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
Mist/Steam Heat Transfer of Multiple Rows of Impinging Jets
Internal mist/steam blade cooling technology is considered the future of high-temperature gas turbine systems that burn hydrogen or synthetic gases. This paper experimentally investigates the mist/steam heat transfer of three rows of circular jet impingement in a confined channel. Fine water droplets with an average diameter of 3-μm are generated by atomizing water through small nozzles under high pressure. The circular jets have a uniform diameter of 8-mm, and the distance between adjacent jets in a row is 3 diameters. Jets in different rows are staggered and the distance between rows is 1.5 diameters. The spacing of nozzle-to-target is 2.8 diameters. Experiments were conducted with Reynolds numbers at 7,500 and 15,000 and heat fluxes ranging from 3,350 to 13,400W/m2 . The results indicate that the wall temperature significantly decreased because of mist injection. A region of high cooling enhancement is observed and more extensive than those employing one row of circular jets or a slot jet. While the details depend on flow conditions, it is seen that the enhanced region of 3-row jets is about 5 jet diameters at Re = 7,500, q” = 7.54 kW/m2 , and ml /ms = 3.5%, compared to 2 jet diameters for single-row jets. The enhancement becomes negligible after a certain distance downstream. The maximum local cooling enhancement is up to 800% by injecting 3.5% of mist at low heat flux condition and 150% for high heat flux condition. The average cooling enhancement can achieve more than 100% within 2 jet-diameter distance from the stagnation line at Re = 15,000 and ml /ms = 1.5%.Copyright © 2004 by ASME
Effects of reservoir volume on performance of pulse tube cooler.
A pulse tube cooler has the advantages of long-life and low-vibration over conventional cryocoolers such as G-M and Stirling coolers because of the absence of moving parts at low temperature. On the other hand, the combination of a reservoir and orifice is indispensable to optimize the performance of pulse tube coolers. In order to make the pulse tube cooler compact for practical applications, the volume of reservoir should be minimized. This paper analyzes the effects of the reservoir volume on the thermodynamic performance of various components in a simple orifice and a double-inlet pulse tube cooler by combining a linearized model with a thermodynamic analysis. Expressions of entropy production for those components are presented. The results show that the reservoir volume has a significant influence on the entropy production in the various components when the reservoir to pulse tube volume ratio is smaller than about 5. The ratio is important to determine the minimum reservoir volume for a pulse tube cooler. Optimum settings for a double-inlet pulse tube cooler are also discussed.