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Adding nanoparticles with high thermal conductivity into the work fluid is one of the most significant ways to enhance heat transfer. In this article, the influences of nanoparticle mass concentration (0.5–10.0 wt.%) and temperature (5–25 °C) were investigated on the viscosity of TiO2-propylene glycol nanofluid. At the same time, eight kinds of mass concentrations (0.5–10.0 wt.%) were used to investigate the changing regularity on the surface tension of nanofluid; Accordingly, the modified correlations including nanoparticle concentration were proposed respectively. The experimental results show that the viscosity of the nanofluid increases with the increase in particle concentration. Within the concentration of 10.0 wt.%, the viscosity increases by about 7.0% for every 1.0 wt.%. While the viscosity decreases with the increase in the temperature. The surface tension of the mixture increases slowly with the increase in particle concentration. Within 2.0 wt.%, the surface tension of nanofluid increases by less than 1.0% for every 0.5 wt.%, when the concentration of nanofluid exceeds 2.0 wt.%, surface tension raises less than 1.0% per 2.0 wt.%. [ABSTRACT FROM AUTHOR]

Nanofluids have become more and more attractive to the modern industry due to their high performance in heat transfer and combustion. As one of the key influencing factors, the atomization mechanism of nanofluids induced by airflow is more complex than that of pure liquids, which has attracted great attention recently. In this study, the spray characteristics of TiO2–propylene glycol nanofluids were investigated by focusing on the effects of nano-TiO2 additives on atomization. On the basis of high-speed shadow imaging, the spray morphology of the base fluid injected from an air atomizing nozzle under different pressures was analyzed first. Then a laser particle size analyzer was used to obtain the droplet size distribution of the nanofluids. The air pressure at the inlet of the atomizer was found to have more contribution to the atomization of nanofluids. And when the air pressure exceeded 0.35 MPa, the Sauter mean diameter (D32) of the base fluid droplets was insensitive to the change of air pressure. Subsequently, the contribution of nanoparticles to atomization was discussed. An empirical correlation was proposed between the Sauter mean diameter (D32) and the dimensionless parameters such as the gas Weber number (Weg), liquid–gas momentum ratio (q), and the volume fraction of nano-TiO2, etc. Results indicated that adding nanoparticles enhanced the jet stability by increasing the viscosity at a low jet velocity, while the jet instability was increased due to the nanoparticles promoting the cavitation at a high jet velocity. [ABSTRACT FROM AUTHOR]

Hydrological conditions drive the distribution of plant communities in wetlands to form vegetation zones where the material cycling varies with plant species. This mediation effect caused by the distribution of vegetation under hydrological conditions will affect the emission of N2O during the nitrogen migration in wetlands. In this study, five vegetation zones in the second largest wetland of China were investigated in situ during high and low water levels to elucidate the effect mediated by vegetation. With the increase in the rate of change of water levels, the zones of the mud flat, nymphoides, phalaris, carex, and reeds were distributed in sequence in the wetland, and the densities of carbon and nitrogen sequestrated by plants also increased. The carbon and nitrogen densities in each zone during low water level was significantly higher than that during high water level, while the organic carbon and the total nitrogen of sediments during high water level was higher. Sediments converted between source and sink for both carbon and nitrogen, during the annual fluctuation in water level. The flux in N2O emissions showed significant differences between the vegetation zones during each water level period. The emission flux decreased with the increasing C : N ratio in sediments, approximating the threshold at 0.23 μg m-2 h-1 when the C : N ratio > 25. The phylum abundance of Firmicutes, Proteobacteria, and Chloroflexi in sediments increased with flooding. The denitrifying nirS and nirK genes and anammox hzsB gene were significantly affected by water level fluctuation, with the maximal variations of these genes occurring in the mud flat and nymphoides zone. The results indicate that the distribution of plants under hydrological conditions modified the stoichiometric ratio of sediments, resulting in the variations of N2O emission fluxes and microbial communities in vegetation zones. Therefore, hydraulic regulation rather than direct planting would be an effective strategy to reduce greenhouse gas emissions in freshwater wetlands. [ABSTRACT FROM AUTHOR]