PhD, Faculty of Engineering and the Built Environment, University of the Witwatersrand / In this study the heat transfer and frictional pressure drop performance characteristics of plate heat exchangers (PHE’s) used as refrigerant liquid overfeed evaporators were investigated. PHE’s have been gaining new applications in the refrigeration industry, especially as evaporators, during the last few decades, but the available information in the open literature for operation in this mode is rather limited. This study aims to extend the knowledge of PHE evaporator performance and to develop a model for use in evaluating heat transfer and pressure drop over as wide a range of operating conditions as possible. A laboratory experimental facility was constructed and the thermal-hydraulic characteristics of three middle-size industrial PHE’s were measured. The exchangers all had 24 plates of the same size but with different chevron angle combinations of 28°/28°, 28°/60°, and 60°/60°. Two sets of tests were carried out with the three units: single-phase performance tests with water, and evaporator performance tests with R134a and R507A, for which the exchangers operated as refrigerant liquid over-feed evaporators. The tests with water served to provide accurate water-side heat transfer information for the evaporator performance analysis which is the primary purpose of this study. In the evaporator performance tests, refrigerant flow boiling heat transfer and two-phase pressure drop data were obtained under steady conditions, over a range of heat flux from 1.9 to 6.9 kW/m2, refrigerant mass flux from 5.6 to 31.4 kg/(m2s), outlet vapour quality from 0.2 to 0/95, and saturation temperatures from 5.9 to 13.0 °C. Additional field data of thermal performance were collected on an ammonia and a R12 PHE water chiller, operating as thermo-siphon evaporators at their design working conditions. All experimental data were reduced and analyzed to obtain the refrigerant-side heat transfer coefficients and frictional pressure drops in the PHE evaporators. The heat transfer results showed a strong dependence on heat flux and a weak dependence on mass flux, vapour fraction and the chevron angle. Along with the ii observations from the ammonia and R12 evaporators, it is concluded that the dominating heat transfer mechanism in this type of evaporator is nucleate boiling rather than forced convection. In contrast to the heat transfer characteristics, the refrigerant two-phase frictional pressure drop was found to be strongly influenced by mass flow rate, vapour fraction and also the chevron angle. An almost linear increase of the frictional pressure drop with the homogeneous two-phase kinetic energy per unit volume was observed for both refrigerants. Based on the experimental data, correlations were developed for predicting the refrigerant boiling heat transfer coefficient and two-phase frictional pressure drop in PHE liquid over-feed evaporators. Two correlations were developed for boiling heat transfer, one of these reflecting the h-q relationship in pool boiling, the other with all constants and exponents determined by regression analysis. The mean absolute errors are respectively 7.3% and 6.8% for these correlations. For two-phase frictional pressure drop, data were correlated using two established methods, namely the homogeneous and the Lockhart-Martinelli methods, with means absolute errors of 6.7% and 4.2%, respectively. The homogeneous model showed a slightly higher discrepancy with the experimental data but is likely to be more physically sound for PHE evaporators, and is much simpler to apply. Validation of these correlations with other data has been difficult due to the shortage of published information. For other refrigerants operating at comparable conditions, these correlations should serve as a guide, while more accurate design or evaluation may need to be based on further testing. The performance analysis carried out in this study was based on systematic experimental investigations and field tests on industrial PHE units. Correlations were developed covering a rather extensive range of flow parameters, plate geometry and various refrigerants. Such correlations have not been reported previously for PHE liquid over-feed evaporators. The results simplify the performance analysis of PHE evaporators and provide a reliable thermalhydraulic model of PHE liquid over-feed evaporators, which can be used for system modeling of water-chilling machines employing this type of evaporator.

Este trabalho visa a utilização de técnicas de otimização para a determinação da melhor configuração para trocadores de calor a placas. A configuração de um trocador a placas define a distribuição das correntes quente e fria ao longo dos seus canais e ela é definida pelo seu número de canais, pelos números de passes em cada lado e pelas localizações dos fluidos e das conexões de alimentação. É utilizado um conjunto de seis parâmetros para a caracterização da configuração. A modelagem estacionária do trocador é desenvolvida na forma de um algoritmo, já que não é possível representá-la como uma função explícita dos seis parâmetros de configuração. O sistema resultante é composto por equações diferenciais ordinárias de valor de contorno e por equações algébricas não-lineares, o qual é resolvido numericamente pelo método de diferenças finitas. Através do estudo de exemplos de simulação, verifica-se que a hipótese de constância do coeficiente global de troca térmica não é limitante para a avaliação global do trocador. A validação experimental da modelagem estacionária é realizada através da estimação de parâmetros de troca térmica para um conjunto de ensaios com diferentes configurações. É ainda apresentada a modelagem dinâmica do trocador a placas para configurações genéricas, visando a análise do seu estado transiente e a simulação de malhas de controle. É proposto um procedimento de screening para a resolução do problema de otimização da configuração do trocador. Neste procedimento, as restrições são aplicadas sucessivamente para a eliminação de elementos inviáveis ou não-ótimos. Através da identificação de configurações equivalentes e da realização de uma busca estruturada, todos os trocadores com a menor área de troca térmica podem ser obtidos com esforço computacional bastante reduzido. O funcionamento e a eficiência do método são analisados em detalhes através de dois casos de otimização. Para o caso dos processos de pasteurização, que usam trocadores com múltiplas seções, é proposto o método de branching para otimização da configuração das seções de aquecimento, resfriamento e regeneração. Este método consiste em um algoritmo de busca muito eficiente, capaz de localizar as configurações que apresentam mínimos custos fixos e operacionais realizando um número extremamente reduzido de avaliações das seções do trocador, em relação às grandes dimensões do problema e sua complexidade. / The aim of this work is to develop optimization techniques for determining the best configuration of gasketed plate heat exchangers. The configuration of a plate heat exchanger defines the distribution of the hot and cold streams inside the plate-pack and it is defined by the number of channels, by the number of passes in each side and by the locations of the fluids and feed connections. A set of six parameters is used for the configuration characterization. The steady-state model of the plate heat exchanger is formulated in an algorithmic form, since it is not possible to represent it explicitly as a function of the six configuration parameters. The resulting system is composed of ordinary differential equations of the boundary value type and non-linear algebraic equations, which is numerically solved with the method of finite differences. The analysis of several simulation examples showed that the assumption of constant overall heat transfer coefficient is not limiting for the overall rating of the heat exchanger. The experimental validation of the steady-state model was accomplished through the estimation of heat transfer parameters for a set of experiments with different configurations. Moreover, the dynamic modeling of the plate heat exchanger is presented intending the simulation of unsteady-state operation and the use of controllers. A screening procedure is proposed for determining the best configuration of the exchanger. In this procedure, the constraints are successively used to eliminate unfeasible and non-optimal cases. Using a structured search method and identifying the equivalent configurations, all the exchangers with the smallest heat exchange area can be obtained employing the proposed method with very reduced computational effort. The performance of the method is studied thoroughly through two optimization example problems. For the case of the pasteurization processes, where the plate heat exchangers have multiple sections, it is proposed a branching method for selecting the best configuration for the heating, cooling and regeneration sections. This method consists of a very efficient search algorithm, able to locate the configurations with minimum fixed and operational costs requiring an extremely reduced number of exchanger evaluations, considering the large dimensions of the problem and its complexity.

Este trabalho visa a utilização de técnicas de otimização para a determinação da melhor configuração para trocadores de calor a placas. A configuração de um trocador a placas define a distribuição das correntes quente e fria ao longo dos seus canais e ela é definida pelo seu número de canais, pelos números de passes em cada lado e pelas localizações dos fluidos e das conexões de alimentação. É utilizado um conjunto de seis parâmetros para a caracterização da configuração. A modelagem estacionária do trocador é desenvolvida na forma de um algoritmo, já que não é possível representá-la como uma função explícita dos seis parâmetros de configuração. O sistema resultante é composto por equações diferenciais ordinárias de valor de contorno e por equações algébricas não-lineares, o qual é resolvido numericamente pelo método de diferenças finitas. Através do estudo de exemplos de simulação, verifica-se que a hipótese de constância do coeficiente global de troca térmica não é limitante para a avaliação global do trocador. A validação experimental da modelagem estacionária é realizada através da estimação de parâmetros de troca térmica para um conjunto de ensaios com diferentes configurações. É ainda apresentada a modelagem dinâmica do trocador a placas para configurações genéricas, visando a análise do seu estado transiente e a simulação de malhas de controle. É proposto um procedimento de screening para a resolução do problema de otimização da configuração do trocador. Neste procedimento, as restrições são aplicadas sucessivamente para a eliminação de elementos inviáveis ou não-ótimos. Através da identificação de configurações equivalentes e da realização de uma busca estruturada, todos os trocadores com a menor área de troca térmica podem ser obtidos com esforço computacional bastante reduzido. O funcionamento e a eficiência do método são analisados em detalhes através de dois casos de otimização. Para o caso dos processos de pasteurização, que usam trocadores com múltiplas seções, é proposto o método de branching para otimização da configuração das seções de aquecimento, resfriamento e regeneração. Este método consiste em um algoritmo de busca muito eficiente, capaz de localizar as configurações que apresentam mínimos custos fixos e operacionais realizando um número extremamente reduzido de avaliações das seções do trocador, em relação às grandes dimensões do problema e sua complexidade. / The aim of this work is to develop optimization techniques for determining the best configuration of gasketed plate heat exchangers. The configuration of a plate heat exchanger defines the distribution of the hot and cold streams inside the plate-pack and it is defined by the number of channels, by the number of passes in each side and by the locations of the fluids and feed connections. A set of six parameters is used for the configuration characterization. The steady-state model of the plate heat exchanger is formulated in an algorithmic form, since it is not possible to represent it explicitly as a function of the six configuration parameters. The resulting system is composed of ordinary differential equations of the boundary value type and non-linear algebraic equations, which is numerically solved with the method of finite differences. The analysis of several simulation examples showed that the assumption of constant overall heat transfer coefficient is not limiting for the overall rating of the heat exchanger. The experimental validation of the steady-state model was accomplished through the estimation of heat transfer parameters for a set of experiments with different configurations. Moreover, the dynamic modeling of the plate heat exchanger is presented intending the simulation of unsteady-state operation and the use of controllers. A screening procedure is proposed for determining the best configuration of the exchanger. In this procedure, the constraints are successively used to eliminate unfeasible and non-optimal cases. Using a structured search method and identifying the equivalent configurations, all the exchangers with the smallest heat exchange area can be obtained employing the proposed method with very reduced computational effort. The performance of the method is studied thoroughly through two optimization example problems. For the case of the pasteurization processes, where the plate heat exchangers have multiple sections, it is proposed a branching method for selecting the best configuration for the heating, cooling and regeneration sections. This method consists of a very efficient search algorithm, able to locate the configurations with minimum fixed and operational costs requiring an extremely reduced number of exchanger evaluations, considering the large dimensions of the problem and its complexity.

Fouling in general and biofouling in specific is a problem concerning many industries. Biofouling occur in environments favorable for biological growth. As an example, industries using cooling water have problems with biofouling. The problem is apparent on heat exchangers as biofilm reduces the heat transfer and thus the performance. There are several different methods to reduce fouling on tube and shell heat exchanger on the market. However, for plate heat exchanger the alternatives are fewer. Generally, cleaning is performed by opening the heat exchanger and cleaning the plates one by one. This thesis aimed to present some of the biofouling reducing methods available on the market, and principally methods that could be applied on plate heat exchangers. Two of the methods were selected to be evaluated in experimentally; Advanced Oxidizing Technology (AOT) and ultrasound. The performances were evaluated by semi quantifying the amount of produced biofilm on plates of stainless steel, polystyrene and titanium. The plates were either reference plates, i.e. under no influence of some reducing method, or they were submerged in the tank when ultrasound or AOT were under operation. The test with ultrasound was performed once, whereas the test with AOT was performed twice. Ultrasound showed the best result; by reducing the amounts of produced biofilm from 68-100 % on all the plates, independent of the material used. AOT showed ambiguous results. From the first test it seemed to affect the production of biofilm, whereas in the second test it did not proof to have the same affect. / Påväxt i allmänhet och biologisk påväxt i synnerhet är ett problem som finns i många industrier/områden inom industrin. Biofilmstillväxt förekommer i miljöer gynnsam för biologisk tillväxt. Till exempel har industrier som använder kylvatten problem med biofilmstillväxt. På värmeväxlare visar sig problemet i form av sämre effektivitet genom försämrad värmeledningsförmåga. Det finns flera olika metoder för tillväxt att förhindra eller motverka tillväxt i tubvärmeväxlare. För plattvärmeväxlare är alternativen däremot färre. Generellt rengörs värmeväxlaren genom att denna öppnas och att plattorna rengörs en efter en. Syftet med detta examensarbete var att presentera några av de metoder som finns på marknaden för att minska och ta bort biologisktillväxt, och då främst metoder som går att använda på plattvärmeväxlare. Två av metoderna valdes ut och testades; Advanced Oxidizing Technology (AOT) och ultraljud. Metoderna utvärderades genom en semi- kvantitativ analys av mängd producerad biofilm på plattor gjorda av rostfritt stål, polystyren och titan. Dessa plattor var antingen referensplattor, det vill säga utan inverkan av någon reduceringsmetod, eller så var de nedsänkta i tankar fyllda med vatten där respektive metod hade verkat. Testet med ultraljud utfördes en gång, medan testet med AOT utfördes två gånger. Ultraljud visade sig vara bäst på att reducera biofilmstillväxt; med en reducering på 68 till 100 %. Oberoende av material minskade ultraljud tillväxten på samtliga plattor. AOT visade tvetydiga resultat; från det första testet tycktes det påverka produktionen av biofilm, medan den inte visade lika tydliga resultat i det andra testet.

In winter it is common with frost formation in plate heat exchangers. During defrosting, the heat recovery efficiency decreases and the heat rate requirement for post-heating increases. One way to avoid frost formation is to preheat the ventilation air with geothermal energy, a so-called GeoMVHR system. This study examines the profitability of eliminating the requirement for post-heating using geothermal energy to preheat the incoming ventilation air. The study evaluates the profitability for two locations in Sweden, Stockholm and Gothenburg. The method used is the internal rate of return. The heat rate requirement for post-heating in an MVHR system without geothermal outdoor preheating and the power for operating a GeoMVHR system that eliminates the requirement for post-heating is calculated. The internal rate of return was 5.7% for Gothenburg and 5.3% for Stockholm. The conclusion was that the GeoMVHR systems could be seen as a profitable investment.

Accurate forecasting is a real problem at many companies and that includes Alfa Laval in Lund. Alfa Laval experiences problems forecasting for future raw material demand. Management is aware that the forecasting methods used today can be improved or replaced by others. A change could lead to better forecasting accuracy and lower errors which means less inventory, shorter cycle times and better customer service at lower costs. The purpose of this study is to analyze Alfa Laval’s current forecasting models for demand of raw material used for pressed plates, and then determine if other models are better suited for taking into consideration trends and seasonal variation.

<p>Accurate forecasting is a real problem at many companies and that includes Alfa Laval in Lund. Alfa Laval experiences problems forecasting for future raw material demand. Management is aware that the forecasting methods used today can be improved or replaced by others. A change could lead to better forecasting accuracy and lower errors which means less inventory, shorter cycle times and better customer service at lower costs.</p><p>The purpose of this study is to analyze Alfa Laval’s current forecasting models for demand of raw material used for pressed plates, and then determine if other models are better suited for taking into consideration trends and seasonal variation.</p>

Orientadores: Vivaldo Silveira Junior, Javier Telis Romero / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-09T22:31:56Z (GMT). No. of bitstreams: 1 Bernardi_Marina_M.pdf: 337845 bytes, checksum: b22d2f1ecde63498948bfd0748a26993 (MD5) Previous issue date: 2008 / Resumo: Neste trabalho são apresentadas a hidrodinâmica e a transferência de calor no escoamento de ovo líquido integral através de dutos com paredes corrugadas, simulando trocadores de calor a placas. A condição de contorno admitida foi a de temperatura da parede constante durante o aquecimento do fluido. A reologia do ovo integral foi determinada experimentalmente em uma ampla faixa de temperaturas (289 ¿ 335K). O ovo apresentou comportamento reológico dependente do tempo, o qual foi explorado neste trabalho. Para os estudos da perda de carga e transferência de calor objetivando o dimensionamento correto de tubulações e equipamentos destinados ao transporte e processamento de fluidos tixotrópicos os parâmetros reológicos independentes do tempo foram empregados. O modelo de Ostwald-De Waelle foi ajustado às curvas reológicas experimentais desconsiderando a dependência do tempo. Foram realizadas medidas experimentais de perda de carga para a determinação do fator de atrito em função de um número de Reynolds generalizado, cujos resultados foram empregados para determinação dos parâmetros geométricos x e u para o regime laminar e dos parâmetros P1 e P2 para o regime turbulento. Esses parâmetros geométricos foram utilizados para correlacionar os coeficientes de transferência de calor convectivos experimentais com as propriedades físicas do fluido, resultando em equações formato clássico, Nusselt=Nu(Reg,Prg) / Abstract: At this work are showed the heat transference and hydrodynamics of liquid egg flow between ducts with corrugated walls, simulating plate heat exchangers. The contour conditions admitted was the constant temperature in the walls during the fluid heating. The whole egg rheology was experimentally determinated in a extend temperature range (289 ¿ 335K). The egg rheology behavior was time dependent, which was explored at the present work. However, to study the loss of load and heat transference this time dependence behavior was not considerated, because, according to Skelland, the correct sizing of equipments and tubings used to tixotropic fluid transport and processing must be done using time independent rheologic parameters. The Ostwald-De Waelle model was adjusted at the experimental rheologycal curves disrespecting the time dependence. It was realized experimental determinations of loss of load to determination of Fanning factor in function of Reynolds generalized number, and the results was used to determination of x and u geometrics parameters to laminar flow and P1 and P2 to turbulent flow. These geometrics parameters were used to correlated the experimental heat transference coefficient with the fluid physic properties resulting in equations on the classic format, Nusselt=Nu(Reg,Prg) / Mestrado / Mestre em Engenharia de Alimentos

Ce travail de recherche examine aux échelles globale et locale les caractéristiques thermo-hydrauliques au sein des échangeurs à plaques ondulées pour les écoulements monophasiques et en mode condensation. Il comprend deux parties :La première partie concerne l'analyse des structures d'écoulement en mode monophasique à partir d'un outil de simulations numériques, et dont les résultats sont validés à partir d'une campagne expérimentale. L'exploitation des résultats de simulations, à partir d'observables judicieusement sélectionnées, a permis de quantifier les grandes classes d'écoulement en fonction des paramètres géométriques et fluidiques de l'échangeur. Ce nouvel éclairement sur les structures d'écoulement a conduit à la proposition d'un modèle général original sur les lois de friction au sein de ces échangeurs de géométrie d'écoulement complexe.La deuxième partie concerne l'étude de la condensation de la vapeur avec et sans surchauffe en entrée de l'échangeur. Ainsi, un dispositif expérimental permettant le contrôle précis des conditions aux limites a été développé, et une métrologie spécifique, basée sur la thermographie infrarouge a également été mis au point, afin de remonter à certaines grandeurs locales le long du condenseur (titre de vapeur, coefficient d'échange thermique...). On observe ainsi une très forte variabilité des coefficients d'échanges thermiques et de la densité de flux de chaleur le long du condenseur, et la surchauffe de la vapeur tend à intensifier les transferts thermiques. Ce complément de mesures remet en question certaines hypothèses de la littérature quant à l'élaboration de corrélations sur les transferts de chaleur dans les condenseurs. / This research work examines at the global and local scales the thermo-hydraulic characteristics of plate heat exchangers with corrugated chevron plates, for single-phase and condensation flows. The study is divided into two parts:The first part concerns the analysis of flow structures of single-phase flows using numerical simulations, which are validated using the results of the experimental campaign. The analysis of the simulations results, from a flow characteristic observable that has been carefully chosen, has allowed quantifying the main flow categories as a function of the heat exchanger geometric parameters and the flow characteristics. This new information on the flow structures has led to the proposal of an original generalized model of the friction law inside this type of heat exchanger with complex geometry.The second part concerns the study of condensation with and without vapor superheating at the inlet of the heat exchanger. Thus, a specific experimental setup allowing precise control of the boundary conditions has been developed. Otherwise a specific metrology, based on infrared thermography, has been set to the point in order to determine the variation of certain local quantities along the condenser (vapor mass fraction, heat transfer coefficient...). Thus, we observe a high and wide variability of the heat transfer coefficients and the heat flux density along the condenser, and the superheating of the vapor tends to increase the heat transfers. These additional measures question certain assumptions of the literature regarding the development of heat transfer correlations in plate heat condensers.

This work deals with the topic "Systems with wall heating". On this theme is elaborated theoretical part. Further experimental part, which deals with the measurement of wall heating and comparing the results with the software CalA. Subsequently, this topic is applied to the specified building in which the wall heating, among other things dealt with. The project addresses the design of central heating, water heating, water heater design power units and air tempering lawn for future newly built free-standing facilities football club. The project is designed in two versions. In the first variant of the heat source heat pumps air-water. In the second variant is the heat source hot water pipe which is connected to transfer water-water station with plate heat exchangers.