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This article investigates the laminar flow of power-law fluids through two porous square cylinders in a side-by-side configuration. The effects of power-law index (n), Darcy number (Da), and gap ratio (g/W) are examined within ranges of g/W = 0.5–5, n = 0.4–0.8, and Da = 10−6–10−2, respectively. Two flow conditions are considered: first, for a creeping flow (unseparated flow) at Re = 1 where Darcy's law is applicable; second, for a viscous dominant flow at Re = 100, where Darcy–Forchheimer-extended model is exercised. Flow patterns behind the porous cylinders are analyzed using streamlines, velocity profiles, pressure distribution curves, and vorticity structural parameters (Г). In low permeability levels, the flow exhibits an irregular nonperiodic vortex shedding characterized by a single large vortex street far off the downstream for g/W = 0.5. However, synchronized wake patterns were observed in either antiphase or in-phase modes for higher gap ratios. Leading-edge separation with two-side recirculation induces quasi-periodicity in the flow for all g/W. It was found that increasing the permeability can prevent the leading edge separation. Additionally, a transition from antiphase to in-phase mode occurs when the permeability is altered while maintaining constant flow-time. The presence of a jet-like flow between cylinders significantly impacts unsteady wake patterns. The impact of g/W, power-law index, and permeability on drag is also examined. A jump in some flow parameters was observed at higher Re for the midrange Darcy number, but no such increase was noted for the high shear-thinning behavior. These findings provide a potential approach for improving the design of fluidic systems involving porous cylinders. [ABSTRACT FROM AUTHOR]

The present study performs a three-dimensional CFD analysis to investigate the hydrodynamic and thermal properties of annular finned tubes in a heat exchange system. All computations are performed in the turbulent flow regime (4330 ≤ Re ≤ 8790), and the Transition SST model is applied for turbulence modelling. The impact of Prandtl number (0.7 ≤ Pr ≤ 50) on the various parameters, such as the heat transfer coefficient, heat transfer rate, and pressure drop, are considered. The results indicate that the thermo-hydraulic behaviour is significantly affected by incrementing both Reynolds and Prandtl numbers. The fin's surface temperature distribution is examined to get a better insight into its thermal performance, and it is observed that the rear portion of the fin contributes the least to heat transfer. Other important parameters like the fin efficiency and Colburn heat transfer factor are found to significantly impact the performance of the heat exchange system for the above range of settings. The velocity contours show the horseshoe vortex formation near the fin-tube junction, and the channelling effect is observed between consecutive tubes. Different fluids are compared based on the j/f factor for enhanced heat transfer at the minimum possible flow resistance. [ABSTRACT FROM AUTHOR]

An investigation of the laminar flow and enhanced heat transfer rate through a triangular array of cylinders embedded in a fluid-saturated porous media is considered. Mixed convection covering forced convection cases has been studied using a finite-volume approach considering the local thermal equilibrium model. Darcy–Brinkman–Forchheimer momentum equations are used to characterize the porous media in question. The study is constrained to the low and intermediate Peclet number (Re = 5 to 40, Pr = 50) and high range of Darcy number (Da = 10−3 to 10−1) for different cylinder spacings (0.7 ≤ φ ≤ 0.99). It is anticipated that porous media would enhance heat transfer, but it derives a multiple order in pressure drop indubitably not desirable in many heat applications. Investigation reveals that both mean drag coefficient (CD) and Nusselt number (Nu) are strong functions of Da and φ; however, the influence of the buoyancy parameter is mainly witnessed in higher permeability levels and high Peclet numbers. The study also details the effect of governing parameters on mean gap velocities and pressure coefficients. Surprisingly, recirculation wakes exist for the lowest cylinder spacing (φ = 0.7) in high fluid momentum. Low φ and high permeability are desirable in a forced convection regime, whereas both φ and Da should be high in the case of mixed convection. This article also quantifies the combined effect of the Darcy number and buoyancy parameter on the heat-transfer enhancement ratio. A maximum of 112% increase in Nu for φ = 0.7 and 452% for φ = 0.99 are reported at Da = 10−1, but at the cost of higher pressure drop in the latter case. [ABSTRACT FROM AUTHOR]