the heat transfer performance of Al203 and Cuo-water nanofluids. They reported an enhanced heat transfer performance for both nanofluids compared to They also concluded nanoparticles have important effect on the convective heat transfer coefficient, due to 20 nm Al203 particle has higher thermal conductivity than 50 nm Cuo nanopar ticle. Among different nanostructures applied for creating nanofluids, carbon nanotubes (CNT) have enhanced the thermal efficiency of different setups due to promising thermal properties [23-26]. The results reported by Azizi et al. 127], xue et al. [28] and Liu et al. (29] showed that nanofluids including nanoparticles with higher heat trans- fer coefficient like graphene and CNT can be more appropriate in terms of heat transfer characteristics. Amiri et al. 130 studied the influence of graphene-water nanofluid on the heat transfer performance and resistance of two-phase closed thermosyphon (TPCT). They reported that increasing the volume fraction leads to the heat transfer enhancement of the TPCT. On the other hand, increase of the input power and the nanoparticles concentration cause a decrease in the thermal resistance of the T two Shanbedi et al. [24,25] considered influence of the covalent and noncovalent functionalization on the performance of concluded that functionalized carbon nanotubes with ethyl ene diamine had better heat transfer coefficient than the non-covalent functional groups. They also presented that covalent functionalization of CNT improved thermal efficiency of the TPCT more than those