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The possibility of applying active control to reduce sound transmission across a practical plenum window is examined experimentally in the present study using measured transfer functions of all related sound transmission paths. As a result of the limited space within the window, the error microphones are located at the indoor window opening while the secondary cancelling sources are mounted along the periphery of the window void. Results show that the cancelling sources near the outdoor window opening corners and within the overlapping region of the window play more useful roles in the control. Also, the highest sound reduction is around 6 dB with six error microphones positioned either at the central region or along the periphery of the indoor window opening. However, the results with the central error microphones suggest the possibility of adopting a dual control system to enhance the low frequency performance. Control systems with fewer error microphones result in lower sound reduction. Besides, it is found that four cancelling sources, located around the outdoor opening of the window, will be enough to achieve meaningful active sound transmission reduction between 100 and 1000 Hz. Involving more cancelling sources does not result in better performance despite the added complexity. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive investigation of flow-induced noise characteristics in ethylene cracking furnace tubes, covering both pre- and postcoking conditions. Large-eddy simulation (LES) was employed in conjunction with a generalized Lighthill's acoustic analogy model. The results indicate that noise sources can be classified as dipole acoustic sources, with energy primarily concentrated ranged from 300 to 1500 Hz, in comparison to standard conditions. The primary location of the acoustic source was identified in the region commonly referred to as the "necking" of the furnace tube, demonstrating a strong correlation with turbulence intensity near the tube wall. As the coke layer thickness in the furnace tube increased from 5 mm to 15 mm, both the sound power level and turbulence intensity exhibited significant growth. Specifically, the sound power level increased by 60.5% while the turbulence intensity increased by 58.5%. Variations in the overall sound pressure level (OASPL) curve measured within the tube could be utilized to assess coking levels. Significant peaks in the OASPL curve were observed as the furnace tube underwent substantial coking, with coke layer thicknesses of 10 mm and 15 mm. The corresponding OASPL values recorded were 79.25 dB and 119.08 dB, respectively. The findings of this work offer significant insights that may contribute to enhanced safety measures in the operation of ethylene cracking furnace tubes. [ABSTRACT FROM AUTHOR]

Knowledge of respiratory bacterium/virus distribution on surfaces is critical for studying disease transmission via the contact route. Here, we investigated the bioaerosol deposition and distribution on a surface from a cough experimentally. A cough generator was used to release bacterium/virus-laden droplets. A solid surface was placed in front of the cough generator at different relative distances (D = 0.2, 0.5, 0.8, and 1.1 m) and angles (θ=30°, 60°, and 90°). Benign bacteria and bacteriophages were used separately. Results showed that droplet jet directly impinged upon the surface and then spread out along the surface. The distributions of droplet volume and viable microorganisms along the surface were unimodal. We then identified the impaction region based on the droplet flow field from a particle imaging velocimetry technique, which corresponded with the peak position and high-volume area. The impaction region contained around 83% of droplet volume along the vertical axis of the surface. The peak position, peak value, and width of the impaction region were related to D and θ. The micro-organisms inside the droplets did not affect the droplet distribution on near surfaces. The front surface can work as a partition to block the cough jet and protect people behind, and can be smaller when it is installed closer to the coughing person. This work demonstrates a methodology to obtain distribution and viability of microorganism deposited on surface, and suggest guidelines to setting up a protective partition as a possible intervention method against disease transmission. Copyright © 2020 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

Resuspension is considered as a source of indoor air pollutants. These airborne pollutants can be in the form of liquid or solid. It has been previously found that the detachment mechanism of liquid droplets is different from the solid particles on the poly(methyl methacrylate) (PMMA) surface. Liquid droplets detach by portion when they are under an increasing normal force field while droplets detach completely when under a tangential force field. In this research, droplet detachment experiments are extended to different substrate materials, which are PMMA, glass, and stainless steel by the means of centrifuge. Also, the differences in detachment between pure glycerol-water (pure fluid) and a glycerol solution with the addition of nanoparticles (nanofluid) are investigated under different substrate materials. It is found that liquid droplets, again, detach by portion under normal force for all the substrate materials. For tangential force, the droplets detach completely if the exerted force was sufficiently large and the threshold values are material dependent, which is further elaborated by retention theory. After the addition of nanoparticles, a higher removal force was required compared to the droplets of pure fluid within the same size range. Also, solid residues with a negligible amount of fluid were found on the substrate after each removal of droplets under both normal and tangential force. The involvement of nanoparticles could be the pioneer work for future studies on commonly found liquid pollutants, which are prone to be contaminated by solid particles, such as in salivary excretion. Copyright © 2018 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

Surface cleaning using air jets is an appropriate method to remove particles from surfaces especially when cleaning by mechanical methods is not suitable. The detachment behavior of droplets using an air jet is not necessarily the same as solid particles and there is a lack of studies regarding this behavior. In this article, the detachment of droplets on a plastic substrate by air jet impingement was investigated experimentally. Droplets of two different size ranges were impinged by an air jet with different impinging angles. For micrometer-sized droplets, a smaller horizontal velocity was required to detach large droplets. Moreover, the horizontal velocity required to detach 50% number fraction of droplets decreased when the air jet impinging angle increased. Millimeter-sized droplets split into many portions. Most portions remained on the substrate and only a few were resuspended. The remaining portions were distributed in a fan shape, with larger droplets traveling further on the substrate. A linear lower bound of traveled distance was observed. Due to the splitting and the small fraction of resuspension, it should not be expected that air jet cleaning of droplets is the same as that for solid particles. Copyright © 2017 American Association for Aerosol Research [ABSTRACT FROM PUBLISHER]