Natural convection has a great its importance in several practical applications. In particular, the configuration of two horizontal parallel walls, with heated upper plate and open cavities, gets considerable attention in many thermal engineering applications, such as cooling of electronic components and devices, chemical vapor deposition systems and solar energy systems. The flow motion is strongly affected by the location of the heated surface, positioned on the upper or the lower wall of the horizontal channel. The main flow in natural convection is caused by the low heat exchanged between flow and walls, and one of the techniques to enhance the heat transfer is expanding the exchange surfaces. Porous media provided with high thermal conductivity, like metal foams, are an adequate method of heat transfer enhancement due to their large surface area to volume ratio and to intense mixing of the flow. In this work, a numerical investigation on two-dimensional steady state natural convection in a horizontal channel partially filled with a porous medium and heated at uniform heat flux from above is carried out. The lower plate is adiabatic. The porous medium is modeled using the Brinkman–Forchheimer-extended Darcy model and the local thermal equilibrium (LTE) hypothesis is assumed. The structure of the porous medium is homogenous and isotropic, the thermophysical properties of the air and the porous medium are temperature independent and the fluid flow is laminar and incompressible. The governing equations in the two-dimensional model is realized and solved by means of the ANSYS-FLUENT code. The computational domain is made up of the principal channel and two lateral extended reservoirs at the open vertical sections. The channel has dimensions L equal to 400 mm and the distance between the two horizontal plates, b, is equal to 40 mm. The two external reservoirs allow to simulate the external ambient and to assign at the boundary of the reservoirs a velocity equal to zero and the ambient temperature. Furthermore, a porous plate is considered near the upper heated plate and it has a thickness equal to 20 mm whereas the length and the width are the same of the channel. The aluminum foam has 10, 20 and 40 PPI and its porosity ranges from 0.89 and 0.97. Rayleigh number values are examined, from 10 to 1000. The main aim of the present study is to analyze the effect of pores per inch and porosity. The numerical simulations are performed with working fluid air. Different values of assigned wall temperatures are considered. Results are presented in terms of velocity and temperature fields, and both temperature and velocity profiles at different significant sections are shown, to obtain a description of the natural convection inside the open-ended cavity. Finally, Average Nusselt number values are evaluated.


Study on Natural Convection in Horizontal Parallel Plate Channels Heated on Upper Wall and Partially Filled With Metal Foam

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Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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