Use of Rib Turbulators to Enhance Postimpingement Heat Transfer for Curved Surface

2017 ◽  
Vol 139 (7) ◽  
Author(s):  
Jahed Hossain ◽  
Andres Curbelo ◽  
Christian Garrett ◽  
Wenping Wang ◽  
Jayanta Kapat ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Pressure Loss ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Curved Surface ◽  
Temperature Sensitive ◽  
Straight Section ◽  
Target Plate ◽  
Cfd Simulations ◽  
Rib Turbulators

The present study aims to investigate the heat transfer and pressure loss characteristics for multiple rows of jets impinging on a curved surface in the presence of rib turbulators. The target plate contains a straight section downstream of the impingement section. The rib turbulators are added only over the straight section, in an attempt to enhance the heat transfer while minimizing the pressure loss. The jet plate configuration in this study has fixed jet hole diameters and hole spacing. For the curved plate, the radius of the target plate is 32 times the diameter of the impingement holes. Impingement array configuration was chosen such that validation and comparison can be made with the open literature. For all the configurations, crossflow air is drawn out in the streamwise direction. Average jet Reynolds numbers ranging from 55,000 to 125,000 were tested. Heat transfer characteristics are measured using steady-state temperature-sensitive paint (TSP) to obtain local heat transfer distribution. The experimental results are compared with computational fluid dynamics (CFD) simulations. CFD results show that CFD simulations predict the heat transfer distribution well in the postimpingement area with turbulators.

Use of Rib Turbulators to Enhance Post-Impingement Heat Transfer for Curved Surface

2016 ◽  
Author(s):  
Jahed Hossain ◽  
Christian Garrett ◽  
Andres Curbelo ◽  
John Harrington ◽  
Wenping Wang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Pressure Loss ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Curved Surface ◽  
Temperature Sensitive ◽  
Straight Section ◽  
Target Plate ◽  
Cfd Simulations ◽  
Rib Turbulators

The present study aims to investigate the heat transfer and pressure loss characteristics for multiple rows of jets impinging on a curved surface in the presence of rib turbulators. The target plate contains a straight section downstream of the impingement section. The rib turbulators are added only over the straight section, in an attempt to enhance the heat transfer while minimizing the pressure loss. The jet plate configuration in this study has fixed jet hole diameters and hole spacing. For the curved plate, the radius of the target plate is 32 times the diameter of the impingement holes. Impingement array configuration was chosen such that validation and comparison can be made with the open literature. For all configurations, crossflow air is drawn out in the streamwise direction. Average jet Reynolds numbers ranging from 55,000 to 125,000 were tested. Heat transfer characteristics are measured using steady state temperature sensitive paint (TSP) to obtain local heat transfer distribution. The experimental results are compared with CFD simulations. CFD results show that CFD simulations predict the heat transfer distribution well in the post-impingement area with turbulators.

Nonuniform Jet Array Impingement on a Curved Surface

2017 ◽  
Vol 140 (5) ◽  
Author(s):  
Jahed Hossain ◽  
John Harrington ◽  
Wenping Wang ◽  
Jayanta Kapat ◽  
Steven Thorpe ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Pressure Loss ◽  
Flow Distribution ◽  
Local Heat Transfer ◽  
Target Surface ◽  
Local Heat ◽  
Temperature Sensitive ◽  
Transfer Coefficients ◽  
Temperature Sensitive Paint ◽  
Jet Array

Experiments to investigate the effect of varying jet hole diameter and jet spacing on heat transfer and pressure loss from jet array impingement on a curved target surface are reported. The jet plate configurations studied have varying hole diameters and geometric spacing for spatial tuning of the heat transfer behavior. The configuration also includes a straight section downstream of the curved section, where the effect on heat transfer and pressure loss is also investigated. The jet plate holes are sharp-edged. A steady-state measurement technique utilizing temperature-sensitive paint (TSP) was used on the target surface to obtain local heat transfer coefficients. Pressure taps placed on the sidewall and jet plate of the channel were used to evaluate the flow distribution in the impingement channel. For all configurations, spent air is drawn out in a single direction which is tangential to the target plate curvature. First row jet Reynolds numbers ranging from 50,000 to 160,000 are reported. Further tests were performed to evaluate several modifications to the impingement array. These involve blocking several downstream rows of jets, measuring the subsequent shifts in the pressure and heat transfer data, and then applying different turbulator designs in an attempt to recover the loss in the heat transfer while retaining favorable pressure loss. It was found that by using W-shaped turbulators, the downstream surface average Nusselt number increases up to ∼13% as compared with a smooth case using the same amount of coolant. The results suggest that by properly combining impingement and turbulators (in the post impingement section), higher heat transfer, lower flow rate, and lower pressure drop are simultaneously obtained, thus providing an optimal scenario.

Heat Transfer Enhancement and Pressure Loss Characteristics of Zig-Zag Channel With Dimples and Protrusions

2015 ◽  
Author(s):  
Sin Chien Siw ◽  
Minking K. Chyu ◽  
Mary Anne Alvin
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Pressure Loss ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Internal Cooling ◽  
Transfer Enhancement ◽  
Test Channel ◽  
Rib Turbulators ◽  
Cooling Passage

This paper described a detailed experimental study to explore an internal cooling passage that mimic a “zig-zag” pattern. There are four passages connected by 110° turning angle in a periodic fashion, hence the name. Experiments are performed in a scaled-up test channel with a cross-section of 63.5mm by 25.4mm, corresponding to the aspect ratio of 2.5:1. Compared to the conventional straight internal cooling passages, the zig-zag channel with several turns will generate additional secondary vortices while providing longer flow path that allows coolant to remove much more heat load prior to discharge into the hot mainstream. Surface features, (1) dimples, and (2) protrusions are added to the zig-zag channel to further enhance the heat transfer, while contributed to larger wetted area. The experiment utilizes the well-established transient liquid crystal technique to determine the local heat transfer coefficient distribution of the entire zig-zag channel. Protrusions exhibit higher heat transfer enhancement than that of dimples. However, both designs proved to be inferior compared to the rib-turbulators. Pressure loss in these test channels is approximately twofold higher than that of straight smooth test channel due to the presence of turns; but the pressure loss is lower than the zig-zag channel with rib-turbulators. The result revealed that one advantage of having either protrusions or dimples as these surface elements will resulted in gradual and more uniform increment of heat transfer throughout the entire channel compared to previous test cases.

Numerical Flow Simulation of Spacer Grids With Mixing Vanes in a 5 × 5 PWR Rod Bundle

2009 ◽  
Author(s):  
Moyse´s Alberto Navarro ◽  
Andre´ Augusto Campagnole dos Santos
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Pressure Loss ◽  
Considerable Increase ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Spacer Grid ◽  
Spacer Grids ◽  
Rod Bundle ◽  
Vane Angle

The spacer grids exert great influence on the thermal hydraulic performance of the PWR fuel assembly. The presence of the spacers has two antagonistic effects on the core: an increase of pressure drop due to constriction on the coolant flow area and increase of the local heat transfer downstream the grids caused by enhanced coolant mixing. The mixing vanes, present in most of the spacer grid designs, cause a cross and swirl flow between and in the subchannels, enhancing even more the local heat transfer at the cost of more pressure loss. Due to this important hydrodynamic feature the spacer grids are often improved aiming to obtain an optimal commitment between pressure drop and enhanced heat transfer. In the present work, the fluid dynamic performance downstream a 5 × 5 rod bundle with spacer grids is analyzed with a commercial CFD code (CFX 11.0). Eleven different split vane spacer grids with angles from 16° to 36° and a spacer without vanes were evaluated. The computational domain extends from ∼10 Dh upstream to ∼50 Dh downstream the spacer grids. The standard k-ε turbulence model with scalable wall functions and the total energy model were used in the simulations. The results show a considerable increase of the average Nusselt number and secondary mixing with the angle of the vane up to ∼20 Dh downstream the spacer, reducing greatly the influence of the vane angle beyond this region. As expected, the pressure loss through the spacer grid also showed considerable increase with the vane angle.

Full Surface Local Heat Transfer Coefficient Measurements in a Model of an Integrally Cast Impingement Cooling Geometry

1998 ◽  
Vol 120 (1) ◽  
pp. 92-99 ◽  
Author(s):  
D. R. H. Gillespie ◽  
Z. Wang ◽  
P. T. Ireland ◽  
S. T. Kohler
Keyword(s):  
Heat Transfer ◽  
Boundary Condition ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Local Heat Transfer Coefficient ◽  
Target Plate ◽  
Impingement Cooling ◽  
Impingement Plate

Cast impingement cooling geometries offer the gas turbine designer higher structural integrity and improved convective cooling when compared to traditional impingement cooling systems, which rely on plate inserts. In this paper, it is shown that the surface that forms the jets contributes significantly to the total cooling. Local heat transfer coefficient distributions have been measured in a model of an engine wall cooling geometry using the transient heat transfer technique. The method employs temperature-sensitive liquid crystals to measure the surface temperature of large-scale perspex models during transient experiments. Full distributions of local Nusselt number on both surfaces of the impingement plate, and on the impingement target plate, are presented at engine representative Reynolds numbers. The relative effects of the impingement plate thermal boundary condition and the coolant supply temperature on the target plate heat transfer have been determined by maintaining an isothermal boundary condition at the impingement plate during the transient tests. The results are discussed in terms of the interpreted flow field.

Heat Transfer Augmentation in a Rectangular Channel With Slit Rib-Turbulators on Two Opposite Walls

1997 ◽  
Vol 119 (3) ◽  
pp. 617-623 ◽  
Author(s):  
Jenn-Jiang Hwang ◽  
Tong-Miin Liou
Keyword(s):  
Heat Transfer ◽  
Rectangular Channel ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Open Area ◽  
Transfer Coefficients ◽  
Turbine Blade Cooling ◽  
Heat Transfer Coefficients ◽  
Ribbed Channel ◽  
Rib Turbulators

The effect of slit ribs on heat transfer and friction in a rectangular channel is investigated experimentally. The slit ribs are arranged in-line on two opposite walls of the channel. Three rib open-area ratios (β = 24, 37, and 46 percent), three rib pitch-to-height ratios (Pi/H = 10, 20, and 30), and two rib height-to-channel hydraulic diameter ratios (H/De = 0.081, and 0.162) are examined. The Reynolds number ranges from 10,000 to 50,000. Laser holographic interferometry is employed to measure the local heat transfer coefficients of the ribbed wall quantitatively, and observe the flow over the ribbed wall qualitatively. The results show that the slit rib has an advantage of avoiding “hot spots.” In addition, the heat transfer performance of the slit-ribbed channel is much better than that of the solid-ribbed channel. Semi-empirical correlations for friction and heat transfer are developed to account for rib spacings and open-area ratios. These correlations may be used in the design of turbine blade cooling passages.

Heat Transfer Characteristics of an Inclined Impinging Jet on a Curved Surface in Crossflow

2014 ◽  
Vol 136 (8) ◽  
Author(s):  
X. L. Wang ◽  
H. B. Yan ◽  
T. J. Lu ◽  
S. J. Song ◽  
T. Kim
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Flat Plate ◽  
Local Heat Transfer ◽  
Impinging Jet ◽  
Local Heat ◽  
Curved Surface ◽  
Heat Transfer Characteristics ◽  
Potential Core ◽  
Transfer Characteristics

This study reports on heat transfer characteristics on a curved surface subject to an inclined circular impinging jet whose impinging angle varies from a normal position θ = 0 deg to θ = 45 deg at a fixed jet Reynolds number of Rej = 20,000. Three curved surfaces having a diameter ratio (D/Dj) of 5.0, 10.0, and infinity (i.e., a flat plate) were selected, each positioned systematically inside and outside the potential core of jet flow where Dj is the circular jet diameter. Present results clarify similar and dissimilar local heat transfer characteristics on a target surface due to the convexity. The role of the potential core is identified to cause the transitional response of the stagnation heat transfer to the inclination of the circular jet. The inclination and convexity are demonstrated to thicken the boundary layer, reducing the local heat transfer (second peaks) as opposed to the enhanced local heat transfer on a flat plate resulting from the increased local Reynolds number.

Full Surface Local Heat Transfer Coefficient Measurements in a Model of an Integrally Cast Impingement Cooling Geometry

1996 ◽  
Author(s):  
David R. H. Gillespie ◽  
Zuolan Wang ◽  
Peter T. Ireland ◽  
S. Toby Kohler
Keyword(s):  
Heat Transfer ◽  
Boundary Condition ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Local Heat Transfer Coefficient ◽  
Target Plate ◽  
Impingement Cooling ◽  
Impingement Plate

Cast impingement cooling geometries offer the gas turbine designer higher structural integrity and improved convective cooling when compared to traditional impingement cooling systems which rely on plate inserts. In this paper, it is shown that the surface which forms the jets contributes significantly to the total cooling. Local heat transfer coefficient distributions have been measured in a model of an engine wall cooling geometry using the transient heat transfer technique. The method employs temperature sensitive liquid crystals to measure the surface temperature of large scale perspex models during transient experiments. Full distributions of local Nusselt number on both surfaces of the impingement plate, and on the impingement target plate are presented at engine representative Reynolds numbers. The relative effects of the impingement plate thermal boundary condition and the coolant supply temperature on the target plate heat transfer has been determined by maintaining an isothermal boundary condition at the impingement plate during the transient tests. The results are discussed in terms of the interpreted flow field.

Heat Transfer, Pressure Loss and Flow Field Measurements Downstream of Staggered Two-Row Circular and Elliptical Pin Fin Arrays

2005 ◽  
Vol 127 (5) ◽  
pp. 458-471 ◽  
Author(s):  
Oguz Uzol ◽  
Cengiz Camci
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Pressure Loss ◽  
Total Pressure ◽  
Local Heat Transfer ◽  
Field Measurements ◽  
Local Heat ◽  
Wake Flow ◽  
Pin Fin ◽  
Pin Fin Arrays

This paper presents the results of heat transfer, total pressure loss, and wake flow field measurements downstream of two-row staggered elliptical and circular pin fin arrays. Two different types of elliptical fins are tested, i.e., a Standard Elliptical Fin (SEF) and a fin that is based on NACA four digit symmetrical airfoil shapes (N fin). The results are compared to those of a corresponding circular pin fin array. The minor axis lengths for both types of elliptical fins are kept equal to the diameter of the circular fins. Experiments are performed using Liquid Crystal Thermography and total pressure probe wake surveys in a Reynolds number range of 18 000 and 86 000 as well as Particle Image Velocimetry (PIV) measurements at ReD=18 000. The pin fins had a height-to-diameter ratio of 1.5. The streamwise and the transverse spacings were equal to one circular fin diameter, i.e., S/D=X/D=2. For the circular fin array, average Nusselt numbers on the endwall within the wake are about 27% higher than those of SEF and N fin arrays. Different local heat transfer enhancement patterns are observed for elliptical and circular fins. In terms of total pressure loss, there is a substantial reduction in case of SEF and N fins. The loss levels for the circular fin are 46.5% and 59.5% higher on average than those of the SEF and N fins, respectively. An examination of the Reynolds analogy performance parameter show that the performance indices of the SEF and the N fins are 1.49 and 2.0 times higher on average than that of circular fins, respectively. The thermal performance indices show a collapse of the data, and the differences are much less evident. Nevertheless, N fins still show slightly higher thermal performance values. The wake flow field measurements show that the circular fin array creates a relatively large low momentum wake zone compared to the SEF and N fin arrays. The wake trajectories of the first row of fins in circular, SEF and N fin arrays are also different from each other. The turbulent kinetic energy levels within the wake of the circular fin array are higher than those for the SEF and the N fin arrays. The transverse variations in turbulence levels correlate well with the corresponding local heat transfer enhancement variations.

Heat Transfer in a Radially Rotating Four-Pass Serpentine Channel With Staggered Half-V Rib Turbulators

2000 ◽  
Vol 123 (1) ◽  
pp. 39-50 ◽  
Author(s):  
G. J. Hwang ◽  
S. C. Tzeng ◽  
C. P. Mao ◽  
C. Y. Soong
Keyword(s):  
Heat Transfer ◽  
Flow Characteristics ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Enhancement ◽  
Serpentine Channel ◽  
Ribbed Channel ◽  
Flow Parameters ◽  
Rib Turbulators ◽  
Rib Arrangement

The present work is concerned with experimental investigation of the convective heat transfer in a radially rotating four-pass serpentine channel. Two types of staggered half-V rib turbulators are considered to examine their effects on heat transfer enhancement. The coolant air is pressurized and pre-cooled to compensate for the low rotating rate and low temperature or density difference in key parameters of thermal and flow characteristics. The geometric dimensions are fixed, whereas the ranges of the thermal and flow parameters in the present measurements are 20,000⩽Re⩽40,000,0⩽Ro⩽0.21, and Gr/Re2∼O10−2. The present results disclose the effects of the pressurized flow, rib arrangement, channel rotation, and centrifugal buoyancy on the local heat transfer in each passage of the channel. Finally, the present data are fitted on correlation equations for evaluation of local heat transfer in the rotating four-pass ribbed channel configurations considered.

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