determining experimentally the pressure drop for both geometries, comparing the results and pointing out the geometry that shows the best features for pressure drop. A comprehensive literature review is also presented and it focuses on studies concerning the effects of several parameters in these heat exchangers performance, including tube geometry. Several results have shown that elliptical tubes have better thermal performance and lower pressure drop when compared to the conventional circular tube. A review of the procedures calculation for fin-tube heat exchangers pressure drop is shown. For the evaporators tested, the spacing between tubes and fins, was kept constant by varying only the tube geometry and the fins were flat. The tests were carried out in a wind tunnel, built in accordance with ANSI/ASHRAE 51-1999. A fan generates an air flow that passes through the finned coil and a nozzle plate. For different air velocities and the pressure drop in the heat exchanger, input and output average air temperature, the velocity and flow of the air were registered. The results showed the dependence on the air velocity and that wing profile tubes have better hydraulic performance than circular tubes. An average reduction of 26% for pressure drop and 16% for friction factor for wing tubes were obtained in comparison to circular tubes, in tests in the regimes from laminar to transition flow. An analysis of ventilation power showed the advantage of wing tubes, and the evaluation of a real situation, on a freezing tunnel, the wing tubes show an average reduction of 12,87 % for total ventilation power when compared with circular tubes. The theoretical models are important tools for designing the evaporator, and in this study some correlations were evaluated to prediction of the air flow friction factor and were compared to experimental results. The Gray and Webb correlation (1986) presented the best fit, with 15% of average error and the dispersion between the measured and calculate values was 31% for circular tubes and 50% for wing tubes.

Orientador: André Luiz Seixlack / Resumo: Evaporadores são trocadores de calor usados em sistemas de refrigeração com a função de transferir calor do ambiente a ser refrigerado. As baixas temperaturas de operação desses trocadores de calor favorecem a formação de geada sobre suas superfícies. O acúmulo de geada, dependendo de sua espessura, pode reduzir a capacidade de refrigeração do evaporador e, consequentemente, reduzir também o desempenho do sistema de refrigeração. Neste trabalho apresenta-se um modelo distribuído para analisar a influência da formação e do adensamento de geada sobre o desempenho de evaporadores do tipo tubo-aletado, comumente usados em refrigeradores frost-free. O escoamento do fluido refrigerante no interior dos tubos é considerado unidimensional e dividido em duas regiões: uma de escoamento bifásico e outra de vapor superaquecido. A queda de pressão do escoamento no interior dos tubos é considerada. As equações fundamentais de conservação da massa, da quantidade de movimento e de conservação de energia são usadas para modelar o escoamento do fluido refrigerante. Na região bifásica o escoamento é analisado segundo o modelo homogêneo. A equação da conservação da energia na parede do tubo também é resolvida, para o cálculo da distribuição de temperatura ao longo dessa parede. Do lado do ar, os princípios de conservação da massa, quantidade de movimento e de conservação da energia são empregados para simular a formação e crescimento da geada sobre a superfície do evaporador. O sistema de equaçõe... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Evaporators are heat exchangers of the refrigeration systems used to transfer heat from the refrigerated environment. Their low operating temperatures favour the frost formation on their surfaces. Frost accumulation, depending on its thickness, can reduce the evaporator cooling capacity and, consequently, also reduce the refrigeration system performance. This work presents a distributed model to analyze the influence of formation and frost densification on the performance of tube-finned evaporators, commonly used in “no-frost” household refrigerators. The refrigerant flow inside the tubes is taken as one-dimensional and divided in a two-phase flow region and a superheated vapor flow region. The pressure drop inside the tubes is considered. The fundamental equations of mass conservation, momentum, and energy conservation are used in order to model the refrigerant flow. The homogeneous flow model is employed for the two-phase flow region. The energy conservation equation for the evaporator tube wall is also solved to obtain of wall temperature distribution. On the air side, the principles of mass conservation, momentum and conservation of energy are employed to simulate the formation and frost growth on the evaporator surface. The system of equations is integrated numerically and solved iteratively by successive substitutions. Comparisons between numerical results obtained in this work and experiments available in open literature show good agreement. Considering the entire rang... (Complete abstract click electronic access below) / Mestre

This thesis investigates the performance of compact brazed plate heat exchangers (CBE) operating as evaporator in heat pump applications. The thesis, and the performances investigated, has been divided into three main sections; One zone evaporator performance; Two zone evaporator performance; and finally Local performance. The 'One zone evaporator performance' section considers the evaporator as one "black box". It was found that "approaching terminal temperatures" were obtained as low overall heat flux is employed. It was also found that the total area averaged film heat transfer coefficient was affected by changes of the brine mass flow rate. This indicates that the widespread Wilson plot method may not be used to determine flow boiling heat transfer coefficients. Further, it seems that co- and counter-current flow configuration performs equally well if the superheat is kept low. A numerical simulation of the above investigations indicates that a nucleate boiling model better predicts the performance compared to a convective evaporation model. Finally, the significant impact of the refrigerant inlet distributor design was illustrated using several CBEs with different inlet geometries but with identical heat transfer surfaces. The 'Two zone evaporator performance section' considers the evaporator as two "black boxes", i.e. the boiling and superheating boxes. Thermochromic liquid crystals (TLC) was used to determine the boiling heat transfer area. The resulting flow boiling heat transfer coefficient was found to correlate with heat flux. The superheated heat transfer area was then estimated using single phase correlations. It was observed that the TLC measurements and the predicted superheating area did not agree. Possible causes for this deviation were discussed. The most likely explanation found was the presence of mist flow at the higher vapor quality range in the boiling section of the evaporator. The 'Local Performance' section considers local pressure drop and flow boiling heat transfer. The Chisholm parameter was found not to be a constant and was found to correlate well with the kinetic energy per volume. The resulting predictions of the pressure drop were better than ± 10%. The resulting local flow boiling heat transfer coefficient, at different vapor quality, mass flux and heat flux, was compared to flow boiling correlations available in the literature. It was found that the saturated nucleate pool boiling correlation by Cooper (1984) and narrow channel flow boiling correlations (Tran 1999, Lazarek and Black 1982) predicted the experimental data better than several traditional flow boiling correlations, developed for larger tubes. / QC 20100524