Abstract
Developing stable nanofluids and improving their thermo-physical properties are highly important in heat transfer applications. In the present work, the stability, thermal conductivity, and rheological properties of tungsten disulphide (WS2) nanoparticles (NPs) with ethylene glycol (EG) were profoundly examined using a particle size analyzer, zeta-sizer, thermal property analyzer, rheometer, and pH measuring system. WS2 NPs were characterized by various techniques, such as XRD (X-Ray Diffraction), FTIR (Fourier Transform Infrared Spectroscopy), FESEM (Field emission scanning electron microscopy), and high-resolution transmission electron microscopy (HRTEM). The nanofluids were obtained with the two-step method by employing three volume concentrations (0.005%, 0.01%, and 0.02%) of WS2. The influence of different surfactants (Sodium dodecyl sulphate (SDS), Sodium dodecylbenzenesulfonate (SDBS), Cetyltrimethylammonium bromide (CTAB)) with various volume concentrations (0.05–2%) on the measured properties has also been evaluated. Pristine WS2/EG nanofluids exhibit low zeta potential values, i.e., −7.9 mV, −9.3 mV, and −5 mV, corresponding to 0.005%, 0.01%, and 0.02% nanofluid, respectively. However, the zeta potential surpassed the threshold (±30 mV) and the maximum values reached of −52 mV, −45 mV, and 42 mV for SDS, SDBS, and CTAB-containing nanofluids. This showed the successful adsorption of surfactants onto WS2, which was also observed through the increased agglomerate size of up to 1720 nm. Concurrently, particularly for 0.05% SDS with 0.005% WS2, thermal conductivity was enhanced by up to 4.5%, with a corresponding decrease in viscosity of up to 10.5% in a temperature range of 25–70 °C, as compared to EG. Conversely, the viscoelastic analysis has indicated considerable yield stress due to the presence of surfactants, while the pristine nanofluids exhibited enhanced fluidity over the entire tested deformation range. The shear flow behavior showed a transition from a non-Newtonian to a Newtonian fluid at a low shear rate of 10 s−1. Besides this, the temperature sweep analysis has shown a viscosity reduction in a range of temperatures (25–70 °C), with an indication of a critical temperature limit. However, owing to an anomalous reduction in the dynamic viscosity of up to 10.5% and an enhancement in the thermal conductivity of up to 6.9%, WS2/EG nanofluids could be considered as a potential candidate for heat transfer applications.
Highlights
Various engineering applications—for instance, solar thermal, automobile engine cooling, and electronic cooling—employ heat exchanging systems to dissipate heat between two or more than two fluids [1,2]
The morphology was confirmed by employing field emission scanning electron microscopy (FESEM, JSM-7600F, operated at 10 kV by JEOL Ltd., Tokyo, Japan) and high-resolution transmission electron microscopy (HRTEM, JEM-2100F by JEOL Ltd., Tokyo, Japan)
For other nanofluid combinations with SDS, the absolute zeta potential values improved, but the rate of improvement with regards to surfactant concentrations became slow as the amount of surfactant increased
Summary
Various engineering applications—for instance, solar thermal, automobile engine cooling, and electronic cooling—employ heat exchanging systems to dissipate heat between two or more than two fluids [1,2]. The common heat transfer fluids used in many commercial heating and cooling processes include water, ethylene glycol, and oils [3,4]. Owing to their low thermal conductivity as compared to bulk metals, they exhibit poor heat dissipation capabilities. The thermo-physical properties of nanofluids, such as thermal conductivity and viscosity, play a vital role in improving the flow thermal system’s efficiency [5,6]. The viscosity is the internal resistance between the layers of fluids, which increases the pumping power [7]. The reduced viscosity can add value in the efficiency improvement of flow thermal systems by decreasing the input pumping power
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