Experimental analysis of heat pipe based evacuated tube solar collector using graphene/ ethylene glycol-water nanofluids.

The efficiency of a heat pipe-based evacuated tube solar collector (HPBETSC) with graphene nanoparticle/ethylene glycol-water as a working fluid has been experimentally investigated in the present study. In this research work, the base fluid was prepared with a 60:40 ratio of ethylene glycol and water (EG-W). Graphene nanoparticles have been added to the base fluid with three different volume concentrations (0.025, 0.075, and 0.1 vol. %). The results showed that for three different graphene nanofluids (GNFs) concentrations of 0.025, 0.075, and 0.1 vol. %, the enhancement in their thermal conductivities observed was 21.9%, 25.8%, and 28.7%, respectively. The HPBETSC achieved its highest efficiency when the temperature of the inlet fluid equals the ambient temperature with 0.1 vol. % concentration of GNFs at 0.41 kg/sec mass flow rate. The efficiency is 36.3% higher when EG-W individually was used as a heat transfer fluid. Also, the achieved efficiency with 0.1 vol. % GNFs was 4.31% higher than 0.075 vol. % and 6.66% higher than 0.025 vol. % of GNFs concentrations at the same mass flow rate. Besides, this experimental study con?rmed that nanofluids are highly favorable to replace the traditional fluids used in solar collectors.