Heat Transfer to Arrays of Impinging Jets in a Crossflow

1987 ◽  
Vol 109 (4) ◽  
pp. 564-571 ◽  
Author(s):  
B. R. Hollworth ◽  
G. H. Cole
Keyword(s):  
Heat Transfer ◽  
Impinging Jets ◽  
Hole Diameter ◽  
Transfer Coefficients ◽  
Target Plate ◽  
Heat Transfer Coefficients ◽  
Air Jets ◽  
Local Measurements ◽  
Geometric Variables ◽  
2D And 3D

Convective heat transfer measurements are reported for staggered arrays of round turbulent air jets impinging upon a heated flat surface. Spent air was constrained by skirts to exit at one end of the test section, thus establishing a crossflow. Geometric variables included the jet hole diameter d, the streamwise spacing X and spanwise spacing Y between jet holes, and the standoff distance Z between the orifice plate and the target plate. Three patterns of holes, all having d = 3.5 mm, were tested. Their (X, Y) were (4d, 4d), (4d, 8d), and (8d, 4d). Values of the standoff were Z = d, 2d, and 3d; and tests were run for 4, 6, and 8 rows of holes. The airflow was varied to achieve a range of mean jet Reynolds number from 2500 to 25,000. Microfoil heat flux sensors were used to determine streamwise variations in (spanwise-averaged) heat transfer. Excellent resolution was obtained by employing a sensor whose streamwise dimension is considerably less than one hole diameter d. Heat transfer profiles were periodic, with a peak corresponding to each spanwise row of holes. Such peaks were displaced in the steamwise direction by the crossflow, and those nearest the exhaust end of the channel exhibited the largest deflections. Array-averaged heat transfer coefficients were obtained by numerically averaging the local measurements; values agree well with the results of other experiments on similar impingement-with-crossflow systems.

Experimental Investigation of Local Heat Transfer Distribution on Smooth and Roughened Surfaces Under an Array of Angled Impinging Jets

2001 ◽  
Author(s):  
Lamyaa A. El-Gabry ◽  
Deborah A. Kaminski
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Cross Flow ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Impinging Jets ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Roughened Surface

Abstract Measurements of the local heat transfer distribution on smooth and roughened surfaces under an array of angled impinging jets are presented. The test rig is designed to simulate impingement with cross-flow in one direction which is a common method for cooling gas turbine components such as the combustion liner. Jet angle is varied between 30, 60, and 90 degrees as measured from the impingement surface, which is either smooth or randomly roughened. Liquid crystal video thermography is used to capture surface temperature data at five different jet Reynolds numbers ranging between 15,000 and 35,000. The effect of jet angle, Reynolds number, gap, and surface roughness on heat transfer efficiency and pressure loss is determined along with the various interactions among these parameters. Peak heat transfer coefficients for the range of Reynolds number from 15,000 to 35,000 are highest for orthogonal jets impinging on roughened surface; peak Nu values for this configuration ranged from 88 to 165 depending on Reynolds number. The ratio of peak to average Nu is lowest for 30-degree jets impinging on roughened surfaces. It is often desirable to minimize this ratio in order to decrease thermal gradients, which could lead to thermal fatigue. High thermal stress can significantly reduce the useful life of engineering components and machinery. Peak heat transfer coefficients decay in the cross-flow direction by close to 24% over a dimensionless length of 20. The decrease of spanwise average Nu in the crossflow direction is lowest for the case of 30-degree jets impinging on a roughened surface where the decrease was less than 3%. The decrease is greatest for 30-degree jet impingement on a smooth surface where the stagnation point Nu decreased by more than 23% for some Reynolds numbers.

scholarly journals Local Heat Transfer Coefficient and Adiabatic Wall Temperature Measurement Beneath Arrays of Staggered and Inline Impinging Jets

1994 ◽  
Author(s):  
Kenneth W. Van Treuren ◽  
Zuolan Wang ◽  
Peter T. Ireland ◽  
Terry V. Jones ◽  
S. T. Kohler
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Wall Temperature ◽  
Impinging Jets ◽  
Hole Diameter ◽  
Channel Height ◽  
Published Data ◽  
Target Plate ◽  
Adiabatic Wall

Recent work, Van Treuren et al. (1993), has shown the transient method of measuring heat transfer under an array of impinging jets allows the determination of local values of adiabatic wall temperature and heat transfer coefficient over the complete surface of the target plate. Using this technique, an inline array of impinging jets has been tested over a range of average jet Reynolds numbers (10,000–40,000) and for three channel height to jet hole diameter ratios (1, 2, and 4). The array is confined on three sides and spent flow is allowed to exit in one direction. Local values are averaged and compared with previously published data in related geometries. The current data for a staggered array is compared to those from an inline array with the same hole diameter and pitch for an average jet Reynolds number of 10,000 and channel height to diameter ratio of one. A comparison is made between intensity and hue techniques for measuring stagnation point and local distributions of heat transfer. The influence of the temperature of the impingement plate through which the coolant gas flows on the target plate heat transfer has been quantified.

MEMS Impinging-Jet Cooling

2000 ◽  
Author(s):  
Qiao Lin ◽  
Shuyun Wu ◽  
Yin Yuen ◽  
Yu-Chong Tai ◽  
Chin-Ming Ho
Keyword(s):  
Heat Transfer ◽  
Heat Exchangers ◽  
Jet Impingement ◽  
Impinging Jet ◽  
Impinging Jets ◽  
Measured Temperature ◽  
Transfer Coefficients ◽  
Element Analysis ◽  
Heat Transfer Coefficients ◽  
Jet Cooling

Abstract This paper presents an experimental investigation on MEMS impinging jets as applied to micro heat exchangers. We have fabricated MEMS single and array jet nozzles using DRIE technology, as well as a MEMS quartz chip providing a simulated hot surface for jet impingement. The quartz chip, with an integrated polysilicon thin-film heater and distributed temperature sensors, offers high spatial resolution in temperature measurement due to the low thermal conductivity of quartz. From measured temperature distributions, heat transfer coefficients are computed for single and array micro impinging jets using finite element analysis. The results from this study for the first time provide extensive data on spatial distributions of micro impinging-jet heat transfer coefficients, and demonstrate the viability of MEMS heat exchangers that use micro impinging jets.

Heat Transfer Enhancement by Turbulent Impinging Jets

2000 ◽  
Author(s):  
M. Kumagai ◽  
R. S. Amano ◽  
M. K. Jensen
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Stokes Equations ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Impinging Jets ◽  
Transfer Model ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

Abstract A numerical and experimental investigation on cooling of a solid surface was performed by studying the behavior of an impinging jet onto a fixed flat target. The local heat transfer coefficient distributions on a plate with a constant heat flux were computationally investigated with a normally impinging axisymmetric jet for nozzle diameter of 4.6mm at H/d = 4 and 10, with the Reynolds numbers of 10,000 and 40,000. The two-dimensional cylindrical Navier-Stokes equations were solved using a two-equation k-ε turbulence model. The finite-volume differencing scheme was used to solve the thermal and flow fields. The predicted heat transfer coefficients were compared with experimental measurements. A universal function based on the wave equation was developed and applied to the heat transfer model to improve calculated local heat transfer coefficients for short nozzle-to-plate distance (H/d = 4). The differences between H/d = 4 and 10 due to the correlation among heat transfer coefficient, kinetic energy and pressure were investigated for the impingement region. Predictions by the present model show good agreement with the experimental data.

Heat Transfer Characteristics of Impinging Two-Dimensional Air Jets

1966 ◽  
Vol 88 (1) ◽  
pp. 101-107 ◽  
Author(s):  
Robert Gardon ◽  
J. Cahit Akfirat
Keyword(s):  
Heat Transfer ◽  
Flat Plate ◽  
Two Dimensional ◽  
Heat Transfer Characteristics ◽  
Transfer Coefficients ◽  
Average Heat ◽  
Heat Transfer Coefficients ◽  
Transfer Characteristics ◽  
Air Jets

Local as well as average heat transfer coefficients between an isothermal flat plate and impinging two-dimensional jets were measured for both single jets and arrays of jets. For a large and technologically important range of variables the results have been correlated in relatively simple terms, and their application to design is briefly considered.

Mass Transfer Technique for Investigation of Heat Transfer by Jet-Impingement Systems

1972 ◽  
Vol 14 (6) ◽  
pp. 389-392 ◽  
Author(s):  
J. Ward ◽  
F. J. K. Ideriah ◽  
S. D. Probert ◽  
A. Duggan
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Jet Impingement ◽  
Impinging Jets ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Heat Transfers

The technique of using mass transfer measurements (by sublimation of naphthalene) together with the Chilton–Colburn analogy is shown to be feasible for evaluation of heat transfers from impinging jets. The method is then used to determine heat transfer coefficients at the burner walls in models of jet–impingement furnaces.

Impingement Cooling of Electronics

1992 ◽  
Vol 114 (3) ◽  
pp. 607-613 ◽  
Author(s):  
B. R. Hollworth ◽  
M. Durbin
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Circuit Board ◽  
Test Model ◽  
Transfer Coefficients ◽  
Low Velocity ◽  
Heat Transfer Coefficients ◽  
Air Jets ◽  
System Pressure ◽  
Uniform Array

Experiments were conducted to determine the performance of a system of low-velocity air jets used to cool a simulated electronics package. The test model consisted of a uniform array of rectangular elements mounted to a circuit board. Each element was cooled by a cluster of four jets, and the spent fluid was vented at one end of the channel formed between the circuit board and the plate from which the jets were discharged. Reported are measurements of system pressure drop and convective heat transfer coefficients for elements at various sites within the array. Results indicate that (for the geometry tested) the largest portion of the total pressure drop occurs across the jet orifices. Further, the crossflow of spent air appears to enhance heat transfer for those elements near the exit end of the channel.

Comparison and Prediction of Local and Average Heat Transfer Coefficients Under an Array of Inline and Staggered Impinging Jets

1996 ◽  
Author(s):  
Kenneth W. Van Treuren ◽  
Zoulan Wang ◽  
Peter Ireland ◽  
Terry V. Jones ◽  
S. T. Kohler
Keyword(s):  
Heat Transfer ◽  
Velocity Ratio ◽  
Impinging Jets ◽  
Published Data ◽  
Correlation Technique ◽  
Transfer Coefficients ◽  
Target Plate ◽  
Local Data ◽  
Adiabatic Wall ◽  
Impingement Plate

Recent work, Van Treuren et al. (1993, 1994), has shown the transient method of measuring heat transfer under an array of impinging jets allows the determination of local values of adiabatic wall temperature and heat transfer coefficient over the complete surface of the target plate. Using this technique, an inline and staggered array of impinging jets was tested over a range of average jet Reynolds numbers (10,000–40,000) for three impingement plate to target plate separations (1, 2 and 4). The array was confined on three sides and spent flow was allowed to exit in one direction. Local and average values are presented. These values for the two array configurations are then compared with each other as well as with previously published data in related geometries. A new correlation technique is presented, based on the local data, which breaks the target surface into jet and crossflow areas of interest, with excellent results. The correlation uses the local jet Reynolds number and local jet-to-crossflow mass velocity ratio. This new technique compared favourably with published correlations. Also presented is the influence of the impingement plate on the target plate heat transfer in the form of an effectiveness parameter. This influence is accounted for in the correlation.

The Cooling Impact of a Pair of Opposed Unsteady Confined Impinging Air Jets

2005 ◽  
Author(s):  
Victor Chiriac ◽  
Jorge L. Rosales
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Unsteady Flow ◽  
Jet Flow ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Air Jets ◽  
Laminar Jets ◽  
Vortex Patterns ◽  
Two Jets

A numerical investigation was performed at two Reynolds numbers to analyze the flow-field and heat transfer characteristics for a pair of laminar jets impinging on opposite walls in a channel. The present study is a continuation of the authors’ earlier work [1] in which the jets flowing out normal to the top channel wall produce a large stagnant bubble between the two jets which greatly reduce the heat transfer removal from the lower wall. In this case, the lower Reynolds number jet flow of 300 produces a symmetric, steady flow hydrodynamic pattern with the jets being deflected laterally. By further increasing the Reynolds number to 750, a complex asymmetric and highly unsteady flow develops between the two jets due to the opposite jet flow interaction. The convective heat transfer coefficients and the unsteady flow development between the jets are studied for each case. The flow unsteadiness is also characterized by analyzing the stagnation point displacement on the channel walls. The complex vortex patterns resulting from the jet interaction at the higher Reynolds number is investigated and its impact on the chip/microelectronics component cooling is thoroughly documented.   This paper was also originally published as part of the Proceedings of the ASME 2005 Heat Transfer Summer Conference.

scholarly journals Heat Transfer Characteristics of Swirling Impinging Jets

2010 ◽  
Author(s):  
Karl J. Brown ◽  
Tim Persoons ◽  
Darina B. Murray
Keyword(s):  
Heat Transfer ◽  
Thermal Imaging ◽  
High Heat ◽  
Impinging Jets ◽  
Transfer Coefficients ◽  
Film Sensor ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer ◽  
Hot Film ◽  
Hot Film Sensor

Impinging jets are well renowned for their abilities to achieve significantly high heat transfer coefficients. It has been found in previous studies that the incorporation of a swirl in the flow can enhance heat transfer but it can also decrease it. The objective of this research is to discover the defining characteristics of swirling impinging jets and to find an optimal swirl geometry for enhancing the heat transfer of the system. Using thermal imaging and hot film sensor techniques the heat transfer distribution of the swirling jet is examined in the context of the flow field; heat flux fluctuations at the impinging surface are investigated also.

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