New data for pressure drop, void fraction and flow pattern in a vertical riser using air–silicone oil as the system fluid are reported in this work. A differential pressure cell (DP cell) was used to measure the pressure drop. Also, void fraction data were recorded simultaneously by an electrical capacitance tomography (ECT) and wire mesh sensor (WMS). The observed flow patterns are the spherical cap bubble, slug and churn flows. However, only the slug flow without the presence of churn flow is seen within the transition line as predicted by the map. The characteristic probability density function (PDF) derived from void fraction data was used to determine the flow patterns. A comparison between present experimental results and the air–water data reported in the literature was carried out and various levels of agreement were achieved. The PDFs obtained from the DP cell signals for spherical cap bubble and slug flows significantly differ from those derived from the ECT and WMS outputs. Current void fraction and pressure gradient results were compared with the values predicted by ten In the current study, an experimental study was carried out on the rheological properties of hybrid non-Newtonian nanofluid (MWCNTs–ZnO/Water–Ethylene glycol (80:20 vol.%)) to develop a new model. The viscosities of nanofluid were evaluated in the temperature range of 25–50 °C with volume fractions of φ = 0.075%, 0.15%, 0.3%, 0.6%, 0.9%, and 1.2%. We find that the effect of changes is more obvious when the φ is increased. So the property of non-Newtonian nanofluid is more likely to appear. In addition to a temperature of 25 °C, the viscosity increase from a φ = 0% to 1.2% is higher than 90%, which is very significant. Also, in the maximum φ, at T = 50 °C, 40 °C and 30 °C, the viscosity reduction is 21%, 17%, and 8%, respectively, relative to the reference temperature (25 °C). The above results can be of great help to engineers in designing thermal systems to increase heat transfer and considering pumping power
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