Multi-objective optimization of operating parameters for dimpled twisted tape inserted heat exchanger tube flowing water/ethylene glycol mixture-based TiO2 nanofluid

Abstract A multi-objective optimization study is conducted to reveal the best operating parameters on a dimpled twisted tape inserted heat exchanger tube flowing water/EG-TiO 2 nanofluid. In this way, the most efficient configuration of a heat exchanger tube used in cold climates is proposed both thermally and hydraulically. The optimization strategy based on the Taguchi method and the Grey relation analysis is used simultaneously to achieve the highest h and the lowest ∆ P . Different volume flow rates (1.04–4.11 m 3 h −1 ), nanofluid mass fractions (0–1%) and various dimpled twisted tape inserts are considered as the operating parameters. Experiments are conducted under turbulent conditions with Reynolds numbers ranging from 5936 to 20,272, where nanofluid mass fractions vary from 0 to 1.00%. Even though the dimpled twisted tape insert is effective for improving the heat exchanger performance when using water, the twisted tape insert is not recommended to be used for W/EG (40:60 by volume)/TiO 2 nanofluid flow. According to the ANOVA, the most effective factor is the volume flow rate, with a contribution percentage of 58.18% and 67.67% for h and ∆ P , respectively. On the other hand, it is concluded that the nanofluid mass fraction has the least effect on both for h and ∆P . As a result, the optimum experiment configuration uses minimum flow rate, maximum nanofluid mass fraction and the smooth tube.