Lubricants and liquid cooling are used in many industrial applications to ensure reliability and longevity of machinery. Oil cooling of both electrical and mechanical applications is of interest since oil is better suited for electrical applications than water and already available in the system as a lubricant. Brazed plate heat exchangers (BPHEs) have many advantages compared to other heat exchanger types commonly used in oil cooling applications. Flow maldistribution inside BPHEs can arise with highly viscous fluids like oil. Since flow is hard to measure when plate heat exchangers are brazed together, Computational Fluid Dynamics (CFD) can be used instead. This study investigates parameters that could affect flow distribution inside BPHEs with the CFD-tool COMSOL Multiphysics. The study is made on three different geometries at different detail levels. The purpose of the study is to expand the knowledge about fluid behavior in BPHEs and how it affects efficiency. It was proved from the Bernoulli equation that flow velocity, gravity and Reynolds number were some parameters that could affect flow distribution inside BPHEs. Two simplified models were built for evaluation of viscosity, gravity and Reynolds number. A more detailed model was provided by SWEP representing the fluid domain of a full-size distribution zone model. Model validation and mesh independence study were made with expressions due to the lack of experimental data. Investigations of viscosity, gravity and Reynolds number were made through isolation and alteration of the respective parameter. The validation and mesh independence study proved the models trustworthy and detailed enough to capture the physical behavior. Small deviations from expected validation results can be explained with the assumptions and simplifications made in the process. Results show that flow maldistribution increases with viscosity differences between channels. Viscosity maldistribution is greater for oil than for water. It is important to consider how the fluid viscosity changes with temperature under the respective working conditions. Gravity has no effect on flow distribution as long as it acts along or opposite the main flow direction. As plate heat exchangers are generally placed vertically, gravity will not affect flow distribution. Gravity has a significant effect on flow distribution if plate packages are places horizontally. High Reynolds numbers have a positive effect on flow distribution and reduce the difference between highest and lowest velocities across the outlet. Very low flow velocities should therefore be avoided since it increases flow maldistribution.

É apresentado um estudo de distribuição do tempo de residência nas etapas de um processo de pasteurização contínuo por trocador de calor a placas (aquecimento, resfriamento, regeneração e retenção). Para o estudo experimental, foi adotada a técnica condutimétrica usando cloreto de sódio em solução aquosa como traçador. Foram verificadas as influências da vazão, da configuração do trocador de calor a placas (número de passes para o arranjo em série) e do tipo de tubo de retenção (tubo em \"S\" e tubo helicoidal). Modelos de distribuição foram usados para representar o comportamento experimental (dispersão axial, tanques em série, laminar modificado, combinado PFR+CSTR). Este estudo foi aplicado para as condições de pasteurização HTST de leite, visando a futura implementação de uma modelagem matemática rigorosa do processo, para otimização do projeto e operação do processo. / It is presented a study of residence time distribution in the steps of a process of continuous pasteurization by plate heat exchanger (heating, cooling, regeneration and holding). For the experimental study, it was adopted a conductimetric technique using sodium chloride in aqueous solution as a tracer. It was also studied the influence of the flow rate, the configuration of the plate heat exchanger (number of passes in series arrangement) and the type of holding tube (\"S\"- shaped tube and helicoidal tube). Distribution models were used for representing the experimental behavior (axial dispersion, tank in series, modified laminar, combined PFR+CSTR). This study was applied for the conditions of HTST pasteurization of milk, targeting the future implementation of a rigorous mathematical modeling of the process, which can be applied for the process operation and optimization of the project design.

O principal objetivo do trabalho foi desenvolver uma ferramenta de simulação, para servir de base para o projeto e dimensionamento de processos contínuos de pasteurização de alimentos líquidos em trocadores de calor a placas, possibilitando minimizar perdas de qualidade sensorial e nutricional, bem como gastos desnecessários com aquecimento e resfriamento, decorrentes do sobreprocessamento, tendo o controle sobre o histórico de temperatura. Foi desenvolvida uma modelagem matemática para o processo contínuo de pasteurização HTST (High Temperature Short Time) de leite em trocador de calor a placas com três seções, para determinação da distribuição de temperatura ao longo do processo e avaliação do impacto sobre o leite. Foram desenvolvidos três modelos e seus resultados confrontados com os dados experimentais, realizados com água e leite. Os três modelos forneceram resultados similares e próximos ao comportamento experimental. O cálculo de letalidade permitiu detectar sobreprocessamento no processo estudado. Ensaios com indicador enzimático (fosfatase alcalina em tampão fosfato) foram realizados para quantificar o impacto do processo sobre o produto e comparar com a letalidade calculada pelos modelos. / The aim of this work was to develop a simulation tool to be used in the design of continuous pasteurization of liquid foods using plate heat exchangers, enabling to minimize the nutritional and sensorial losses as well as unnecessary costs during heating and cooling, caused by the overprocessing. The control is made by the temperature profile. A mathematical model was developed for continuous milk HTST (High Temperature Short Time) pasteurization with a three section plate heat exchanger to determine the temperature profile and to evaluate the process impact on the product. Three models were tested and the simulation results compared with the experimental data using water and milk. The results of the three models were similar among them and close to the experimental behavior. Calculating the lethality of the process showed it was overprocessing the product. Tests using enzymatic indicator (alkaline phosphatase in phosphate buffer) were held to quantify the impact of the process on the product and compare to the lethality calculated using the models.

The heat flux demands for electronics cooling applications are quickly approaching the limits of conventional thermal management systems. To meet the demand of next generation electronics, a means for rejecting high heat fluxes at low temperatures in a compact system is an urgent need. To answer this challenge, in this work a gasketed chevron plate heat exchanger in conjunction with a slurry consisting of highly endothermic solid ammonium carbamate and a heat transfer fluid. A reduced-order 1-dimensional model was developed and used to solve the coupled equations for heat, mass, and momentum transfer. The feasibility of this chosen design for satisfying the heat rejection load of 2kW was also explored in this study. Also, a decomposition reaction using acetic acid and sodium bicarbonate was conducted in a plate heat exchanger (to simulate a configuration similar to the ammonium carbamate reactions). This enabled the experimental validation of the numerical predictions for the momentum transfer correlations used in this study (which in turn, are closely tied to both the heat transfer correlations and chemical kinetics models). These experiments also reveal important parameters of interest that are required for the reactor design. A numerical model was developed in this study and applied for estimating the reactor size required for achieving a power rating of 2 kW. It was found that this goal could be achieved with a plate heat exchanger weighing less than 70 kg (~100 lbs) and occupying a volume of 29 L (which is roughly the size of a typical desktop printer). Investigation of the hydrodynamic phenomena using flow visualization studies showed that the flow patterns were similar to those described in previous studies. This justified the adaptation of empirical correlations involving two-phase multipliers that were developed for air-water two-phase flows. High-speed video confirmed the absence of heterogeneous flow patterns and the prevalence of bubbly flow with bubble sizes typically less than 0.5 mm, which justifies the use of homogenous flow based correlations for vigorous gas-producing reactions inside a plate heat exchanger. Absolute pressure measurements - performed for experimental validation studies - indicate a significant rise in back pressure that are observed to be several times greater than the theoretically estimated values of frictional and gravitational pressure losses. The predictions from the numerical model were found to be consistent with the experimental measurements, with an average absolute error of ~26%

O principal objetivo do trabalho foi desenvolver uma ferramenta de simulação, para servir de base para o projeto e dimensionamento de processos contínuos de pasteurização de alimentos líquidos em trocadores de calor a placas, possibilitando minimizar perdas de qualidade sensorial e nutricional, bem como gastos desnecessários com aquecimento e resfriamento, decorrentes do sobreprocessamento, tendo o controle sobre o histórico de temperatura. Foi desenvolvida uma modelagem matemática para o processo contínuo de pasteurização HTST (High Temperature Short Time) de leite em trocador de calor a placas com três seções, para determinação da distribuição de temperatura ao longo do processo e avaliação do impacto sobre o leite. Foram desenvolvidos três modelos e seus resultados confrontados com os dados experimentais, realizados com água e leite. Os três modelos forneceram resultados similares e próximos ao comportamento experimental. O cálculo de letalidade permitiu detectar sobreprocessamento no processo estudado. Ensaios com indicador enzimático (fosfatase alcalina em tampão fosfato) foram realizados para quantificar o impacto do processo sobre o produto e comparar com a letalidade calculada pelos modelos. / The aim of this work was to develop a simulation tool to be used in the design of continuous pasteurization of liquid foods using plate heat exchangers, enabling to minimize the nutritional and sensorial losses as well as unnecessary costs during heating and cooling, caused by the overprocessing. The control is made by the temperature profile. A mathematical model was developed for continuous milk HTST (High Temperature Short Time) pasteurization with a three section plate heat exchanger to determine the temperature profile and to evaluate the process impact on the product. Three models were tested and the simulation results compared with the experimental data using water and milk. The results of the three models were similar among them and close to the experimental behavior. Calculating the lethality of the process showed it was overprocessing the product. Tests using enzymatic indicator (alkaline phosphatase in phosphate buffer) were held to quantify the impact of the process on the product and compare to the lethality calculated using the models.

É apresentado um estudo de distribuição do tempo de residência nas etapas de um processo de pasteurização contínuo por trocador de calor a placas (aquecimento, resfriamento, regeneração e retenção). Para o estudo experimental, foi adotada a técnica condutimétrica usando cloreto de sódio em solução aquosa como traçador. Foram verificadas as influências da vazão, da configuração do trocador de calor a placas (número de passes para o arranjo em série) e do tipo de tubo de retenção (tubo em \"S\" e tubo helicoidal). Modelos de distribuição foram usados para representar o comportamento experimental (dispersão axial, tanques em série, laminar modificado, combinado PFR+CSTR). Este estudo foi aplicado para as condições de pasteurização HTST de leite, visando a futura implementação de uma modelagem matemática rigorosa do processo, para otimização do projeto e operação do processo. / It is presented a study of residence time distribution in the steps of a process of continuous pasteurization by plate heat exchanger (heating, cooling, regeneration and holding). For the experimental study, it was adopted a conductimetric technique using sodium chloride in aqueous solution as a tracer. It was also studied the influence of the flow rate, the configuration of the plate heat exchanger (number of passes in series arrangement) and the type of holding tube (\"S\"- shaped tube and helicoidal tube). Distribution models were used for representing the experimental behavior (axial dispersion, tank in series, modified laminar, combined PFR+CSTR). This study was applied for the conditions of HTST pasteurization of milk, targeting the future implementation of a rigorous mathematical modeling of the process, which can be applied for the process operation and optimization of the project design.

With increasing global energy consumption, stringent environmental protection legislation and safety regulations in industrialised nations, energy saving has been put under high priority. One of the most efficient ways of energy reduction is through heat transfer enhancement for additional heat recovery. Applying compact heat exchanger is one of the main strategies of heat transfer enhancement. However, the application of compact heat exchangers is prohibited by the lack of design methodology. Therefore, the aim of this research is to tackle the problem of developing optimisation methodologies of plate/plate-fin heat exchanger design. A mathematical model of plate-fin heat exchanger design is proposed to consider fin type selection with detailed geometry and imposed constraints simultaneously. The concept of mix-and-match fin type combinations is put forward to include all possible fin type combinations in a heat exchanger. The mixed integer nonlinear programming (MINLP) model can be converted to a nonlinear programming (NLP) model by employing continuous heat transfer and pressure drop correlations and considering the basic fin geometric parameters as continuous variables. The whole optimisation is based on volumetric minimisation or capital cost minimisation and completed by CONOPT solver in GAMS. Case studies are carried out to demonstrate the effectiveness and benefits of the new proposed methodology. For plate heat exchangers, the design methodology is developed on the basis of plate-fin heat exchanger methodology, and takes phase change, plate pattern selection, flow arrangement and pressure drop constraints simultaneously. The phase change problem is tackled by dividing the whole process into several subsections and considering constant physical properties in each subsection. The performances of various flow arrangements are evaluated by correction factors of logarithmic mean temperature difference. For two-phase conditions, the heat transfer and pressure drop performance are predicted by continuous two-phase Nusselt number and Fanning friction factor correlations to avoid the MINLP problem. The optimisation is solved by CONOPT solver as well. The feasibility and accuracy of the new proposed methodology is examined by case studies.

Anodiseringsanläggningar förbrukar stora mängder elektricitet som omsätts i värme. Samtidigt kräver processen en konstant temperatur på cirka 20 °C för att ytskiktet som bildas ska hålla en jämn kvalitét. Nedkylningen av baden är därför kritisk och där finns möjligheter att effektivisera ur ett energi och tillförlitlighetsperspektiv. Genom att få bättre kännedom om processen kan kostsamma produktionsavbrott undvikas samtidigt som möjligheten att optimera parametrarna för energiåtervinningen kan undersökas. En viktig utmaning är att det med tiden byggs upp beläggningar på plattvärmeväxlarnas ytor, så kallad fouling, som minskar värmeväxlarnas kyleffekt. Studien har därför fokuserat på att mäta och beräkna foulingnivåer för att kunna förutsäga nödvändiga serviceintervaller samt öka tillförlitligheten. Metoden i den här rapporten grundar sig på datainsamling från mätinstrument som registrerar temperaturer och flöden ur produktionssystemet. Den information som samlats in har därefter att analyseras statistiskt och matematiskt. Resultatet visar att det går att följa systemets utveckling antingen med hjälp av filtrerade medelvärden och styrdiagram, eller genom att anpassa matematiska funktioner härledda ur teorin. Fördelen med att anpassa funktioner är att dessa kan användas för att extrapolera systemets k-värden i framtiden. Vidare föreslås möjliga åtgärder för att förebygga fouling i framtiden.

A pasteurização é um processo térmico para inativar micro-organismos patogênicos e deterioradores em alimentos líquidos. O controle do processo é fundamental para a manutenção da temperatura de pasteurização, de forma que a modelagem dinâmica se torna útil no desenvolvimento, nos testes de controladores e nos procedimentos de operação. O objetivo deste trabalho foi o desenvolvimento e a validação experimental da modelagem dinâmica de um pasteurizador a placas com três seções de troca térmica para estudar sua operação em regime transiente. A modelagem consiste em balanços diferenciais de energia entre canais e placas do trocador, perda de calor para o ambiente do tubo de retenção e conexões e as respectivas condições iniciais e de contorno. Os coeficientes de troca térmica do equipamento foram determinados experimentalmente. Na simulação foram adotados métodos de diferenças finitas e a resolução matemática foi realizada através do software gPROMS. O modelo foi aplicado para representar o comportamento de um pasteurizador a placas de escala laboratorial (Armfield FT43A), operando em duas condições: sem e com a influência da incrustação na seção de aquecimento do trocador. Para a validação do modelo foram realizados ensaios experimentais da partida e de perturbação das vazões de alimentação do processo. Foram inseridos termopares em diversos pontos do equipamento e as temperaturas foram registradas com um sistema de aquisição de dados. Para estudar a influência da incrustação na pasteurização, foram realizados ensaios experimentais com dois tipos de leite para se ter alta e baixa incrustação. As placas do trocador foram pesadas e fotografadas antes e depois dos ensaios de incrustação para avaliar o depósito formado. Foram utilizados modelos genéricos de incrustação para a simulação desse efeito sobre o processo de pasteurização. Através da comparação dos resultados experimentais e simulados foi verificada que a modelagem matemática para a operação transiente do processo de pasteurização analisado foi muito satisfatória. / Pasteurization is a thermal process used to inactivate pathogenic and deteriorative microorganisms in liquid foods. Process control is essential for the temperature maintenance of pasteurization, so that the dynamic model is an important tool in the development, controller tests, and also in the procedure of operation. The aim of this work was the development and experimental validation of the dynamic model of a plate pasteurizer with three sections of heat exchange studying the transient state operation. The model consists of differential equations of thermal energy balance between channels and plates of heat exchanger, heat loss to the environment of the holding tube and connections and their respective initial and boundary conditions. The heat transfer coefficients of plate heat exchanger and tubes were determined experimentally. In the simulation, finite difference methods were adopted and the math solving was performed using the gPROMS software. The model was applied to represent the behavior of a plate pasteurizer in laboratory scale (Armfield FT43A), operating in two conditions: free of fouling and with fouling influence on the heating section of the heat exchanger. Experimental tests of the start-up and of disturbances in flow rates of the process were performed for the model validation. Thermocouples were inserted at various points of the equipment and the temperatures were recorded with a data acquisition system. In order to study the influence of the fouling, experimental tests were performed with two kinds of milk to obtain high and low fouling. Plates of the heat exchanger were weighed and photographed before and after of the fouling tests for evaluate the deposit formed. Generic models of fouling were used to simulate the effect of fouling on the pasteurization process. Through the comparison of experimental and simulated results, it was verified that the mathematical modeling for the transient operation of the pasteurization process was very satisfactory.

O principal objetivo do trabalho foi o desenvolvimento de um modelo matemático de um pasteurizador a placas visando a determinação da distribuição de temperatura e de letalidade ao longo dos canais do trocador de calor em todas as suas seções, nas conexões tubulares e no tubo de retenção para a avaliação do decaimento logarítmico da concentração de um microorganismo alvo ou da atividade de uma enzima alvo em um processo de pasteurização contínua. A modelagem matemática foi composta pelo balanço diferencial de energia e letalidade nos canais do trocador, no tubo de retenção e nas suas conexões, levando em conta a perda de calor para o ambiente nos tubos. O modelo construído apresentou um conjunto de equações diferenciais ordinárias de primeira ordem e sua resolução foi feita pelo método das diferenças finitas usando o software gPROMS. Um estudo de caso foi analisado e a modelagem descreveu de forma coerente o processo térmico e a letalidade e futuramente ela poderá ser utilizada para a otimização do processo de pasteurização em trocadores de calor a placas, visando a obtenção de produtos seguros e de alta qualidade. A verificação do processo de pasteurização que o modelo desenvolvido contempla foi realizada a partir da validação experimental utilizando um integrador tempo-temperatura e ensaios laboratoriais com indicador enzimático (fosfatase alcalina em tampão fosfato), que mostraram que o modelo desenvolvido se aproxima de maneira satisfatória dos resultados reais. / The main objective of this study was to develop a mathematical model in a plate pasteurizer in order to determine the temperature and lethality distribution along the channels of the heat exchanger in all its sections, in tubular connections and holding tube evaluating the logarithmic decay in concentration of a target microorganism or enzyme activity in a continuous pasteurization process. Mathematical modeling was composed of the differential energy balance and lethality in the channels of the exchanger, the holding tube and its connections, taking into account the heat loss to the environment in the tubes. The constructed model presented a set of ordinary differential equations of first order and its resolution was made by the finite difference method using the gPROMS software. A case study was analyzed and the modeling described the thermal and the lethality process very well and in the future it can be used to optimize the process of pasteurization in plate heat exchangers, aiming the achievement of safe and with high quality products. A verification of the pasteurization process that the model developed contemplates has been performed based on experimental validation using time-temperature integrator and testing with enzymatic indicator (alkaline phosphatase in phosphate buffer), which showed that the model developed satisfactorily approximates the actual results.