| 1. |
- Andreasen, Jesper Graa, et al.
(author)
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Multi-Objective Optimization of Organic Rankine Cycle Power Plants Using Pure and Mixed Working Fluids
- 2016
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In: Energies. - : MDPI AG. - 1996-1073 .- 1996-1073. ; 9:322
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Journal article (peer-reviewed)abstract
- For zeotropic mixtures, the temperature varies during phase change, which is opposed to the isothermal phase change of pure fluids. The use of such mixtures as working fluids in organic Rankine cycle power plants enables a minimization of the mean temperature difference of the heat exchangers, which is beneficial for cycle performance. On the other hand, larger heat transfer surface areas are typically required for evaporation and condensation when zeotropic mixtures are used as working fluids. In order to assess the feasibility of using zeotropic mixtures, it is, therefore, important to consider the additional costs of the heat exchangers. In this study, we aim at evaluating the economic feasibility of zeotropic mixtures compared to pure fluids. We carry out a multi-objective optimization of the net power output and the component costs for organic Rankine cycle power plants using low-temperature heat at 90 ◦C to produce electrical power at around 500 kW. The primary outcomes of the study are Pareto fronts, illustrating the power/cost relations for R32, R134a and R32/R134a (0.65/0.35mole). The results indicate that R32/R134a is the best of these fluids, with 3.4 % higher net power than R32 at the same total cost of 1200 k$.
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| 2. |
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| 3. |
- Christoph, Richter, et al.
(author)
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Identification of optimum molten salts for use as heat transfer fluids in parabolic trough CSP plants. A techno-economic comparative optimization
- 2017
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In: AIP Conference Proceedings. - : American Institute of Physics (AIP). - 0094-243X .- 1551-7616. - 9780735417571
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Journal article (peer-reviewed)abstract
- Parabolic trough power plants using thermal oil as heat transfer fluid are the most mature concentrating solar power technology and state of the art. To further increase their efficiency and lower costs, molten salts can be used as heat transfer fluid. This results in higher operating temperature differences for improved cycle efficiencies and enables direct thermal energy storage at lower costs due to omission of the oil-to-salt heat exchanger and the need for smaller storage sizes. As a variety of salts are available to choose from, this study uses a multi-objective optimization to identify the most suitable heat transfer fluid for three locations in South Africa, Spain and Chile. The lowest values for the levelized costs of electricity (LCOE) can be found in Chile using Solar Salt as heat transfer fluid (75.0 $/MWhe). Generally, Solar Salt offers the lowest LCOE values followed by thermal oil and Hitec. The results also suggest that the choice of the heat transfer fluid is dependent on the direct normal irradiance (DNI) at each location. Thermal oil is competitive with Solar Salt in small systems at locations with low DNI values, whereas Hitec can be cheaper than thermal oil in large systems at locations with high DNI. Furthermore, it is also investigated at which freeze alert temperature set point the activation of the freeze protection system is optimal. The results indicate that this temperature should be chosen close to the solar field inlet temperature for small systems, while it can be lowered significantly for large systems to reduce electricity consumption from the freeze protection system.
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| 4. |
- Ferruzza, Davide, et al.
(author)
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Optimal start-up operating strategies for gas-boosted parabolic trough solar power plants
- 2018
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In: Solar Energy. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0038-092X .- 1471-1257. ; 176, s. 589-603
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Journal article (peer-reviewed)abstract
- Concentrating solar power plants are taking an increasing share in the renewable energy generation market. Parabolic trough is one of such technologies and the most commercially mature. However, this technology still suffers from technical challenges that need to be addressed. As these power plants experience daily start-up procedures, the optimal performance in transient operation needs to be considered. This paper presents a performance based modelling tool for a gas-boosted parabolic trough power plant. The objective of the paper is to define an optimal operational strategy of the power plant start-up procedure with the aim of minimizing its fuel consumption while at the same time maximizing its electric energy output, taking into account all the thermo-mechanical constraints involved in the procedure. Heating rate constraints of the steam generator and the booster heater, and the steam turbine start-up schedule were considered. The simulation model was developed based on a power plant located near Abu Dhabi, and was validated against real operational data with a maximum integral relative deviation of 4.3% for gross electric energy production. A multi-objective optimization was performed for a typical operating week during winter and spring weather conditions. The results suggest that in order to minimize the fuel consumption and at the same time maximize the electric energy production, an evaporator heating rate of 6 K/min is an optimal value both for winter and spring conditions.
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| 5. |
- Fuente, Santiago Suárezde la, et al.
(author)
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Selection of cooling fluid for an organic Rankine cycle unit recovering heat on a container ship sailing in the Arctic region
- 2017
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In: Energy. - : Elsevier BV. - 0360-5442 .- 1873-6785. ; 141, s. 975-990
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Journal article (peer-reviewed)abstract
- As Arctic sea ice coverage declines it is expected that marine traffic could increase in this northern region due to shorter routes. Navigating in the Arctic offers opportunities and challenges for waste heat recovery systems (WHRS). Lower temperatures require larger heating power on board, hence a larger demand for waste heat usage, to cover services and maintaining on board spaces temperatures. However, a lower heat rejection temperature increases the WHRS thermal efficiency. The air temperature for the Arctic route selected is colder than that of the seawater, opening the opportunity of having air as coolant. This paper explores the use of two different coolants, air and seawater, for an organic Rankine cycle (ORC) unit using the available waste heat in the scavenge air system of a container ship navigating in Arctic Circle. Using a two-step single objective optimisation process, detailed models of air and seawater heat exchangers are evaluated as the WHRS condensers. The results suggest that an ORC unit using R1233zd(E) as its working fluid coupled with seawater as its coolant is the preferable option to reduce CO2 emissions. Using the ambient air as the coolant while a less effective option could be cheaper to instal
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| 6. |
- Larsen, Ulrik, 1972, et al.
(author)
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A comparison of advanced heat recovery power cycles in a combined cycle for large ships
- 2014
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In: Energy. - : Elsevier BV. - 0360-5442 .- 1873-6785. ; 74
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Journal article (peer-reviewed)abstract
- Strong motivation exists within the marine sector to reduce fuel expenses and to comply with ever stricter emission regulations. Heat recovery can address both of these issues. The ORC (organic Rankine cycle), the Kalina cycle and the steam Rankine cycle have received the majority of the focus in the literature. In the present work we compare these cycles in a combined cycle application with a large marine two-stroke diesel engine. We present an evaluation of the efficiency and the environmental impact, safety concerns and practical aspects of each of the cycles. A previously validated numerical engine model is combined with a turbocharger model and bottoming cycle models written in Matlab. Genetic algorithm optimisation results suggest that the Kalina cycle possess no significant advantages compared to the ORC or the steam cycle. While contributing to very high efficiencies, the organic working fluids possess high global warming potentials and hazard levels. It is concluded that the ORC has the greatest potential for increasing the fuel efficiency, and the combined cycle offers very high thermal efficiency. While being less efficient, the steam cycle has the advantages of being well proven, harmless to the environment as well as being less hazardous in comparison.
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| 7. |
- Larsen, Ulrik, 1972, et al.
(author)
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Development of a model for the prediction of the fuel consumption and nitrogen oxides emission trade-off for large ships
- 2015
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In: Energy. - : Elsevier BV. - 0360-5442 .- 1873-6785. ; 80, s. 545-555
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Journal article (peer-reviewed)abstract
- The international regulations on fuel efficiency and NOx emissions of commercial ships motivate the investigation of new system layouts, which can comply with the regulations. In combustion engines, measures to reduce the fuel consumption often lead to increased NOx emissions and careful consideration of this trade-off mechanism is required in the design of marine propulsion systems. This study investigates five different configurations of two-stroke diesel-based machinery systems for large ships and their influence on the mentioned trade-off. Numerical models of a low-speed two-stroke diesel engine, turbochargers and an ORC (organic Rankine cycle), are used for the optimisation of the NOx andfuel consumption at design and part-load conditions, using a multi-objective genetic algorithm. Moreover, the effects of engine tuning and exhaust gas recirculation are investigated. The results suggest that increased system complexity can lead to lower fuel consumption and NOx. Fuel consumption reductions of up to 9% with a 6.5% NOx reduction were achieved using a hybrid turbocharger and organic Rankinecycle waste heat recovery system.
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| 8. |
- Svensson, Anette, 1972-, et al.
(author)
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Textuniversum i praktiken
- 2018
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Conference paper (peer-reviewed)abstract
- Samhällets och skolans pågående digitalisering medför nya litteraturdidaktiska förutsättningar och utmaningar i klassrummet. Ämnesplaner har reviderats och innehåller förtydliganden kring digitalisering. I ämnesplanen för svenska på gymnasiet står det till exempel att "eleverna [ska] ges förutsättningar att utveckla sin förmåga att orientera sig, läsa, sovra och kommunicera i en digital textvärld med interaktiva och föränderliga texter” (Skolverket, 2018). Dagens elever har förkunskaper och är förtrogna med andra medier än de som traditionellt sett är dominerande i skolan. Idag är det vanligt att ungdomar ser filmen, läser boken, spelar spelet, lyssnar på soundtrack och tittar på tv-serien, det vill säga de deltar i textuniversum. Ett textuniversum bygger på att en berättelse, eller delar därav, återskapas i olika text- och medieformat (Lundström & Svensson, 2017). Denna presentation bygger på tre pilotstudier där arbete med olika textuniversum har genomförts på olika skolstadier. Syftet med det övergripande arbetet är att bidra med kunskap om hur textuniversum tillsammans med en lektionsdesign kan bidra till att elever utvecklar ett analytiskt och kreativt tänkande. Pilotstudierna genomförsmed ett praktiknära förhållningssätt där delar av lektionsdesignen genomförs kollaborativt och både forskare och lärare är aktiva. Lektionsdesignen består av tre faser; planeringsfasen, genomförandefasen och utvärderingsfasen. I planeringsfasen samarbetar forskaren och läraren, här fastställs lektionsdesignen och textuniversum väljs. I genomförandefasen genomför och dokumenterar läraren designen som innebär att först arbeta medkärntexten, sedan gruppvis med andra delar av textuniversumet (fragment) och slutligen skapas tvärgrupper med syftet att skapa en transmedial produkt. I utvärderingsfasen genomförs intervjuer med elever och lärare samt analyser av dokumentation och insamlade produkter. I resultatdelen presenteras de genomförda pilotstudierna; Harry Potter, Stolthet & fördom och The Walking Dead med fokus på att visa resultat från datainsamlingen samt att levandegöra textuniversumen för att förtydliga och konkretisera arbetet i klassrummet.
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