Parametric case study of a concentric counter‐flow tubular heat exchanger using graphene/water nanofluid and <scp>PEG</scp> ‐400: Influence of particle loading and mass‐flow rates

Abstract This work presents a case study on a concentric counter‐flow tubular heat exchanger where a graphene‐sheet/water nanofluid flows in the inner tube and a polymer coolant (PEG‐400) flow in the annulus. A property‐consistent modelling framework is developed: particle shape anisotropy is captured via the Hamilton–Crosser (HC) model with shape factor inferred from thindisk sphericity; nanofluid viscosity follows the Krieger–Dougherty law with platelet intrinsic viscosity; internal convection uses Sieder–Tate (laminar) and Dittus–Boelter (turbulent) correlations; overall performance is computed via the ε –NTU method with full wall and fouling resistances. A parametric study varies nanofluid inlet temperature (50–70°C), graphene volume fraction (0–3 vol.%), polymer inlet temperature (20–30°C), and mass‐flow rates (nanofluid = 0.05–0.20 kg/s; polymer = 0.10–0.30 kg/s). Results show that, for the chosen geometry ( L = 6 m; inner tube: 10 mm inner diameter and 12 mm outer diameter; outer tube: 25 mm inner diameter) and fouling levels, mass‐flow control provides the strongest leverage on heat duty, while small graphene loadings produce modest gains.