Assessing thermal and hydrodynamic performance of non-Newtonian nano-coolant flow through a porous backward-facing step channel with non-Darcian effects

Akter, Z; Nag, P; Akter, H; Molla, MM; Saha, G

Assessing thermal and hydrodynamic performance of non-Newtonian nano-coolant flow through a porous backward-facing step channel with non-Darcian effects

Akter, Z Nag, P Akter, H Molla, MM Saha, G

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Publisher:: ELSEVIER
Publication Type:: Journal Article
Citation:: Results in Engineering, 2025, 27
Issue Date:: 2025-09-01

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Field	Value	Language
dc.contributor.author	Akter, Z
dc.contributor.author	Nag, P
dc.contributor.author	Akter, H
dc.contributor.author	Molla, MM
dc.contributor.author	Saha, G https://orcid.org/0000-0001-6467-298X
dc.date.accessioned	2025-12-19T04:15:56Z
dc.date.available	2025-12-19T04:15:56Z
dc.date.issued	2025-09-01
dc.identifier.citation	Results in Engineering, 2025, 27
dc.identifier.issn	2590-1230
dc.identifier.issn	2590-1230
dc.identifier.uri	http://hdl.handle.net/10453/191024
dc.description.abstract	This research examines the hydrodynamic and thermal characteristics of Al<inf>2</inf>O<inf>3</inf>-water as a shear-thinning non-Newtonian nano-coolant (NC) flowing through a porous structure. The rheological characteristics of the coolant have been deemed to be shear-thinning based on the weight percentage (ϕ) of suspended nanoparticles. The flow dynamics are examined within a homogeneous saturated porous substrate placed in a backward-facing step (BFS) channel featuring an expansion ratio of 1:2. The lengths of the upstream and downstream channels, before and after the step of height h, are maintained in a ratio of 6h:30h. The Darcy–Brinkman–Forchheimer (DBF) porous model, incorporating non-Newtonian viscous NC flow, has been numerically solved within the computational domain using a finite volume method with second-order accuracy. The investigations were conducted with varying key parameters, including Reynolds number (300≤Re≤1000), Rayleigh number (10<sup>5</sup>≤Ra≤10<sup>6</sup>), porosity (0.4≤ϵ≤0.99), and Darcy number (10<sup>−1</sup>≤Da≤10<sup>−3</sup>). Findings indicate a 50% reduction in skin friction coefficient (C<inf>f</inf>) when doubling Re, highlighting the complex relationship between flow dynamics and thermal exchange within the porous substrate. The recirculation zone after the step shrinks with decreasing ϵ, emphasizing the improved heat transfer (HT) from the wall interface through a stronger porous medium. Increasing the porous strength by reducing ϵ from 0.9 to 0.4 leads to over 200% improvement in average thermal exchange rate (Nu<inf>avg</inf>) for the shear-thinning coolant (ϕ=4%) even at low permeability (Da=0.001). The study also evaluates the thermal performance criterion (PEC), which increases with higher Re but decreases with ϕ. The outcomes of PEC provide practical insights into the thermal engineering aspects, underscoring the significance of comprehending nano-coolant dynamics within a porous matrix for optimizing thermal transport processes.
dc.language	English
dc.publisher	ELSEVIER
dc.relation.ispartof	Results in Engineering
dc.relation.isbasedon	10.1016/j.rineng.2025.106027
dc.rights	info:eu-repo/semantics/openAccess
dc.subject.classification	40 Engineering
dc.title	Assessing thermal and hydrodynamic performance of non-Newtonian nano-coolant flow through a porous backward-facing step channel with non-Darcian effects
dc.type	Journal Article
utslib.citation.volume	27
pubs.organisational-group	University of Technology Sydney
pubs.organisational-group	University of Technology Sydney/Faculty of Engineering and Information Technology
utslib.copyright.status	open_access	*
dc.rights.license	This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License (CC BY-NC 4.0). To view a copy of this license, visit https://creativecommons.org/licenses/by-nc/4.0/
dc.date.updated	2025-12-19T04:15:54Z
pubs.publication-status	Published
pubs.volume	27

Abstract:

This research examines the hydrodynamic and thermal characteristics of Al2O3-water as a shear-thinning non-Newtonian nano-coolant (NC) flowing through a porous structure. The rheological characteristics of the coolant have been deemed to be shear-thinning based on the weight percentage (ϕ) of suspended nanoparticles. The flow dynamics are examined within a homogeneous saturated porous substrate placed in a backward-facing step (BFS) channel featuring an expansion ratio of 1:2. The lengths of the upstream and downstream channels, before and after the step of height h, are maintained in a ratio of 6h:30h. The Darcy–Brinkman–Forchheimer (DBF) porous model, incorporating non-Newtonian viscous NC flow, has been numerically solved within the computational domain using a finite volume method with second-order accuracy. The investigations were conducted with varying key parameters, including Reynolds number (300≤Re≤1000), Rayleigh number (10⁵≤Ra≤10⁶), porosity (0.4≤ϵ≤0.99), and Darcy number (10⁻¹≤Da≤10⁻³). Findings indicate a 50% reduction in skin friction coefficient (Cf) when doubling Re, highlighting the complex relationship between flow dynamics and thermal exchange within the porous substrate. The recirculation zone after the step shrinks with decreasing ϵ, emphasizing the improved heat transfer (HT) from the wall interface through a stronger porous medium. Increasing the porous strength by reducing ϵ from 0.9 to 0.4 leads to over 200% improvement in average thermal exchange rate (Nuavg) for the shear-thinning coolant (ϕ=4%) even at low permeability (Da=0.001). The study also evaluates the thermal performance criterion (PEC), which increases with higher Re but decreases with ϕ. The outcomes of PEC provide practical insights into the thermal engineering aspects, underscoring the significance of comprehending nano-coolant dynamics within a porous matrix for optimizing thermal transport processes.

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