Thermal conductivity and rheological investigation of aqueous poly(ethylene) glycol/MXene as a novel heat transfer fluid

In this study, aqueous poly (ethylene) glycol (PEG)-based MXene nanoflakes dispersed nanofluids as a novel heat transfer fluid (HTF) with highly promising thermal and rheological properties were prepared. Synthesis of MXene (Ti3C2) flakes was conducted using wet chemistry etching method (lithium fluoride & HCL). Amphiphilic structure of poly (ethylene) glycol allows the dispersion of water and MXene nanoflakes appropriately. The studied nanofluids were prepared with mixing of 70 % of PEG with molecular weight of 400 and 30% of deionized (DI) water. The prepared aqueous PEG was mixed with Ti3C2 nanoflakes with two different loading concentrations of 0.05 and 0.1 wt.%. Thermal conductivity measurements of the prepared PEG/Water/MXene nanofluids were conducted using a Tempos thermal properties analyzer (METER group). KS-3 sensor was utilized for thermal conductivity measurements. Enhancements of thermal conductivity of the PEG/Water/MXene nanofluids (0.1 wt.%) were found ∼23-29% over aqueous PEG with the rising temperature from 25 to 45 °C. The high thermal conductivity values proved that this promising heat transfer fluid is dependent on temperature and loading concentrations of MXene nanoflakes in terms of thermal conduction performance. This high thermal conductivity might be due to the presence of extremely large basal plane of MXene sheets in aqueous PEG which can conduct heat through the MXene nanoflake's basal plane. The viscosity of this nanofluid was measured using Rheometer Anton Paar (MCR92). Shear rate measurement as a function of temperature was conducted for all samples in three different individual temperatures (25, 50 and 85 °C). T-Ramp measurements were conducted within the rising temperature ranges from 25 to 85 °C. The promising results proved that aqueous PEG/Water/MXene nanofluids behave as Newtonian fluid. This finding is perceived for all three different investigated temperatures as well. It was observed that viscosity was decreased at elevated temperatures. The acquired viscosity values for aqueous PEG at the temperatures of 25, 50 and 85 °C were ∼35, ∼16 and ∼5 mPa.S respectively, which shows ∼85% decrease at temperature of 85 °C, over temperature of 25 °C. Similar trend was observed for PEG/Water/MXene nanofluids with loading concentration of 0.05 and 0.1 wt.%.