Nanofluids stability on rest is important to characterize the nanofluids thermophysical properties before being used on different thermal systems. However, this stability can be modified during devices operation because of different thermal loads, fluid movements and phase changes. Particularly, in Two Phase Closed-Thermosyphon (TPCT). Input response are heat input, flow rate and inclination angle. Graphene and fe304 nanofluids used as working fluid in the fill ratio of 50%. An attempt is made to optimise the process parameters with Response Surface Methodology (RSM) using Box - Behnken design for 6063 aluminium alloy (AA) semi-circular two phase closed thermosyphon (TPCT). Experiments are conducted by varying the mass flow rates of water at condenser section and by varying the heat input at evaporator section and varying inclination angle. The effects of variables on the process parameters are studied. The study, predominantly, aims at assessing how the variables affect the process parameters.