The combined effect of water-based GO and Al₂O₃ nanofluids and Propeller Turbulator (PT) insert on enhancement in thermal performance of counter-flow double tube heat exchanger is investigated experimentally. Experiments were carried out with a hot water flowrate of Re = 2500 in the inner tube fitted with apropeller insert (NP: 6, 8, 10) and variable flow rates (500 ≤ Re ≤ 5000) of water-based GO and Al₂O₃ nanofluid (vol.%: 0.05, 0.1, 0.15) flowing in the annulus. Experimental results show that, Nusselt number increased by29.43% and TPF by 1.32 times for tube fitted with 10 propellers and 0.15 vol.% of Al₂O₃ nanofluid. In the conducted combinations, the extreme increase was noted for the higher number of propellers and higher vol.% of Al₂O_{3 nanofluid combination, with a slight increase in friction factor. Nusselt number and friction factor correlations were developed and predicted well within -14% to +10% and -10% to +5%, respectively.}