On the forced convective flow inside thermal collectors enhanced by porous media: from macro to micro-channels

Purpose Aiming at finding the velocity distribution profile and other flow characteristic parameters such as the Poiseuille (Po) number, this study aims to focus on the three-dimensional forced convective flow inside rectangular ducts filled with porous media commonly used in air-based solar thermal collectors to enhance the thermal performance. The most general model for the fluid flow (i.e. the non-linear Darcy–Brinkman–Forchheimer partial differential equation subjected to slip and no-slip boundary conditions) is considered. Design/methodology/approach The general governing equations are solved analytically based on the perturbation technique and the results are validated against numerical simulation study based on a finite-difference solution over a non-uniform but structured grid. Findings The analytical velocity distribution profile based on exponential functions for the above-mentioned general case is obtained, and accordingly, expressions for the Po are introduced. It is found that the velocity distribution tends to be uniform by increasing the aspect ratio of the duct. Moreover, a criterion for considering/neglecting the nonlinear drag term in the momentum equation (i.e. the Forchheimer term) is proposed. According to the sensitivity analysis, results show that the nonlinear drag term effects on the Nusselt number are important only in porous media with high Darcy numbers. Originality/value A general analytic solution for three-dimensional forced convection flows through rectangular ducts filled with porous media for the general model of Darcy–Brinkman–Forchheimer and the general boundary condition including both no-slip and slip-flow regimes is obtained. An analytic expression to calculate Po number is obtained which can be practical for engineering estimations and a basis for validation of numerical simulations. A criterion for considering/neglecting the nonlinear drag term in the momentum equation is also introduced.

Modeling and numerical computation of nonsimilar forced convective flow of viscous material towards an exponential surface

The objective of this paper is to study the mixed convective nonsimilar flow above an exponentially stretching sheet saturated by nanofluid. The leading partial differential equations (PDEs) of the problem have been modified towards dimensionless nonlinear PDEs utilizing newly proposed nonsimilarity transformations. Furthermore, local nonsimilarity procedure up to-second truncation has been operated to change the dimensionless PDEs into ordinary differential equations (ODEs). MATLAB-based algorithm bvp4c is used to observe the consequences of the distinct parameters namely Prandlt number [Formula: see text], magnetic field [Formula: see text], Lewis number [Formula: see text], Brownian motion [Formula: see text], Eckert number [Formula: see text], thermophoresis [Formula: see text] on velocity, concentration and temperature distribution are shown in graphical portray. Additional outcomes presume the heat penetration into the fluid enhances with increase in Biot number and Brownian motion. Increasing values of [Formula: see text] and [Formula: see text] cause decrease of temperature profile.

Ohmic and Viscous Dissipation Effect on Free and Forced Convective Flow of Casson Fluid in a Channel

Analytical study of the free and forced convective flow of Casson fluid in the existence of viscous dissipation, ohmic effect and uniform magnetic field in a porous channel to the physical model. The nonlinear coupled partial differential equations are converted to linear partial differential equations using similarity transformation and the classical perturbation method. The physical parameters such as Prandtl number (Pr), viscous dissipation (Vi), Schmidt number (Sc), Reynolds number (R), thermal buoyancy parameter (λ), Ohmic number (Oh), Casson fluid parameter (β), Darcy number (Da), Hartmann number (M2), the concentration of buoyancy parameter (N), chemical reaction rate (γ) effect on velocity, temperature and concentration have been studied with pictorial representation. For the particular case, the present paper analysis is compared with the previous work and is found good agreement.

Dynamics and modeling of nonlinear forced convective flow of Carreau-fluid (non-Newtonian fluid) with Marangoni convection

This paper deals with Marangoni convective flow of Carreau fluid. Boundary condition for momentum equation is considered to be Marangoni type. Thermal energy produces when current passes through the electrical conductor and this process is called Joule heating. Viscous dissipation is also applied in thermal equation. Nonlinear mixed convection for temperature is considered. Governing equations of PDE's are converted to ODE's by implementation of transformation. ND-Solve MATHEMATICA method is used to solve the equations. Parameters result against temperature, velocity, entropy rate, Bejan number, Skin friction and Nusselt number is examined via graphs. Due to increase in fluid parameter velocity of the fluid reduces while increasing impact is seen for temperature. Temperature is increasing function of Eckert number. Entropy generation also shows rising impact via fluid parameter while Bejan number decays. Drag force of surface decays via fluid parameter. Nusselt number is in direct relation with Prandtl and Eckert number.