Heat Transfer and Flow Characteristics of the Jet Array Impingement

2021 ◽  
Author(s):  
Min Ren ◽  
Xueying Li ◽  
Jing Ren
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Cross Flow ◽  
High Heat ◽  
Thermochromic Liquid Crystal ◽  
High Heat Transfer ◽  
Transfer Region ◽  
Performance Of Heat Transfer

Abstract An experimental and numerical study is performed to investigate heat transfer and pressure loss characteristics for impingement. Experimental heat transfer is measured by the thermochromic liquid crystal. The CFD model uses a steady state RANS approach and the shear stress transport (SST). The effect of Reynolds number (5000–25000), the distance between the holes and the distance from the hole to target on the impingement is investigated in the present study. Local Nusselt number as well as area and line average values are gotten experimentally and numerically. Besides, numerical simulations provide the detailed flow characteristics of the problem and complement experimental measurements. The result shows that the heat transfer increases with Reynolds number increasing. But the qualitative distribution of local heat transfer does not change with the increase of Reynolds number, when it is sensitive to P/D and Z/D. The performance of heat transfer is best when Z/D = 2. And the high heat transfer region of Z/D = 1 is closer to the exit than that of Z/D = 2 and Z/D = 3. The main reason is the effect of cross flow and the momentum of the jet reaching the wall. The performance of heat transfer is best when P/D = 5. And the high heat transfer region of P/D = 4 is closer to the exit than that of P/D = 5 and P/D = 6. The main reason is the effect of cross flow and interactions between jets.

Channel Height and Jet Spacing Effect on Heat Transfer and Uniformity Coefficient on an Inline Row Impingement Channel

2010 ◽  
Author(s):  
Mark Ricklick ◽  
Roberto Claretti ◽  
J. S. Kapat
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Cross Flow ◽  
High Heat ◽  
Channel Height ◽  
Transfer Coefficients ◽  
Uniformity Coefficient ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer ◽  
Side Walls

Future high performance turbine airfoils will likely be cooled in a near wall configuration, potentially employing a combination of narrow, distributed internal cooling channels and impingement. In such applications, the jets impinge against a target surface, and then exit along the channel formed by the jet plate, target plate, and side walls. Local convection coefficients are the result of both the jet impact, as well as the channel flow produced from the exiting jets and the complex interaction between the jet and the cross flow. Numerous studies have explored the effects of jet array and channel configurations on both target and jet plate heat transfer coefficients, yet with little consideration of thermal stress related effects. A detailed study on the uniformity coefficient that these jets and cross flow generate on the surface is carried out. It is important to maintain a high uniformity coefficient while still having a high heat transfer coefficients to reduce thermal stresses. It is also important to use as little flow as possible while maintaining a high heat transfer coefficient. The study presented experimentally investigates the effects of wall height, jet Reynolds number, and jet spacing on the Nusselt number and uniformity of a narrow inline row impingement channel. The channel height was set at 1, 3, and 5 diameters, jet spacing was 5 and 15 diameters, and the channel width was kept constant at 4 diameters. Although heat transfer coefficients are highly sensitive to the jet Reynolds number and channel height, the uniformity of the distribution is mainly governed by the channel height and jet spacing. A channel height of 3 jet diameters tended to produce the best uniformity coefficients, regardless of the jet to jet spacing; with side walls out performing target surfaces.

Enhancement of heat transfer in a square channel by roughened surfaces in rib-elements and turbulent flow manipulation

2017 ◽  
Vol 27 (7) ◽  
pp. 1571-1595 ◽  
Author(s):  
Jian Liu ◽  
Gongnan Xie ◽  
Bengt Ake Sunden ◽  
Lei Wang ◽  
Martin Andersson
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Research Work ◽  
Flow Characteristics ◽  
High Heat ◽  
The Novel ◽  
Content Type ◽  
Flat Surfaces ◽  
Square Channel ◽  
High Heat Transfer

Purpose The purpose of this paper is to augment heat transfer rates of traditional rib-elements with minimal pressure drop penalties. Design/methodology/approach The novel geometries in the present research are conventional cylindrical ribs with rounded transitions to the adjacent flat surfaces and with modifications at their bases. All turbulent fluid flow and heat transfer results are presented using computation fluid dynamics with a validated v2f turbulence closure model. Turbulent flow characteristics and heat transfer performances in square channels with improved ribbed structures are numerically analyzed in this research work. Findings Based on the results, it is found that rounded transition cylindrical ribs have a large advantage over the conventional ribs in both enhancing heat transfer and reducing pressure loss penalty. In addition, cylindrical ribs increase the flow impingement at the upstream of the ribs, which will effectively increase the high heat transfer areas. The design of rounded transition cylindrical ribs and grooves will be an effective way to improve heat transfer enhancement and overall thermal performance of internal channels within blade cooling. Originality/value The novel geometries in this research are conventional cylindrical ribs with rounded transitions to the adjacent flat surfaces and with modifications at their bases. The combination of cylindrical ribs and grooves to manipulate the turbulent flow.

An Analytical Study of the Optimized Performance of an Impingement Heat Sink

2004 ◽  
Vol 126 (4) ◽  
pp. 528-534 ◽  
Author(s):  
S. B. Sathe ◽  
B. G. Sammakia
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Heat Sink ◽  
High Performance ◽  
Cross Flow ◽  
High Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer ◽  
Flow Through

The results of a study of a new and unique high-performance air-cooled impingement heat sink are presented. An extensive numerical investigation of the heat sink performance is conducted and is verified by experimental data. The study is relevant to cooling of high-power chips and modules in air-cooled environments and applies to workstations or mainframes. In the study, a rectangular jet impinges on a set of parallel fins and then turns into cross flow. The effects of the fin thickness, gap nozzle width and fin shape on the heat transfer and pressure drop are investigated. It is found that pressure drop is reduced by cutting the fins in the central impingement zone without sacrificing the heat transfer due to a reduction in the extent of the stagnant zone. A combination of fin thicknesses of the order of 0.5 mm and channel gaps of 0.8 mm with appropriate central cutout yielded heat transfer coefficients over 1500 W/m2 K at a pressure drop of less than 100 N/m2, as is typically available in high-end workstations. A detailed study of flow-through heat sinks subject to the same constraints as the impingement heat sink showed that the flow-through heat sink could not achieve the high heat transfer coefficients at a low pressure drop.

Numerical Study on Flow and Heat Transfer Characteristics of Jet Impingement Cooling

2011 ◽  
Vol 148-149 ◽  
pp. 680-683
Author(s):  
Run Peng Sun ◽  
Wei Bing Zhu ◽  
Hong Chen ◽  
Chang Jiang Chen
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Numerical Study ◽  
Cross Flow ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Transfer Characteristic ◽  
Heat Transfer Characteristics ◽  
Impingement Cooling ◽  
Transfer Characteristics

Three-dimensional numerical study is conducted to investigate the heat transfer characteristics for the flow impingement cooling in the narrow passage based on cooling technology of turbine blade.The effects of the jet Reynolds number, impingement distance and initial cross-flow on heat transfer characteristic are investigated.Results show that when other parameters remain unchanged local heat transfer coefficient increases with increase of jet Reynolds number；overall heat transfer effect is reduced by initial cross-flow；there is an optimal distance to the best effect of heat transfer.

Transient Leading to Periodic Fluid Flow and Heat Transfer in a Differentially-Heated Cavity Due to an Insulated Rotating Object

2007 ◽  
Author(s):  
Y.-C. Shih ◽  
J. M. Khodadadi ◽  
K.-H. Weng ◽  
H. F. Oztop
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Convection Heat Transfer ◽  
Reynolds Numbers ◽  
High Heat ◽  
Thermal Fields ◽  
Flow And Heat Transfer ◽  
High Heat Transfer ◽  
Transient Variations ◽  
Rotating Objects

Computational analysis of transient phenomenon followed by the periodic state of laminar flow and heat transfer due to an insulated rotating object in a square cavity is investigated. A finite-volume-based computational methodology utilizing primitive variables is used. Various rotating objects (circle, square and equilateral triangle) with different sizes are placed in the middle of the cavity. A combination of a fixed computational grid with a sliding mesh was utilized for the square and triangle shapes. The cavity is maintained as a differentially-heated enclosure and the motionless insulated object is set in rotation at time t = 0. Natural convection heat transfer is neglected. For a given shape of the object and a constant angular velocity, a range of rotating Reynolds numbers are covered for a Pr = 5 fluid. The Reynolds numbers were selected so that the flow fields are not generally affected by the Taylor instabilities (Ta < 1750). The evolving flow field and the interaction of the rotating objects with the recirculating vortices at the four corners are elucidated. The corresponding thermal fields in relation to the evolving flow patterns and the skewness of the temperature contours in comparison to conduction-only case were discussed. The skewness is observed to become more marked as the Reynolds number is lowered. At the same time, similarity of the thermal fields for various shapes for the same Reynolds number varifies the appropriate selection of the hydraulic diameter. Transient variations of the average Nusselt numbers on the two walls show that for high Re numbers, a quasi-periodic behavior due to the onset of the Taylor instabilities is dominant, whereas for low Re numbers, periodicity of the system is clearly observed. Time-integrated average Nusselt number of the cavity is correlated to the rotational Reynolds number and shape of the object. The triangle object clearly gives rise to high heat transfer followed by the square and circle objects.

Numerical Study of the Heat Transfer in Micro Gas Turbines

2006 ◽  
Vol 129 (4) ◽  
pp. 835-841 ◽  
Author(s):  
T. Verstraete ◽  
Z. Alsalihi ◽  
R. A. Van den Braembussche
Keyword(s):  
Heat Transfer ◽  
Gas Turbines ◽  
Numerical Study ◽  
Three Dimensional ◽  
High Heat ◽  
Large Temperature ◽  
Radial Compressor ◽  
Micro Gas Turbine ◽  
High Heat Transfer ◽  
The Impact

This paper presents a numerical investigation of the heat transfer inside a micro gas turbine and its impact on the performance. The large temperature difference between turbine and compressor in combination with the small dimensions results in a high heat transfer causing a drop in efficiency of both components. Present study aims to quantify this heat transfer and to reveal the different mechanisms that contribute to it. A conjugate heat transfer solver has been developed for this purpose. It combines a three-dimensional (3D) conduction calculation inside the rotor and the stator with a 3D flow calculation in the radial compressor, turbine and gap between stator and rotor. The results for micro gas turbines of different size and shape and different material characteristics are presented and the impact on performance is evaluated.

Experimental Study on Heat Transfer of Leading Edge Film-Cooling With Counter-Inclined Cylindrical and Laid-Back Holes

2020 ◽  
Vol 142 (6) ◽  
Author(s):  
Lin Ye ◽  
Cun-liang Liu ◽  
Feng Liu ◽  
Yu-quan Yang ◽  
Hui-ren Zhu
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Leading Edge ◽  
High Heat ◽  
Spanwise Direction ◽  
High Heat Transfer ◽  
Transfer Region ◽  
Transient Measurement ◽  
The Heat Transfer Coefficient ◽  
Core Flows

Abstract The heat transfer coefficient of counterinclined film holes fed by different intake structures on the turbine vane leading edge (LE) model is experimentally investigated in this paper. A semicylinder model is adopted to model the vane leading edge, which is arranged with one single row of film holes per side, which are located from the stagnation at a 15-deg angle. The four leading edge models, which are the combinations of the hole-shapes (cylindrical hole and laid-back hole) and intake structures (plenum and impingement), are tested at four blowing ratios M. The contours of the heat transfer coefficient, which are characterized by the Frössling number Fr, since it includes the Reynold number effect, are acquired by the transient measurement technique based on double thermochromic liquid-crystals (LCs). The lateral-averaged Fr of the nonfilm-cooled model is provided by using the same experimental platform with an identical main-flow condition. It is then compared with the published data, which indicates the reliability of the present transient measurement techniques. The results illustrate that a core region with a higher heat transfer appears in the hole-exit downstream, and its distribution is slightly skewed to the inclination direction of the film holes. The shape of the high heat transfer region gradually inclines in the spanwise direction as M increases. The heat transfer in the region where the jet core flows through is relatively low, while the jet edge region is relatively high. The effect of impingement leads to the outflow of each hole becoming increasingly uniform, which can reduce the difference in the heat transfer between the region where the jet core flows through and the jet edge. The heat transfer strength may increase due to the intense turbulence caused by the introduction of the impingement. Compared with the cylindrical hole, the laid-back hole has a spanwise expansion feature, which makes the shape of the high heat transfer region wider in the spanwise direction and increases the heat transfer level. Additionally, the magnitude of the enhancement increases with an increasing M.

Effect of Radial Location of Nozzles on Heat Transfer in Preswirl Cooling Systems

2010 ◽  
Vol 133 (2) ◽  
Author(s):  
V. U. Kakade ◽  
G. D. Lock ◽  
M. Wilson ◽  
J. M. Owen ◽  
J. E. Mayhew
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer Coefficient ◽  
Rotating Disk ◽  
High Heat ◽  
Thermochromic Liquid Crystal ◽  
Disk System ◽  
Dimensional Solution ◽  
Flow Rates ◽  
Measure Surface Temperature ◽  
High Heat Transfer

This paper investigates heat transfer in a rotating disk system using preswirled cooling air from nozzles at high and low radius. The experiments were conducted over a range of rotational speeds, flow rates, and preswirl ratios. Narrow-band thermochromic liquid crystal (TLC) was specifically calibrated for application to experiments on a disk, rotating at ∼5000 rpm and subsequently used to measure surface temperature in a transient experiment. The TLC was viewed through the transparent polycarbonate disk using a digital video camera and strobe light synchronized to the disk frequency. The convective heat transfer coefficient h was subsequently calculated from the one-dimensional solution of Fourier's conduction equation for a semi-infinite wall. The analysis was accounted for the exponential rise in the air temperature driving the heat transfer, and for the experimental uncertainties in the measured values of h. The experimental data was supported by “flow visualization,” determined from CFD. Two heat transfer regimes were revealed for the low-radius preswirl system: a viscous regime at relatively low coolant flow rates, and an inertial regime at higher flow rates. Both regimes featured regions of high heat transfer where thin, boundary layers replaced air exiting through receiver holes at high radius on the rotating disk. The heat transfer in the high-radius preswirl system was shown to be dominated by impingement under the flow conditions tested.

The Effect of Freestream Turbulence on Film Cooling Heat Transfer Coefficient

2002 ◽  
Author(s):  
James E. Mayhew ◽  
James W. Baughn ◽  
Aaron R. Byerley
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Boundary Conditions ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Convective Heat Transfer Coefficient ◽  
High Heat ◽  
Freestream Turbulence ◽  
Thermochromic Liquid Crystal ◽  
High Heat Transfer

The film-cooling performance of a flat plate in the presence of low and high freestream turbulence is investigated using thermochromic liquid crystal thermography. Full-surface distributions of the convective heat transfer coefficient are determined for three blowing rates on a model with three straight holes spaced three diameters apart. An increase in heat transfer coefficient due to mass injection is clearly observed in the images and is quantitatively determined for both the low and high freestream turbulence cases. The increase in heat transfer coefficient is greater than in previously published research, possibly due to the use of different, more representative thermal boundary conditions upstream of the injection location. These boundary conditions, along with high resolution images, may account for the appearance of “fork tine” patterns of high heat transfer due to the presence of these vortices, not previously seen. Although the driving potential for heat transfer is less, it is observed that in some instances film cooling may cause an increase in overall heat transfer due to the increase in heat transfer coefficient.

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