Nanoparticle's radius effect on unsteady mixed convective copper-water nanofluid flow over an expanding sheet in porous medium with boundary slip

Abstract

Nanofluid and its higher thermal performance are displayed more promising outcomes when the flow medium is assumed to be a porous medium. Additionally, the radius size of nanoparticles plays a significant role in enhancing this thermal performance. So, present analysis aims to investigate the time-dependent flow of copper-water nanofluid in porous medium on an expanding sheet in presence of buoyancy force and slip phenomenon under various nanoparticle's radii. The flow is assumed to be boundary layer, two-dimensional, viscous, incompressible, laminar and unsteady. Governing coupled PDEs are changed into ODEs by suitable transformations and the converted ODEs are solved numerically. The study discloses that velocity rises with larger radius of nanoparticles and enlargement in assisting buoyancy force, whereas with unsteadiness of the flow, less permeability of porous material and boundary slip it drops. Also, magnitude of wall-drag force grows with larger radius of nanoparticles and flow unsteadiness. Importantly, for higher value of nanoparticle's radius surface-drag force massively enhances when permeability of porous medium is less. Temperature increment exhibits for boundary slip and less permeability of the porous material. Lastly, wall cooling rate intensifies with flow unsteadiness and higher value of nanoparticle's radius.