Mist/Steam Heat Transfer With Jet Impingement Onto a Concave Surface

2003 ◽  
Vol 125 (3) ◽  
pp. 438-446 ◽  
Author(s):  
Xianchang Li ◽  
J. Leo Gaddis ◽  
Ting Wang
Keyword(s):  
Stagnation Point ◽  
Heated Surface ◽  
Leading Edge ◽  
Jet Impingement ◽  
Future Generation ◽  
Heat Fluxes ◽  
Concave Surface ◽  
Surface Cooling ◽  
Cooling Enhancement ◽  
Confined Channel

Internal mist/steam blade cooling technology is proposed for the future generation of Advanced Turbine Systems (ATS). Fine water droplets about 5 μm were carried by steam through a slot jet onto a concave heated surface in a confined channel to simulate inner surface cooling at the leading edge of a turbine blade. Experiments covered Reynolds numbers from 7500 to 22,000 and heat fluxes from 3 to 21 kW/m2. Results indicate that the cooling is enhanced significantly near the stagnation point by the mist, decreasing downstream. Unlike impingement onto a flat target where the enhancement vanished at six jet diameters downstream, the cooling enhancement over a concave surface prevails at all points downstream. Similar to the results of the flat surface, the cooling enhancement declines at higher heat fluxes. Up to 200 % cooling enhancement at the stagnation point was achieved by injecting approximately 0.5 % of mist.

Mist/Steam Heat Transfer With Jet Impingement Onto a Concave Surface

2002 ◽  
Author(s):  
Xianchang Li ◽  
J. Leo Gaddis ◽  
Ting Wang
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Stagnation Point ◽  
Flat Surface ◽  
Leading Edge ◽  
Jet Impingement ◽  
Heat Fluxes ◽  
General Level ◽  
Transfer Enhancement ◽  
Surface Cooling

Internal mist/steam blade cooling technology has been considered for the future generation of Advanced Turbine Systems (ATS). Fine water droplets about 5 μm were carried by steam through a single slot jet onto a concave heated target surface in a confined channel to simulate inner surface cooling at the leading edge of a turbine blade. Experiments covered Reynolds numbers from 7,500 to 22,000 and heat fluxes from 3 to 21 kW/m2. The general level of heat transfer coefficient is, within experimental uncertainty, the same as the flat surface at comparable conditions. The experimental results indicate that the cooling is enhanced significantly near the stagnation point by the mist, decreasing downstream. Unlike impingement onto a flat plate the enhancement continues at all points downstream. Similar to the results of the flat surface, the heat transfer enhancement declines at higher heat fluxes. Up to 200% heat transfer enhancement at the stagnation point was achieved by injecting approximately 0.5% of mist.

Mist/Steam Heat Transfer in Confined Slot Jet Impingement

2000 ◽  
Vol 123 (1) ◽  
pp. 161-167 ◽  
Author(s):  
X. Li ◽  
J. L. Gaddis ◽  
T. Wang
Keyword(s):  
Heat Transfer ◽  
Stagnation Point ◽  
Jet Impingement ◽  
Target Surface ◽  
Future Generation ◽  
Reynolds Numbers ◽  
Heat Fluxes ◽  
Stagnation Region ◽  
Blade Cooling ◽  
Confined Channel

Internal mist/steam blade cooling technology has been considered for the future generation of Advanced Turbine Systems (ATS). Fine water droplets of about 5 μm were carried by steam through a single slot jet onto a heated target surface in a confined channel. Experiments covered Reynolds numbers from 7500 to 25,000 and heat fluxes from 3 to 21 kW/m2. The experimental results indicate that the cooling is enhanced significantly near the stagnation point by the mist, decreasing to a negligible level at a distance of six jet widths from the stagnation region. Up to 200 percent heat transfer enhancement at the stagnation point was achieved by injecting only ∼1.5 percent of mist. The investigation has focused on the effects of wall temperature, mist concentration, and Reynolds number.

Mist/Steam Heat Transfer in Confined Slot Jet Impingement

2000 ◽  
Author(s):  
X. Li ◽  
J. L. Gaddis ◽  
T. Wang
Keyword(s):  
Heat Transfer ◽  
Stagnation Point ◽  
Jet Impingement ◽  
Target Surface ◽  
Future Generation ◽  
Reynolds Numbers ◽  
Heat Fluxes ◽  
Stagnation Region ◽  
Blade Cooling ◽  
Confined Channel

Internal mist/steam blade cooling technology has been considered for the future generation of Advanced Turbine Systems (ATS). Fine water droplets about 5 μm were carried by steam through a single slot jet onto a heated target surface in a confined channel. Experiments covered Reynolds numbers from 7500 to 25000 and heat fluxes from 3 to 21 kW/m2. The experimental results indicate that the cooling is enhanced significantly near the stagnation point by the mist, decreasing to a negligible level at a distance of 6 jet widths from the stagnation region. Up to 200% heat transfer enhancement at the stagnation point was achieved by injecting only ∼1.5% of mist. The investigation has focused on the effects of wall temperature, mist concentration, and Reynolds number.

Free Jet Impingement Heat Transfer of a High Prandtl Number Fluid Under Conditions of Highly Varying Properties

1999 ◽  
Vol 121 (3) ◽  
pp. 592-597 ◽  
Author(s):  
J. E. Leland ◽  
M. R. Pais
Keyword(s):  
Heat Transfer ◽  
Heated Surface ◽  
Jet Impingement ◽  
Turbulent Jets ◽  
Heat Fluxes ◽  
Lubricating Oil ◽  
Fluid Temperature ◽  
Transfer Coefficients ◽  
Constant Property ◽  
Wide Range

An experimental investigation was performed to determine the heat transfer rates for an impinging free-surface axisymmetric jet of lubricating oil for a wide range of Prandtl numbers (48 to 445) and for conditions of highly varying properties (viscosity ratios up to 14) in the flowing film. Heat transfer coefficients were obtained for jet Reynolds numbers from 109 to 8592, nozzle orifice diameters of 0.51, 0.84 and 1.70 mm and a heated surface diameter of 12.95 mm. The effect of nozzle to surface spacing (1 to 8.5 mm), was also investigated. Viscous dissipation was found to have an effect at low heat fluxes. Distinct heat transfer regimes were identified for initially laminar and turbulent jets. The data show that existing constant property correlations underestimate the heat transfer coefficient by more than 100 percent as the wall to fluid temperature difference increases. Over 700 data points were used to generate Nusselt number correlations which satisfactorily account for the highly varying properties with a mean absolute error of less than ten percent.

Effect of Rotation on Heat Transfer of a Concave Surface With Array Impingement Jet

2013 ◽  
Author(s):  
Eui Yeop Jung ◽  
Chan Ung Park ◽  
Dong Hyun Lee ◽  
Jun Su Park ◽  
Sehjin Park ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Stagnation Point ◽  
Turbine Blades ◽  
Leading Edge ◽  
Target Surface ◽  
Concave Surface ◽  
Heat Transfer Characteristics ◽  
Impingement Jet ◽  
Transfer Characteristics ◽  
Inner Surface

Turbine blades are directly exposed to hot oncoming combustion gases, so their leading edges require effective cooling techniques. Here, we investigated the heat transfer characteristics in a concave duct with an array of impingement jets, including the effect of rotation. The concave duct was used to simulate the inner surface of the leading edge of a blade. The inner surface was cooled by the impingement array jet method. The jet Reynolds number (Re) based on the jet nozzle diameter was fixed at 3,000, and the ratio of the height to target surface (H/d) was set to 2.0. The injection holes (d = 5 mm) were positioned in a staggered pattern, and the rotation number was about 0.032. We focused on the effects of rotating position orientations. We investigated front, leading, and trailing orientations. Naphthalene sublimation method was used to determine the local heat/mass transfer distributions, and the flow pattern was obtained by numerical simulation. Crossflow in the jet arrays was generated by the spent air from the impingement jet. The crossflow changes the flow characteristics at the stagnation point along the streamwise direction on a concave surface. Rotation of the duct increased the flow mixing compared with the stationary case. The jet flow was deflected because of the Coriolis force in the leading and trailing orientations. However, in the front orientation, the heat transfer characteristics showed deflection in the clockwise direction in the developing flow away from the stagnation point. Overall, the averaged heat transfer values were enhanced in the rotating cases. The trailing orientation case showed the highest averaged heat transfer among all tested cases.

Evaluation of the Stagnation Point Region Overshoot

1992 ◽  
Vol 114 (1) ◽  
pp. 73-78
Author(s):  
H. H. Sogin
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Stagnation Point ◽  
Heated Surface ◽  
Leading Edge ◽  
Outer Edge ◽  
Local Similarity ◽  
Total Rate ◽  
Total Heat Transfer ◽  
Circular Disks

Stagnation point region overshoot is the augmentation of total heat transfer owing to the presence of insulation at the stagnation point region of an otherwise isothermal body. Evidence summarized by the present work indicates that this paradoxical event can be made to occur. The overshoot is due to the singularly high temperature gradient that is impressed upon the boundary layer just as it arrives at the leading edge of the heated surface after passing over the insulated central portion. The evidence comprises experimental results based on the mass-heat analog using sublimation of naphthalene and on theoretical boundary layer calculations using a method of local similarity. In the experiments, the insulated surfaces were simulated with inert wax, and isothermal regions with active naphthalene. The surfaces were circular disks facing uniform airstreams. The finding was that the total rate of mass transfer would be as much as 10 percent greater than that of a fully active disk if the radius of the central inert region were half the radius of the disk. Put another way, if only the 30-percent annulus at the outer edge of the disk were active, it would transfer mass at the same rate as the completely active disk under the same circumstances of flow. Corresponding results are expected from analogically heated disks operating with Prandtl number near unity and disk Reynolds number ranging from 5000 to 250,000.

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

2011 ◽  
Vol 134 (2) ◽  
Author(s):  
Ting Wang ◽  
T. S. Dhanasekaran
Keyword(s):  
Jet Impingement ◽  
Elevated Pressure ◽  
Operating Conditions ◽  
Model Verification ◽  
Concave Surface ◽  
Cfd Model ◽  
Cooling Performance ◽  
Cooling Enhancement ◽  
Mist Cooling ◽  
Steam Cooling

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.

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

2010 ◽  
Author(s):  
Ting Wang ◽  
T. S. Dhanasekaran
Keyword(s):  
Jet Impingement ◽  
Elevated Pressure ◽  
Operating Conditions ◽  
Model Verification ◽  
Concave Surface ◽  
Cfd Model ◽  
Cooling Performance ◽  
Cooling Enhancement ◽  
Mist Cooling ◽  
Steam Cooling

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 2-D 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 difficultly in conducting experiments at elevated pressure and temperature working conditions, 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% deviation 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 condition. The predicted results show an off-center cooling enhancement with a local maximum of 200% at s/d = 2 and an average cooling enhancement of about 150%. 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 3-D 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.

Sign in / Sign up

Export Citation Format

Share Document