Combustion is by far the most commonly used technology for energy conversion. The analysis of entropy generation and exergy loss is normally used to optimize thermal energy technologies such as gas turbines. The loss of exergy in the combustor is the largest of all component losses in gas turbine systems. The exergy efficiency of gas turbine combustors is typically 20-30%. In recent years the focus on reduction of climate gas and pollutant emissions from combustion has been a driving factor for research on combustion efficiency. The emphasis on fuel economy and pollution reduction from combustion motivates a study of the exergy efficiency of a combustion process. A bulk exergy analysis of the combustor does not take into account the complexity of the combustion process. The spatial dimensions of the flame must be accounted for in order gain detailed information about the entropy generation. This motivates a study of the local entropy production in a flame and quantifying the mechanisms that reduce the exergetic efficiency. The entropy production in combustion is also believed to have an effect on the stability of the flame. As most combustors operate with turbulent flow the emphasis of this report is on turbulent combustion.The source of exergy destruction or irreversibility in combustion is generally attributed to four different mechanisms: chemical reaction, internal heat transfer, mass diffusion of species, and viscous dissipation. The irreversibilities from the first three sources have been computed for a turbulent hydrogen H2 jet diffusion flame using prescribed probability density functions and data from experiments. The contribution of each source of exergy destruction is locally quantifed in the flame. Two different modeling assumptions are made, one based on a fast chemistry assumption and the other based on curve fitted relations from experimental data. The second law efficiency of the flame was found to be 98.7% when assuming fast chemistry, and 76.0% when curve fits from experimental data where used.The contribution from viscous dissipation has in previous studies been found to be negligible, and in order to simplify the modeling of the turbulent flow its contribution to the total entropy production has not been studied in this report.

SIMPLE, SIMPLER, SIMPLEC and IDEAL are solution procedures originally developed for incompressible flows and staggered grids. For SIMPLE, SIMPLER and SIMPLEC, extensions for collocated grids and for treatment of flows at all speeds have already been proposed. For IDEAL, only an extension for collocated grids has been found, and an extension for treatment of flows at all speeds is proposed here. Extended versions of SIMPLE and SIMPLER are implemented in Brilliant, a multiphysics CFD-program developed by Petrell AS. These implemented algorithms are compared to the existing solution procedure in Brilliant, an extended version of the SIMPLEC algorithm. As expected, SIMPLE and SIMPLEC gave almost identical solutions for all the three presented test cases. The values given by the SIMPLER algorithm differed slightly from the values given by the two other algorithms. When simulating a shock tube, all three algorithms showed large deviations from the quasi-analytical solution in some regions of the shock tube. The SIMPLER algorithm spent the least CPU time for this simulation example, while SIMPLE and SIMPLEC spent less CPU time than SIMPLER when simulating methane flow in a pipe. Even though the CPU time was not registered for the last simulation example, a pressure relief pipe, it was noticed that the time consumption was much greater for the SIMPLER algorithm than for SIMPLE and SIMPLEC.

In this paper theory on cylinder and wind turbine wakes have been studied, and experimental work on the wake behind a wind turbine have been carried out in the Fluids engineering laboratory at NTNU.The objective of this paper is to show and explain how the wake from the tower of a wind turbine develops and interacts with the rotor wake. It is desirable to study the wake for different operating conditions of the wind turbine to see how the wake development is affected. A summary of classical wake theory, aerodynamics and wind turbine wakes will be given. Measurements in the wake of a cylinder fitted with pressure taps for drag calculation will be compared to theory and used as a reference. Also, the wake behind the wind turbine tower with the blades taken off will be studied and compared to the tower wake found behind the operating wind turbine.For comparison, reference measurements were done in the wake behind a cylinder and behind the free standing wind turbine tower without blades. The drag coefficient obtained from pressure measurements on the cylinder surface were 1.077 and match the expected value of 1.2 fairly well. However, neither the shape nor the maximum velocity deficit measured in the wake fit the theoretical profile. Drag coefficients calculated from the momentum deficit across the wake were only in the range of 0.65, which is almost half of the expected, and the huge deviation from theory could not be explained. With values between 1.07 and 1.50 the measured drag coefficients in the wake of the tower alone were also not consistent with theory. The shape of the tower wake profile coincides better with theory than the cylinder wake, but the maximum velocity deficit is generally lower than predicted by theory. Difference in drag can be explained with blockage effect and the smaller velocity deficit may be attributed to the free stream flow over the top of the tower interfering with the wake downstream of the tower.Wake surveys behind the wind turbine were done at three operating conditions: Optimum tip speed ratio; low tip speed ratio, with power output half of output at best point operation; and high tip speed ratio, with power output half of output at best point operation. The increased turbulence level behind the rotor the flow seen by the tower is believed to creates a turbulent boundary layer which stays attached to the surface to a point further back on the tower, creating a narrower and weaker wake compared the free standing tower wake. Optimum turbine operation gives a stronger rotation of the wake doe to the higher torque on the blades compared to the two other cases. At high TSR the wake is more uniform, and the tower wake disappears faster than in the wake of the turbine operating at lower TSR. The Strouhal number found in all the wakes match well with theory and does not seem to be affected by the rotor wake except that the tower vortices dies out quicker.

Gevinstene ved høy delta T i fjernvarmenett er velkjente; lavere varmetap, høyere virkningsgrad i varmeproduksjonsenheter, mindre pumpearbeid og større kapasitet i nettet. Hvor stor delta T i fjernvarmenettet blir, avhenger i stor grad av utformingen av abonnentsentralene og reguleringen av dem. Antall trinn varmeveksling i abonnentsentralen har innvirkning på total delta T, og ulike studier har her konkludert noe forskjellig. Enkelte har funnet at tre-trinns-sentraler gir best nedkjøling av primærvannet ved høye utetemperaturer, mens to-trinns-sentraler er best ved lave. Andre studier har funnet det teoretiske potensialet for nedkjøling til å være likt for to- og tre-trinns-sentraler.Underdimensjonering og tilsmussing av varmevekslere fører til lavere primær delta T. Seriekobling av radiatorsystem og ventilasjonssystem gir bedre nedkjøling av primærvannet. Akkumulatortanker i tappevannssystemet kan ha praktiske fordeler, men reduserer delta T.Riktig innstilling av ulike børverdier i tappevannssystemet er viktig for å oppnå høyest mulig delta T. Vannstrømmen i sirkulasjonsledningen bør være lavest mulig. For innstilling av alle parametre i tappevannsystemet må man samtidig passe på å overholde temperaturkrav i forhold til legionellasmitte. Optimalisering av vannstrøm og temperatur i radiatorsystem gir også en gevinst. Målinger er utført i en totrinns abonnentsentral tilknyttet fjernvarmenettet i Trondheim. I sentralen er det installert en tank mellom ettervarmeren og blandeventilen i tappevannssystemet for å dempe temperatursvingninger. To radiatorkretser og en ventilasjonskrets er koblet i parallell.Temperaturen ut fra blandeventilen bør være 65 °C for å holde temperaturen over 60 °C i hele sirkulasjonsledningen. Den sekundære temperaturen ut fra ettervarmeren bør være 72,5 °C for å holde 70 °C ut fra tanken. Dette gir en temperaturforskjell på 7,5 °C. Den målte temperaturen mellom disse målepunktene er hele 17 °C i gjennomsnitt. Dette fører til en større enn nødvendig innblanding av kaldt vann i blandeventilen, og lavere total delta T over sentralen. Fjernvarmeleverandørene krever en primær delta T på 50 °C over varmeveksleren for romoppvarming ved dimensjonerende utetemperatur(-19 °C i Trondheim). Målinger viser at dette kravet brytes allerede ved utetemperaturer rundt -5 °C og estimater peker mot en delta T på 30-33 °C ved dimensjonerende utetemperatur. Dette skyldes at varmeveksleren for romoppvarming er underdimensjonert.Systemvirkningsgraden er forholdet mellom levert energi til sluttmålet og den primære energien som trengs for å få det til. Primærenergifaktor for elektrisk energi er 3,31 mens den for varmeenergi levert til fjernvarmenettet i Trondheim er 1,46. Det er da antatt at søppel har en primærenergifaktor på 1.Systemvirkningsgraden for tappevannssystemet i den undersøkte abonnentsentralen er funnet til å være 0,2367. Det største varmetapet foregår i fordelingsnettet i bygget. 59 % av varmeenergien levert til abonnentsentralen går tapt her. Hvis man regner med at 25 % av den tapte energien kan nyttes til romoppvarming ender man opp med en systemvirkningsgrad på 0,3238.Beregninger viser at systemvirkningsgraden kun blir marginalt lavere ved å innføre akkumulering av tappevann i tappevannssystemet.

The goal of this thesis is to evaluate if flutter is a challenge to a 10 MW wind turbine. Flutter is an aeroelastic instability which occurs due to the interaction between the aerodynamic forces and the elasticity of the blade. Torsional motions of the blade lead to variations in the aerodynamic forces due to changes in the angle of attack of the airfoil. The variation in aerodynamic forces creates flapwise vibration of the blade. When the vibrations of the blades are in an unfavourable phase with the aerodynamic forces, flutter occurs. Flutter may lead to rapidly increasing vibrations of the blade and failure of the blade. The 10 MW reference turbine from NOWITECH, Norwegian Research Centre for Offshore Wind Technology, was studied. An aeroelastic stability analysis was performed using the aeroelastic stability tool HAWCStab2. It was found that this wind turbine becomes unstable at approximately twice the operational speed of the turbine. The turbine does not experience flutter in normal power producing operation. A simulation in the time domain was also performed, using the aeroelastic tool HAWC2. In a run-away situation, the turbine was found to become unstable with flutter before it reached the run-away speed. The turbine was then analysed with other blades. A softer blade and a stiffer blade were studied. The soft blade was found to become unstable at 1.8 times the operational speed of the turbine. The stiff blade was found to become unstable at around 2.5 times the operational speed. The stiff blade was the only blade where the turbine was able to reach the run-away speed without experiencing instabilities.

Sediment erosion is a large problem for turbines operated in sand laden water, especially in the Himalayas and the Andes Mountains, where the contents of hard minerals in the rivers are high. A program called <i>RenewableNepal</i> supports the development of a new design philosophy for hydraulic turbines. NTNU and Kathmandu University cooperate within this program, and this master thesis is part of that cooperation.The objective of this thesis is to carry out the hydraulic design of a Francis turbine with reduced velocities. As part of that, a design software has been developed, using Matlab as programming tool. This software has been used to generate a reference design with the same physical dimensions as for the existing runners at Jhimruk Hydrorelectric Centre in Nepal. CFD analysis has been performed to verify the design software output, showing good results. Analysis of erosion from CFD were not successful as mesh independency for the analysis could not be established. Hence results for erosion prediction from CFD studies has not been presented in this thesis.A parametric study has been carried out, varying either the outlet diameter, the number of pole pairs, the inlet velocity, the acceleration of the flow through the runner, the height of the shroud or the blade angle distribution. An erosion model was implemented in the design software, and used as a control variable for the parametric study. CFD analyses using Ansys CFX were performed for selected designs with lower erosion than the reference design. The largest reduction of erosion was obtained when increasing the number of pole pairs, which implies that the rotational speed of the turbine is decreased. This does however increase the size of both the turbine and the generator, which cause increased investment costs as well. CFD analysis shows that the hydraulic efficiency for this design is higher than for the reference design. It was also discovered that by changing the blade angle distribution, and consequently also the energy distribution, a substantial reduction of erosion was possible without changing the physical dimensions or the rotational speed of the turbine. The efficiency for this design is also higher than for the reference design. The most promising design was found as a combination of these two effects, giving a reduction of the erosion of 50 percent compared to the reference design. CFD analysis for this design show a good efficiency and acceptable flow conditions in the runner. This and other designs with the modified blade angle distribution will have an unconventional energy conversion through the runner, leading to larger hydraulic forces on the trailing edge of the blades. Strength analyses of the blade would be beneficial, but have not been performed.The main focus in this thesis has been on developing the design software and developing runner designs for reducing sediment erosion. There have been no attempts for optimizing the designs of the guide vanes and stay vanes due to time constraints.

Med inspirasjon frå lekkasja etter «Deepwater Horizon»/Macondobrønnulukka i2010, er det foreslått og modellert eit nytt system for innfanging og oppsamlingav olje rett frå brønnhovudet ved lekkasje på store havdjup. Dette systemetbestår av eit stigerøyr som er senka frå eit farty ned på lekkasjestaden, med einoppsamlingskuppel i nedre enden. Systemet blir tetta ved å påføre eit lågare indretrykk i denne kuppelen enn det hydrostatiske havbotntrykket, slik at koplingamellom kuppelen og havbotnen blir hydrodynamisk foresgla.Denne modellen, som også innheld ein grov modell for heile brønnen, gjennomgårdatasimuleringar, kor han er diskretisert med karakteristikkmetoden.Alle simuleringane er i 1D, einfase. Det er lagt hovudvekt på oppstarten avsystemet. Som plattform for datasimuleringane er MATLAB nytta, og alle simuleringarer gjort på ei 64-bits bærbar datamaskin.Det viser seg at den vanskelegaste delen av oppstarten er tida frå strøyminga istigerøyret er stilleståande, til trykket i oppsamlingskuppelen synk under brønnhovudtrykket,slik at dei to systema blir eitt. Ei løysing på dette ser ut til å vereein sakte, liten, ikkjelineær senking av stigerøyrets topptrykk i to steg, først tilforsegling og samanslåing er oppnådd. Etter dette blir systemet meir medgjørleg,og kan enkelt påførast kva sluttrykk ein treng for å få oppsamlingskuppelen til åsetje seg i havbotnen.

I denne rapporten er det sett på integrasjonen mellom kraftverk og CO2 fangstenhet, og hvordan avtapping av damp for å dekke energibehovet i reboileren påvirker ytelsen og virkningsgraden til kraftverkene. Dette er gjort ved å beregne energibehovet til fangstanlegget og deretter se hvordan kraftverkene ble påvirket når den dampmengden som fangstanlegget krevde ble fjernet fra dampturbinprosessene. Ved å se på både NGCC kraftverk og kullkraftverk får man et bredere grunnlag for å evaluere påvirkningen av avtappingen.Ved å beregne α - verdien for kraftverksprosessen med avtapping av damp får man et godt mål på hvor stor påvirkning avtappingen har på kraftverkets ytelse. α – verdien som, også omtales som faktoren for verdien av damp, er et forhold mellom energimengden som tappes ut og tap i produsert kraft. Simuleringene som er gjort for å finne α – verdien viser at trykknivået i overgangen mellom MT- og LT- turbinen har en markant påvirkning på yteevnen. Kullkraftverket fikk redusert den elektriske kraftproduksjonen med 11,8MW som følge av forhøyet trykk i avtappingspunktet. Tilsvarende tap for NGCC kraftverket ble på 6,6MW. Disse tapene utgjør rundt en prosent av den totale virkningsgraden til kraftverket.Slike tap i produksjon av elektrisk kraft vil føre til store økonomiske tap for kraftverket. Det viser seg også at det er stort potensial i optimalisering av de forskjellige prosessene.

SummaryThis Master Thesis is a conclusion on work done as part of the Resource Optimizationand recovery in the Materials industry project (Roma). This project is involved in thedevelopment of a new technology for power production from low temperature heat sourcesfor off gases from aluminum production cells. The technology is based on an transcriticalRankine cycle with CO2 as a working fluid, as the work recovery circuit. The center ofthe test facility is the expander, a prototype provided by Obrist Engineering . 81 testswere perfomed to investigate the behavoir of the expander cycle. Effect of three mainparameters were investigated:• Effect CO2 massflow rate• Effect of heat source temperature• Effect of CO2 condensation pressureFor each parameter combination, the high pressure side of the expander cycle was variedin order to find the maximum power output.This study clearly showed limitation of the turbine which cannot maintain large pressuredifference probably due to large internal leakages. As a result, turbine outlet is highlysuperheated. This superheat is lost energy for the power cycle, and is simply dumpedinto the heat sink. One possible improvement would be to include a recuperator thatrecovers superheat after the pump.The results also indicate that the fan of the air loop is too small: increasing the CO2 flowrate to limit superheat at turbine outlet leads to turbine inlet temperature reduction.Last, for large CO2 mass flow rate (3.5 kgmin) which is required for proper operation ofthe turbine, the power generated is too large for the generator installed on the loop. Itstemperature reached 120 °C for some conditions. A new solution should be seeked.Based on experimental results, a mode of the power cycle was implemented in Pro/IIand simulations were run in order to find an improved design. The main goal is to beable to run the cycle at high CO2 mass flow rate: 3.5 kgmin. It was found that the airloop fan should be able to deliver up to 1 260 m3h . The new generator or braking systemshould be able to absorb up to 297 W.

Våtgasskompressorer er en ny teknologi, og kan være svaret på hvordan uprosessert gass kan transporteres til prosessanleggene. Lykkes industrien med dette kan det føre til store kostnadsbesparelser som vil gjøre marginale felt lønnsomme. I tillegg vil teknologien føre til økt gassutvinning på eksisterende felt. I denne oppgaven er diffusor- og spiralhusdesign til eksisterende kompressor i laben på NTNU optimalisert. Ved hjelp av CFD programmet ANSYS 13.0 har de nye designene blitt simulert og strømningsbildet, ytelseskarakteristikk og polytropisk virkningsgrad har blitt dokumentert. I tillegg har simuleringer med partikkelinjeksjon blitt gjort for å se på hvilke innvirkning dette har for strømningsbildet i kompressoren. I diffusoren har fire nye design blitt laget. To er laget med nye diffusorbredder, et hvor innløpet har blitt innsnevret og et hvor diffusorutløpet ikke er avrundet. I spiralhuset har to nye design med økt tverrsnittareal blitt laget. I tillegg har eksisterende CFD modell av kompressoren på NTNU blitt oppdatert for å gjøre modellen mer lik kompressoren. Denne modellen benyttes som et sammenligningsgrunnlag for de andre designene. Analyse av de nye designene har vist at designet med det største spiralhuset har høyest trykkgjenvinning og polytropisk virkningsgrad for alle volumstrømmer. Maksimalt trykkforhold er 1,35 og maksimal polytropisk virkningsgrad er 85,1 % ved 0,86 m3/s. Eksisterende design har maksimal trykkøkning på 1,33 ved 0,76 m3/s og maksimal virkningsgrad på 82,7 % ved 0,86 m3/s. Simuleringene viste stor grad av seperasjon i diffusoren med det store spiralhuset, og kompressorytelsen vil økes ytterligere ved forbedring av diffusoren. Innsnevring av diffusor har redusert seperasjon i diffusoren, og dette har økt ytelsen. I tillegg har et ikke-avrundet diffusorutløp redusert virvelstrømning i spiralhuset betydelig.Partikkelsimuleringene har vist at partiklene legger seg på høytrykksiden av impelleren og blir kastet tangentielt mot spiralhuset. Partikkelinjeksjon reduserte strømningsvinkelen til gassen, α, i sentrum og mot shroud i diffusoren, mens vinkelen økte ved hub. Reduksjon i strømningsvinkel forbedret trykkøkningen til kompressoren med 4 %.