Plasmon-enhanced ammonia borane (AB) methanolysis, as an efficient, controllable, and safe method for hydrogen release, has attracted increasing attention. However, the mechanism remains controversial since it is difficult to directly observe the interface interaction in the plasmonic field. Here, CuAg alloy nanoparticles (NPs) with controlled compositions are synthesized and exhibit an excellent H 2 yield (17.1 μmol min −1 ) under light illumination. Theories and experiments show that both hot carriers and photoinduced local-field enhancement contribute to the improved catalytic activity under light irradiation. More impressively, plasmon-induced interfacial charge transfer between single CuAg NPs and reactant molecules was explored in situ by a singleparticle confocal microscope system, and a complete photoluminescence (PL) quenching phenomenon of CuAg NPs was observed when immersed in a methanol solution, not ammonia borane. The PL quenching indicates the transfer of hot electrons to methanol, which is the rate-limiting step of the AB dehydrogenation reaction. In contrast, charge transfer from the plasmonic NP to AB (the most widely proposed path to date) does not work here. This work provides direct evidence for the hot electron transfer from CuAg to methanol via single-particle PL measurement and provides insights for plasmon-enhanced AB methanolysis.
Fault characteristic extraction is attracting a great deal of attention from researchers for the fault diagnosis of rotating machinery. Generally, when a gearbox is damaged, accurate identification of the side-band features can be used to detect the condition of the machinery equipment to reduce financial losses. However, the side-band feature of damaged gears that are constantly disturbed by strong jamming is embedded in the background noise. In this paper, a hybrid signal-processing method is proposed based on a spectral subtraction (SS) denoising algorithm combined with an empirical wavelet transform (EWT) to extract the side-band feature of gear faults. Firstly, SS is used to estimate the real-time noise information, which is used to enhance the fault signal of the helical gearbox from a vibration signal with strong noise disturbance. The empirical wavelet transform can extract amplitude-modulated/frequency-modulated (AM-FM) components of a signal using different filter bands that are designed in accordance with the signal properties. The fault signal is obtained by building a flexible gear for a helical gearbox with ADAMS software. The experiment shows the feasibility and availability of the multi-body dynamics model. The spectral subtraction-based adaptive empirical wavelet transform (SS-AEWT) method was applied to estimate the gear side-band feature for different tooth breakages and the strong background noise. The verification results show that the proposed method gives a clearer indication of gear fault characteristics with different tooth breakages and the different signal-noise ratio (SNR) than the conventional EMD and LMD methods. Finally, the fault characteristic frequency of a damaged gear suggests that the proposed SS-AEWT method can accurately and reliably diagnose faults of a gearbox.
A double shell-pass shell-and-tube heat exchanger with continuous helical baffles (STHXCH) has been invented to improve the shell-side performance of STHXCH. At the same flow area, the double shell-pass STHXCH is compared with a single shell-pass STHXCH and a conventional shell-and-tube heat exchanger with segmental baffles (STHXSG) by means of numerical method. The numerical results show that the shell-side heat transfer coefficients of the novel heat exchanger are 12-17% and 14-25% higher than those of STHXSG and single shell-pass STHXCH, respectively; the shell-side pressure drop of the novel heat exchanger is slightly lower than that of STHXSG and 29-35% higher than that of single shell-pass STHXCH. Analyses of shell-side flow field show that, under the same flow rate, double shell-pass STHXCH has the largest shell-side volume average velocity and the most uniform velocity distribution of the three STHXs. The shell-side helical flow pattern of double shell-pass STHXCH is more similar to longitudinal flow than that of single shell-pass STHXCH. Its distribution of fluid mechanical energy dissipation is also uniform. The double shell-pass STHXCH might be used to replace the STHXSG in industrial applications to save energy, reduce cost, and prolong the service life.
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