Numerical Study of Turbulent Flow and Heat Transfer in A Novel Design of Serpentine Channel Coupled with D-Shaped Jaggedness Using Hybrid Nanofluid

Abstract

This study aimed to examine numerically the effects of a dimpled surface over a mini-channel heat exchanger on the flow characteristics and heat transfer across a serpentine channel with a uniform rectangular cross-section. The dimples were arranged in parallel with a spanwise (y/d) distance of 3.125 and streamwise (x/d) distance of 11.25 along just one side of the serpentine channel's surface. Turbulent flow regime with Reynolds number ranging from 5x103 to 20x103 in the channel with surface modification was studied using water and various volume concentrations (φ = 0.1%, 0.33%, 0.75%, 1%) of Al2O3-Cu/water hybrid nanofluid as the coolant to achieve a three-step passive heat transfer enhancement. Applying the Finite Volume Method (FVM), RNG k-ε turbulence model, and a constant heat flux of 50kW/m2 , simulations were run assuming the mixture of Al2O3-Cu nanoparticles homogenous using ANSYS 2020 R1. The second-order upwind approach is used for approximation of solution and discretization with SIMPLE pressure-velocity coupling. Taking heat transfer increment and pressure drop penalty into consideration, the dimpled serpentine channel provides a 147% improvement in thermal efficiency using water as the coolant, and the dimpled channel with 1% vol. Al2O3-Cu/water nanofluid enhanced thermal efficiency by a remarkable maximum of 267% at Re 5x103 . The study also indicates that thermal efficiency increased with an increasing volume concentration of the nanofluid and increment in thermal efficiency gradually decreased as the Re increased. Such kind of improvement in thermal performance is extremely desirable in the current era of powerful and compact electrical devices which need better cooling and have small space for a heat exchanger.