Thermohydraulic sensitivity analysis and multi-objective optimization of Fe3O4/H2O nanofluid flow inside U-bend heat exchangers with longitudinal strip inserts

•Fe3O4/H2O nanofluid in U-bend exchanger with longitudinal strip insert is sought.•Entropy generation and system performance criteria are used as target functions.•Adding 0.03% nanoparticle leads up to 6.2% reduction of entropy generation number.•Increasing aspect ratio of longitudinal strip insert reduces entropy generation.•Optimal Reynolds number is 22,478 at optimum geometrical conditions.