Heat transfer and friction factor of nanodiamond-nickel hybrid nanofluids flow in a tube with longitudinal strip inserts

The heat transfer and friction factor of a new kind of nanodiamond-nickel (ND-Ni) hybrid nanofluids flow in a tube with and without longitudinal strip inserts were studied experimentally. The hybrid ND-Ni nanoparticles were synthesized using in-situ and chemical coprecipitation method and characterized with different techniques. The bulk quantity of hybrid ND-Ni nanofluids were prepared and used for heat transfer and friction analysis. The experiments were conducted in the Reynolds number range from 3000 to 22,000, for the volume concentrations of 0.1% and 0.3%, and for different aspect ratios (AR = 1, 2 and 4) of the longitudinal strip inserts. The Nusselt number is enhanced by 35.43% (without insert) and further enhanced by 93.30% with longitudinal strip insert (AR = 1) for 0.3% volume concentration of nanofluid and at Reynolds number of 22,000 compared to water data. The friction factor penalty of 1.12-times without inserts and further penalty of 1.248-times with longitudinal strip insert (AR=1) at 0.3% volume concentration of nanofluid and at Reynolds number of 22,000 compared to water data. The obtained experimental Nusselt number of hybrid nanofluids was compared with that of other kind of hybrid nanofluids available in the literature. The Nusselt number and friction factor correlations were developed based on the experimental data. (C) 2017 Elsevier Ltd. All rights reserved.