A Novel Apparatus for Simultaneous Laser-Light-Sheet Optical Particle Counting and Video Recording in the Same Measurement Chamber at High Temperature.

A novel apparatus was developed, to investigate the detachment of particle structures consisting of soot and ash from a single fibre or a fibre array in hot gas flow. Key features of the novel apparatus are operation at high temperatures while two different measurement techniques are applied simultaneously in the same measurement chamber to observe particle structure detachment from a loaded fibre array. A heated inlet can heat the air stream at the position of the fibre array up to 470 °C, allowing detachment investigations at temperatures relevant for the operation of, e.g., soot particle filters. The first measurement technique integrated in the setup is video recording of the fibre array, which gives qualitative information on the rearrangement or detachment of particulate matter on the fibre. Because it is often difficult to distinguish rearrangement and detachment from pure visual observations, a second measurement technique is applied. This technique is a laser-light-sheet optical particle counter, which can detect detached particle structures and determine their size. The measurable size range is 257 to 1523 µm for glass spheres. This paper presents and discusses the novel apparatus, its calibration and first detachment measurement results.

Generation, characterization, and comparison of human exhaled and technical aerosols for the evaluation of different air-purifying technologies against infectious aerosols.

In light of the COVID-19 pandemic, the importance of protective measures against infectious aerosols has drastically increased, as the transmission of diseases via airborne particles is impacting many aspects of everyday life. The protective measures against such infections are determinant in the operation of schools and kindergartens, hygiene in hospitals and medical facilities, in offices, administrative and production facilities, hotels, and the event industry, among others. To test these protective measures, suitable test aerosols and processes are needed. These aerosols ought to be similar to aerosols exhaled by humans as those carry the pathogens and thus need to be removed from the air or inactivated. The exhaled aerosols of several healthy test subjects were characterized by their particle concentration and size distribution. In previous studies, it was found that exhaled particle concentration varies significantly from subject to subject and most of the particles can be found in the submicron size range. Aerosols technically generated through nebulization were emitted by the generators in particle concentrations several orders of magnitude higher than those exhaled by humans, independent of the aerosol generation method and nebulized fluid. The particle size distribution generated by the two nebulizers used, however, was quite similar to the measured size distributions of the human aerosols, with most of the particles below 1 µm in size. Consequently, the used aerosol generators are not suitable to mimic single individuals as active aerosol sources, but rather to provide a sufficient amount of aerosol similar to human aerosols in size distribution, which can be used in the testing of air purification technologies.

[Aerosols and SARS-CoV-2: Statement of the "Expert Group Aerosols" on the development, infectivity, spread and reduction of airborne, virus-containing particles in the air]. / Stellungnahme des "Expertenkreises Aerosole": Aerosole und SARS-CoV-2 ­ Entstehung, Infektiosität, Ausbreitung und Minderung luftgetragener, virenhaltiger Teilchen in der Atemluft.

Aerosols are currently seen as one of the main transmission routes for SARS-CoV-2, but a comprehensive understanding of the processes and appropriate action/adaptation of protection concepts requires the exchange of information across interdisciplinary boundaries. Against this background, the Baden-Württemberg state government launched in October 2020 a multidisciplinary "Expert Group Aerosols" comprising engineers, natural scientists and medical professionals. In its statement, the group has compiled the current state of knowledge in all relevant disciplines in the context of airborne SARS-CoV-2 infection. In addition to the well-known hygiene and social distancing rules, the importance of the correct use of effective masks is emphasized. Furthermore, the necessity for dynamic and correct ventilation is pointed out and illustrated with ventilation intervals and periods for different scenarios as examples. The effectiveness of stationary or mobile cabin air filters as an important component in the protection concept is discussed. The first opinion of the expert group makes it clear that the existing hygiene and social distancing rules offer the best possible protection against SARS-CoV-2 infection only when correctly applied in combination.

Experimental investigation on the change of pull-off force between bulk particulate material and an elastic polymeric filter fiber.

HYPOTHESIS: Adhesion between particles and a filter fiber is an important process of the filtration as it dictates the process of separation and in the following the detachment process of particles during filter regeneration. In addition to the shear stress that a new polymeric stretchable filter fiber implements into the particulate structure, the elongation of the substrate (fiber) is also expected to cause a structural change in the surface of the polymer. Thus, the changed contact area and surface energy could affect the adhesion force between particles and fibers. EXPERIMENTS: Systematic measurements of adhesion forces between a single particle and the stretchable substrate were performed using Atomic Force Microscope (AFM). The substrate surface characteristics (roughness) was changed directly beneath the modified measurement head using piezo-motors to achieve stepless elongation state. Polystyrene particles and particles made of Spheriglass were applied. FINDINGS: In the experiments, a reduced adhesion force between the particles and the filter fiber was found for a new high range of substrate roughness and peak-to-peak distance, in which the Rabinovich model has not been used before [1]. Further, the influence of high and low energy surface particulate material was evaluated to understand the detachment process in the new real adaptive filter and in DEM-simulation.

Penetration of Water-Soluble Material through Gas-Cleaning Filters.

To predict the behavior of gas-cleaning filters during real-world operation, it is essential to understand their response to ambient conditions. The temporary presence of water droplets in gas-cleaning filtration systems due to fog, spray rain, or condensation, as examples of irregular events, has an impact on the filters' operating performance, especially when soluble particles are present. In this work, surface filters were loaded with mixtures of water-soluble salt particles and insoluble glass spheres. These were, subsequently, exposed to water mist and dried by a particle-free gas stream. A novel approach to analyze the drainage of solution on filters with soluble filter cakes is presented, which allows the detection of solubles on the clean gas side of the filter. As a result, this work, for the first time, presents a sighting of the penetration of soluble filter cake material through gas-cleaning filters. Furthermore, filter performance, in terms of differential pressure and fractional separation efficiency, was determined and a characteristic differential pressure evolution for hydrophilic filters during exposure to water mist was also identified. The fractional separation efficiency of gas-cleaning filters decreases due to exposure to water mist. The findings are supported by scanning electron microscopy (SEM) images, energy-dispersive X-ray (EDX), and X-ray microtomography (µ-CT analysis) images.