Viscous dissipative forced convection in thermal non-equilibrium nanofluid-saturated porous media embedded in microchannels

In this paper, we examine the effect of local thermal non-equilibrium LTNE condition on the non-Newtonian forced convection flow through channels filled with porous media. Four representative dimensionless parameters are used in formulating the problem. Numerical solutions obtained over broad ranges of these parameters are utilized to map conditions at which local thermal non-equilibrium condition is important, occurrence of LTNE is found to be driven by higher modified Peclet number, lower modified Biot number, lower fluid-to-solid thermal conductivity ratio, lower power-law fluid index, and lower microscopic and macroscopic frictional flow resistance coefficients. The proportional effect of each parameter as related to others is investigated.

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Review of non-equilibrium flow and transport models in saturated porous media

WEENTECH Proceedings in Energy ◽

10.32438/wpe.222021 ◽

2021 ◽

pp. 228-245

Author(s):

Aman Chandel ◽

Deepak Swami

Keyword(s):

Porous Media ◽

Solute Transport ◽

Dispersion Equation ◽

Chemical Interaction ◽

Joint Probability ◽

Saturated Porous Media ◽

Soil Matrix ◽

Lumped Model ◽

Advection Dispersion ◽

Non Equilibrium

This study deals with review of different improvements done in the formulation of the governing equations to simulate accurate solute transport in saturated porous media over the years. The traditional advection-dispersion equation (ADE) model is the simplest lumped model founded on the assumptions of Fick’s law of diffusion. But it typically underestimates the breakthrough concentration in leading and/or tailing region due to non-fickian transport. It is modified into mobile-immobile model (MIM) considering the medium having micropores with stagnant water pockets but allowing solute exchange by diffusion between mobile and immobile zone which is quantified by mass transfer coefficient. Multi-process non-equilibrium (MPNE) model further simulates for a system with both physical and chemical non-equilibrium by assuming instantaneous and rate-limited sorption in advective and non-advective domains. Using the concept of dual permeability, slow fast transport (SFT) model divides the liquid phase in the domain into three zones i.e. fast, slow and immobile. Here chemical interaction between the fluid and soil matrix takes place only in slow and immobile zones. Non-fickian solute transport does not follow Brownian motion rules so a random variable is required to explain it. Hence continuous time random walk (CTRW) model is used where solute transport is characterized by joint probability variable. Special case of CTRW with solute having considerable probability of moving long distances and follow power law gives Fractional advection-dispersion equation (FADE) model. These models varying from relatively simple to more complex formulations and assumptions are discussed here highlighting the merits and demerits of each.

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