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    An Experimental Study on SiO2-ND Hybrid Nanofluid: Thermal Conductivity, Viscosity, and Stability with New Forecast Models
    (Bentham Science Publ Ltd, 2022) Yalcin, Gokberk; Oztuna, Semiha; Dalkilic, Ahmet Selim; Nakkaew, Santiphap; Wongwises, Somchai
    Objective: In the present investigation, thermal conductivity and viscosity properties of water-based SiO2-ND hybrid nanofluid were measured, experimentally. Methods: Nanofluids were prepared by using a two-step method and with three different (0.5%, 0.75%, and 1%) concentrations. Every concentration had three different SiO2-ND mixtures (50% SiO2 - 50% ND, 33% SiO2 - 66% ND, 66% SiO2 - 33% ND). Results: The most stable sample was measured as -33.4 mV. Measurements of viscosity and thermal conductivity were done from 20oC to 60oC at every 10oC. Thermal conductivity data were measured by thermal conductivity analyzer and viscosity data were measured by tube viscometer. The highest thermal conductivity enhancement was measured for 1% SiO2 (0.33): ND (0.66) at 40oC and the highest relative dynamic viscosity was calculated as 4.19 for 1% SiO2 (0.33): ND (0.66) at 40oC. A comparison table is also given to show the zeta potential values-concentration relations. Conclusion: Finally, two different correlations for predicting thermal conductivity and viscosity were proposed for practical usage.
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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.