A transient, one-dimensional, model of the membrane of a proton exchange membrane fuel cell is presented. The role of the membrane is to transport protons from the anode to cathode of the fuel cell while preventing the transport of other reactants. The membrane is modeled assuming mono-phase, multi-species flow. For water transport, the principle driving forces modeled are a convective force, an osmotic force (i.e. diffusion), and an electric force. The first of these results from a pressure gradient, the second from a concentration gradient, and the third from the migration of protons from anode to cathode and their effect (drag) on the dipole water molecules. Equations are developed for the conservation of protons and water, the conservation of thermal energy, and the variation of proton potential within the membrane. The model is solved using a fully implicit finite difference approach. Results showing the effects of current density, pressure gradients, water and heat fluxes, and fuel cell start-up on water concentration, temperature, and proton potential across the membrane are presented. / Master of Science

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.

Den nationella planen för vattenverksamheter antogs år 2020 och innebär att vattenverksamheter ska förses med moderna miljövillkor för att öka vattenmiljönytta och att bibehålla den effektiva tillgången till vattenkraftsel. Emån som är ett Natura 2000-område är det största vattendraget i sydöstra Sverige och vattendraget är utifrån konnektiviteten klassificerat som måttlig. Högsby vattenkraftverk, som ligger i Emån och ägs av Uniper, ska omprövas utifrån miljövillkor enligt den nationella planen och idag har Högsby vattenkraftverk ingen fastställd minimitappning för sin anläggning. Målet med studien är att undersöka storleken på vattenflödet av minimitappningen som kan användas i den ursprungliga naturfåran i Högsby för att möjliggöra longitudinella spridningsmöjligheter i uppströms och nedströms riktning för de fiskarter som historiskt sett har kunnat vandra genom Högsby. En sektion i naturfåran är uppdämd av en tröskeldamm som bedöms vara den svåraste passagen i naturfåran med undantag från utskovsdammen. Metoden som används i rapporten är en endimensionell stationär modellering i HEC-RAS över den naturfåra som kan möjliggöra fiskvandring förbi vattenkraftverk. Två modeller har skapats – med och utan tröskeldamm. Utifrån resultatet är den högsta medelvattenhastigheten i sektionen nedanför tröskeldammen i båda scenarion, detsamma gäller medelvattendjupet.  De konnektivitetshöjande åtgärder som diskuteras är minimitappning och olika fiskvägar i naturfåran för att behålla den historiska forsmiljön som funnits. Både rivning av tröskeldamm och fiskväg runt dammen har diskuterats. Därutöver anses havsöring och lax vara fiskarter som med stor säkerhet har kunnat passera Högsby historiskt sett. Högsby är klass 1 i relativt reglerbidrag, vilket bör tas i beaktning vid bedömning av minimitappning. Det finns osäkerheter med modellen, såsom batymetri och randvillkor samt validering av modellen. Därför går det inte med säkerhet att säga att vattendjup eller vattenhastigheter stämmer överens med verkligheten. Slutsatsen är att det inte heller med säkerhet går att säga vilka fiskarter som historiskt sett har vandrat genom Högsby, inte heller en minimitappning kan fastställas som kan möjliggöra fiskvandring för alla fiskarter. Däremot kommer implementeringen av en fastställd minimitappning och fiskvägar öka konnektiviteten. / In 2020 the national plan for hydropower plants was implemented in Sweden. The national plan aims to increase the environmental standards for hydropower plants for the benefit of the water body and still maintain an efficient access to electricity originated from hydropower. Emån is the largest river in the south-eastern part of Sweden. The river a Natura 2000 area and it is classified as moderate based on connectivity according to environmental norm for rivers and water bodies. Högsby hydropower plant located along Emån is owned by Uniper and are included within the national plan, which indicate that it needs to meet the environmental standard. Högsby hydropower plant currently has no established minimum discharge. The aim of the study is to investigate a minimum discharge for the natural dry stream located in Högsby to enable higher connectivity for the fish species that have historically been able to migrate through Högsby.  The natural stream is downstream the spillway dam in Högsby. Within the stream a weir is considered to be the most difficult passage for fish migration, with the exception of the spillway dam. The method used in the report is a one-dimensional steady flow model in HEC-RAS for the natural stream to investigate the possibility for fish migration past the hydropower plant. Two scenarios have been considered – with and without the crest dam present. Based on the result from the model, the highest mean water velocity is the section below the weir for both scenarios and same applies to the mean water depth. Implementation of a minimum discharge and various fish ways in the natural stream is measures for increasing connectivity that are being discussed which would also maintain the rapids that has existed in the stream. The fish ways that have been discussed is based on the scenarios if the weir is present or not. The fish species that with great certainty have been able to migrate through Högsby historically is sea trout and salmon. Högsby hydropower plant have the highest classified regulation of the hydropower plants in Emån which need to be considered when determining minimum discharge.  There are a few uncertainties with the hydraulic model such as bathymetry and the boundary conditions. The model is not validated which means that the water depth and the velocity might not reflect the true values. It is not certain which fish species that have migrated through Högsby historically, nor can an established minimum discharge be said to enable fish migration. However, an implementation of a minimum discharge and the fish ways that have been discussed will increase the connectivity in Högsby.