Master of Science / Department of Grain Science and Industry / Sajid Alavi / Extrusion is a widely used processing technology for various food products and is also commonly applied in non-food applications involving plastics, rubber and metal. Expanded products for human and animal consumption such as snacks, breakfast cereal, pet food and aquatic food typically consist of a biopolymer matrix of starch and proteins that have natural physical, chemical and polymeric variability. Additionally, variability in extrusion parameters such as water injection and screw speed is often observed depending on the process controls employed. This can potentially lead to inconsistency in product quality. Stochastic modeling helps in studying the impact of variability of various parameters on the end product, which in turn helps in better process and product quality control. The primary purpose of this research was to develop a mathematical model for flow behavior of biopolymer melts inside extruder barrel and bubble growth dynamics after exiting the extruder using mass, heat and momentum transfer equations. This model was integrated with a Monte-Carlo based stochastic interface for input of randomly generated process data (based on experimental data acquisition) and output of simulated distributions of end-product properties such as expansion ratio and cellular architecture parameters (cell size and wall thickness). The mathematical model was experimentally validated using pilot-scale twin screw extrusion for processing of cereal-based cellular products. Process and product data were measured at different in-barrel moisture contents (19-28% dry basis) and experimental screw speeds (250-330 rpm). Experimental process parameters such as specific mechanical energy (212.8-319.3 kJ/kg), die temperature (120.7-170.6oC), die pressure (3160-7683 kPa) and product characteristics such as expansion ratio (3.29-16.94) and cell size or bubble radius (435-655 microns) compared well with simulated results from the mathematical model viz., specific mechanical energy (217.6-323.9 kJ/kg), die temperature (116.8-176.1oC), die pressure (3478-6404 kPa), expansion ratio (4.56-19.4) and bubble radius (426-728 microns). Experimental variability in product characteristics was quantified using coefficient of variation which compared well with simulation results (example, 2.5-4.9% versus 0.24-3.1% respectively for expansion ratio). The stochastic model was also used to conduct sensitivity analysis for understanding which raw material and process characteristics contribute most to product variability. Sensitivity analysis showed that the water added in extruder affects the magnitude and variability of expansion ratio the most, as compared to screw speed and consistency index.

The UK Health & Safety Executive are responsible for advising on ways to ensure the safety of employees within the workplace. One of the main areas of concern is the potential problem of unwanted fire, and it has been identified that within the area of large-scale storage in warehouses, there is an uncertainty posed by large quantities of thermoplastic. Some forms of thermoplastic exhibit melt-flow behaviour when heated, and a large vertical array exposed to a fire may melt and ignite forming a pool fire in addition to a wall fire. This project is largely experimental, and aimed at quantifying the effect of a growing pool fire fuelled by a melting wall on overall fire growth rate. The pool fire has been found to increase melting and burning rates, producing a much faster growing fire. It has also been found that - 80% of flowing and burning material will enter a potential pool fire, with only 20 - 25% of total mass loss actually burning from the original array. During the project 400+ small-scale tests and several medium-scale experiments have been undertaken at both Edinburgh University and the HSE's Fire & Explosion Laboratory, Buxton. The experiments have confirmed the main parameters governing pool fire development are molecular weight degradation rate and mechanism, which control flow viscosity. There have also been investigations into other influences, the most significant of which was found to be flooring substrate. These parameters then form the basis of a simple 1-D model. A semi-infinite heat transfer approximation is used to determine temperature profile through a thermoplastic exposed to its own flame flux, with extrapolated temperature dependant material properties. The derived profile is then inserted into a gravity driven flow model, to produce estimates of flow rate and quantity for plastics undergoing either random or end chain scission thermal degradation processes. The model identifies property data which are required to permit its use as a hazard assessment tool.

Metal  additive  manufacturing  technologies  are  widely  employed  in  the aerospace, automotive  and  medical  industries. Selective  laser  melting  is  a type  of  metal additive manufacturing process in which powders are consolidated layer by layer in a predefined pattern with the help of a laser beam to create a component.   Powder characteristics are critical in influencing the quality of the printed component.  Metal powders must be within a specific size range and have spherical morphology to exhibit good  flow  and  spread behaviour  during  the  additive  manufacturing  process.   It  is necessary to understand the flow behaviour to comprehend the powder’s performance during the  process.   The  study  investigates  the  effect  of  powder  characteristics like particle  shape,  particle  size  and  size  distribution  on  the  flow behaviour  of  steel powders.   Powder  characterisation  techniques  relevant  to the  powders  for  additive manufacturing application is identified and performed. Sieve analysis fails to incorporate the particle shape during the particle size estimation. Optical microscopy is not a robust method for determining the particle shape.  Flow behaviour of the powders was studied using flowmeter test, rheometric analysis and static angle of repose test.  Rheometric analysis is more sensitive to minor variations in the flow behaviour compared to flowmeter tests. The static angle of repose test fails to incorporate the stresses experienced by the powder during the process and can be used to get a rough estimate for the powder flow behaviour in terms of cohesion.  Of the seven steel powders examined, the same powder with flow time 12 [s/(50 g)] kept being ranked in the top three for all the flow tests. So this powder is recommended for use in additive manufacturing. In addition, one other powder that failed in flowmetertests was consistently placed towards the bottom of all tests. / Metalladditiv tillverkningsteknik används i stor utsträckning inom flyg­, fordons­, och medicinsk industri. Selektiv lasersmältning är en typ av metalladditiv tillverknings­ process där pulver konsolideras lager för lager i ett fördefinierat mönster med hjälp av en laserstråle för att skapa en komponent. Pulveregenskaper är avgörande för att påverka kvaliteten på den tryckta komponenten. Metallpulver måste ligga inom ett visst storleksintervall och ha en sfärisk morfologi för att uppvisa ett bra flödes­, och dispersionsbeteende under den additiva tillverkningsprocessen. Det är nödvändigt att förstå flödesbeteendet för att förstå pulvrets prestanda under processen. Studien undersöker effekten av pulveregenskaper som partikelform, partikelstorlek och storleksfördelning på flödesbeteendet hos stålpulver. Pulverkarakteriseringstekniker som är relevanta för pulvren för tillsatstillverkning identifieras och utförs. Siktanalysen misslyckas med att införliva partikelformen under partikelstorleksupp­ skattningen. Optisk mikroskopi är inte en robust metod för att bestämma partikelformen. Pulvrets flödesbeteende studerades med hjälp av flödesmätartest, reometrisk analys och statisk vinkel på vilotest. Reometrisk analys är mer känslig för mindre variationer i flödesbeteendet jämfört med flödesmätartester. Det statiska vilovinkeltestet misslyckas med att införliva de påfrestningar som pulvret upplever under processen och kan användas för att få en grov uppskattning av pulverflödesbeteendet i termer av kohesion. Av de sju stålpulver som undersöktes rankades samma pulver med flödestiden 12 [s/(50 g)] i topp tre för alla flödestester. Så detta pulver rekommenderas för användning i additiv tillverkning. Dessutom placerades ett annat pulver som misslyckades i flödesmätartester konsekvent mot botten av alla tester.

A spillway is an important component of a dam and serves as a flood release structure. It achieves controlled discharge of water and protects the dam from overtopping. The majority of the hydropower dams were built before the 1980s, and many spillways are undersized in light of the present design flood guidelines. Another issue that arises in connection with the high design floods is the energy dissipation capacity. Many existing energy-dissipating arrangements are insufficient or construed only for a design flood standard at the time of dam construction. The increment in the flood discharges requires that the energy dissipation should be improved to obtain sufficient capacity or higher efficiency. In addition, the high-velocity flow is a major concern in the design of spillways. If the flow velocity exceeds approximately 20 m/s, the risk of cavitation may arise. In Sweden, many dams belong to this category. To address these issues, an assessment of their discharge behaviours is required. Innovative engineering solutions for better energy dissipation and cavitation mitigation are also necessary for safe operation. This thesis presents machine learning based methods for discharge estimation. Three data-driven models are developed to study the discharge behaviours of the overflow weirs. Their reliability is validated through the comparison with the experimental and empirical results. These models are capable of giving accurate predictions and show superiority over the conventional approaches. With high accuracy and adaptability, data-driven models are an effective and fast alternative for spillway discharge prediction. This research also focuses on the hydraulic design of stepped spillways, aiming to devise innovative engineering solutions to enhance energy dissipation and reduce cavitation risks. Consequently, several unconventional step layouts are conceived and their hydraulic behaviours are investigated. The modified configurations include steps with chamfers and cavity blockages, non-linear steps and inclined steps. This part attempts to gain insight into the effects of the step geometries on the spillway hydraulics via computational fluid dynamics, which provides references for engineering applications. / Ett utskov är en viktig komponent i en damm och fungerar som ett skydd mot översvämning. Det avbördar vatten på ett kontrollerat sätt och skyddar dammen från överströmning. Majoriteten av vattenkraftsdammarna byggdes före 1980-talet och många utskov är underdimensionerade i förhållande till de nuvarande riktlinjerna för utformning med avseende på dimensionerande flöden. En annan fråga som uppstår i samband med höga flöden är energiomvandlingskapaciteten. Många befintliga arrangemang för reducering omvandling av vattnets rörelseenergi är otillräckliga eller endast anpassade för det dimensionerande flöde som gällde vid tidpunkten för dammens uppförande. En avbördningsökning kräver i sin tur att energiomvandlingsförmågan förbättras för att uppnå tillräcklig kapacitet eller högre effektivitet. Dessutom är höghastighetsflödet ett stort bekymmer vid utformningen av utskov. Om flödeshastigheten överstiger t.ex. 20 m/s uppstår risk för kavitation i vattenvägar. I Sverige hör många dammar till denna kategori. För att lösa dessa problemställningar behöver en utvärdering av avbördningsanordningar göras. Innovativa tekniska lösningar som syftar till effektiv hantering av flödesenergi och kavitationsreducering, vilka utgör nödvändiga förutsättningar för säker drift av anläggningar. Denna uppsats presenterar maskininlärningsbaserade metoder för att prognostisera avbördning i dammar. Tre datadrivna modeller har utvecklats för att studera avbördningsegenskaper hos överfallsdammarna. Deras tillförlitlighet valideras genom jämförelse med experimentella och empiriska resultat. Modellerna kan ge noggrann uppskattning, som kan användas som ett tillförlitligt alternativ för bestämning av avbördning. Forskningen fokuserar också på den hydrauliska utformningen av stegade bräddavlopp (s.k. stepped spillway), i syfte att utveckla innovativa tekniska lösningar för att åstadkomma hög energiförlust och minska kavitationsrisker. Flera okonventionella stegformade geometrier föreslås och deras hydrauliska egenskaper undersöks. Denna del syftar till att, via numerisk simulering, ge en inblick i vilka effekter olika steggeometrier har på avbördningshydrauliken, vilken tillhandahåller referens för tekniska applikationer. / <p>QC 20210205</p>