Forced Convection In Porous Media Research Articles

A pore-scale assessment of the dynamic response of forced convection in porous media to inlet flow modulations

An increasing number of technologies require prediction of unsteady forced convection in porous media when the inlet flow is unsteady. To gain further insight into this problem, the unsteady equations of continuity, Navier Stokes and energy are solved within the pores formed by several cylindrical flow obstacles. The system is modulated by sine waves superimposed on the inlet flow velocity, and the spatio-temporal responses of the flow and temperature fields are calculated. The results are then utilised to assess the linearity of the thermal response represented by the Nusselt number on the obstacles. It is shown that for linear cases, a transfer function can be devised for predicting the dynamic response of the Nusselt number. It is further argued that such a transfer function can be approximated by a classic low-pass filter which resembles the average response of the individual obstacles. This indicates that there exists a frequency threshold above which the thermal system is essentially insensitive to flow modulations. The results also show that changes in Reynolds number and porosity of the medium can push the dynamic response of the system towards non-linearity. Yet, there appears to be no monotonic change in the linearity of the response with respect to the Reynolds number and porosity. In general, it is found that for low Reynolds numbers, the dynamics of heat convection can be predicted decently by taking a transfer function approach. The findings of this study can enable further understanding of unsteady forced convection in porous media subject to time-varying inlet flows.

A note on the confusion associated with the interfacial heat transfer coefficient for forced convection in porous media

This note is provided to clear away possible confusion associated with the correlation proposed by Kuwahara et al. (2001) [1] for the interfacial heat transfer coefficient for forced convection in porous media.

Electromagnetic field effects on transport through porous media

The effect of an imposed electromagnetic field on forced convection in porous media is analyzed in this work. The transient Maxwell’s equations are solved to simulate the electromagnetic field inside the waveguide and within a porous medium. The Brinkman–Forchheimer extended Darcy (generalized model) equations are used to represent the flow fluid inside a porous medium. The local thermal non-equilibrium (LTNE) is taken into account by solving the two-energy equation model for fluid and solid phases. Computational domain is represented for a range of Darcy number from 10 −5 to 10 −7 and dimensionless electromagnetic wave power P ∗ from 0 to 1600, and dimensionless electromagnetic wave frequency f ∗ from 0 to 8. The effect of variations of the pertinent electromagnetic field parameters in affecting the flow and thermal fields and the Nusselt number are analyzed. This investigation provides the essential aspects for a fundamental understanding of forced convection in porous media while experiencing an applied electromagnetic field such as applications in the material-processing field.

A two-equation model for thermally developing forced convection in porous medium with viscous dissipation

This study extends the earlier work on fully developed convection with viscous dissipation in the fluid phase and in the presence of a porous medium, by including the thermally developing effects. The governing two-equation model is solved by finding the particular and homogeneous solutions. The characteristics of temperature profiles along the axial direction when solid conduction is dominant, are distinctive in the two-equation model, unlike the local thermal equilibrium model. The local heat transfer coefficients depend strongly on the relative thermal resistance to fluid and solid conduction and to a lesser extent on Brinkman number and porous medium shape factor.

Field synergy principle analysis on fully developed forced convection in porous medium with uniform heat generation

In the presence of uniform heat source, the energy equation for forced convective heat transfer in porous medium between two parallel plates is solved for fully developed flow. Field synergy analysis is performed with emphasis on the intersection angle between the velocity vector and temperature gradient vector with the inclusion of heat generation. Maximum local intersection angle corresponds to location with the highest resistance to heat convection. Relationship between Nusselt number and field synergy for forced convection in the presence of heat generation is studied. It is necessary to define a modified intersection angle in order to compare the wall heat transfer coefficient for convective heat transfer processes with uniform heat source.

A modification of a Nusselt number correlation for forced convection in porous media

We report numerical simulations of forced convection heat transfer rates of a steady laminar flow in a two-dimensional model of porous media to elucidate the differences observed between the numerical predictions of Kuwahara et al. (2001) [Int. J Heat Mass Trans. 44, 1153–1159] and Gamrat et al. (2008) [Int. J Heat Mass Trans. 51, 853–864]. A modification in the correlation given by Kuwahara et al. (2001) is proposed to make the results of the three numerical studies comparable and in agreement with the experimental data.

Effects of viscous dissipation on fully developed forced convection in porous media

An analytical study on fully developed forced convection in a homogeneous porous medium is presented. Closed form solutions for the temperature distributions in the transverse direction with the inclusion of frictional heating due to viscous dissipation are obtained, with variations of Darcy number and Brinkman number. The frictional heating effect on the temperature distributions is investigated and analyzed for both heating and cooling processes. Variations of Nusselt number as a function of Darcy number and Brinkman number are examined, and the deviations of the Nusselt numbers with that of the model without incorporating the effect of frictional heating are presented in a contour deviation map for a more holistic comparison.

Entropy generation analysis of thermally developing forced convection in fluid-saturated porous medium

Entropy generation for thermally developing forced convection in a porous medium bounded by two isothermal parallel plates is investigated analytically on the basis of the Darcy flow model where the viscous dissipation effects had also been taken into account. A parametric study showed that decreasing the group parameter and the Peclet number increases the entropy generation while for the Brinkman number the converse is true. Heatline visualization technique is applied with an emphasis on the Br < 0 case where there is somewhere that heat transfer changes direction at some streamwise location to the wall instead of its original direction, i.e., from the wall.

Unsteady forced convection heat transfer on a flat plate embedded in the fluid-saturated porous medium with inertia effect and thermal dispersion

For an unsteady forced convection on a flat plate embedded in the fluid-saturated porous medium with inertia effect and thermal dispersion, this paper presents a precise and rigorous method to obtain the entire solutions from one-dimensional transient conduction ( ξ=0) to steady forced convection in porous medium ( ξ=1) under conditions of uniform wall temperature and uniform heat flux, respectively. It is worth noted that the rate of unsteady heat transfer can be accelerated by the thermal dispersion, which may be regarded as the effect of mixing or agitating, to enhance the heat transfer in porous medium. Additionally, it is found that the time response, from the transient heat conduction to a steady forced convection in Darcy's flow, is τ=1, and is independent of wall heating condition and thermal dispersion strength ( φ).

Numerical experiments on free and forced convection in porous media

Understanding the patterns of flow induced by geothermal sources in deep ground is still a problem, although the basic hydraulic regimes are identified. The interaction of flow and heat-transport results in different flow phenomena depending on the variability and range of the parameters involved. A qualitative and quantitative characterization is given in this paper.

Heatline visualization of forced convection in porous media

The patterns of heatlines reported in this paper illustrate for the first time the true path of convective heat transfer through a saturated porous medium. Heatline patterns are reported for the following fundamental configurations: the boundary layer near an isothermal wall, the boundary layer near a wall with uniform heat flux, and the two-dimensional porous layer confined by two parallel plates. Emphasis is placed on the convection features that are being visualized for the first time by the heatline method, i.e., not by traditional methods such as the use of isotherms. It is shown that the heatlines of a flow in which the wall serves as heat sink are unlike the heatlines of the same flow with a wall that serves as heat source. The seepage flow with slip at the boundary is visualized by heatlines that leave a hot wall at an angle. The wall heat-flux distribution is visualized by the density of the heatlines that intersect the wall. The heatline pattern in fully developed flow of a pure fluid through a parallel-plate channel is also reported in order to emphasize that the pure-fluid pattern is not exactly the same as the pattern in the corresponding two-dimensional space filled with seepage flow through a porous medium.

Convection mixte en milieu poreux

For conception of nuclear reactors of thermal insulation purposes a theoretical study and a experimental investigation were conducted to determine the flow interaction between free and forced convection in porous media. The equations describing the model are presented and a numerical computer code is developed. The analytical results are in good agreement with the experiments. The exploitation of the code show the governing parameters.