| 271. |
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| 272. |
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| 273. |
- Saadatfar, Bahram, et al.
(författare)
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Conceptual modeling of nano fluid ORC for solar thermal polygeneration
- 2014
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Ingår i: 2013 ISES SOLAR WORLD CONGRESS. - : Elsevier BV. ; , s. 2696-2705
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Konferensbidrag (refereegranskat)abstract
- A model has been developed for thermodynamic cycle of the solar thermal production of power, heating and cooling utilizing nano fluid as a working fluid in Organic Rankine Cycle. The proposed working fluid provides enhancement in power, heating, and cooling as useful outputs. Initial studies were performed with silver-nano pentane as a working fluid in the cycle. This work extends the application of the cycle to working fluids consisting of organic fluid mixtures. Nano Organic fluid could be used successfully in solar thermal power plants, as working fluids in Rankine cycles. An advantage of using nano fluid as a working fluid is that there are mature experiences with building components for these fluids. A commercially available modeling program has been used to model and investigate the performance of the system. The potential and advantages of using nano fluid are discussed. It is found that the thermodynamic efficiencies achievable with nano organic fluid, under optimum conditions, are higher than those obtained from the base fluid. Further, the size of heat exchangers, evaporator, and condenser are lower than those using the base fluid.
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| 274. |
- Saadatfar, Bahram, et al.
(författare)
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Exergo-environmental analysis of nano fluid ORC low-grade waste heat recovery for hybrid trigeneration system
- 2014
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Ingår i: Energy Procedia. - : Elsevier. ; , s. 1879-1882
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Konferensbidrag (refereegranskat)abstract
- In this work, a thermodynamic model based on theoretical and experimental data is developed for utilizing nano fluid organic Rankine cycle (nORC) in a trigeneration hybrid system. The trigeneration hybrid system composed of a solid biomass boiler, gas turbine cycle, a nORC, cooling, and a heating system. The exergy of the system analyzed; moreover, environmental impact assessments and interrelated parametric studies are examined. The results show higher exergy efficiency for the hybrid trigeneration employed nORC, and indicate that carbon dioxide emissions for utilizing nano fluid in nORC trigeneration system are less than conventional working fluid system.
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| 275. |
- Saadatfar, Bahram, et al.
(författare)
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Nano Organic Rankine Cycle for Enhanced Heat Recovery
- 2013
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Ingår i: ASME ORC 2013, 2nd International seminar on ORC power systems.
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Konferensbidrag (refereegranskat)abstract
- There will be an incredible energy challenge in the future. With growing population, more and more energy needs to meet society’s demands. Fossil fuels are limited resources; hence there will be need more renewable energy as well as more efficient use of energy by recovering low-grade heat source. An organic Rankine cycle (ORC) system would be attractive and promising technology for energy conversion systems in low temperature thermal energy sources. Many actual ORC’s applications have been installed; nevertheless, one of the major challenges in the ORC technology is working fluid. The difficulties involved in the accurate thermophysical properties in addition to safety of organic fluids that are commonly found in ORC, may result in relatively low efficiency as well as heat exchanger and component size. In the organic Rankine cycle, heat exchangers, including evaporators and condensers, are the dominant components with most working fluid accumulation. Moreover, the working fluid is linked to the expansion part; therefore, selecting an organic fluid and expander should be performed at the same time. Conventional Organic Rankine Cycle uses organic fluid as a working fluid, whereas nano fluid organic Rankine cycle (nORC) uses nano material and organic compound as a working fluid and it is particularly suitable for utilizing small scale heat exchangers, due to creating better thermal match both in boiling and condensing, in low temperature applications. In this work, utilizing nano organic fluid as a working fluid for ORC for Some types of nanoparticles are studied; thermophysical properties of nano ORC candidate in the specific temperature range are measured and analyzed. Also, this study presents acceptable operating conditions and expansion machine by investigating the interaction among the expansion part and nano organic working fluid.
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| 276. |
- Saha, Ranjan, 1984-, et al.
(författare)
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Aerodynamic Implication of Endwall and Profile Film Cooling in a Transonic Annular Cascade
- 2013
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Ingår i: 21st ISABE Conference. - Busan, Korea.
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Konferensbidrag (refereegranskat)abstract
- An experimental study is performed to observe the aerodynamic implications of endwall and profile film cooling on flow structures and aerodynamic losses. The investigated vane is a geometrically similar transonic nozzle guide vane with engine-representative cooling geometry. Furthermore, a new formulation of the cooling aerodynamic loss equation is presented and compared with the conventional methods. Results from a 5-hole pneumatic probe show that the film coolant significantly alters the secondary flow structure. The effect of different assumptions for the loss calculation is shown to significantly change the measured loss.
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| 277. |
- Saha, Ranjan, 1984-
(författare)
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Aerodynamic Investigation of Leading Edge Contouring and External Cooling on a Transonic Turbine Vane
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Efficiency improvement in turbomachines is an important aspect in reducing the use of fossil-based fuel and thereby reducing carbon dioxide emissions in order to achieve a sustainable future. Gas turbines are mainly fossil-based turbomachines powering aviation and land-based power plants. In line with the present situation and the vision for the future, gas turbine engines will retain their central importance in coming decades. Though the world has made significant advancements in gas turbine technology development over past few decades, there are yet many design features remaining unexplored or worth further improvement. These features might have a great potential to increase efficiency. The high pressure turbine (HPT) stage is one of the most important elements of the engine where the increased efficiency has a significant influence on the overall efficiency as downstream losses are substantially affected by the prehistory. The overall objective of the thesis is to contribute to the development of gas turbine efficiency improvements in relation to the HPT stage. Hence, this study has been incorporated into a research project that investigates leading edge contouring near endwall by fillet and external cooling on a nozzle guide vane with a common goal to contribute to the development of the HPT stage. In the search for HPT stage efficiency gains, leading edge contouring near the endwall is one of the methods found in the published literature that showed a potential to increase the efficiency by decreasing the amount of secondary losses. However, more attention is necessary regarding the realistic use of the leading edge fillet. On the other hand, external cooling has a significant influence on the HPT stage efficiency and more attention is needed regarding the aerodynamic implication of the external cooling. Therefore, the aerodynamic influence of a leading edge fillet and external cooling, here film cooling at profile and endwall as well as TE cooling, on losses and flow field have been investigated in the present work. The keystone of this research project has been an experimental investigation of a modern nozzle guide vane using a transonic annular sector cascade. Detailed investigations of the annular sector cascade have been presented using a geometric replica of a three dimensional gas turbine nozzle guide vane. Results from this investigation have led to a number of new important findings and also confirmed some conclusions established in previous investigations to enhance the understanding of complex turbine flows and associated losses. The experimental investigations of the leading edge contouring by fillet indicate a unique outcome which is that the leading edge fillet has no significant effect on the flow and secondary losses of the investigated nozzle guide vane. The reason why the leading edge fillet does not affect the losses is due to the use of a three-dimensional vane with an existing typical fillet over the full hub and tip profile. Findings also reveal that the complex secondary flow depends heavily on the incoming boundary layer. The investigation of the external cooling indicates that a coolant discharge leads to an increase of profile losses compared to the uncooled case. Discharges on the profile suction side and through the trailing edge slot are most prone to the increase in profile losses. Results also reveal that individual film cooling rows have a weak mutual effect. A superposition principle of these influences is followed in the midspan region. An important finding is that the discharge through the trailing edge leads to an increase in the exit flow angle in line with an increase of losses and a mixture mass flow. Results also indicate that secondary losses can be reduced by the influence of the coolant discharge. In general, the exit flow angle increases considerably in the secondary flow zone compared to the midspan zone in all cases. Regarding the cooling influence, the distinct change in exit flow angle in the area of secondary flows is not noticeable at any cooling configuration compared to the uncooled case. This interesting zone requires an additional, accurate study. The investigation of a cooled vane, using a tracer gas carbon dioxide (CO2), reveals that the upstream platform film coolant is concentrated along the suction surfaces and does not reach the pressure side of the hub surface, leaving it less protected from the hot gas. This indicates a strong interaction of the secondary flow and cooling showing that the influence of the secondary flow cannot be easily influenced. The overall outcome enhances the understanding of complex turbine flows, loss behaviour of cooled blade, secondary flow and interaction of cooling and secondary flow and provides recommendations to the turbine designers regarding the leading edge contouring and external cooling. Additionally, this study has provided to a number of new significant results and a vast amount of data, especially on profile and secondary losses and exit flow angles, which are believed to be helpful for the gas turbine community and for the validation of analytical and numerical calculations.
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| 278. |
- Saha, Ranjan, 1984-
(författare)
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Aerodynamic Investigations of a High Pressure Turbine Vane with Leading Edge Contouring at Endwall in a Transonic Annular Sector Cascade
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Efficiency improvement is an important aspect to reduce the use of fossil-based fuel in order to achieve a sustainable future. Gas turbines are mainly fossil-fuel based turbomachines, and, therefore, efficiency improvement is still the subject of many on-going research activities in the gas turbine community. This study is incorporated into a research project that investigates design possibilities of efficiency improvement at the high pressure turbine (HPT) stage. In the search for HPT-stage efficiency gains, leading edge (LE) contouring near the endwall is one of the methods found in the published literature that has shown a potential to increase the efficiency by decreasing the amount of secondary losses. The overall objective of the thesis is to contribute to the development of gas turbine efficiency improvements in relation to the HPT stage. Particularly, the influence of the LE fillet on losses and flow structure is investigated concentrating on the secondary flow. The core investigation is of an experimental nature. Detailed investigations of the flow field in an annular sector cascade (ASC) are presented with and without the LE fillet, using a geometric replica of a modern gas turbine nozzle guide vane (NGV) with a contoured tip endwall. Furthermore, a separate investigation is performed on a hub-cooled NGV, which focuses on endwalls, specifically the interaction between the hub film cooling and the mainstream (MS). The experimental investigations indicate that the LE fillet has no significant effect on the flow and energy losses of the investigated NGV. The reason why the LE fillet does not affect the losses might be due to the use of a three-dimensional vane with an existing typical fillet over the full hub and tip profile. Findings also reveal that the complex secondary flow depends heavily on the incoming boundary layer. Oil flow visualisation for the baseline case displays a clear saddle point, with a separation line where the horseshoe (HS) vortex separates into the suction side (SS) and the pressure side (PS), whereas for the filleted case, the saddle point is not noticeable. The investigation of a cooled vane, using a tracer gas carbon dioxide (CO2), reveals that the upstream platform film coolant is concentrated along the SS surfaces and does not reach the PS of the hub surface, leaving it less protected from the hot gas.
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| 279. |
- Saha, Ranjan, 1984-, et al.
(författare)
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Experimental studies of leading edge contouring influence on secondary losses in transonic turbines
- 2012
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Ingår i: ASME Turbo Expo 2012. - : ASME Press. - 9780791844748 ; , s. 1109-1119
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Konferensbidrag (refereegranskat)abstract
- An experimental study of the hub leading edge contouring using fillets is performed in an annular sector cascade to observe the influence of secondary flows and aerodynamic losses. The investigated vane is a three dimensional gas turbine guide vane (geometrically similar) with a mid-span aspect ratio of 0.46. The measurements are carried out on the leading edge fillet and baseline cases using pneumatic probes. Significant precautions have been taken to increase the accuracy of the measurements. The investigations are performed for a wide range of operating exit Mach numbers from 0.5 to 0.9 at a design inlet flow angle of 90°. Data presented include the loading, fields of total pressures, exit flow angles, radial flow angles, as well as profile and secondary losses. The vane has a small profile loss of approximately 2.5 % and secondary loss of about 1.1%. Contour plots of vorticity distributions and velocity vectors indicate there is a small influence of the vortex-structure in endwall regions when the leading edge fillet is used. Compared to the baseline case the loss for the filleted case is lower up to 13 % of span and higher from 13% to 20 % of the span for a reference condition with Mach no. of 0.9. For the filleted case, there is a small increase of turning up to 15 % of the span and then a small decrease up to 35 % of the span. Hence, there are no significant influences on the losses and turning for the filleted case. Results lead to the conclusion that one cannot expect a noticeable effect of leading edge contouring on the aerodynamic efficiency for the investigated 1st stage vane of a modern gas turbine.
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| 280. |
- Saha, Ranjan, et al.
(författare)
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Influence of pre-history and leading edge contouring on aero-performance of a 3D nozzle guide vane
- 2013
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Ingår i: Proceedings of the ASME Gas Turbine India Conference -2013- ; presented at ASME 2013 Gas Turbine India Conference, December 5-6, 2013, Bangalore, India. - : ASME Press.
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Konferensbidrag (refereegranskat)abstract
- Experiments are conducted to investigate the effect of the pre-history in the aerodynamic performance of a threedimensional nozzle guide vane with a hub leading edge contouring. The performance is determined with two pneumatic probes (5 hole and 3 hole) concentrating mainly on the endwall. The investigated vane is a geometrically similar gas turbine vane for the first stage with a reference exit Mach number of 0.9. Results are compared for the baseline and filleted cases for a wide range of operating exit Mach numbers from 0.5 to 0.9. The presented data includes loading distributions, loss distributions, fields of exit flow angles, velocity vector and vorticity contour, as well as, mass-averaged loss coefficients. The results show an insignificant influence of the leading edge fillet on the performance of the vane. However, the pre-history (inlet condition) affects significantly in the secondary loss. Additionally, an oil visualization technique yields information about the streamlines on the solid vane surface which allows identifying the locations of secondary flow vortices, stagnation line and saddle point.
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