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Evaporation is used in the dairy industry to reduce the production costs of powder production (including milk powder) as it is more energy efficient to remove water by evaporation than by drying. There are significant economic reasons why gaining a greater understanding of the complex interactions occurring between the liquid and vapour phases in evaporators is advantageous. The multiphase flows in industrial dairy falling film evaporators were studied. Several computational fluid dynamic (CFD) models were created using Ansys CFX 10. Two case studies were chosen. The first case involved modelling the dispersed droplets that require separation from the water vapour evaporated from the feed of the evaporator. The CFD results were able to show that fouling was not caused by a lack of separation. The predicted separation agreed with experimental measurements. The atomisation process was found to be critical in the prediction of the separation. The atomisation process is not well understood and introduced the greatest error to the model. A plug flow assumption is currently used as a basis for the design the separators. The CFD solutions found no validity to this assumption. The second case study aimed to model and solve the distribution of the feed into the heat transfer tubes at the top of the falling film evaporators. The goal of this study was to be able to accurately predict wetting of the tubes. The volume of fluid (VOF) method using the continuum surface force method (CSF) to account for surface tension was chosen to model the system. The poor curvature estimate of the CSF method was found to produce parasitic currents that limited the stability of the solutions. Small VOF timesteps prevented the solver from diverging and the parasitic currents would oscillate the interface around the correct location. The small timesteps required significantly more computational power than was available and the model for the distribution process could not be solved. The CSF VOF method showed considerable promise, particularly because it can predict free surface topography without user input. There are still questions about numerical creeping of films, but the method was able to correctly predict several different surface tension and contact angle dominated film flows expected to be needed to accurately model the distribution of the falling film evaporator. Validated solutions of jet, meniscus, sessile, "overfall" and 3-D weir models were obtained and these agreed with published results in literature. A 2-D weir solution showed qualitative agreement with the expected form of the film. A 2-D hydraulic jump model without surface tension was created and agreed with experimental work in the literature to within 22%. The 3-D hydraulic jump solution only showed partial agreement with published experimental, the solutions were not mesh independent and not well converged so few conclusions can be drawn. The solutions of a rivulet model showed qualitative similarities with experimental work. The predicted wetting rate did not agree with values in the published literature because the spatial domain modelled was believed to be too narrow. An extended model of rivulet flow agreed with the idealised rivulet profile in literature and the predicted wetting rate agreed with some of the published literature. Again the solutions were not mesh independent so few conclusions can be confirmed.

Submitted by Nathália Faria da Silva (nathaliafsilva.ufv@gmail.com) on 2017-07-28T13:57:52Z No. of bitstreams: 1 texto completo.PDF: 1092273 bytes, checksum: 61189e2f9ff1c859ecd3bbb9a9959c9a (MD5) / Made available in DSpace on 2017-07-28T13:57:52Z (GMT). No. of bitstreams: 1 texto completo.PDF: 1092273 bytes, checksum: 61189e2f9ff1c859ecd3bbb9a9959c9a (MD5) Previous issue date: 2002-02-28 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Um sistema de medição e controle foi desenvolvido para o estudo de respostas fisiológicas de aves sujeitas a mudanças térmicas como meio de alívio de estresse térmico. O sistema faz o controle automático da temperatura (t a,SP ±0,2 oC) e da umidade relativa do ar (RH SP ±2 %); sendo que a velocidade do ar foi controlada manualmente (V SP ±0,1 m· s -1 ); e contínuo armazenamento das termografias (ex., temperatura superficial, t surf ) e da temperatura corporais (t b ) dos animais. As condições térmicas controladas na zona de ocupação animal (AZO) são atingidas pela operação de um pequeno túnel de vento (V = 0 to 1,5 m· s -1 ) colocado no interior de uma sala ambiental com t a e RH controlados (5,0 m comprimento × 3,5 m largura × 3,0 m altura). Os valores desejados de t a e RH foram alcançados por meio de aquecedores e umidificadores controlados em dois estágios via um módulo de controle e medição programável, e periféricos. Termografias (discernabilidade de 0.06°C) são adquiridas com uma camera infravermelho cuja operação é controlada remotamente por um PC. t b (±0.1°C) é armazenado em uma unidade de telemetria, sem a necessidade de intervenção cirurgica, que também é conectado a um PC. Em adição, um sistema de video tem sido usado para observar e arquivar os comportamentos do animal. A instrumentação desenvolvida foi usada em um experimento para ajustar equações empíricas para descrever as necessidades de molhamento parcial da superfície em galinhas poedeiras (Hy-Line W98, com 34 ± 1 semanas) sujeitas a condições de estresse térmico. A água necessária para limitar o aumento da temperatura superficial das galinhas foi expressada em termos de intervalo de aspersão (SI 10 , min) para uma dosagem constante (10 ml· aspersão -1 ) ou para uma taxa de evaporação (ER, ml.min -1 ) de água aspergida. As exposições térmicas consistiram de uma combinação fatorial de 3 temperaturas de bulbo seco (t db ) (35, 38 e 41 °C) x 2 temperaturas de ponto de orvalho (t dp ) (21,1 e 26,7 °C) x 3 velocidades do ar (V) (0,2, 0,7 e 1,2 m· s -1 ). As condições ambientais foram expressas como 18 combinações de déficit de vapor de pressão do ar (VPD air ) x V. ER foi diretamente proporcional ao produto VPD air · V . As relações podem servir como a base para a otimizar o sistema de resfriamento superficial intermitente para alívio de estresse térmico em galinhas criadas em gaiolas. Ademais, um índice de desconforto térmico (TDI) foi derivado com base nas respostas fisiológicas, temperatura superficial (t surf ) e temperatura corporal (t b ), de galinhas sujeitas a exposições térmicas. Com base no aumento da t b aos 50 min de exposição térmica (Δt b,50 ), um TDI foi relacionado ao VPD air e a V da seguinte forma: TDI = -15.17 + 18.62 (t db ) n – 0.92 · (VPD air · V ) n . Usando TDI, quatro zonas de desconforto térmico (segura, alerta, perigo e fatal) foram definidas para as várias combinações de condições térmicas. Um modelo teórico de transferência de calor e massa em regime transiente também foi proposto para predizer Δt b,50 em função das condições ambientais, das condições fisiológicas das aves e do nível de molhamento (β). O modelo proporciona uma ferramenta conveniente e interativa para determinar Δt b,50 nas galinhas submetidas ou não ao molhamento superficial para t db variando de 35 a 38 °C. / A control and measurement system was developed for studying physiological responses of poultry to thermal challenges and means of thermal stress relief. The system features automatic control of air temperature (t a,SP ±0.2 oC) and relative humidity (RH SP ± 2 %); manual setting of air velocity (V SP ± 0.1 m· s -1 ); and continuous recording of thermographs (i.e., core body temperature (t b ) of the animal. surface temperature, t surf ) and The controlled thermal conditions in the animal-occupied zone (AOZ) are achieved through operation of a small wind tunnel (V = 0 to 1.5 m· s -1 ) inside a t a - and RH-controlled environmental room (5 m L × 3.5 m W × 3.0 m H). Target t a and RH values are achieved by controlling auxiliary heaters and humidifiers in two stages via a programmable measurement and control module and peripherals. Thermographs (0.06°C discernability) are acquired with an infrared (IR) imager whose operation is remotely controlled by a PC. Core body temperature (t b , ±0.1°C) is recorded with a surgery-free telemetric sensing unit that is also interfaced with a PC. In addition, a video monitoring system is used to observe and archive animal behaviors. The instrumentation developed was used in an experiment to establish empirical equations to describe the need of partial surface wetting for cooling laying hens (Hy-Line W-98, 34 ±1 wk old) subjected to a range of thermal stress conditions. The thermal exposures consisted of a factorial combination of 3 dry bulb temperatures (t db ) (35, 38 and 41 °C) × 2 dew point temperatures (t dp ) (21.1 and 26.7 ° C) × 3 air velocities (V) (0.2, 0.7 and 1.2 m· s - ). The environmental conditions were expressed as 18 combinations of air vapor pressure deficit (VPD air ) × V. The water necessary to limit hen surface temperature from rising was expressed in terms of sprinkle interval (SI 10 , min) for a constant spray dosage (10 ml· spray -1 ) or evaporation rate (ER, ml· min -1 ) of the sprayed water. ER was directly proportional to VPD air · V . The relationships may serve as the basis for optimizing an intermittent partial surface cooling system for thermal stress relief of caged layers. Also from the study, a thermal discomfort index (TDI) was derived based on physiological responses, surface temperature (t surf ) and core body temperature (t b ) of the control (non-cooled) hens. Based on t b rise after 50 min of thermal exposure (Δt b,50 ), TDI related to VPD air and V as: TDI = -15.17 + 18.62 (t db ) n – 0.92· (VPD air · was V ) n . Using TDI, four zones of thermal discomfort (safe, alert, danger, and fatal) were defined for various combinations of thermal conditions. Furthermore, theoretical transient heat and mass transfer model was proposed to predict Δt b,50 as a function of environmental conditions, physiological responses of the hens and surface wetness level (β). The model provides a convenient, interactive tool for determining Δt b,50 on wetted and non-wetted hens for t db ranging from 35 to 38 °C.

other / no / The effect of sulphuric acid on the chemical and physical behaviour of the piston ring lubricant in a marine engine cylinder was investigated. To reveal the basic influence of H2SO4 on the lubricant film, the saturated hydrocarbon Squalane (C30H62) was chosen as a simple model oil. The interfacial tension between aqueous H2SO4 (0-98% w/w) and C30H62 was measured between -3 and 165 degrees C to understand droplet formation in the lubricant. Interfacial tension decreases with increasing acid concentration and is temperature dependent. / The wettability of engine parts with corrosive sulphuric acid was characterised by the contact angle. The contact angle of H2SO4 (0-98% w/w) on a grey cast iron cylinder liner material (Wartsila, RT84) and a piston ring chrome-ceramic coating (Federal Mogul Goetze, CKS, empty set960 mm) immersed in C30H62 was measured over a temperature range from 20 to 165 degrees C. In general, larger contact angles were measured under higher temperature conditions and on chrome surfaces. / In addition to the physical measurements, chemical reaction between H2SO4 and C30H62 was observed which influenced the interfacial tension, visual appearance, phase separation and formation of solid matter. The reaction time was found to be faster than the neutralisation times of commercially formulated lubricants. The reaction products were analysed using FTIR spectroscopy and EDX to find oxidation and sulphonation.

Kolloidpartikel die von zwei nicht mischbaren Fluiden benetzt werden, tendieren dazu sich an der fluiden Grenzfläche aufzuhalten um die Oberflächenspannung zu minimieren. Bei genügender Anzahl solcher Kolloide werden diese zusammengedrückt und lassen die fluide Grenzfläche erstarren. Das gesamte System aus Fluiden und Kolloiden bildet dann eine spezielle Emulsion mit interessanten Eigenschaften. In dieser Arbeit wird ein kontinuum Model für solche Systeme entwickelt, basierend auf den Prinzipien der Massenerhaltung und der themodynamischen Konsistenz. Dabei wird die makroskopische Zwei-Phasen-Strömung durch eine Navier-Stokes Cahn-Hilliard Gleichung modelliert und die mikroskopischen Partikel an der fluiden Grenzfläche durch einen Phase-Field-Crystal Ansatz beschrieben. Zur Evaluation des verwendeten Strömungsmodells wird ein Test verschiedener Navier-Stokes Cahn-Hilliard Modelle anhand eines bekannten Benchmark Szenarios durchgeführt. Die Ergebnisse werden mit denen von anderen Methoden zur Simulation von Zwei-Phasen-Strömungen verglichen. Desweiteren wird eine neue Methode zur Simulation von Zwei-Phasen-Strömungen in komplexen Gebieten vorgestellt. Dabei wird die komplexe Geometrie implizit durch eine Phasenfeldvariable beschrieben, welche die charakteristische Funktion des Gebietes approximiert. Die Strömungsgleichungen werden dementsprechend so umformuliert, dass sie in einem größeren und einfacheren Gebiet gelten, wobei die Randbedingungen implizit durch zusätzliche Quellterme eingebracht werden. Zur Einarbeitung der Oberflächenkolloide in das Strömungsmodell wird schließlich die Variation der freien Energie des Gesamtsystems betrachtet. Dabei wird die Energie der Partikel durch die Phase-Field-Crystal Energie approximiert und die Energie der Oberfläche durch die Ginzburg-Landau Energie. Eine Variation der Gesamtenergie liefert dann die Phase-Field-Crystal Gleichung und die Navier-Stokes Cahn-Hilliard Gleichungen mit zusätzlichen elastischen Spannunngen. Zur Validierung des Ansatzes wird auch eine sharp interface Version der Gleichungen hergeleitet und mit der zuvor hergeleiteten diffuse interface Version abgeglichen. Die Diskretisierung der erhaltenen Gleichungen erfolgt durch Finiten Elemente in Kombination mit einem semi-impliziten Euler Verfahren. Durch numerische Simulationen wird die Anwendbarkeit des Modells gezeigt und bestätigt, dass die oberflächenaktiven Kolloide die fluide Grenzfläche hinreichend steif machen können um externen Kräften entgegenzuwirken und das gesamte System zu stabilisieren. / Colloid particles that are partially wetted by two immiscible fluids can become confined to fluidfluid interfaces. At sufficiently high volume fractions, the colloids may jam and the interface may crystallize. The fluids together with the interfacial colloids compose an emulsion with interesting new properties and offer an important route to new soft materials. Based on the principles of mass conservation and thermodynamic consistency, we develop a continuum model for such systems which combines a Cahn-Hilliard-Navier-Stokes model for the macroscopic two-phase fluid system with a surface Phase-Field-Crystal model for the microscopic colloidal particles along the interface. We begin with validating the used flow model by testing different diffuse interface models on a benchmark configuration for a two-dimensional rising bubble and compare the results with reference solutions obtained by other two-phase flow models. Furthermore, we present a new method for simulating two-phase flows in complex geometries, taking into account contact lines separating immiscible incompressible components. In this approach, the complex geometry is described implicitly by introducing a new phase-field variable, which is a smooth approximation of the characteristic function of the complex domain. The fluid and component concentration equations are reformulated and solved in larger regular domain with the boundary conditions being implicitly modeled using source terms. Finally, we derive the thermodynamically consistent diffuse interface model for two-phase flow with interfacial particles by taking into account the surface energy and the energy associated with surface colloids from the surface PFC model. The resulting governing equations are the phase field crystal equations and Navier-Stokes Cahn-Hilliard equations with an additional elastic stress. To validate our approach, we derive a sharp interface model and show agreement with the diffuse interface model. We demonstrate the feasibility of the model and present numerical simulations that confirm the ability of the colloids to make the interface sufficiently rigid to resist external forces and to stabilize interfaces for long times.

No description available.