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  • Küçük Resim Yok
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    Determination of dynamic viscosity and stability for single and hybrid nanofluids of SiO2, TiO2, MWCNT and ZnO nanoparticles
    (Springer, 2024) Atmaca, Baran; Yalcin, Gokberk; Kucukyildirim, Bedri Onur; Arkadumnuay, Thana; Leunanonchai, Witsawat; Manova, Stephen; Dalkilic, Ahmet Selim
    In this study, the stability and viscosity of four different nanoparticles are discussed in conjunction with the physical properties of these nanoparticles. The aim is to provide guidance for nanoparticle selection in future nanofluid applications. Additionally, our goal is to examine hybrid nanofluids in comparison to single nanofluids, exploring their potential benefits and evaluating their industrial applications. A two-stage approach was employed, using ethylene glycol (EG) as a base fluid, to create these nanofluids. Single nanofluids were formed with SiO2, TiO2, MWCNT, and ZnO nanoparticles at 0.1%, 0.5%, and 1% volume concentrations. Additionally, binary (SiO2-TiO2/EG), ternary (SiO2-TiO2-MWCNT/EG), and quaternary (SiO2-TiO2-MWCNT-ZnO/EG) hybrid nanofluids were formed with 0.1% volume concentrations. The dynamic viscosity of all nanofluids was evaluated over the temperature range of 20-50 degrees C. Analysis of nanofluids was extended by characterization studies using field emission transmission electron microscopy (FE-SEM), field emission scanning electron microscopy (FE-TEM), Zeta potential testing, and visual inspection. SiO2 nanoparticles exhibited the greatest stability, remaining in suspension for more than 28 days without sedimentation, while ZnO nanoparticles were the least stable, collapsing in < 7 days. Compared to ethylene glycol, ZnO/EG had the most increased viscosity (42.79%) at 20 degrees C and a 1% volume concentration. However, SiO2-TiO2-MWCNT/EG showed the largest decrease in viscosity (9.99%) at 20 degrees C. Hybrid nanofluids exhibit better viscosity performance compared to their base fluids and single nanofluids, enhancing the thermal efficiency of these heat transfer fluids. Additionally, this study is groundbreaking research as it emphasizes the efficiency of hybrid nanofluids as well as introducing quaternary nanofluids to the literature.
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    Experimental study on the thermal conductivity of water-based CNT-SiO2 hybrid nanofluids
    (Pergamon-Elsevier Science Ltd., 2018) Dalkilic, Ahmet Selim; Yalcin, Gokberk; Kucukyildirim, Bedri Onur; Oztuna, Semiha; Eker, Aysegul Akdogan; Jumpholkul, Chaiwat; Nakkaew, Santiphap; Wongwises, Somchai
    This experimental study includes measurement of thermal conductivity of distilled water-based CNT-SiO2 hybrid nanofluids. Nanofluids were prepared by using two-step method, 3 different concentrations and 4 different mass range of CNT-SiO2. SiO2 has 2200 kg m(-)(3) density, 1.4 W m(-1) K (-1) thermal conductivity and 7 nm average particle size. CNT has 2620 kg m(-3) density, 25 W m (-1) K(-1 )thermal conductivity and 6-10 nm average particle size. Samples were placed in ultrasonic homogenizer maximum power capacity for 3 h. Throughout sonication process temperature of nanofluids have been kept under control in order not to chance volumetric fraction of nanofluids. All measurements of thermal conductivity were done by using thermal conductivity meter. Thermal conductivity meter was calibrated by di-water. Measurements of thermal conductivity was done range from 25 degrees C to 60 degrees C for every 5 degrees C. Validation of measurements had been performed by using di-water and shown in a thermal conductivity-temperature figure. Minimum and maximum thermal conductivity enhancements were revealed in detail. Alteration of the thermal conductivity with temperature according to various volumetric fractions were in literature rated and it is found that the thermal conductivity increases with temperature and vol. fraction clearly. Enhancement on the thermal conductivity to di-water were also depicted for various temperatures and vol. fraction in figures. Almost well-known correlations in the literature were given with their predictable rates. Moreover, comparisons with other studies were provided in this present study. A practical correlation was proposed for other researchers.