Full-Field Flow Measurements and Heat Transfer of a Compact Jet Impingement Array With Local Extraction of Spent Fluid

2009 ◽  
Vol 131 (8) ◽  
Author(s):  
Andrew J. Onstad ◽  
Christopher J. Elkins ◽  
Robert J. Moffat ◽  
John K. Eaton
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Jet Impingement ◽  
Smooth Transition ◽  
Transfer Coefficients ◽  
Flow Measurements ◽  
Extraction Area ◽  
Number Range ◽  
Full Field ◽  
High Heat Transfer

Jet impingement cooling is widely used due to the very high heat transfer coefficients that are attainable. Both single and multiple jet systems can be used, however, multiple jet systems offer higher and more uniform heat transfer. A staggered array of 8.46 mm diameter impingement jets with jet-to-jet spacing of 2.34 D was examined where the spent fluid is extracted through one of six 7.36 mm diameter extraction holes regularly located around each jet. The array had an extraction area ratio (Ae/Ajet) of 2.23 locally and was tested with a jet-to-target spacing (H/D) of 1.18 jet diameters. Magnetic resonance velocimetry was used to both quantify and visualize the three dimensional flow field inside the cooling cavity at jet Reynolds numbers of 2600 and 5300. The spatially averaged velocity measurements showed a smooth transition is possible from the impingement jet to the extraction hole without the presence of large vortical structures. Mean Nusselt number measurements were made over a jet Reynolds number range of 2000–10,000. Nusselt numbers near 75 were measured at the highest Reynolds number with an estimated uncertainty of 7%. Large mass flow rate per unit heat transfer area ratios were required because of the small jet-to-jet spacing.

Flow and Heat Transfer of Confined Impingement Jets Cooling

2000 ◽  
Author(s):  
Ting Wang ◽  
Mingjie Lin ◽  
Ronald S. Bunker
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Flow Structure ◽  
Experimental Studies ◽  
Cross Flow ◽  
Jet Impingement ◽  
Target Surface ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Transfer Behavior

Experimental studies on heat transfer and flow structure in confined impingement jets were performed. The objective of this study was to investigate the detailed heat transfer coefficient distribution on the jet impingement target surface and flow structure in the confined cavity. The distribution of heat transfer coefficients on the target surface was obtained by employing the transient liquid crystal method coupled with a 3-D inverse transient conduction scheme under Reynolds number ranging from 1039 to 5175. The results show that the average heat transfer coefficients increased linearly with the Reynolds number as Nu = 0.00304 Pr0.42Re. The effects of cross flow on heat transfer were investigated. The flow structure were analyzed to gain insight into convective heat transfer behavior.

Heat Transfer to Mercury Flowing In-Line Through a Bundle of Circular Rods

1964 ◽  
Vol 86 (2) ◽  
pp. 180-186 ◽  
Author(s):  
M. W. Maresca ◽  
O. E. Dwyer
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Turbulent Flow ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Number Range ◽  
Heat Transfer Coefficients ◽  
Turbulent Flow Regime ◽  
Measuring Surface ◽  
Theoretical Predictions

Experimental results were obtained for the case of in-line flow of mercury through an unbaffled bundle of circular rods, and they were compared with theoretical predictions. The bundle consisted of 13 one-half-in-dia rods arranged in an equilateral triangular pattern, the pitch:diameter ratio being 1.750. Measurements were taken only on the central rod. Six different rods were tested. All rods in the bundle were electrically heated to provide equal and uniform heat fluxes throughout the bundle. The rods were of the Calrod type. The test rods had copper sheaths with fine thermocouples imbedded below the surface for measuring surface temperatures. Some rods were plated with a layer of nickel, followed by a very thin layer of copper, to provide “wetting” conditions, while others were chromeplated to provide “nonwetting” conditions. Heat-transfer coefficients were obtained under the following conditions: (a) Prandtl number, 0.02; (b) Reynolds number range, 7500 to 200,000; (c) Peclet number range, 150 to 4000; (d) “Wetting” versus “nonwetting”; (e) Both transition and fully established flow; (f) Variation of Lf/De ratio from 4 to 46. The precision of the results is estimated to be within 2 to 3 percent. An interesting finding, consistent with earlier predictions, was that the Nusselt number, under fully established turbulent-flow conditions, remained essentially constant, at the lower end of the turbulent flow regime, until a Reynolds number of about 40,000 was reached.

Heat Transfer Characterization of a Finned-Tube Heat Exchanger (With and Without Condensation)

1990 ◽  
Vol 112 (1) ◽  
pp. 64-70 ◽  
Author(s):  
S. A. Idem ◽  
A. M. Jacobi ◽  
V. W. Goldschmidt
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Exchanger ◽  
Factor Versus ◽  
Finned Tube ◽  
Transfer Coefficients ◽  
Number Range ◽  
Tube Heat Exchanger ◽  
Pressure Losses ◽  
Finned Tube Heat Exchanger

The effects upon the performance of an air-to-water copper finned-tube crossflow heat exchanger due to condensation on the outer surface are considered. A four-tube, two-pass heat exchanger was tested over a Reynolds number range (based on hydraulic diameter) from 400 to 1500. The coil was operated both in overall parallel and overall counterflow configurations. Convective heat and mass transfer coefficients are presented as plots of Colburn j-factor versus Reynolds number. Pressure losses are, similarly, presented as plots of the friction factor versus Reynolds number. Enhancement of sensible heat transfer due to the presence of a condensate film is also considered.

Experimental and Computational Flow Field Studies of an Integrally Cast Cooling Manifold With and Without Rotation

2006 ◽  
Author(s):  
Ioannis Ieronymidis ◽  
David R. H. Gillespie ◽  
Peter T. Ireland ◽  
Robert Kingston
Keyword(s):  
Reynolds Number ◽  
Rotation Number ◽  
Discharge Coefficient ◽  
Thermal Contact ◽  
Leading Edge ◽  
Secondary Flows ◽  
Transfer Coefficients ◽  
Number Range ◽  
High Heat Transfer ◽  
Cooling Passage

This paper presents detailed pressure measurements and discharge coefficient data for a long, low aspect ratio manifold; part of a novel blade cooling scheme. The cooling geometry, in which a series of racetrack passages are connected to a central plenum, provides high heat transfer coefficients in regions of the blade in good thermal contact with the outer blade surface. The Reynolds number changes along its length because of the ejection of fluid through a series of 19 transfer holes in a staggered arrangement, which are used to connect ceramic cores during the casting process. For rotation number RN = 0 the velocity down each hole remains almost constant. A correlation between hole discharge coefficient and Velocity Head Ratio is also presented. Pressure loss coefficients in the passage and through the holes are also discussed. A High Pressure (HP) rig was tested to investigate compressibility effects and expand the inlet Reynolds number range. A CFD model was validated against the experimental data, and then used to investigate the effects of rotation on the hole discharge coefficients. Results are presented for an inlet Reynolds number of 43477. At an engine representative rotation number of 0.08 corresponding buoyancy number of 0.17 there was little effect of rotation. However, at high rotational speeds secondary flows in the cooling passage and the exit plenum greatly reduce the hole discharge coefficient by increasing the local cross flow at the hole entrances and capping the hole exits in a manner similar to that seen in leading edge film-cooling geometries.

Experimental Investigation of Area Ratio on Microjet Array Heat Transfer

2009 ◽  
Author(s):  
Gregory J. Michna ◽  
Eric A. Browne ◽  
Yoav Peles ◽  
Michael K. Jensen
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Performance ◽  
Electronics Cooling ◽  
Jet Impingement ◽  
Area Ratio ◽  
Heat Fluxes ◽  
Working Fluid ◽  
Transfer Performance ◽  
Transfer Coefficients ◽  
High Heat Transfer

Electronics cooling is becoming increasingly difficult due to increasing power consumption and decreasing size of processor chips. Heat fluxes in processors and power electronics are quickly approaching levels that cannot be easily addressed by forced air convection over finned heat sinks. Jet impingement cooling offers high heat transfer coefficients and has been used effectively in conventional-scale applications such as turbine blade cooling and the quenching of metals. However, literature in the area of microjet arrays is scarce and has not studied arrays of large area ratios. Hence, the objective of this study is to experimentally assess the heat transfer performance of arrays of microjets. The microjet arrays were fabricated using MEMS processes in a clean room environment. The heat transfer performance of several arrays using deionized water as the working fluid was investigated. Inline and staggered array arrangements were investigated, and the area ratio (total area of the jets divided by the surface area) was varied between 0.036 and 0.35. Reynolds numbers defined by the jet diameter were in the range of 50 to 3,500. Heat fluxes greater than 1,000 W/cm2 were obtained at fluid inlet-to-surface temperature differences of less than 30 °C. Heat transfer performance improved as the area ratio was increased.

An Experimental Setup for Multiple Air Jet Impingement Over a Surface

2018 ◽  
Author(s):  
Flávia V. Barbosa ◽  
João P. V. Silva ◽  
Pedro E. A. Ribeiro ◽  
Senhorinha F. C. F. Teixeira ◽  
Delfim F. Soares ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Jet Impingement ◽  
Thermal Design ◽  
Test Facility ◽  
Experimental Setup ◽  
Optimized Design ◽  
Transfer Coefficients ◽  
Reflow Soldering ◽  
Air Jet ◽  
High Heat Transfer

Air jet impingement technology receives considerable attention due to its high performance for heat transfer enhancement in thermal equipment, providing high heat transfer rates. Due to its inherent characteristics of high average heat transfer coefficients and uniformity of the heat transfer over the impinging surface, this technology is implemented in a variety of engineering applications and industrial processes, such as reflow soldering, drying of textile, cooling of turbojet engine blades and fusion reactors. Multiple jet impingement involves several variables such as: jets arrangement, jet diameter, nozzle-to-surface distance, nozzle shape, jet-to-jet spacing, jet velocity and Reynolds number, among others. However, the total control of all these parameters is still one of the remarkable issues of the thermal design of jet impingement systems. In some industries that have implemented this technology in their processes, such as reflow soldering, the range of values of these variables are established through empiricism and “trial and error” techniques. To improve the process and to reduce time and costs, it is fundamental to define accurately all the process parameters in order to obtain an optimized design with a high degree of control of the heat transfer over the target surface. To perform an accurate and complete study of the multiple jet impingement variables for a specific application, the development of both experimental and numerical studies is fundamental in order to obtain reliable results. In that sense, this work reports the project and construction of a purpose-built test facility which has been commissioned, using a PIV system. This experimental setup is based on the oven used in the reflow soldering process. The optimization of the multiple jets geometry which is integrated in the experimental setup is herein described and discussed both experimentally and numerically. The numerical simulation of the jet impingement inside the oven was conducted using the ANSYS software, specially designed to predict the fluid behavior. Regarding the relevance of the multiple jet impingement, this work intends to improve the knowledge in this field and to give reliable and scientifically proved answers to the industries that apply this technology in their processes.

Comparison of Trip-Strip/Impingement/Dimple Cooling Concepts at High Reynolds Numbers

2003 ◽  
Author(s):  
Yong W. Kim ◽  
Leonel Arellano ◽  
Mark Vardakas ◽  
Hee-Koo Moon ◽  
Kenneth O. Smith
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Engine Performance ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Strip Surface ◽  
Number Range

Modern industrial combustor liners employ various cooling schemes such as, but not limited to, impingement arrays, trip-strips, and film cooling. With an increasing demand for a higher turbine inlet temperatures and lower emissions, there is less air available to cool the combustor liner. To ensure the required liner durability without compromising engine performance more innovative cooling schemes are required. In the present work, three different cooling concepts, i.e., strip-strips, jet array impingement and dimples, operating at unusually high flow conditions were investigated. There is very little data available in the open literature for the aforementioned cooling schemes in the indicated Reynolds Number range (ReDh>60,000). The wall flow friction characteristics as well as the local heat transfer were measured. The heat transfer coefficients were obtained using a transient liquid crystal technique. The test configurations consisted of a 90° trip-strip surface (only one side turbulated), a fixed staggered array with varying impingement hole sizes, and a fixed staggered dimple pattern. For the Reynolds numbers investigated (26,000< ReDh <360,000), the jet-impingement cooling provided the highest average heat transfer enhancement followed by the trip-strip channel, and then by the dimpled channel. In terms of the overall thermal performance, the dimpled channel tends to stand out as the most effective cooling scheme. This is consistent with findings from other investigators at lower Reynolds numbers.

Heat Transfer Investigations in Multiple Impinging Jets at Low Reynolds Number

2010 ◽  
Author(s):  
Arvind G. Rao ◽  
Myra Kitron-Belinkov ◽  
Vladimir Krapp ◽  
Yeshayahou Levy
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Low Reynolds Number ◽  
Turbine Blades ◽  
Jet Impingement ◽  
High Heat ◽  
Geometrical Parameters ◽  
Transitional Region ◽  
High Heat Transfer ◽  
Low Reynolds

Jet impingement is a well established cooling methodology used for cooling turbine blades in gas turbine engines. Jet impingement results in high heat transfer coefficients as compared to other conventional modes of single phase heat transfer. Most of the research in jet impingement has been confined to high Reynolds number regime. In order to increase the applicability of this technique to non conventional applications like in a low pressure micro turbine combustors or turbine blades, the behavior of such systems in the low Reynolds number regime should be understood. The present paper is a continuation of earlier investigations on the heat transfer behavior of a large jet impingement array in the low Reynolds number regime, especially in the laminar and transitional region. More experiments have been conducted with different geometrical parameters of the array to analyze the effect of these parameters on the average heat transfer coefficient. Numerical simulations with existing CFD tools were carried out in order to understand the fluid mechanics inside such a complex system. The CFD model was validated with the experiments. Different turbulence models were used and it was found that the SST-k-ω model was the best for modeling jet impingement phenomena. It is anticipated that the results obtained from the present exercise will give better insights in optimizing the design of multiple jet impingement cooling systems for high heat density applications.

An Experimental Study of Impingement Cooling on Latticework in a Wide Channel

2019 ◽  
Author(s):  
Jin Xu ◽  
Ruishan Lu ◽  
Ke Zhang ◽  
Jiang Lei ◽  
Junmei Wu
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Lattice Model ◽  
Pressure Loss ◽  
Side Wall ◽  
Jet Impingement ◽  
Target Distance ◽  
Transfer Coefficients ◽  
Number Range ◽  
Wide Channel

Abstract Previous researches on latticework were focused on the convective heat transfer performance on pressure and suction sides of a blade model. Besides, it has an effect on leading edge by impingement. Thus, the present study provides heat transfer enhancement and pressure loss of jet impingement of a latticework on side wall in a wide channel (AR = 4). Two latticework configurations with impingement effects are employed in this study. Three kinds of sub-channel models are used in this experiment, which is according to different cooling designs. The angle of the rib is 45° and the numbers of subchannel are 4, 6 and 8, respectively. Reynolds number range is from 10000 to 30000 with an increment of 10000. The wall temperature is obtained by using wide band liquid crystal technique, and then the heat transfer coefficients on the target surface of the channel are achieved. Pressure drop of the latticework channel is also measured by pressure taps. The result shows that these two latticework models have different flow and heat transfer characteristics. The Nusselt number distribution is not similar to that of traditional jet array impingement. The range of Nusselt number enhancement is 2.3 to 6.4 compared to that of a smooth convective channel (the Nusselt number is based on the channel hydraulic diameter). The jet-to-target distance could reduce the overall averaged heat transfer on side wall. But it could also lead to a high Nu region. To the normal lattice model, more sub-channels there are, more pressure loss it has. To the novel lattice model, sub-channel number cannot affect the pressure loss, but the jet-to-target distance could affect the friction factor obviously.

Heat Transfer and Flow Characteristics of Two-Pass Parallelogram Channels With Attached and Detached Transverse Ribs

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
T. M. Liou ◽  
S. W. Chang ◽  
Y. A. Lan ◽  
S. P. Chan ◽  
Y. S. Liu
Keyword(s):  
Heat Transfer ◽  
Flow Characteristics ◽  
Height Ratio ◽  
Differential Heat ◽  
Flow Measurements ◽  
Number Range ◽  
Full Field ◽  
Performance Factors ◽  
Nusselt Numbers ◽  
Design Activities

The full-field Nusselt number (Nu) distributions and flow fields are presented, respectively, using steady-state infrared thermography (IR) and particle image velocimetry (PIV) in the two-pass parallelogram channels with attached and detached transverse ribs. These square transverse ribs on two opposite channel walls are in-line arranged with rib-height to duct-height ratio of 0.1 and rib pitch-to-height ratio of 10. For the detached ribs, the detached distance between rib and channel wall is 0.38 rib height. With the measurements of Fanning friction factor (f), the thermal performance factors (TPF) for the attached and detached-rib cases are comparatively examined. A set of Nu, f, and TPF with the associated flow measurements at the Reynolds number range of 5000 ≤ Re ≤ 20,000 is selected to disclose the differential heat transfer mechanisms and efficiencies between the attached and detached ribbed channels. Empirical correlations evaluating the area-averaged Nusselt numbers (Nu¯) and f factors are devised to assist the relevant design activities.

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