Abstract
The effect of porous material position on the heat transfer inside a pipe working in a turbulent regime is studied here to obtain a detailed understanding of the heat transfer enchantment mechanisms in different porous substrate positions. To this end, an in-house Fortran code is developed to solve the governing equations using the finite volume method and SIMPLE algorithm. Turbulent flow in porous media is modeled using a modified version of k–ε model. The flow field and heat transfer inside the partially filled pipe are investigated for the two cases of central and boundary configurations. The porous and flow characteristics including Reynolds number, Darcy number, the conductivity ratios of solid to fluid and the thickness of inserted porous layer are varied and the heat transfer performance is studied in different cases. It is observed that two entirely different phenomena enhance the heat transfer in central and boundary configurations. While the channeling of fluid between the porous media and the pipe wall highly affects the heat transfer performance in the former, the thermal conductivity of porous media plays a highly critical role in the latter configuration. It is shown that, for the same filling ratio, inserting the porous layer at the core of the pipe is more effective than placing it at the wall. Investigating porous materials with different solid conductivities revealed that covering the pipe wall with a porous material is justified only for solid matrixes with high thermal conductivities.
Highlights
Convective heat transfer in many systems, including porous media, is of great importance for a large number of applications such as geothermal energy recovery, solid matrix heat exchangers, drying of iron ore pellets, pebble bed reactors, electronics cooling, solar collectors, and has attracted many researchers from a wide range of disciplines [1, 2]
A reverse trend is observed as will be discussed in the following of Fig. 13, which is due to counteracting of different phenomena affecting heat transfer in boundary arrangement, making the decision for heat transfer enhancement more complex in this configuration
The present results suggest that the insertion of porous media at the center of the pipe enhances the heat transfer performances regardless of porous media thermal characteristics
Summary
Convective heat transfer in many systems, including porous media, is of great importance for a large number of applications such as geothermal energy recovery, solid matrix heat exchangers, drying of iron ore pellets, pebble bed reactors, electronics cooling, solar collectors, and has attracted many researchers from a wide range of disciplines [1, 2]. Nimvari et al [17, 18] evaluated the heat transfer enhancement in a channel partially filled with porous media in two different configurations They have used a turbulence model in porous media whose additional terms in turbulent kinetic energy and dissipation rate equations are calculated at high Reynolds number, and the coefficients in these additional terms are constant. The effect of different parameters including turbulence modeling [17], porous media parameters in channel [18] and double pipe heat exchanger [23] has been previously studied by the present authors, a detailed investigation of mechanisms that are behind the heat transfer enhancement in different configurations of porous media in a pipe is of interest to reach the best thermal performance in different applications. A comparison is carried out between the Nusselt number calculated with two porous configurations in the pipe with the same filling ratio, which helps to find the appropriate arrangement of porous layers when they occupy the cross-sectional area of the pipe
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