Effect of Orifice Jet Configuration on Heat Transfer in a Channel With Inclined Target Surface Cooled by Single Array of Impinging Jets With Outflow in Both Directions

2008 ◽  
Author(s):  
Ali A. Al-Mubarak ◽  
S. M. Shaahid ◽  
Luai M. Al-Hadhrami
Keyword(s):  
Heat Transfer ◽  
Leading Edge ◽  
Target Surface ◽  
Impinging Jets ◽  
Percentage Increase ◽  
Heat Transfer Characteristics ◽  
Target Plate ◽  
Aspect Ratios ◽  
Transfer Behavior ◽  
Feed Channel

An experimental work has been carried out to investigate the effect of orifice-jet plate configuration on heat transfer behavior in a channel with inclined heated target plate cooled by single array of equally spaced impinging jets. Air ejected from an array of orifices is impinges on the heated target surface. The target plate forms the leading edge of a gas turbine blade. The study includes the effect of various orifice-jet plate configurations, feed channel aspect ratios H/d = 5, 7, and 9, and Reynolds number Re = 9300, 14400, and 18880 on the heat transfer characteristics for a given outflow orientation (outflow passing out in both the directions). Three orifice-jet plate configurations (centered, staggered, and tangential holes) have been examined. It has been noticed that Nusselt number (Nu) is high for higher aspect ratios. For a given plate-1 with single array of equally spaced centered jets and for Re = 18800 (outflow passing out in both directions), the local Nu for H/d = 9 has been found to be greater than Nu of H/d = 7 by 5%. The percentage increase in average Nu has been found to be about 11% with centered holes as compared staggered orifice-jet plate. The percentage increase in average Nu has been found to be about 11% with staggered jet-plate as compared to tangential orifice-jet plate configuration.

Heat Transfer in a Channel With Inclined Target Surface Cooled by Single Array of Impinging Jets

2007 ◽  
Author(s):  
Luai M. Al-Hadhrami ◽  
S. M. Shaahid ◽  
Ali A. Al-Mubarak
Keyword(s):  
Heat Transfer ◽  
Leading Edge ◽  
Target Surface ◽  
Impinging Jets ◽  
Heat Transfer Characteristics ◽  
Target Plate ◽  
Transfer Characteristics ◽  
Aspect Ratios ◽  
Channel Aspect Ratio ◽  
Feed Channel

An experimental investigation has been carried out to study the heat transfer characteristics in a channel with heated target plate inclined at an angle cooled by single array of centered impinging jets. The target plate forms the leading edge of a gas turbine blade. The work includes the effect of various exit outflow orientations and crossflow and feed channel aspect ratios on the heat transfer characteristics for a given orifice-jet plate configuration. Three feed channel aspect ratios (H/d = 5, 7, 9) and have been examined. In general, it has been observed that Nu is high for higher aspect ratios. This increase can be attributed to increase in strength of impinging jets due to increase in feed channel aspect ratio. Additionally, for a given jet-orifice plate with centered holes and for a given Re = 18800, the heat transfer is almost the same through out the target surface for the outflow passing out in both the directions.

scholarly journals Heat transfer in a channel with inclined target surface cooled by single array of centered impinging jets

2013 ◽  
Vol 17 (4) ◽  
pp. 1195-1206
Author(s):  
Mubarak Al ◽  
S.M. Shaahid ◽  
Luai Al-Hadhramic
Keyword(s):  
Heat Transfer ◽  
Target Surface ◽  
Reynolds Numbers ◽  
Impinging Jets ◽  
Heat Transfer Characteristics ◽  
Target Plate ◽  
Maximum Heat ◽  
Transfer Characteristics ◽  
Aspect Ratios ◽  
Feed Channel

An experimental investigation has been carried out to study the heat transfer characteristics in a channel with heated target plate inclined at an angle cooled by single array of equally spaced centered impinging jets for three different jet Reynolds numbers (Re=9300, 14400 and 18800). Air ejected from an array of orifices impinges on the heated target surface The target plate forms the leading edge of a gas turbine blade cooled by jet impingement technique. The work includes the effect of jet Reynolds numbers and feed channel aspect ratios (H/d = 5, 7, 9 where H=2.5, 3.5, 4.5 cm and d=0.5 cm) on the heat transfer characteristics for a given orifice jet plate configuration with equally spaced centered holes with outflow exiting in both directions (with inclined heated target surface). In general, It has been observed that, H/d=9 gives the maximum heat transfer over the entire length of the target surface as compared to all feed channel aspect ratios. H/d=9 gives 3% more heat transfer from the target surface as compared to H/d=5 (for Re=14400). Also, it has been observed that the magnitude of the averaged local Nusselt number increases with an increase in the jet Reynolds number for all the feed channel aspect ratios studied.

Arrays of Impinging Jets with Spent Fluid Removal through Vent Holes on the Target Surface—Part 1: Average Heat Transfer

1980 ◽  
Vol 102 (4) ◽  
pp. 994-999 ◽  
Author(s):  
B. R. Hollworth ◽  
L. Dagan
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Target Surface ◽  
Local Heat ◽  
Impinging Jets ◽  
Superior Performance ◽  
Jet Flows ◽  
Target Plate ◽  
Average Heat ◽  
Fluid Removal

Measurements of average convective heat transfer are reported for square arrays of impinging air jets. The target plate on which the jets impinge is perforated so that spent air is withdrawn through the plate rather than at one or more edges of the array, as is usually the case in such investigations. Jet holes and vent holes had the same diameters, but the spacing of the jet holes was twice that of the vent holes. This information is especially relevent to the design of hybrid cooling configurations, in which a surface is cooled by the combined mechanisms of impingement and transpiration. Tests were conducted for both inline arrangements (with a vent hole opposite each jet orifice) and for staggered arrangements; and the latter always yielded higher average heat transfer. The degradation of performance of inline arrays was most pronounced when the clearance between the jet orifice plate and the target plate was small. Under these conditions, a significant portion of each jet flows directly out through the opposing vent without “scrubbing” the target surface. Arrays with staggered vent holes yield heat transfer rates consistently higher (sometimes by as much as 35 percent) than the same jet array with edge venting. The authors attribute the superior performance of the former geometry to high local heat transfer due to boundary layer suction in the vicinities of the vent holes.

Characteristics of Cooling of the Leading Edge With a Row of Dual Impinging Jets

2008 ◽  
Author(s):  
X. C. Li ◽  
P. Corder
Keyword(s):  
Heat Transfer ◽  
Turbine Blades ◽  
Leading Edge ◽  
Local Heat Transfer ◽  
Target Surface ◽  
Impinging Jets ◽  
Internal Cooling ◽  
Stagnation Region ◽  
High Heat Transfer ◽  
Two Jets

The leading edge of turbine blades is one of the critical areas that need to be cooled effectively because of the high local heat transfer rate of the main flow. Film cooling with different shaped holes as well as internal cooling by impinging jets has successfully been applied in modern gas turbine applications. This paper numerically studies the cooling of the leading edge with a row of dual impinging jets — two jets close to each other. Heat transfer of the dual jets is compared to that of a single jet (in a row) based on the same flow rate or jet velocity. The effect of the distance between the dual jets and the jet inclination angle is examined to seek the best geometric parameters. In addition, the curvature of the leading edge surface is considered to examine the heat transfer difference between curved and flat walls. Various jet-to-target spacing and Reynolds numbers are also studied. Results show that the dual impinging jets generally produce two high heat transfer regions in the stagnation point, and the peak value is slightly higher than the single row of jets with the same Reynolds number. When the distance between two jets is 3d, the jet flow after bouncing back from the symmetry line affects the heat transfer as a crossflow. The target surface curvature has little effect on the overall heat transfer, but the peak heat transfer coefficient is lower on the curved surface than that on the flat surface. The dual impinging jets present a higher average heat transfer around the stagnation region.

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.

Leading Edge Impingement With Racetrack Shaped Jets and Varying Inlet Supply Conditions

2013 ◽  
Author(s):  
C. Neil Jordan ◽  
Cassius A. Elston ◽  
Lesley M. Wright ◽  
Daniel C. Crites
Keyword(s):  
Heat Transfer ◽  
Test Section ◽  
Turbine Blades ◽  
Leading Edge ◽  
Target Surface ◽  
Reynolds Numbers ◽  
Impinging Jets ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Crossflow Velocity

Impinging jets are often employed within the leading edge of turbine blades and vanes to combat the tremendous heat loads incurred as the hot exhaust gases stagnate along the exterior of the airfoil. Relative to traditional cylindrical jets, racetrack shaped impinging jets have been shown to produce favorable cooling characteristics within the turbine airfoil. This investigation experimentally and numerically quantifies the cooling characteristics associated with a row of racetrack shaped jets impinging on a concave, cylindrical surface. Detailed Nusselt number distributions are obtained using both a transient liquid crystal technique and commercially available CFD software (Star CCM+ from CD-Adapco). Three geometrical jet inlet and exit conditions are experimentally investigated: a square edge, a partially filleted edge (r/dH,Jet = 0.25), and a fully filleted edge (r/dH,Jet = 0.667). Additionally, to investigate the effect of high crossflow velocities at the inlet of the jet, a portion of the flow supplied to the test apparatus radially bypasses the impingement section. Thus, the mass flow rate into the test section is varied to achieve the desired inlet crossflow conditions and jet Reynolds numbers. As a result, jet Reynolds numbers (ReJet) of 11500 and 23000 are investigated at supply duct Reynolds numbers (ReDuct) of 20000 and 30000. The results are compared to baseline cases where no mass bypasses the test section. Additionally, the relative jet – to – jet spacing (s/dH,Jet) is maintained at 8, the relative jet – to – target surface spacing (z/dH,Jet) is 4, the target surface curvature – to – jet hydraulic diameter (D/dH,Jet) is 5.33, and the relative thickness of the jet plate (t/dH,Jet) is 1.33. Measurements indicate that the addition of fillets at the edges of the jet orifice and the introduction of significant crossflow velocity at the inlet of the jet can significantly degrade the cooling characteristics on the leading edge of the turbine blade. The magnitude of such degradation generally increases with increasing fillet size and inlet crossflow velocity. The V2F model is adequate for predicting the flow field and target surface heat transfer in the absence of inlet crossflow; however, it is believed the turbulence within the jet is overpredicted by the CFD leading to elevated heat transfer coefficients (compared to the experimental results).

Effect of Feed Channel Width on Heat Transfer in a Rectangular Duct With an Array of Off-Set Jets

2006 ◽  
Author(s):  
Luai M. Al-Hadhrami
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Target Surface ◽  
Reynolds Numbers ◽  
Impinging Jets ◽  
The Other ◽  
Channel Width ◽  
Rectangular Duct ◽  
Feed Channel ◽  
Plate Distance

Experimental investigation was carried out to study the heat transfer characteristics in a rectangular duct cooled by an array of impinging jets. Air ejected from an array of orifices is aimed at the heated target surface and exits from the radial outlets. The effect of feed channel widths (5 ≤ H / d ≤ 9), jet to target plate distance (4 ≤ S/d ≤ 8), outflow orientation and jet Reynolds numbers (9300 ≤ Rej ≤ 18800) with a single array of equally spaced off-set orifice jets of diameter d = 0.5 cm on heat transfer was studied. Results indicated that the outflow orientation causing crossflow effect significantly affects the Nusselt number distributions on the target surface. Relatively higher Nusselt number values were obtained for the outflow orientation where the flow exits in both the directions. The feed channel width H/d = 7 gave relatively higher values of heat transfer compared to the other two feed channel widths. The jet-to-plate distance S/d = 4 resulted in higher heat transfer compared to the other jet-to-plate distances.

Arrays of Impinging Jets With Spent Fluid Removal Through Vent Holes on the Target Surface, Part 2: Local Heat Transfer

1983 ◽  
Vol 105 (2) ◽  
pp. 393-402 ◽  
Author(s):  
B. R. Hollworth ◽  
G. Lehmann ◽  
J. Rosiczkowski
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Target Surface ◽  
Local Heat ◽  
Impinging Jets ◽  
Extensive Study ◽  
Heat Transfer Characteristics ◽  
Fluid Removal ◽  
Air Jets ◽  
Approximate Mathematical Model

An extensive study was conducted to determine the heat transfer characteristics of arrays of turbulent air jets impinging on perforated target surfaces. Spent air was withdrawn through vent holes on the surface, rather than along one or more of its edges, as had been done in all previous investigations. An earlier publication presented average heat transfer data for such systems; this paper gives results of comprehensive measurements of local heat transfer. Also given are the results of flow visualization studies, and an approximate mathematical model which predicts distributions of local heat transfer which agree satisfactorily with test data.

Experimental and Numerical Investigation of a Shower Head Advanced Jet Impingement on Concave Surfaces

2018 ◽  
Author(s):  
Alankrita Singh ◽  
Bhamidi V. S. S. S. Prasad
Keyword(s):  
Heat Transfer ◽  
Leading Edge ◽  
Jet Impingement ◽  
Target Surface ◽  
Curvature Effect ◽  
Heat Transfer Characteristics ◽  
Impingement Cooling ◽  
Impingement Heat Transfer ◽  
Gap Ratio ◽  
Improved Performance

A novel configuration of jet impingement cooling for leading edge of a gas turbine blade is proposed in this paper. The new configuration is obtained by rearranging the jet impingement holes in a shower head fashion with a combination of circular and elliptic holes. The entire configuration is simulated by a jet impingement pipe (JIP) to experimentally investigate the improved performance of cooling of concave target surfaces. The central JIP has circular ends, remaining four neighboring JIP have 45° chamfer at one of its ends facing target surface to ensure uniformity and extension in cooling coverage. The heat transfer characteristics of jet impingement were investigated both experimentally and numerically by varying jet Reynolds number and gap ratio. Simulations are also carried out for different curvature ratios to determine the relative surface curvature effect on jet impingement heat transfer. This is accomplished by varying diameter of concave surface. The augmentation in heat transfer by both the elliptic (chamfered JIP) and circular (whose all JIP ends are circular) shower head arrangements are compared.

On the heat transfer characteristics of a Lamilloy cooling structure with curvatures with different pin fins configurations

2020 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Lei Luo ◽  
Yifeng Zhang ◽  
Chenglong Wang ◽  
Songtao Wang ◽  
Bengt Ake Sunden
Keyword(s):  
Heat Transfer ◽  
Leading Edge ◽  
Target Surface ◽  
Edge Region ◽  
Heat Transfer Characteristics ◽  
Content Type ◽  
Pin Fin ◽  
Transfer Characteristics ◽  
Turbine Vane ◽  
Pin Fins

Purpose The pin fin is applied into a Lamilloy cooling structure which is broadly used in the leading edge region of the modern gas turbine vane. The purpose of this paper is to investigate effects of the layout, diameter and shape of pin fins on the flow structure and heat transfer characteristics in a newly improved Lamilloy structure at the leading edge region of a turbine vane. Design/methodology/approach A numerical method is applied to investigate effects of the layout, diameter and shape of pin fins on the flow structure and heat transfer characteristics in a newly improved Lamilloy structure at the leading edge of a turbine vane. The diverse locations of pin fins are Lp = 0.35, 0.5, 0.65. The diameter of the pin fins varies from 8 mm to 32 mm. Three different ratios of root to roof diameter for pin fins are also investigated, i.e. k = 0.5, 1, 2. The Reynolds number ranges from 10,000 and 50,000. Results of the flow structures, heat transfer on the target surface and pin fin surfaces, and friction factor are studied. Findings The heat transfer on the pin fin surface gradually decreases and then increases as the location of the pin fins increases. Increasing the diameter of the pin fins causes the heat transfer on the pin fin surface to gradually increase, while a lower value of the friction factor occurs. Besides, the heat transfer on the pin fin surface at a small root diameter increases remarkably, but a slight heat transfer penalty is found at the target surface. It is also found that both the Reynolds analogy performance and the thermal performance are increased compared to the baseline whose diameter and normalized location of pin fins are set as 16 and 0.5 mm, respectively. Social implications The models provide a basic theoretical study to deal with nonuniformity of the temperature field for the turbine vane leading edge. The investigation also provides a better understanding of the heat transfer and flow characteristics in the leading edge region of a modern turbine vane. Originality/value This is a novel method to adopt pin fins into a Lamilloy cooling structure with curvature. It presents that the heat transfer of the pin fin surface in a pin-fin Lamilloy cooling structure with curvature can be significantly increased by changing the parameters of the pin fins which may lead to various flow behavior. In addition, the shape of the pin fin also shows great influence on the heat transfer and flow characteristics. However, the heat transfer of the target surface shows a small sensitivity to different layouts, diameter and shape of pin fin.

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