The effects of combined using of water-graphene nanoplatelet nanofluid and three different conical wire coils (converging, converging-diverging and diverging) on thermohydraulic performance of a heat exchanger tube are experimentally studied. Three different weight fractions 0.5, 0.75 and 1% of Graphene-Water nanofluids are used and converging, converging-diverging, diverging conical wire coils with two different pitch ratios 2 and 3 are selected for the experiments. The experiments are conducted under constant heat flux and Reynolds number ranging from 4000 to 27,000. The results indicated that use of conical wire coils cause to increase both the heat transfer rate and fluid friction as expected, in addition, adding the graphene nanoplatelet in pure water leads to strongly increase in heat transfer rate meanwhile cause to slightly increase in friction factor. Experimental results revealed that combination of diverging conical wire coil insert with weight fraction of 1% Graphene-Water nanofluid provides higher heat transfer performance than the other cases. The highest Performance Evaluation Criteria of 1.73 is observed while the diverging conical wire coil, which has the pitch ratio of 2, at Reynolds number of 6128 for weight fraction of 1% Graphene-Water nanofluid.