A comparative investigation on the effect of different nanofluids on the thermal performance of two-phase closed thermosyphon

The heat transfer performance of single and hybrid nanofluids in a two-phase closed thermosyphon (TPCT) was experimentally studied and compared with deionized water (DW). Al2O3 and TiO2 nanoparticles with a volume concentration of 0.2% were added to the DW in two steps to prepare stable nanofluid suspensions (Al2O3-H2O, TiO2-H2O, 75% Al2O3 + 25% TiO2-H2O, 50% Al2O3+ 50% TiO2-H2O, and 25% Al2O3 + 75% TiO2-H2O). The TPCT was made of a carbon steel tube of length 500 mm, outer diameter 20 mm, and wall thickness 2 mm. In this study, through an orthogonal experiment, the five types of nanofluids were analyzed to obtain the single and hybrid nanofluids with the best heat transfer performance. These were compared with DW under various conditions of the heating power, which were varied from 200 to 400 W in equal steps of 50 W, the liquid filling ratio (30%, 50%, 70%), and the cooling water flow rate (0.4, 0.48, 0.56 L/min). The results showed that when the hybrid nanofluid 25% Al2O3+ 75% TiO2-H2O and the single nanofluid TiO2-H2O were used instead of DW, the best heat transfer performance was displayed. For the heating input of 400 W, filling ratio of 50%, and cooling water flow of 0.4 L/min, the thermal resistance of the TPCT was reduced by 26.8% and 22.8%, the equivalent heat transfer coefficient increased by 25.78% and 21.62%, the thermal efficiency was increased by 10.6% and 9.2%, respectively. (C) 2019 Elsevier Ltd. All rights reserved.