Generation of entropy and forced convection of heat in a conduit partially filled with porous media – Local thermal non-equilibrium and exothermicity effects

Abstract

h i g h l i g h t sLocal and total entropy generations in endothermic/exothermic channels are investigated. Convection interface boundary condition has been incorporated into the modelling. Partial filling of the channel with LTE and LTNE for energy equations are considered. Bifurcation phenomena for temperature and local entropy generation are observed. Analytical solutions for temperature and entropy generation rates are obtained. a b s t r a c tThe performance of a two-dimensional, axisymmetric channel with porous inserts attached to the walls is analyzed from the perspective of the first and second laws of thermodynamics. In this analysis, the flow is assumed to be fully developed with a constant heat flux imposed on the external surfaces of the walls, while heat could be internally generated by the fluid and solid phases. Using a Darcy-Brinkman model of momentum transport along with a two-equation thermal energy model, a convective model was developed to describe the thermal boundary conditions on the porous-fluid interface. The so-called Model A was employed on the walls of the channel and semi-analytical solutions were developed for the hydrodynamic, temperature, entropy generation fields and the Nusselt number, and an extensive parametric study was subsequently, conducted. The results indicated that the inclusion of exothermicity leads to significant modifications in the thermal and entropic behaviour of the system. In particular, through comparison with the recent literature, it was demonstrated that exothermicity can significantly impact the influence of the porous-fluid interface model upon the generation of both the local and total entropy within the system.

The effects of exothermic catalytic reactions upon combined transport of heat and mass in porous microreactors

“…A general feature of these figures is the clear distinction between the temperature fields of the fluid and porous solid phases, rendering a strong deviation from local thermal equilibrium (LTE). This is consistent with the findings of the previous investigations of internally heat generating porous channels[25,48,60] and highlights the significance of LTNE approach in the current analysis. The effects of variation in the thermal conductivity ratio, , are shown inFig.…”

“…The heat flux is then split based on the thermal conductivities of the respective phases of the porous material and the corresponding temperature gradients. Splitting the heat flux in this manner is referred to as Model A [25,[44][45][46] and has been widely used in literature (see for example [39,40,47,48]). In enacting this procedure, the effective thermal conductivity of each phase is used.…”

Combined heat and mass transfer analyses in catalytic microreactors partially filled with porous material - The influences of nanofluid and different porous-fluid interface models

“…Although using LTNE method is more costly compared with LTE, it is more reliable and provides more accurate results prediction of the temperature fields inside the system [16]. Most importantly, it has been recently shown that the results of this approach are superior to those of LTE, particularly in the presence of heat generating/consuming chemical reactions [10] [17]. This superiority also improves the mass transfer analysis when the dispersion and energy equations of the fluid phase are coupled by the thermal diffusion of mass [18] [19].…”

“…A few points follow from the preceding review of literature. First, the general problem of partially filled porous channels and microchannels have already received significant attention, see for example [17] [25][26] [27]. As an essential commonality, all these investigations ignore the existence of the channel walls.…”

Non-Equilibrium Thermodynamic Analysis of Double Diffusive, Nanofluid Forced Convection in Catalytic Microreactors with Radiation Effects

“…This approach has been applied by a number of scholars to investigate the effects of radiation on the entropy generation of thermal systems [41]. Hence, the local entropy generation rate across the entire microchannel can be formulated as follows [42][43][44]. …”