A Numerical and Experimental Investigation on Impinging Round Jets in Channel Partially Filled With Porous Media

In this paper a numerical and experimental investigation on impinging jets with metal foam is carried out. The channel is partially filled with porous media. The physical model and geometry has been made considering that the lower impinging surface is heated at uniform heat flux, qw, and the upper surface is adiabatic. The flow is 2D, unsteady, laminar, and incompressible. The distance between the upper confining surface and the lower heated surface is H (40 mm). Fully developed fluid dynamic and thermal flow is assumed at the outlet sections and the fluid is air. The porous material is considered as homogeneous and isotropic. All the thermophysical properties of the fluid and the solid matrix of the porous medium are assumed constant except for the variation in density with the temperature giving rise to the buoyancy forces. Metal foam of 10 PPI is considered. It was investigated many configuration taking into account the ratio s/H and Dj/H. The values of ratio s/H ranging from 0 to 1 while values of the ratio Dj/H raging from 0.3–1.2. Results in terms of wall temperature profiles, local and average Nusselt numbers are presented for different Reynolds values. For the considered parameters, it is obtained that Nusselt number has a weak dependence of Dj/H, in fact, for the ratio equal to 0.3, it is noted that Nu is higher than the ratio equal to 0.6.

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Thermo-Fluid Dynamics of an Array of Impinging Ionic Jets in a Crossflow

2010 14th International Heat Transfer Conference, Volume 5 ◽

10.1115/ihtc14-23149 ◽

2010 ◽

Author(s):

Walter Grassi ◽

Daniele Testi

Keyword(s):

Fluid Dynamic ◽

Impinging Jets ◽

Negative Ion ◽

Forced Flow ◽

Heated Wall ◽

Electrical Currents ◽

Square Duct ◽

Liquid Crystal Thermography ◽

Nusselt Numbers ◽

Bottom Side

Laminar to weakly turbulent mixed convection in a square duct heated from the bottom side is highly strengthened by ionic jets generated by an array of high voltage points, opposite to the heated strip. Negative ion injection is activated within the dielectric liquid HFE-7100. Local temperatures on the heated wall are measured by liquid crystal thermography. Distributions of the Nusselt number are obtained at different forced flow rates, applied heat flows, and transiting electrical currents. In correspondence of the point emitters, higher Nusselt numbers in the impingement areas are measured and an analogy with the thermo-fluid dynamic behavior of an array of submerged impinging jets in a crossflow is drawn. The diameter of the ionic jets is evaluated and an electrohydrodynamic Reynolds number is employed for correlation and similarity purposes.

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Experimental investigation on narrow gap heat transfer with porous media under downward-facing horizontal heated surface

Nuclear Engineering and Design ◽

10.1016/j.nucengdes.2009.09.009 ◽

2009 ◽

Vol 239 (12) ◽

pp. 3155-3160 ◽

Cited By ~ 4

Author(s):

B.X. Hu ◽

G.H. Su ◽

Y.W. Wu ◽

K. Sugiyama ◽

S.Z. Qiu

Keyword(s):

Heat Transfer ◽

Experimental Investigation ◽

Porous Media ◽

Heated Surface ◽

Narrow Gap

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Experimental Investigation of Natural Convection in an Asymmetrically Heated Vertical Channel with an Asymmetric Chimney

Journal of Heat Transfer ◽

10.1115/1.1928909 ◽

2005 ◽

Vol 127 (8) ◽

pp. 888-896 ◽

Cited By ~ 12

Author(s):

Oronzio Manca ◽

Marilena Musto ◽

Vincenzo Naso

Keyword(s):

Heat Flux ◽

Experimental Investigation ◽

Natural Convection ◽

Aspect Ratio ◽

Vertical Channel ◽

Expansion Ratio ◽

Uniform Heat Flux ◽

Geometrical Parameters ◽

Nusselt Numbers ◽

Lower Maximum

An experimental investigation on air natural convection, in a vertical channel asymmetrically heated at uniform heat flux, with downstream unheated parallel extensions, is carried out. One extension is coplanar to the unheated channel wall and the distance between the extensions is equal to or greater than the channel gap (geometrically asymmetric chimney). Experiments are performed with different values of the wall heat flux, aspect ratio (Lh∕b), extension ratio (L∕Lh) and expansion ratio (B∕b). For the largest value of the aspect ratio (Lh∕b=10), the adiabatic extensions improve the thermal performance in terms of lower maximum wall temperature of the channel. Optimal configurations of the system with asymmetrical chimney are detected. Flow visualization shows a cold inflow in the channel-chimney system that penetrates down below the channel exit section. Maximum wall temperatures and channel Nusselt numbers are correlated to the channel Rayleigh number, Ra*, and to the geometrical parameters, in the ranges 3.0×102⩽Ra*B∕b⩽1.0105, 1.0⩽B∕b⩽3.0 and 1.0⩽L∕Lh⩽4.0 with Lh∕b=5.0 and 10.0.

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Analysis of Transient Three-Dimensional Natural Convection in Porous Media

Journal of Heat Transfer ◽

10.1115/1.3244448 ◽

1981 ◽

Vol 103 (2) ◽

pp. 242-248 ◽

Cited By ~ 32

Author(s):

Y. T. Chan ◽

S. Banerjee

Keyword(s):

Heat Transfer ◽

Porous Media ◽

Natural Convection ◽

Thermophysical Properties ◽

Fluid Phase ◽

Spherical Particles ◽

Solid Matrix ◽

Time Step ◽

Nusselt Numbers ◽

Convection In Porous Media

Transient multidimensional natural convection in porous media has been studied using a numerical method based on the simplified marker and cell technique with local cancellation of low order, diffusional truncation errors. The conservation equations and boundary conditions were phrased in terms of the primitive variables, velocity and temperature. Differences in temperature between the fluid and the solid matrix are considered. Heat transfer between the solid and liquid phases was modelled by representing the porous medium as an assemblage of spherical particles, and solving the conduction problem within the spheres at every time step. Nusselt numbers at walls were calculated from the temperature and velocity profiles. Numerical results for heat transfer through fluid saturated porous media heated from below are in good agreement with published experiments. Consideration of heat transfer between the solid and fluid phase leads to Nusselt numbers that vary with the thermophysical properties of the solid material, even when the Rayleigh number and fluid thermophysical properties are kept constant. This is also observed in experiments. The calculations also show convective instabilities of the right period at high Rayleigh numbers.

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Buoyant Convection in Superposed Metal Foam and Water Layers

Heat Transfer: Volume 1 ◽

10.1115/ht2008-56028 ◽

2008 ◽

Author(s):

V. Kathare ◽

F. A. Kulacki ◽

Jane H. Davidson

Keyword(s):

Heat Transfer ◽

Metal Foam ◽

Heated Surface ◽

Transfer System ◽

Transfer Coefficients ◽

Heat Transfer Coefficients ◽

Nusselt Numbers ◽

Water Layers ◽

Heat Transfer System ◽

Vertical Cavity

Experiments on natural convection in superposed metal foam and water layers are reported. The heat transfer system comprises a vertical cavity heated from below and held at constant temperature at the top. Two systems are considered: a water-filled cavity with a foam layer on the heated surface and a water-filled cavity with foam layers on the upper and lower surfaces. The present experiments use open cell copper foams with a nominal porosity of 92%, and the relative thicknesses of the water and foam layers are varied. Steady state Nusselt numbers show the presence of foam on the boundaries enhances overall heat transfer coefficients over that for the water-only layer. Enhancement of overall Nusselt numbers varies from 12 to 60% depending on Rayleigh number. Sub-layer configurations with foam on both heat transfer surfaces are more effective for enhancement than a configuration with foam only on the heated surface.

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Thermo-Fluid Dynamics of an Array of Impinging Ionic Jets in a Crossflow

Journal of Heat Transfer ◽

10.1115/1.4024280 ◽

2013 ◽

Vol 135 (8) ◽

Cited By ~ 5

Author(s):

Daniele Testi ◽

Walter Grassi

Keyword(s):

High Efficiency ◽

Fluid Dynamic ◽

Impinging Jets ◽

Negative Ion ◽

Forced Flow ◽

Heated Wall ◽

Electrical Currents ◽

Square Duct ◽

Nusselt Numbers ◽

Potential Applications

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Buoyant Convection in Superposed Metal Foam and Water Layers

Journal of Heat Transfer ◽

10.1115/1.3194767 ◽

2009 ◽

Vol 132 (1) ◽

Cited By ~ 7

Author(s):

V. Kathare ◽

F. A. Kulacki ◽

Jane H. Davidson

Keyword(s):

Heat Transfer ◽

Metal Foam ◽

Heated Surface ◽

Lower Boundary ◽

Foam Layer ◽

Transfer Coefficients ◽

Open Cell ◽

Heat Transfer Coefficients ◽

Nusselt Numbers ◽

Water Layers

Heat transfer measurements for natural convection in superposed metal foam and water layers are reported. Two systems heated at the lower boundary are considered: a water-filled cavity with a foam layer on the heated surface and a water-filled cavity with foam layers on the upper and lower surfaces. The present experiments use open cell copper foams with a nominal porosity of 92%, and the relative thicknesses of the water and foam layers are varied. Steady state Nusselt numbers show that the presence of foam on the boundaries enhances overall heat transfer coefficients over that for the water-only layer. Enhancement of overall Nusselt numbers varies from 12% to 60% depending on Rayleigh number. Sublayer configurations with foam on both heat transfer surfaces are more effective for enhancement than a configuration with foam only on the heated surface.

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Mist/Steam Cooling by a Row of Impinging Jets

Volume 3: Heat Transfer; Electric Power; Industrial and Cogeneration ◽

10.1115/2001-gt-0151 ◽

2001 ◽

Author(s):

X. Li ◽

J. L. Gaddis ◽

T. Wang

Keyword(s):

Heat Transfer ◽

Heat Transfer Coefficient ◽

Transfer Coefficient ◽

Cfd Simulation ◽

Heated Surface ◽

Impinging Jets ◽

Stagnation Line ◽

Round Jets ◽

Steam Cooling ◽

The Heat Transfer Coefficient

Closed loop steam has been chosen for cooling airfoils in heavy frame Advanced Turbine Systems (ATS) to improve efficiency. Enhanced cooling by the use of mist is considered to have potential to augment cooling by internal steam alone. Water droplets generally less than 10μm are added to 1.3 bar steam and injected through a row of four discrete round jets onto a heated surface. The Reynolds number is varied from 7500 to 22500 and the heat flux varied from 3.3 to 13.4 kW/m2. The mist increases the heat transfer coefficient along the stagnation line and downstream wanes in about 5 jet diameters. The heat transfer coefficient improves by 50 to 700 percent at the stagnation line for mist concentrations 0.75 to 3.5 percent by weight, depending on conditions. Off-axis maximum cooling occurs in most of the mist/steam flow but not in the steam-only flow. CFD simulation indicates that this off-axis cooling peak is caused by droplets’ interaction with the target walls.

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