The current study deals with a numerical simulation of heat transfer inside enhanced tubes having the coaxial
double-twisted tape in the presence of an eco-friendly nanofluid containing graphene nanoplatelets (GNPs). The
results unveil that when the particle concentration (ϕ) escalates, the thermal entropy generation rate (S˙h) tends
to decline, whereas the heat transfer coefficient enhances. It was found that around 21.6% reduction in the S˙h is
attained by a decrease of the twisted ratio (ω) from 3.5 to 2.5 at the concentration of 0.075% and Reynolds
number of 10,000. Adding more GNPs to the water yields an increment in either the pressure drop or the frictional entropy generation. The findings refer to this issue that a multi-criterion optimization to find the best
optimum state is required. A genetic algorithm-based optimization with the entropy generation rate, heat
transfer, and pressure loss results in the optimum values at Re = 16,995.4, ϕ = 0.093%, and ω = 3.41.