Numerical simulation of dual-tube heat exchanger equipped with an innovative turbulator containing two-phase hybrid nanofluid: Hydrodynamic and exergy analysis

Abstract

Due to the energy requirements of industries and the limitations of energy resources in the world, energy storage and prevention of energy loss are of particular importance. Therefore, energy loss and energy storage are among the most important new concerns of human beings. Heat exchangers (HE) are one of the most widely used heat transfer (HT) equipment that transfer heat from one fluid to another. For the simulation of water/silicon oxide-iron oxide hybrid nanofluid (HN), the mixed two-phase model has been used. The flow is turbulent and the turbulence model is RNG k-ε. The inlet Reynolds number (Re) and the volume fraction (φ) of SiO2 and Fe3O4 nanoparticles changes from 30,000 to 45,000 and 2% to 5%, respectively. Four different geometries of the novel turbulator with different values of pitch ratio (λ=0.15, 0.35, 0.55, 0.75) are modeled inside the HE and its effects on the average Nusselt number (Nuave), pressure drop (Δp), performance evaluation criterion (PEC), and exergy efficiency are examined. The results demonstrate that the use of water in the HE system leads to lower thermal performance compared to water/silicon oxide-iron oxide HN for all cases. Also, as λ and φ are enhanced, the values ​​of Nuave, Δp, and PEC are increased. In a dual-tube heat exchanger (DTHE) equipped with an innovative turbulator with maximum amounts of λ, using a HN with φ = 5% results in an enhancement in Nuave by 105.59% when Re changes from 30,000 to 45,000. Also, according to the values of the PEC, although the use of the turbulator leads to an increment in Δp, the enhancement of the thermal performance is higher. According to the exergy analysis, increasing the inlet velocity of the inner tube of the double-tube heat exchanger enhances the exergy efficiency. For all geometries, the maximum exergy efficiency corresponds to Re = 45,000.