Optimising Hybrid Nanofluid Heat Transfer in Vertical Ducts

The Bottom Line

Silver and magnesium oxide nanoparticles, when suspended in water, create a composite fluid that significantly alters thermal dynamics in vertical heating systems. This numerical study quantifies how specific physical parameters affect flow and temperature. Optimising hybrid nanofluid heat transfer is a priority for next-generation nuclear power and petrochemical cooling systems, where conventional fluids no longer suffice.

These results were observed under controlled laboratory conditions, so real-world performance may differ.

The Problem: Thermal Saturation

Standard thermal duct systems face a ceiling. In sectors like nuclear power generation and chemical processing, the heat loads are immense. Water and standard oils possess limited thermal conductivity. They cannot remove energy fast enough. This leads to overheating, equipment degradation, and forced throttling of production capacity. Engineers need a medium with superior thermal properties that can function within existing vertical duct geometries without requiring a total infrastructure overhaul. The challenge is balancing the enhanced heat absorption of nanoparticles against the increased viscosity they introduce.

The Solution: Numerical Modelling

Researchers analysed the buoyancy-driven convective transport of a silver/magnesium oxide-water hybrid nanofluid (HNF). The simulation modelled a rigid, vertical rectangular duct. The geometry included insulated upper and lower boundaries, with the side walls heated isothermally. To solve the non-dimensional nonlinear boundary value problems, the team employed a custom finite difference method (FDM) code. They verified the accuracy of this code by benchmarking it against previous studies and performing mesh independence tests. This allowed for a precise prediction of how the fluid behaves under varying physical stresses.

Mechanics of Hybrid Nanofluid Heat Transfer

The study isolated four critical variables: Grashof number (buoyancy force), Brinkman number (viscous heating), aspect ratio, and solid volume fraction. The interaction between these forces dictates efficiency.

Velocity Dynamics: The simulation indicates that velocity rises as the Grashof and Brinkman numbers increase. Stronger buoyancy drives faster flow. However, increasing the solid volume fraction—adding more nanoparticles—has the opposite effect. The fluid becomes thicker. Drag increases. Velocity drops.

Thermal Asymmetry: The most specific finding concerns the heat transfer rate. It is not uniform. As the values for Grashof, Brinkman, aspect ratio, and solid volume percentage increase, the heat transfer rate falls at the right wall but rises at the left wall. This asymmetry is critical. It implies that the fluid behaves differently depending on its position relative to the heating source and flow direction.

The Impact: Engineering Implications

These findings suggest that simply maximizing particle concentration is not a valid strategy. While adding silver and magnesium oxide boosts thermal conductivity, it retards flow velocity. If the fluid moves too slowly, the heat removal rate may stall despite the material's conductive properties.

Furthermore, the observed asymmetry in heat transfer presents a structural risk. Uneven cooling leads to thermal stress. Materials warp. Welds crack. Engineers designing vertical ducts for petrochemical or nuclear applications must account for this variance. The data indicates that flow parameters must be tuned to balance buoyancy against viscosity to prevent hot spots on the duct walls. This dossier provides the baseline calibration data required to construct those balanced systems.