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The transformer-oil based (TOB) nanofluid suspensions were prepared through adding 0.05 to 0.80 wt% multiwall carbon nanotube (MWCNTs) functionalized with a -COOH group. The sodium dodecyl sulfate was used to stabilize the suspensions. The resulting material was used as a coolant in a double pipe heat exchanger operated under co- and counter-current flow conditions. The nanofluid thermo-physical features such as the thermal conductivity, viscosity, and density were determined at various temperatures and mass fractions. Then pertinent semi-empirical relations were developed. To verify any multiwall carbon nanotube’s (MWCNT’s) and sodium dodecyl sulfate’s (SDS) interactions with the transformer-oil based (TOB) material, the Fourier-transform infrared (FTIR) analysis was performed. Moreover, the stability of the nanofluid suspension was understudied through the UV-Visible and thermogravimetric analysis (TGA) techniques. In addition, the maximum heat transfer coefficient improvement was determined to be 86.7% at a multiwall carbon nanotube (MWCNT) mass fraction of 0.8 wt%. Meanwhile, average increments of the overall heat transfer coefficient and thermal conductivity of the prepared nanofluid were revealed about 37.2% and 138%, respectively in comparison with that of the base fluid. Furthermore, the optimum thermal conductivity of 0.388 W/m.K was obtained at 45 °C and 0.8 wt% of the multiwall carbon nanotube (MWCNT). Ultimately, a sensitivity analysis emphasized that, the understudied system’s behaviors were within an accuracy limit of ±97%.

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The purpose of this study is to determine the equilibrium conditions for the formation of a mixture of propane and normal butane hydrates including temperature, pressure and mole fraction. In order to prevent the formation of hydrates in the cooling path, it is necessary to examine the conditions of hydrate formation and provide solutions. Modeling of hydrate formation conditions was performed using Hydoff software and compared with experimental results in this field, which obtained an acceptable error percentage. The range of temperature is between 267-276 °C and the molar percentage of propane is 0.7,0.8 and 0.9 and the mathematical equation was presented to predict hydrate formation. By analyzing the results, it was found that by increasing the concentration of ethane in the presence of other compounds, hydrate growth increased and hydrates formed more stable, also by increasing the concentration of propane and normal butane the amount of equilibrium pressure will decrease.