An Investigation of Applicability of Transporting Water Mist for Cooling Turbine Vanes
This paper presents a numerical study to investigate the feasibility of transporting mist through the internal cooling channel in high-pressure turbine vanes for film cooling over the vane’s surface. The idea of using mist film cooling to enhance conventional air cooling has been proven to be a feasible technique in the laboratory conditions and by computational simulations. However, there is a challenge to this technique to prove that the water mist can survive in the very hot environment inside the gas turbine casings and internal air passages and be delivered to the film injection holes. Both a zero-dimensional mist evaporation analytical model and 3-D computational fluid dynamic (CFD) scheme are employed for analysis. In the CFD simulation, the Lagrangian /Eulerian method is used along with the discrete phase model (DPM) to track the evaporation process of water droplets. The high-pressure water mist is injected into the stream of cooling air extracted from the compressor through the outer gas turbine casing near the vane before it reaches the vane internal cooling cavity. Using the mist equivalent of 10% of the cooling air mass flow rate, the results show that, when the liquid droplets are atomized to 30 μm in diameter initially, the droplets can survive inside the internal cooling passages and be delivered to the film cooling injection hole location with droplets of 20 μm in diameter; and alternatively, an initially 20 μm droplet can be delivered at 12μm in diameter, which is sufficiently large for completing the required external film cooling task.Copyright © 2012 by ASME
An Experimental Study of Mist Film Cooling With Fan-Shaped Holes on an Extended Flat Plate: Part 1 — Heat Transfer
Motivated by the need to further improve film cooling in terms of both cooling effectiveness and coolant coverage area, the mist/air film cooling scheme is investigated through experiments using fan-shaped holes over an extended downstream length in this study. Both an existing wind tunnel and test facility, used in previous work, have been retrofitted. The first modification was extending the length of the flat plate test section to cover longer distances downstream of the injection holes, up to X/D = 100, in order to investigate whether mist cooling can be harnessed farther downstream where single-phase film cooling is not effective. The second modification was to incorporate a fan-shaped diffusion hole geometry in order to investigate whether mist can further enhance the film cooling performance of the already highly effective fan-shaped holes. A Phase Doppler Particle Analyzer (PDPA) system is employed to measure droplet size, velocity, and turbulence information. An infrared camera and thermocouples are both used for temperature measurements. Part 1 is focused on the heat transfer result on the wall, and Part 2 is focused on the two-phase droplet multiphase flow behavior. Three blowing ratios are investigated.The results show that, at low blowing ratios when the film is attached to the surface, the enhancement of the mist film cooling effectiveness, compared to the air-only case, on the centerline of the hole ranges from 40% in the near hole region to over 170% at X/D = 100. Due to the diffusive nature of the fan-shaped hole, the laterally-averaged enhancement is on par with that on the centerline. The significant enhancement over the extended downstream distance from X/D = 40–100 is attributed to the evaporation time needed to evaporate all of the droplets. Each droplet acts as a cooling sink and flies over a distance before it completely vaporizes. This “distributed cooling” characteristic allows controlled cooling by manipulating the size distribution of the water droplets to extend the cooling effects of the droplets farther downstream from the injection location. At higher blowing ratios, when the cooling film is lifted off from the surface, the cooling enhancement drops below 40%. Although the enhancement in the near hole region X/D < 40 is about 20% lower than that achieved by using the cylindrical holes, the magnitudes of the mist adiabatic film cooling effectiveness using fan-shaped holes are still much higher than those of the cylindrical holes.Copyright © 2014 by ASME
Bodies of Evidence: Burial, Memory and the Recovery of Missing Persons in Cyprus
List of Figures and Maps Acknowledgements Chapter 1. Heirs of Antigone: Disappearances and Political Memory Chapter 2. Suppressed Experiences Chapter 3. Testimonies of Fragmentation, Recollections of Unity Chapter 4. The Missing as a Set of Representations Chapter 5. The Martyrdom of the Missing Chapter 6. L'image Juste, or Juste une Image? Chapter 7. Painting Absences, Describing Losses Chapter 8. Antigone's Doubt, Creon's Dilemma Chapter 9. Power, Complicity, and Public Secrecy Bibliography Appendices Index