Turbulent Impinging Jet Into a Confined Porous Layer

2005 ◽  
Author(s):  
Marcelo J. S. de Lemos ◽  
Daniel R. Graminho
Keyword(s):  
Porous Layer ◽  
Control Volume ◽  
Numerical Technique ◽  
Flow Distribution ◽  
Simple Algorithm ◽  
Local Heat Transfer ◽  
Impinging Jet ◽  
Local Heat ◽  
Impinging Jets ◽  
Transfer Coefficients

Turbulent impinging jets on heated surfaces are widely used in industry to modify local heat transfer coefficients. The addition of a porous substrate covering the surface contributes to a better flow distribution, which favors many engineering applications. Motivated by this, the present work shows numerical results for a turbulent impinging jet against a cylindrical enclosure with and without a porous layer at the bottom. The macroscopic time-averaged equations for mass, momentum and energy are obtained based on a concept called double decomposition, which considers spatial deviations and temporal fluctuations of flow properties. The numerical technique employed for discretizing the governing equations is the control volume method in conjunction with a boundary-fitted non-orthogonal coordinate system. The SIMPLE algorithm is used to handle the pressure-velocity coupling. The influence of characteristics of the porous layer on the mean and statistical flow fields within the cylinder is presented.

Turbulent Impinging Jets Into Permeable Media

2006 ◽  
Author(s):  
Marcelo J. S. de Lemos ◽  
Daniel R. Graminho
Keyword(s):  
Control Volume ◽  
Numerical Technique ◽  
Flow Distribution ◽  
Simple Algorithm ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Impinging Jets ◽  
Porous Substrate ◽  
Transfer Coefficients ◽  
Permeable Media

Impinging jets are widely used in industry to modify local heat transfer coefficients. The addition of a porous substrate covering the surface contributes to better flow distribution, which favors many engineering applications. Motivated by that, this work shows numerical results for a turbulent jet impinging against a cylindrical enclosure with a porous substrate at the bottom. Macroscopic time-averaged equations for mass and momentum are obtained based on a concept called double decomposition, which considers spatial deviations and temporal fluctuations of flow properties. The numerical technique employed for discretizing the governing equations is the control volume method in conjunction with a boundary-fitted coordinate system. The SIMPLE algorithm is used to handle the pressure-velocity coupling. The influence of the cylinder height on the mean and statistical flow fields within the entire cavity is presented.

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.

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.

Numerical Simulation of Laminar Confined Impinging Jet in a Composite Channel

2008 ◽  
Author(s):  
Marcelo J. S. de Lemos
Keyword(s):  
Porous Layer ◽  
Control Volume ◽  
Numerical Technique ◽  
Simple Algorithm ◽  
Local Distribution ◽  
Governing Equations ◽  
Stagnation Region ◽  
Volume Method ◽  
Material Porosity ◽  
Macroscopic Equations

This work shows numerical results for a jet impinging onto a flat plane covered with a layer of a porous material. Porosity of the porous layer is varied in order to analyze its effect on the local distribution of Nu. Macroscopic equations for mass and momentum ae obtained based on the volume-average concept. The numerical technique employed for discretizing the governing equations was the control volume method with a boundary-fitted non-orthogonal coordinate system. The SIMPLE algorithm was used to handle the pressure-velocity coupling. Results indicate that inclusion of a porous layer decreases the peak in Nu avoiding excessive heating or cooling near the stagnation region.

An Analysis of the Effect of Entrainment Temperature on Jet Impingement Heat Transfer

1984 ◽  
Vol 106 (4) ◽  
pp. 804-810 ◽  
Author(s):  
S. A. Striegl ◽  
T. E. Diller
Keyword(s):  
Heat Transfer ◽  
Analytical Solutions ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Impinging Jet ◽  
Local Heat ◽  
Impinging Jets ◽  
Recirculation Region ◽  
Plate Temperature ◽  
Single Plane

An analytical model is developed to determine the effect of the temperature of entrained fluid (entrainment temperature) on the local heat transfer to a single, plane, turbulent impinging jet. Solutions of the momentum and energy equations for a single impinging jet are accomplished using similarity and series analyses. Solutions of the energy equation are obtained for the two limiting cases of entrainment temperatures equal to the plate temperature and the initial jet temperature. The analytical solutions are superposed to obtain the solution for all intermediate entrainment temperatures. The constants in the turbulence model are determined by comparing the analytical solutions to experimentally determined local heat transfer rates for single impinging jets issuing into an environment with a controlled entrainment temperature. When the single jet model is applied to jet arrays it predicts that the entrainment in the recirculation region between the jets can significantly affect the heat transfer. Comparison of the model to heat transfer measurements performed for jet arrays shows that the model successfully predicts the local heat transfer in jet arrays.

Convective Heat Transfer Enhancement Due to Intermittency in an Impinging Jet

1993 ◽  
Vol 115 (1) ◽  
pp. 91-98 ◽  
Author(s):  
D. A. Zumbrunnen ◽  
M. Aziz
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Impinging Jets ◽  
Transfer Coefficients ◽  
Stagnation Line ◽  
High Heat Transfer ◽  
Short Period

An experimental investigation has been performed to study the effect of flow intermittency on convective heat transfer to a planar water jet impinging on a constant heat flux surface. Enhanced heat transfer was achieved by periodically restarting an impinging flow and thereby forcing renewal of the hydrodynamic and thermal boundary layers. Although convective heat transfer was less effective during a short period when flow was interrupted, high heat transfer rates, which immediately follow initial wetting, prevailed above a threshold frequency, and a net enhancement occurred. Experiments with intermittent flows yielded enhancements in convective heat transfer coefficients of nearly a factor of two, and theoretical considerations suggest that higher enhancements can be achieved by increasing the frequency of the intermittency. Enhancements need not result in an increased pressure drop within a flow system, since flow interruptions can be induced beyond a nozzle exit. Experimental results are presented for both the steady and intermittent impinging jets at distances up to seven jet widths from the stagnation line. A theoretical model of the transient boundary layer response is used to reveal parameters that govern the measured enhancements. A useful correlation is also provided of local heat transfer results for steadily impinging jets.

Numerical Analysis of Local Heat Transfer From a Flat Plate to a Swirling Air Impingining Jet

2006 ◽  
Author(s):  
X. Terry Yan ◽  
Rahul S. Kalvakota
Keyword(s):  
Heat Transfer ◽  
Flat Plate ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Local Heat Transfer ◽  
Impinging Jet ◽  
Local Heat ◽  
Flow Profile ◽  
Transfer Coefficients ◽  
Stagnation Region

Local heat transfer from a flat plate to a swirling circular air impinging jet is investigated numerically. Reynolds Averaged Navier-Stokes equations (RANS) and energy equation are solved for the axisymmetric, three dimensional flow. Eddy-viscosity based turbulence models, RNG and V2F, are used. Non-uniform meshes are used for the three dimensional flows and mesh independent solutions are obtained. The flow Reynolds number, which is based on the jet diameter, is kept at 23,000. In the analysis, local heat transfer coefficients are obtained for different swirl numbers, S = 0.21, 0.35 and 0.47 and jet-to-plate distance, L/D, ranging from 2 to 9. Investigation of the effect of swirl flow profile at the exiting plane of the jet on heat transfer is also presented. It is found that different swirl profiles with the same swirl number lead to very different heat transfer behaviors in the stagnation region of the impinging jet.

Local Heat Transfer Coefficient Distribution With Air Impingement Into a Cavity

1972 ◽  
Author(s):  
F. Burggraf
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Impinging Jets ◽  
Local Heat Transfer Coefficient ◽  
Cavity Surface ◽  
Transfer Coefficients ◽  
Coefficient Distribution

Impingement heat transfer coefficients are presented for a row of holes impinging into an oval cavity with the spent air leaving through holes on one or both sides of the cavity. The distribution around the cavity surface is obtained and is correlated with a survey of the recent literature. In addition, local heat flux gages were used with an impingement jet air supply which could be changed in location along the axis of the test section. This permitted the determination of local heat transfer coefficient distribution over the surface both around the cavity and also in the region between the impinging jets. This two-dimensional distribution is shown to be influenced by the bleed geometry and the shape of the impinging jet holes.

Turbulent Impinging Jet Into a Rigid Porous Layer

2011 ◽  
Author(s):  
Marcelo J. S. de Lemos
Keyword(s):  
Porous Layer ◽  
Control Volume ◽  
Numerical Technique ◽  
Simple Algorithm ◽  
Stagnation Region ◽  
Thermally Conducting ◽  
Energy Equations ◽  
Volume Method ◽  
Highly Porous ◽  
Macroscopic Equations

This work shows simulations for a turbulent jet impinging against a flat plane covered with a layer of permeable and thermally conducting material. Distinct energy equations are considered for the porous layer attached to the wall and for the fluid that impinges on it. Parameters such as Reynolds number, porosity, permeability, thickness and thermal conductivity of the porous layer are varied in order to analyze their effects on the local distribution of Nu. The macroscopic equations for mass, momentum and energy are obtained based on volume-average concept. The numerical technique employed for discretizing the governing equations was the control volume method with a boundary-fitted non-orthogonal coordinate system. The SIMPLE algorithm was used to handle the pressure-velocity coupling. Results indicate that inclusion of a porous layer eliminates the peak in Nu at the stagnation region. For highly porous and highly permeable material, simulations indicate that the integral heat flux from the wall is enhanced when a thermally conducting porous material is attached to the wall.

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