A comprehensive thermo-hydraulic analysis and optimization of turbulent TiO2/W-EG nano-fluid flow inside double-pipe heat exchangers with helical coil inserts

Abstract

The main aim in current work is to optimize TiO2/W-EG nano-fluid (with 60 vol% of water and 40 vol% of ethylene glycol) flow within the inner tube of the double-pipe heat exchangers with helical coil inserts. The entropy generation is selected as the target function and is to be minimized. To reach this goal, at the first step, a comprehensive sensitivity analysis is carried out taking into account all of the nano-fluid flow conditions (including nanoparticle volume fraction $$\phi$$ , Reynolds number Re and Prandtl number Pr) and geometric parameters of the helical coil inserts (including thepitch-to-diameter ratio of coil $$\Pi$$ ). Afterward, the genetic algorithm (GA) is utilized in the optimization process. The results of sensitivity analysis reveal that $$\phi$$ and $$\Pi$$ , respectively, have the highest and lowest impact on the thermodynamics characteristics. Also, the addition of up to 0.02 vol% nanoparticles leads to a maximum of 13.93% improvement in dimensionless entropy generation ( $${\text{DEG}}$$ ). The outputs of the GA are $$\phi_{\text{opt}}$$ = 0.0198%, $${\text{Re}}_{\text{opt}}$$ = 8421.173, $${ \Pr }_{\text{opt}}$$ = 32.833, $$\Pi_{\text{opt}}$$ = 2.437 and $${\text{DEG}}_{\text{opt}}$$ = 0.005086. Furthermore, based on the optimization results, a useful correlation is proposed to find the optimum geometry of the helical coil based on the nano-fluid flow conditions.