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Research Papers

Model Verification of Mist/Steam Cooling With Jet Impingement Onto a Concave Surface and Prediction at Elevated Operating Conditions

[+] Author and Article Information
Ting Wang

Energy Conversion and Conservation Center, University of New Orleans, New Orleans, LA 70148-2220twang@uno.edu

T. S. Dhanasekaran

Energy Conversion and Conservation Center, University of New Orleans, New Orleans, LA 70148-2220tdhanase@uno.edu

J. Turbomach 134(2), 021016 (Jun 28, 2011) (11 pages) doi:10.1115/1.4003056 History: Received June 29, 2010; Revised July 15, 2010; Published June 28, 2011; Online June 28, 2011

Abstract

Internal mist/steam blade cooling technology is proposed for advanced gas turbine systems that use the closed-loop steam cooling scheme. Previous experiments on mist/steam heat transfer with a 2D slot jet impingement onto a concave surface showed cooling enhancement of up to 200% at the stagnation point by injecting approximately 0.5% of mist under low temperature and pressure laboratory conditions. Realizing the difficulty in conducting experiments at elevated pressure and temperature working conditions, computational fluid dynamics (CFD) simulation becomes an opted approach to predict the potential applicability of the mist/steam cooling technique at real GT operating conditions. In this study, the CFD model is first validated within 3% and 6% deviations from experimental results for the flows of steam-only and mist/steam flow cases, respectively. The validated CFD model is then used to simulate a row of multiple holes impinging jet onto a concave surface under elevated pressure, temperature, and Reynolds number conditions. The predicted results show an off-center cooling enhancement with a local maximum of 100% at $s/d=2$ and an average cooling enhancement of about 50%. The mist cooling scheme is predicted to work better on a concave surface than on the flat surface. The extent of wall jet and the size of 3D recirculation zones are identified as a major influencing parameter on the curvature effect on mist cooling performance. The mist enhancement from a slot jet is more pronounced than a row of round jets. The effects of wall heat flux and mist ratio on mist cooling performance are also investigated in this study.

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Figures

Figure 1

(a) Experimental setup (5) and (b) geometry details of the slot jet CFD computational domain

Figure 2

Droplet-wall interaction models

Figure 3

Computational domain and enlarged elements near the impingement area

Figure 4

Effect of radiation on wall temperature for the steam-only validation case: Re=7500 and q″=3350 W/m2

Figure 5

Validation of the CFD model (steam-only) of a slot jet impinging over a concave surface at two heat fluxes and Reynolds number cases

Figure 6

Validation of CFD results with the experimental data for steam and mist slot impinging jet over concave surface at the lower heat flux condition with q″=3350 and Re=7500; a 3°C prediction error in the stagnation region is grossly translated into 45% discrepancy in h-value due to the wall temperature approaching the saturation temperature

Figure 7

Mist impinging results with higher q″=7540 W/m2 and Re=15,000 over the concave surface: (a) Tw, (b) h-values, and (c) cooling enhancement

Figure 8

Geometry details for a single row of round jets impinging onto a concave surface

Figure 9

Computed mist/steam cooling results of a single row of round impinging jets on a concave surface under laboratory conditions (no experimental data are available for comparison)

Figure 10

Velocity vector plot at the middle plane of (a) the slot jet, (b) a round jet hole, (c) the secondary flow, and (d) droplet pathlines

Figure 11

Computed effect of heat flux on a single row of round impinging jets on the concave surface under laboratory conditions

Figure 12

Computed effect of mist ratio for a single row of round impinging jets on a concave surface under laboratory conditions

Figure 13

Simulated results of a single row of impinging jets over a concave surface at elevated condition

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