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A numerical model was used to simulate natural convection heat transfer in a two-dimensional square enclosure filled with nanofluid and saturated with porous media. The enclosure contained three heated tubes with Rayleigh numbers (Ra) ranging from 102 to 3 × 104. The governing equations with Boussinesq approximation for natural convection were solved iteratively using the finite volume technique through ANSYS FLUENT-CFD commercial package. The Darcy–Forchheimer–Brinkman and Local Thermal Equilibrium models were applied for water and nanofluid flow across the porous zone. The numerical analysis was executed systematically for significant parameters that have a substantial impact on natural convection heat transfer, namely, aspect ratio (AR = 1.25 − 3.75), nanoparticle volume fraction (Φ = 0.25%, 0.5%, 0.7% and 1%), and the porosity of metal foam (ε = 0.3, 0.4, 0.5, 0.6 and 0.7). The aspect ratio was found to have a considerable impact on the averaged Nusselt number (Nuave). For AR = 3.75, the value of Nuave for all Rayleigh numbers increased by approximately 5.22 times compared to AR = 1.25. Moreover, Nuave remained approximately constant as the concentration of alumina-water nanofluid increased from 0.25% to 1%. The novelty of this study lies in the multi-objective optimal design approach adopted by adopting DX-12 with the outcomes of ANSYS FLUENT-CFD. The averaged Nusselt number and convection heat transfer rate reached their optimal values by nearly 13 and 9 times, respectively, at the lowest possible porosity (ε = 0.3), the lowest possible nanofluid concentration (Φ = 0), and the highest possible aspect ratio value (AR = 3.75). [ABSTRACT FROM AUTHOR]

Tube-bank heat exchangers with porous media are highly beneficial for many industrial and thermal engineering applications as they enhance heat transfer efficiency. The purpose and innovation of the current numerical investigation are to study the impact of the porous medium (aluminium foam) on the optimal thermo-hydraulic performance of a staggered flat-tube bank by adopting ANSYS FLUENT-CFD software in conjunction with response surface methodology (RSM). Therefore, a steady two-dimensional analysis examines incompressible laminar forced airflow through a staggered flat-tube bundle heat exchanger embedded with metal foam. Various parameters are considered in this study, such as Reynolds numbers (Re K = 20, 40, 60, 80 and 100), the flat-tube tilt angle (θ = 0°, 30° and 45°), the flat-tube aspect ratios (L/D = 1.5, 2 and 2.5) and the flat-tube surface temperatures (T h = 30, 40, 50, 60 and 70 °C). Furthermore, optimisation analysis is performed for various aluminium foam characteristics, including porosity (ε = 0.85, 0.9 and 0.95), pores per inch (PPI = 5, 20 and 35), and inlet airflow temperatures (T in = 10, 25 and 40 °C). The novel multi-objective optimisation design is achieved to obtain the optimum design of the porous flat-tube heat exchanger. The numerical outcomes have revealed that the critical optimum values of the design parameters are ε = 0.95, PPI = 5 and T in = 10 at Re K = 100, L/D = 2.5, θ = 0° and T h = 50 °C. Where these values led to a normalised friction factor (f P /f NoP = 2.91), a normalised Colburn factor (j P /j NoP = 7.63) and a normalised area goodness factor (AGF P /AGF NoP = 5.35). [ABSTRACT FROM AUTHOR]

The characteristics of convective heat transfer and fluid flow within a square cross-section serpentine channel are experimentally studied for two groups of polymeric viscoelastic fluids, shear-thinning and constant-viscosity Boger solutions. The elastic turbulence can be created by the non-linear interaction between elastic stresses generated within the flowing high-molecular-weight polymer solutions and the streamline curvature. In order to confirm elastic turbulence in this geometry, pressure drop across the serpentine channel was measured. The findings indicate that the measurements of non-dimensional pressure-drop increase approximately from 1.48 to 4.82 for viscoelastic solutions compared with the Newtonian fluid over a range of Weissenberg number from 4 to 211. The convective heat transfer enhances due to elastic turbulence by up to 200% for low polymer concentration (dilute) solutions and reaches up to 380% for higher polymer concentration (semi-dilute) solutions under creeping-flow conditions in comparison to that achieved by the equivalent Newtonian fluid flow at low Graetz number (up to 14.6). We propose a modified Weissenberg number which is able to approximately collapse the mean Nusselt number data for each solution group. [ABSTRACT FROM AUTHOR]