Meistarafyrirlestrar í verkfræðideildum og Raunvísindadeild - brautskráning febrúar 2024

Námsleið: Byggingarverkfræði
Leiðbeinandi: Sigurður Erlingsson
Prófdómari: Bergþóra Kristinsdóttir, framkvæmdastjóri þjónustusviðs hjá Vegagerðinni

Ágrip

Efstu lög vega og gatna eru alla jafna úr malbiki sem er blanda af steinefni, biki og ýmsum íaukum. Til eru margar gerðir malbiksblandna sem henta fyrir mismunandi aðstæður. Malbik sýnir flókna hitastigsháða fjaðrandi – seiga – deiga hegðun undir aflrænu álagi þar sem þættir eins og bikgerð, bikmagn, holrýmd, íaukar og steinefnagerð hafa áhrif á hegðunina. Helstu eiginleikar sem taka þarf tillit til við hönnun blöndunnar eru m.a. stífnieiginleikar, slitþol gegn nagladekkjaáraun, viðnám gegn þreytubroti, veðrunarþol, viðnám gegn skriði og viðnám gegn steinlosi. Í þessu verkefni er stífni algengra íslenskra malbiksblandna rannsökuð og voru tvennskonar stífniprófanir framkvæmdar. Annarsvegar svokallað álagspúlspróf og hinsvegar tíðnipróf. Prófaðar voru 9 malbiksblöndur með og án íaukum. Blöndurnar flokkast í þrjá flokka, þ.e. AC16, AC11 og BRL16 þar sem AC malbik er efsta malbikslagið (slitlag) og BRL malbik er burðarlagsmalbik sem liggur neðar í vegbyggingunni. AC malbik hefur alla jafna lægri holrýmd en BRL malbik til að hindra að vatn safnist fyrir í slitlaginu og einnig til að hindra að vatnið komist niður í neðri lög vegbyggingarinnar. Að sama skapi inniheldur BRL malbik yfirleitt minna bik en AC malbik. Niðurstöður benda til þess að ekki virðist vera einfalt samband stífni við stærstu steinastærð, bikgerð eða íaukann SBS sem hafi afgerandi áhrif á stífni malbiksblandanna. Aftur á móti má samt sjá að malbiksblöndurnar AC16 eru að öllu jöfnu stífari en AC11 og BRL16 blöndurnar. Malbiksblöndur sem innihalda SBS virðast flestar vera stífari en þær sem ekki innihalda íauka og þá sérstaklega við hátt hitastig. Einnig sýna prófanir að blöndur sem innihalda hart bik (PG 70/100) eru almennt stífari en blöndur sem innihalda mjúkt bik (PG 160/220). Út frá samanburður við svipaðar malbiksblöndur frá Svíþjóð og Noreg kemur í ljós að íslensku malbiksblöndurnar hafa nokkuð lægri stífni. Vert er þó að taka fram að ýmsir aðrir þættir en steinastærð og stungudýpt biks hafa áhrif á stífni malbiks. Þar má nefna holrýmd, bikinnihald, kornakúrfa og íaukar en ekki voru þekktir þessir eiginleikar fyrir sænsku og norsku blöndurnar sem skoðaðar voru. Einnig gæti haft áhrif á niðurstöðurnar að íslensku kjarnarnir sem voru prófaðir eru borkjarnar teknir úr götu en sænsku og norsku kjarnarnir voru framleiddir til á tilraunastofu.       

Study programme: Civil Engineering
Advisor: Sigurður Erlingsson
Examiner: Bergþóra Kristinsdóttir, The Icelandic Road and Coastal Administration   

Abstract

The top layers of roads and streets are generally made of asphalt, which is a mixture of minerals, bitumen and various additives. There are many different types of asphalt mixtures that are suitable for different conditions, and the design of the mixture must take this into account. Asphalt exhibits a complex temperature-dependent elastic–viscous behaviour under mechanical stress where factors such as bitumen type, bitumen content, porosity, additives and minerals influence the results. The main features that need to be taken into account when designing the mixture are among other things stiffness properties, tire wear resistance, fatigue fracture resistance, erosion resistance and skid resistance. In Iceland there are no requirement made for stiffness or fatigue properties of asphalt mixtures, and in this project the stiffness of common Icelandic asphalt mixtures is tested. Stiffness properties can be determined in a variety of ways in the laboratory. In this study, two types of stiffness tests were performed. A so-called stress pulse test where a "haversine" stress pulse is placed vertically through a cross-section in the centre of the core at three different temperatures. Also, a sinusoidal frequency test was carried out, where the master curve and phase angle of the asphalt mixtures are found by repeatedly applying a load on the asphalt cores, which alternates between tensile and compressive loads in the core. The test is therefore carried out with different frequencies of the load but at one fixed temperature, and then a so-called master curve is created by comparing the results. Nine different asphalt mixtures were tested, they can be sorted into AC16, AC11 and BRL16, where AC asphalt is the top asphalt layer and BRL asphalt is the base layer asphalt that lies below in the road structure. AC asphalt generally has a lower porosity than BRL asphalt to prevent water from accumulating in the pavement and to prevent the water from reaching the lower layers in the road structure. BRL asphalt contains less bitumen than AC asphalt. The results indicate that there does not seem to be a simple relationship between stiffness and the largest stone size, bitumen type or the additive SBS, which has a decisive effect on the stiffness of the asphalt mixes, although there is some correlation between them. On the other hand, it can still be seen that the asphalt mixes AC16 are generally stiffer than the AC11 and BRL16 mixes. Asphalt mixtures that contain SBS seem to be more rigid than those that do not contain additives, especially at high temperatures. Tests also show that mixtures containing hard bitumen (PG 70/100) are generally stiffer than mixtures containing soft bitumen (PG 160/220), but this becomes clear when examining the mixtures which do not contain the additive SBS. A comparison with similar asphalt mixes from Sweden and Norway was made and it turns out that the Icelandic asphalt mixes have considerably lower stiffness than those from the neighbouring countries. It is worth noting, however, that various factors other than stone size and bitumen penetration depth affect the stiffness of the asphalt. These include void space, bitumen content, grading curve and additives, but these properties are not known for the Swedish and Norwegian mixes. The results could also be affected by the fact that the Icelandic cores that were studied in this project are cores taken from the street, while the Swedish and Norwegian cores were created in a laboratory.

Námsleið: Vélaverkfræði
Leiðbeinendur: Halldór Pálsson og Jón Hreiðar Ríkharðsson
Prófdómari: Guðrún Arnbjörg Sævarsdóttir, Prófessor við Háskólann í Reykjavík

Ágrip

Verkefnið fjallar um varmafræðilega greiningu á inntaks og úttaks straumum „solid oxide“ rafgreinis til að besta orkunotkun við háhita vetnisframleiðslu með varmaorkunýtingu. Líkön voru sett upp í Aspen Hysys til að greina staðsetningar í inntaksstraumnum með möguleika á aukinni varmaorku nýtingu og varmfræðilega eiginleika vökvans. CoolProp var notað til að herma og besta varmadælur fyrir staðsetningarnar í inntaksstraumnum sem greindar voru í Aspen. Þrjár staðsetningar voru greindar sem hafa mismunandi áhrif á heildar raforku notkun kerfisins. Fyrsta staðsetninging hefur möguleikann á að minnka varmaorkuþörfina um 57,3 kWth og lækka nauðsynlegt hitastig varmaorkugjafans í 127°C. Önnur staðsetningin getur minnkað raforkuþörf inntakskerfisins um 4,8-6,6%, sem nemur um 0,18-0,24% af heildar raforkunotkun fyrir vetnis framleiðsluna. Niðurstöður þessarar staðsetningar eru allar fræðilega þar sem úttakshitastig þjöppunar er hærra en hámarks úttakshitastig þjappa á markaðnum í dag. Þriðja staðsetningin hefur mestu möguleika fyrir betri orkunýtingu en er metin tæknilega óraunhæf og var því ekki skoðuð nánar. Notkun varmadæla til að minnka nauðsynlegt hitastig varmaorkugjafans til gufuframleiðslu fyrir SOE kerfi var einnig skoðað. Niðurstöður benda til þess að hitastig niður í 90-100°C geta verið notuð með tvegga-skrefa varmadælu fyrir svipaðan kostnað og notkun á 163°C heitum jarðvarma beint.

Study programme:  Mechanical Engineering
Advisors: Halldór Pálsson and Jón Hreiðar Ríkharðsson
Examiner: Guðrún Arnbjörg Sævarsdóttir, Professor at Reykjavík University

Abstract
In this study SOE inlet and outlet streams are analyzed from a thermodynamic point of view to optimize energy usage in high temperature hydrogen production with thermal energy integration. Thermodynamic models were developed in Aspen Hysys to analyze locations in the feed stream with potential for increased thermal energy integration and determine fluid properties. CoolProp was used to model and optimize heat pumps for the feed stream locations identified in Aspen. In total three locations were identified with varying effects on the total electricity use of the system. The first location has the potential to reduce the thermal energy demand by 57.3 kWth and the required source temperature to 127°C. The second location can reduce the total electrical energy demand of the feed system by 4.8-6.3%, equivalent to 0.18-0.24% of the total electrical energy used for hydrogen production. Results at location 2 are theoretical as the compressor outlet temperature exceeds the maximum discharge temperatures of commercially available compressors. The third location identified has the highest potential for energy savings but is evaluated as unfeasible for the foreseeable future and was not studied further. The possibility of lowering the required thermal energy source temperature for steam generation was also considered. Results indicate that it is possible to achieve steam generation for an SOE feed with source temperatures as low as 90-100°C with a two-stage heat pump at a very similar cost to direct geothermal utilization with 163°C source temperatures.  

Námsleið: Umhverfis- og auðlindafræði
Leiðbeinendur: Christiaan Richter & Ólafur Ögmundarson
Prófdómari: Alexandra Kjeld, umhverfisverkfræðingur hjá Eflu

Ágrip

Í þessari ,,cradle-to-grave“ LCA, eru umhverfisáhrif tveggja ökutækjategunda, dísel ICEV og BEV, og þriggja eldsneytisvalkosta, hefðbundinnar dísilolíu, B7 lífdísilblöndu og rafmagns, reiknuð og metin til að ákvarða þau umhverfisvænustu í samhengi Albaníu.

Study programme:  Environment and Natural Resources
Advisors: Christiaan Richter & Ólafur Ögmundarson
Examiner: Alexandra Kjeld, Environmental Engineer at Efla

Abstract
In this comparative cradle-to-grave life cycle assessment, the environmental impacts of three product systems combining two vehicles, a diesel ICEV and a BEV, and three fuelling options, conventional diesel, a B7 biodiesel blend, and electricity, are calculated and evaluated to determine the most environmentally benign in the context of Albania. While the Government of Albania has stipulated its goal of reducing GHG emissions by shifting to alternative vehicle powertrains and fuels by 2030, there has been little research on the impacts, including GWP, over their life cycle. The life cycle assessment methodology used in this study relies on SimaPro for product system modelling and Ecoinvenent 3.9.1 as the source database for the calculation of impacts from the vehicle production stage through the end-of-life stage. Results indicate that, from a life-cycle perspective, the ICEV fuelled by conventional diesel outperforms the ICEV fuelled by B7 and the BEV to a small extent in the majority of impact categories. However, in impact categories where the BEV performs better, it does so to a much greater degree, including in GWP due to the Albanian electricity grid mix being generated from RES. The ICEV powered by B7 produced from palm oil is not preferrable in any environmental impact category. The results of this study make a strong case for the Albanian government’s continued push for development of diversified RES alongside the adoption of BEVs in the country’s vehicle population and also point to the necessity of exploring other feedstocks for the production of biodiesel for the Albanian market.