No 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.

Summary In this study, polyaniline (PANI) nanocomposite‐based nanofluids (NFs) in ethylene glycol were obtained with a two‐step method by varying volume concentrations from 0.005% to 0.02%. Tungsten disulphide (WS2) nanoparticles were doped in PANI having different weight percentage (1%, 2% and 5%) via oxidative in situ polymerization employing ammonium persulphate oxidant in an acidic environment. The nanocomposites were comprehensively characterised using various techniques, such as Fourier transform infrared spectroscopy, thermogravimetric analysis, field emission scanning electron microscopy and high‐resolution transmission electron microscopy. The formulated NFs were extensively investigated with zeta‐sizer, particle size analyzer, thermal property analyzer and rheometer in a temperature range of 25°C to 70°C. The zeta potential results (up to 54.5 mV) were evident of extraordinary stability of NFs at all targeted temperatures along with polydispersity index <30% and mean particle/agglomerate size in the range of 335.8 to 489 nm. Additionally, a remarkable thermal conductivity improvement (~20.7%) was achieved with intrinsic PANI‐based NFs at an operating temperature of 50°C. Subsequently, it varied substantially with WS2 doping within PANI matrix and reached to 117.9%. Furthermore, the rheological measurements have revealed the viscoelastic nature of NFs along with a remarkable reduction in apparent viscosity (up to 8.4%). The temperature sweep viscosity indicated the transition of relative viscosity from high to low at a critical temperature of about 55°C. The NF10 (WS2 + PANI 5, at 0.005 vol%) was found to be the best candidate with 63.8% thermal conductivity enhancement and 6.4% viscosity reduction as compared with the base fluid at an operating temperature of 50°C. Thus, WS2 doping within PANI has proved to be crucial in the proliferation of thermal conductivity and mitigation of viscosity.