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During the transportation process of heavy oil, wax deposition is prone to occur for the low temperature outside the tube and strong heat exchange, which will adversely affect the pipeline transportation of heavy oil. Based on the experimental data of the indoor deposition loop, this paper considered the impact of strong environmental heat transfer and oil flow shear on wax deposition and established a kinetic model of wax deposition for pipeline transportation of heavy oil. Numerical simulation was performed on the flow field and temperature field during the wax deposition process to obtain the model parameters. Through analyzing the deposition rate computed by the model, this paper reveals the effect of oil flow velocity, oil temperature and wall temperature difference on wax deposition.

BACKGROUND Using a norfloxacin ( NFLX)-Nd3+-cetyltrimethylammonium bromide ( CTAB) system for the detection of NFLX, a simple and sensitive method based on fluorescence enhancement was developed. RESULTS In pH 7.0 buffer solution, NFLX reacted with Nd3+ to form a complex, which resulted in fluorescence enhancement of NFLX, and the maximum emission peak shifted from 415 nm for NFLX to 450 nm for NFLX-Nd3+. Moreover, the fluorescence intensity increased further when the surfactant CTAB was added to NFLX-Nd3+. Under the optimum conditions, the fluorescence intensity of the NFLX-Nd3+- CTAB system was linearly correlated with the NFLX concentration in the range 0.038-10 µmol L−1, with a correlation coefficient ( R2) of 0.9997. The detection limit (3 σ/ k) was 0.021 µmol L−1, indicating that this method can be applied to detect trace NFLX levels. The mechanism of fluorescence enhancement is discussed. The method was used to detect NFLX in fish and chicken samples with satisfactory results. CONCLUSION The present results indicate that this method has the potential for fast and real-time determination of NFLX in food samples © 2016 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

A simple and sensitive spectrofluorometry method for the determination of ascorbic acid was reported. In alkaline solution, the nonfluorescent thiamine was oxidized by potassium ferricyanide and formed the fluorescent thiochrome with an excitation maximum at 367 nm and an emission peak at 441 nm. However, the fluorescence intensity gradually decreased in the presence of ascorbic acid. The decreased fluorescence was linearly dependent under the optimum conditions with the concentration of ascorbic acid from 0.086–1.5 µmol L−1with a correlation coefficient of 0.9996. The detection limit of 0.026 µmol L−1was lower than many other methods. Additionally, the mechanism underlying the enhancement and quenching of this method was discussed. The protocol was used to determine ascorbic acid in tablets and juice with satisfactory results. [ABSTRACT FROM AUTHOR]