Nanofluids have great application prospects in industrial heat exchange systems because they can significantly improve the heat and mass transfer efficiency. However, the presence of nanoparticles in the fluid might also affect the formation and attachment of inorganic scales, such as calcium carbonate, on the heat exchange surface. The effects of carbon nanoparticles on the crystallization of calcium carbonate in aqueous solution were studied by the scale inhibition test, solution analysis, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR). The results showed that carbon nanoparticles had an excellent surface scale inhibition performance for calcium carbonate, which could effectively prevent the adhesion of scale on the heat exchange surface. The carbon nanoparticles did not affect the solubility of calcium carbonate in water, but changed the crystal form of the precipitated calcium carbonate, making it difficult to adsorb on the heat exchange surface and achieving a surface scale inhibition effect. Carbon nanofluids effectively inhibit the adhesion of calcium carbonate to heat exchange surfaces.
The effects of Al2O3 nanoparticles on the precipitation behavior of CaCO3 and on the anti-scale performance of 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA) in CaCO3 growth solution were studied by means of solution analysis, gravimetric
methods, scanning electron microscopy, Fourier transform infrared spectroscopy and X-ray diffraction. The results illustrate that Al2O3 nanoparticles had little effect on the concentration of calcium ions in the test solution without PBTCA, but significantly changed the
form and morphology of calcium carbonate crystals, which were transformed from calcite to aragonite. As a commonly used and effective scale inhibitor, PBTCA showed good Ca2+ retention ability in the test solution, distorting the calcite crystal lattice and promoting the formation
of vaterite. When Al2O3 nanoparticles co-existed with PBTCA in the test solution, calcium carbonate was more likely to precipitate, and the Ca2+ retention ability of PBTCA reduced. A newly designed gravimetric method was used to evaluate the scale inhibition
performance of Al2O3 nanoparticles on the heat exchange surface. When the concentration of Al2O3 nanoparticles reached 1 g/L, the surface scale inhibition efficiency of Al2O3 nanoparticles exceeded 80%.
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