Purpose: The main purpose of this numerical study is to study on entropy generation in natural convection of nanofluid in a wavy cavity using a single-phase nanofluid model. Design/methodology/approach: The cavity is heated non-uniformly from the wavy wall and cooled from the right side while it is insulated from the horizontal walls. The physical domain of the problem is transformed into a rectangular geometry in the computational domain using an algebraic coordinate transformation by introducing new independent variables ξ and η. The governing dimensionless partial differential equations with corresponding initially and boundary conditions were numerically solved by the finite difference method of the second-order accuracy. The governing parameters are Rayleigh number (Ra = 1000-100000), Prandtl number (Pr = 6.82), solid volume fraction parameter of nanoparticles (φ = 0.0-0.05), aspect ratio parameter (A = 1), undulation number (κ = 1-3), wavy contraction ratio (b = 0.1-0.3) and dimensionless time (τ = 0-0.27). Findings: It is found that the average Bejan number is an increasing function of nanoparticle volume fraction and a decreasing function of the Rayleigh number, undulation number and wavy contraction ratio. Also, an insertion of nanoparticles leads to an attenuation of convective flow and enhancement of heat transfer. Originality: The originality of this work is to analyze the entropy generation in natural convection within a wavy nanofluid cavity using single-phase nanofluid model. The results would benefit scientists and engineers to become familiar with the flow behaviour of such nanofluids, and will be a way to predict the properties of this flow for the possibility of using nanofluids in advanced nuclear systems, in industrial sectors including transportation, power generation, chemical sectors, ventilation, air-conditioning, etc.

The article treats the study on free convection of a hybrid nanoliquid confined within contrariwise T-shaped enclosure saturated by two porous media with different material and structure. Nanocomposite particles of multiwall carbon nanotubes–Fe₃O₄ are dispersed into water. Variable magnetic source located to the bottom wall has been analyzed in terms of heat transport performance and nanofluid motion behavior in the enclosure. The governing equations with boundary conditions formulated using the primitive dimensionless variables have been numerically worked out by the finite element technique. Impacts of the Hartmann number, magnetic number, Rayleigh number, ratio of thermal conductivity, porosity ratio, the Darcy number, and convective heat transfer coefficient at solid–nanofluid interface have been investigated. It has been found that low values of dimensionless convection parameter ratio at the border between solid and nanoliquid phases characterize high values of the nanofluid dimensionless convective heat transfer parameter. The average Nusselt number for the solid state has maximum value for high quantities of ratio of Darcy number and low values of dimensionless convection parameter ratio at the border between solid and nanoliquid phases.