*2.2.2 Synthesis of iron oxide nanoparticle*

In 5 mL of distilled water, Iron (II) chloride tetrahydrate powder and 50 mL of isobutanol were added after which Fe2+ions were formed. The aqueous organic mixture was heated to 75 °C, added dropwise for 2 hours with 0.8 M NaOH and stirred for 30 min at 500 rpm. The synthesized iron oxide nanoparticles were washed with distilled water at 75 °C and dried in an oven at 50 °C. The dried particles of iron oxide nanoparticles were calcined for 2 h at 300 °C, 100 minutes at 400 and 600 °C. The hybrid nanofluid was prepared by dispersing the synthesized mono nanofluid in a volume fraction of 0.2 iron oxide with 0.8 fractions of graphene nanofluid to form graphene/iron oxide combination. The prepared hybrid fluid thermal properties as given in **Table 1** are used for further simulations.
