Impingement Heat Transfer on a Cylindrical, Concave Surface With Varying Jet Geometries

2012 ◽  
Author(s):  
C. Neil Jordan ◽  
Lesley M. Wright ◽  
Daniel C. Crites
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Mass Flow Rate ◽  
Flow Rate ◽  
Leading Edge ◽  
Target Surface ◽  
Reynolds Numbers ◽  
Hole Shape ◽  
Cylindrical Holes

Jet impingement is often employed within the leading edge of modern turbine airfoils to combat the extreme heat loads incurred within this region. This experimental investigation employs a transient liquid crystal technique to obtain detailed Nusselt number distributions on a concave, cylindrical surface that models the leading edge of a turbine airfoil. The effect of hole shape as well as differing hole inlet and exit conditions are investigated. Two hole shapes are studied: cylindrical and racetrack shaped holes; for each hole shape, the hydraulic diameter and mass flow rate into the array of jets is conserved. As a result, the jet’s Reynolds number (Rejet) varies between the two jet arrays. Reynolds numbers of 13600, 27200, and 40700 are investigated for the cylindrical holes and Reynolds numbers of 11500, 23000, and 34600 are investigated for the racetrack holes. Three inlet and exit conditions are investigated for each hole shape: a square edged, a partially filleted, and a fully filleted hole. The ratio of the fillet radius to hole hydraulic diameter (r / dH,Jet) is set at 0.25 and 0.667 for the partially and fully filleted holes, respectively. The relative jet–to–jet spacing (s / dH,Jet) is maintained at 8, the jet–to–target surface spacing (z / dH,Jet) is maintained at 4, the jet–to–target surface curvature (D / dH,Jet) is maintained at 5.33, and the relative jet plate thickness (t / dH,Jet) is maintained at 1.33. Results show the Nusselt number is directly related to the jet Reynolds number for both cylindrical and racetrack shaped holes. The racetrack holes are shown to provide enhanced heat transfer compared to the cylindrical holes for a set mass flow rate. The degree of filleting at the inlet and outlet of the holes affects whether the heat transfer on the leading edge model is further enhanced or degraded.

Impingement Heat Transfer on a Cylindrical, Concave Surface With Varying Jet Geometries

2016 ◽  
Vol 138 (12) ◽  
Author(s):  
C. Neil Jordan ◽  
Lesley M. Wright ◽  
Daniel C. Crites
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Leading Edge ◽  
Jet Impingement ◽  
Reynolds Numbers ◽  
Hydraulic Diameter ◽  
Hole Shape ◽  
Impingement Heat Transfer ◽  
Cylindrical Holes

Jet impingement is often employed within the leading edge of turbine airfoils to combat the heat loads incurred within this region. This experimental investigation employs a transient liquid crystal technique to obtain detailed Nusselt number distributions on a concave, cylindrical surface that models the leading edge of a turbine airfoil. The effect of hole shape and differing hole inlet and exit conditions are investigated. Two hole shapes are studied: cylindrical and racetrack-shaped holes; for each hole shape, the hydraulic diameter and mass flow rate into the array of jets is conserved. As a result, the jet's Reynolds number varies between the two jet arrays. Reynolds numbers of 13,600, 27,200, and 40,700 are investigated for the cylindrical holes, and Reynolds numbers of 11,500, 23,000, and 34,600 are investigated for the racetrack holes. Three inlet and exit conditions are investigated for each hole shape: a square edged, a partially filleted, and a fully filleted hole. The ratio of the fillet radius to hole hydraulic diameter is set at 0.25 and 0.667 for the partially and fully filleted holes, respectively, while all other geometrical features remain constant. Results show the Nusselt number is directly related to the Reynolds number for both cylindrical and racetrack-shaped holes. The racetrack holes are shown to provide enhanced heat transfer compared to the cylindrical holes. The degree of filleting at the inlet and outlet of the holes affects whether the heat transfer on the leading edge model is further enhanced or degraded.

scholarly journals Experimental Study of Heat Transfer on the Internal Surfaces of a Double-Wall Structure with Pin Fin Array

Energies ◽  
2020 ◽  
Vol 13 (24) ◽  
pp. 6573
Author(s):  
Wei Zhang ◽  
Huiren Zhu ◽  
Guangchao Li
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Target Surface ◽  
Reynolds Numbers ◽  
Wall Structure ◽  
Pin Fin ◽  
Internal Surfaces ◽  
Double Wall ◽  
Impingement Surface

The double-wall structure is one of the most effective cooling techniques used in many engineering applications, such as turbine vane/blade, heat exchangers, etc. Heat transfer on the internal surfaces of a double-wall structure was studied at impinging Reynolds numbers ranging from 1 × 104 to 6 × 104 using the transient thermochromic liquid crystal (TLC) technique. The two-dimensional distributions of Nusselt numbers and their averaged values were obtained on the impingement surface, target surface and the pin fin surface. The Nusselt number correlations on the surfaces mentioned above were determined as a function of Reynolds number. The results show that the second peak values of the Nusselt number distribution appear on the target surface at all Reynolds numbers studied in this paper for a short distance of the target surface to impingement surface. This phenomenon becomes significant with the further increase of the Reynolds number. The difference between the Nusselt number at the second peak and the stagnation point decreases with the increasing Reynolds number. The maximal Nusselt number regions on the impingement surface appear at the left and right sides of the pin fins between the two impingement holes. The Nusselt numbers of the pin fin surfaces are highly dependent on their various locations in the double-wall structures. The contributions of the impingement surface, pin fin surface and target surface to the overall heat transfer rate are analyzed. The target surface contributed the largest amount of heat transfer rate with a value of about 62%. The heat transfer contribution is from 18% to 21% for the impingement surface and 16% to 18% for the pin fin surfaces within the studied Reynolds numbers.

scholarly journals Optimization of A Swirl with Impingement Compound Cooling Unit for A Gas Turbine Blade Leading Edge

Energies ◽  
2020 ◽  
Vol 13 (1) ◽  
pp. 210 ◽  
Author(s):  
Hamza Fawzy ◽  
Qun Zheng ◽  
Naseem Ahmad ◽  
Yuting Jiang
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Gas Turbine ◽  
Turbine Blade ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Gas Turbine Blade ◽  
Temperature Ratio ◽  
Cooling Unit

In this article, a compound unit of swirl and impingement cooling techniques is designed to study the performance of flow and heat transfer using multi-conical nozzles in a leading-edge of a gas turbine blade. Reynolds Averaged Navier-Stokes equations and the Shear Stress Transport model are numerically solved under different nozzle Reynolds numbers and temperature ratios. Results indicated that the compound cooling unit could achieve a 99.7% increase in heat transfer enhancement by increasing the nozzle Reynolds number from 10,000 to 25,000 at a constant temperature ratio. Also, there is an 11% increase in the overall Nusselt number when the temperature ratio increases from 0.65 to 0.95 at identical nozzle Reynolds number. At 10,000 and 15,000 of nozzle Reynolds numbers, the compound cooling unit achieves 47.9% and 39.8% increases and 63.5% and 66.3% increases in the overall Nusselt number comparing with the available experimental swirl and impingement models, respectively. A correlation for the overall Nusselt number is derived as a function of nozzle Reynolds number and temperature ratio to optimize the results. The current study concluded that the extremely high zones and uniform distribution of heat transfer are perfectly achieved with regard to the characteristics of heat transfer of the compound cooling unit.

Heat transfer enhancement using second mode self-oscillating structures

2019 ◽  
Vol 30 (7) ◽  
pp. 3827-3842
Author(s):  
Samer Ali ◽  
Zein Alabidin Shami ◽  
Ali Badran ◽  
Charbel Habchi
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Laminar Flow ◽  
Flow Regime ◽  
Vortex Generator ◽  
Reynolds Numbers ◽  
Content Type ◽  
Laminar Flow Regime ◽  
Second Mode

Purpose In this paper, self-sustained second mode oscillations of flexible vortex generator (FVG) are produced to enhance the heat transfer in two-dimensional laminar flow regime. The purpose of this study is to determine the critical Reynolds number at which FVG becomes more efficient than rigid vortex generators (RVGs). Design/methodology/approach Ten cases were studied with different Reynolds numbers varying from 200 to 2,000. The Nusselt number and friction coefficients of the FVG cases are compared to those of RVG and empty channel at the same Reynolds numbers. Findings For Reynolds numbers higher than 800, the FVG oscillates in the second mode causing a significant increase in the velocity gradients generating unsteady coherent flow structures. The highest performance was obtained at the maximum Reynolds number for which the global Nusselt number is improved by 35.3 and 41.4 per cent with respect to empty channel and rigid configuration, respectively. Moreover, the thermal enhancement factor corresponding to FVG is 72 per cent higher than that of RVG. Practical implications The results obtained here can help in the design of novel multifunctional heat exchangers/reactors by using flexible tabs and inserts instead of rigid ones. Originality/value The originality of this paper is the use of second mode oscillations of FVG to enhance heat transfer in laminar flow regime.

Heat Transfer and Flowfield Measurements in the Leading Edge Region of a Stator Vane Endwall

1999 ◽  
Vol 121 (3) ◽  
pp. 558-568 ◽  
Author(s):  
M. B. Kang ◽  
A. Kohli ◽  
K. A. Thole
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Edge Region ◽  
Leading Edge Vortex ◽  
Stator Vane ◽  
Edge Vortex ◽  
The Mean

The leading edge region of a first-stage stator vane experiences high heat transfer rates, especially near the endwall, making it very important to get a better understanding of the formation of the leading edge vortex. In order to improve numerical predictions of the complex endwall flow, benchmark quality experimental data are required. To this purpose, this study documents the endwall heat transfer and static pressure coefficient distribution of a modern stator vane for two different exit Reynolds numbers (Reex = 6 × 105 and 1.2 × 106). In addition, laser-Doppler velocimeter measurements of all three components of the mean and fluctuating velocities are presented for a plane in the leading edge region. Results indicate that the endwall heat transfer, pressure distribution, and flowfield characteristics change with Reynolds number. The endwall pressure distributions show that lower pressure coefficients occur at higher Reynolds numbers due to secondary flows. The stronger secondary flows cause enhanced heat transfer near the trailing edge of the vane at the higher Reynolds number. On the other hand, the mean velocity, turbulent kinetic energy, and vorticity results indicate that leading edge vortex is stronger and more turbulent at the lower Reynolds number. The Reynolds number also has an effect on the location of the separation point, which moves closer to the stator vane at lower Reynolds numbers.

Numerical Simulations of Resonant Heat Transfer Augmentation at Low Reynolds Numbers

2001 ◽  
Author(s):  
Miles Greiner ◽  
Paul F. Fischer ◽  
Henry Tufo
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Natural Frequency ◽  
Flow Rate ◽  
Low Reynolds Number ◽  
Reynolds Numbers ◽  
Spectral Element ◽  
Pumping Power ◽  
Number Systems ◽  
Low Reynolds

Abstract The effect of flow rate modulation on low Reynolds number heat transfer enhancement in a transversely grooved passage was numerically simulated using a two-dimensional spectral element technique. Simulations were performed at subcritical Reynolds numbers of Rem = 133 and 267, with 20% and 40% flow rate oscillations. The net pumping power required to modulate the flow was minimized as the forcing frequency approached the predicted natural frequency. However, mixing and heat transfer levels both increased as the natural frequency was approached. Oscillatory forcing in a grooved passage requires two orders of magnitude less pumping power than flat passage systems for the same heat transfer level. Hydrodynamic resonance appears to be an effective method of increasing heat transfer in low Reynolds number systems where pumping power is at a premium, such as micro heat transfer applications.

Investigating Gas Turbine Internal Cooling Using Supercritical CO2 at High Reynolds Numbers for Direct Fired Cycle Applications

2021 ◽  
Author(s):  
Matthew Searle ◽  
Arnab Roy ◽  
James Black ◽  
Doug Straub ◽  
Sridharan Ramesh
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Gas Turbines ◽  
Cfd Simulation ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Process Conditions ◽  
Internal Cooling ◽  
Air Breathing

Abstract In this paper, experimental and numerical investigations of three variants of internal cooling configurations — dimples only, ribs only and ribs with dimples have been explored at process conditions (96°C and 207bar) with sCO2 as the coolant. The designs were chosen based on a review of advanced internal cooling features typically used for air-breathing gas turbines. The experimental study described in this paper utilizes additively manufactured square channels with the cooling features over a range of Reynolds number from 80,000 to 250,000. Nusselt number is calculated in the experiments utilizing the Wilson Plot method and three heat transfer characteristics — augmentation in Nusselt number, friction factor and overall Thermal Performance Factor (TPF) are reported. To explore the effect of surface roughness introduced due to additive manufacturing, two baseline channel flow cases are considered — a conventional smooth tube and an additively manufactured square tube. A companion computational fluid dynamics (CFD) simulation is also performed for the corresponding cooling configurations reported in the experiments using the Reynolds Averaged Navier Stokes (RANS) based turbulence model. Both experimental and computational results show increasing Nusselt number augmentation as higher Reynolds numbers are approached, whereas prior work on internal cooling of air-breathing gas turbines predict a decay in the heat transfer enhancement as Reynolds number increases. Comparing cooling features, it is observed that the “ribs only” and “ribs with dimples” configurations exhibit higher Nusselt number augmentation at all Reynolds numbers compared to the “dimples only” and the “no features” configurations. However, the frictional losses are almost an order of magnitude higher in presence of ribs.

Heat Transfer and Flow Friction Characteristics for Compact Cold Plates

2003 ◽  
Vol 125 (1) ◽  
pp. 104-113 ◽  
Author(s):  
Chang-Yuan Liu ◽  
Ying-Huei Hung
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Nusselt Number ◽  
Thermal Resistance ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Average Nusselt Number ◽  
Cold Plate ◽  
Air Mass

Both experimental and theoretical investigations on the heat transfer and flow friction characteristics of compact cold plates have been performed. From the results, the local and average temperature rises on the cold plate surface increase with increasing chip heat flux or decreasing air mass flow rate. Besides, the effect of chip heat flux on the thermal resistance of cold plate is insignificant; while the thermal resistance of cold plate decreases with increasing air mass flow rate. Three empirical correlations of thermal resistance in terms of air mass flow rate with a power of −0.228 are presented. As for average Nusselt number, the effect of chip heat flux on the average Nusselt number is insignificant; while the average Nusselt number of the cold plate increases with increasing Reynolds number. An empirical relationship between Nu¯cp and Re can be correlated. In the flow frictional aspect, the overall pressure drop of the cold plate increases with increasing air mass flow rate; while it is insignificantly affected by chip heat flux. An empirical correlation of the overall pressure drop in terms of air mass flow rate with a power of 1.265 is presented. Finally, both heat transfer performance factor “j” and pumping power factor “f” decrease with increasing Reynolds number in a power of 0.805; while they are independent of chip heat flux. The Colburn analogy can be adequately employed in the study.

scholarly journals Effect of Reynolds Number and Property Variation on Fluid Flow and Heat Transfer in the Entrance Region of a Turbine Blade Internal-Cooling Channel

2005 ◽  
Vol 2005 (1) ◽  
pp. 36-44 ◽  
Author(s):  
R. Ben-Mansour ◽  
L. Al-Hadhrami
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Mass Flow Rate ◽  
Heat Transfer Rate ◽  
Turbine Blade ◽  
Flow Rate ◽  
Transfer Rate ◽  
Internal Cooling ◽  
Cooling Channel ◽  
Flow And Heat Transfer

Internal cooling is one of the effective techniques to cool turbine blades from inside. This internal cooling is achieved by pumping a relatively cold fluid through the internal-cooling channels. These channels are fed through short channels placed at the root of the turbine blade, usually called entrance region channels. The entrance region at the root of the turbine blade usually has a different geometry than the internal-cooling channel of the blade. This study investigates numerically the fluid flow and heat transfer in one-pass smooth isothermally heated channel using the RNGk−εmodel. The effect of Reynolds number on the flow and heat transfer characteristics has been studied for two mass flow rate ratios (1/1and1/2) for the same cooling channel. The Reynolds number was varied between10 000and50 000. The study has shown that the cooling channel goes through hydrodynamic and thermal development which necessitates a detailed flow and heat transfer study to evaluate the pressure drop and heat transfer rates. For the case of unbalanced mass flow rate ratio, a maximum difference of8.9% in the heat transfer rate between the top and bottom surfaces occurs atRe=10 000while the total heat transfer rate from both surfaces is the same for the balanced mass flow rate case. The effect of temperature-dependent property variation showed a small change in the heat transfer rates when all properties were allowed to vary with temperature. However, individual effects can be significant such as the effect of density variation, which resulted in as much as9.6% reduction in the heat transfer rate.

Impingement Cooling of a Semi-Spherical Concave Surface Covered by Porous Medium with a Jet Trapping Hole

2014 ◽  
Vol 348 ◽  
pp. 162-170
Author(s):  
Pey Shey Wu ◽  
Yi Hung Lin ◽  
Yue Hua Jhuo ◽  
Hsiao Ying Chan
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Porous Material ◽  
Target Surface ◽  
Temperature Fields ◽  
Concave Surface ◽  
Far Field ◽  
Impingement Heat Transfer ◽  
Plate Distance

Impingement heat transfer between a circular jet and a semi-spherical concave surface with or without coverage of porous material is investigated experimentally and numerically. For cases with coverage of the porous material on the target plate, a trapping hole for the jet fluid is fabricated. Measured local Nusselt number distributions along a meridian are documented. The flow and temperature fields at the conditions similar to that of experiments were computed with CFD software to support the experimental results and help to explain the physics. Varying parameters include Reynolds number, nozzle-to-plate distance, relative curvature, and a target surface with or without the covered porous material. Results show that the attachment of a porous material increases Nusselt number, with more influence at the stagnation zone than the far field. Increasing Reynolds number usually increases Nusselt number unless it is too high. Although an increase in the nozzle-to-plate distance decreases stagnation Nusselt number, the influence in heat transfer is small in the far field. The trapping-hole diameter should be the same as that of the jet diameter for best heat transfer enhancement.

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