Abstract
Nanofluids (NFs) as a new generation of heat transfer media can be applied inter alia as engine coolants, in the microelectronic industry for the cooling of electronic components and systems, and in solar panels. In the present study, the extraordinarily, that is, more than 1 year, stable NFs composed of multi-walled carbon nanotubes (MWCNTs), biomass-derived 1,2-propanediol or 1,3-propanediol, and poly(N-vinylpyrrolidone) were created and studied. The thermal conductivity and density of NFs did not change over 8 months, and NFs did not sediment over 14 months. The real image of NFs determined using transmission electron cryo-microscopy allowed us to prove that the extraordinary stability and enhanced thermal conductivity were resulted by fully individualized MWCNTs in the continuous phase and MWCNTs stabilized in dispersions by shorter carbon nanoparticles and mostly homogenous poly(N-vinylpyrrolidone) coating. The maximum enhancement in thermal conductivity was 22 and 20% for NFs composed of 2 wt % MWCNTs in comparison with that of pure 1,2-propanediol and 1,3-propanediol, respectively. The improved thermal properties were accompanied by the practically Newtonian nature of all NFs. The cytotoxicity test on normal human dermal fibroblasts indicated that the use of diols diminished the toxicity of MWCNTs. Finally, the thermal conductivity and Prandtl number of bio-based NFs—as compared with those of commercial heat transfer fluids DOWCAL 200 and DOWCAL N—predestine them as superb green heat transfer media in sustainable energy systems.
Highlights
The obligation to limit the current consumption of fossil fuels necessitates the use of alternative, greener energy sources which improve the efficiency and effectiveness of the heat exchange devices
The maximum enhancement in thermal conductivity was 22 and 20% for NFs composed of 2 wt % multi-walled carbon nanotubes (MWCNTs) in comparison with that of pure 1,2-PG and 1,3-PG, respectively
The addition of the MWCNTs into 1,2-PG and 1,3-PG as well as stabilization with PVP, which is a rare case for carbon-based NFs, leads to enhancements in thermal conductivity of 22 and 20% for NFs composed of 2 wt % MWCNTs in comparison with that of pure 1,2-PG and 1,3-PG, respectively
Summary
The obligation to limit the current consumption of fossil fuels necessitates the use of alternative, greener energy sources which improve the efficiency and effectiveness of the heat exchange devices. In addition to the green chemistry aspect, these are sustainable products with a low carbon footprint and a wide industrial use Their production is characterized by a 50% reduction in CO2 emission when compared to that in the fossil processing.[4] Susterra 1,3-PG, of a “cradle-to-grave” life cycle, generates up to 56% less emission of greenhouse gases and consumes 42% less non-renewable energy than the petroleumbased 1,3-PG.[5] In addition, PGs are characterized by low freezing temperature, non-toxicity, and faster biodegradation than EG.[6] The toxicity of EG surpasses that of 1,3-PG considering lethality, acute effects, and reproductive, developmental, and kidney toxicity.7 1,3-PG is characterized by Received: March 21, 2021 Revised: May 4, 2021 Published: May 18, 2021
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