@article{BecherVoelkerRodehorstetal., author = {Becher, Lia and V{\"o}lker, Conrad and Rodehorst, Volker and Kuhne, Michael}, title = {Background-oriented schlieren technique for two-dimensional visualization of convective indoor air flows}, series = {Optics and Lasers in Engineering}, volume = {2020}, journal = {Optics and Lasers in Engineering}, number = {Volume 134, article 106282}, doi = {https://doi.org/10.1016/j.optlaseng.2020.106282}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20220810-46972}, pages = {9}, abstract = {This article focuses on further developments of the background-oriented schlieren (BOS) technique to visualize convective indoor air flow, which is usually defined by very small density gradients. Since the light rays deflect when passing through fluids with different densities, BOS can detect the resulting refractive index gradients as integration along a line of sight. In this paper, the BOS technique is used to yield a two-dimensional visualization of small density gradients. The novelty of the described method is the implementation of a highly sensitive BOS setup to visualize the ascending thermal plume from a heated thermal manikin with temperature differences of minimum 1 K. To guarantee steady boundary conditions, the thermal manikin was seated in a climate laboratory. For the experimental investigations, a high-resolution DLSR camera was used capturing a large field of view with sufficient detail accuracy. Several parameters such as various backgrounds, focal lengths, room air temperatures, and distances between the object of investigation, camera, and structured background were tested to find the most suitable parameters to visualize convective indoor air flow. Besides these measurements, this paper presents the analyzing method using cross-correlation algorithms and finally the results of visualizing the convective indoor air flow with BOS. The highly sensitive BOS setup presented in this article complements the commonly used invasive methods that highly influence weak air flows.}, subject = {Raumklima}, language = {en} } @article{BecherGenaAlsaadetal., author = {Becher, Lia and Gena, Amayu Wakoya and Alsaad, Hayder and Richter, Bernhard and Spahn, Claudia and V{\"o}lker, Conrad}, title = {The spread of breathing air from wind instruments and singers using schlieren techniques}, series = {Indoor Air}, volume = {2021}, journal = {Indoor Air}, number = {volume 31, issue 6}, publisher = {Wiley Blackwell}, address = {Oxford}, doi = {10.1111/ina.12869}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20220209-45817}, pages = {1798 -- 1814}, abstract = {The spread of breathing air when playing wind instruments and singing was investigated and visualized using two methods: (1) schlieren imaging with a schlieren mirror and (2) background-oriented schlieren (BOS). These methods visualize airflow by visualizing density gradients in transparent media. The playing of professional woodwind and brass instrument players, as well as professional classical trained singers were investigated to estimate the spread distances of the breathing air. For a better comparison and consistent measurement series, a single high note, a single low note, and an extract of a musical piece were investigated. Additionally, anemometry was used to determine the velocity of the spreading breathing air and the extent to which it was quantifiable. The results showed that the ejected airflow from the examined instruments and singers did not exceed a spreading range of 1.2 m into the room. However, differences in the various instruments have to be considered to assess properly the spread of the breathing air. The findings discussed below help to estimate the risk of cross-infection for wind instrument players and singers and to develop efficacious safety precautions, which is essential during critical health periods such as the current COVID-19 pandemic.}, subject = {Covid-19}, language = {en} } @article{AlsaadSchaelteSchneeweissetal., author = {Alsaad, Hayder and Sch{\"a}lte, Gereon and Schneeweiß, Mario and Becher, Lia and Pollack, Moritz and Gena, Amayu Wakoya and Schweiker, Marcel and Hartmann, Maria and Voelker, Conrad and Rossaint, Rolf and Irrgang, Matthias}, title = {The Spread of Exhaled Air and Aerosols during Physical Exercise}, series = {Journal of Clinical Medicine}, volume = {2023}, journal = {Journal of Clinical Medicine}, number = {Volume 12, issue 4, article 1300}, publisher = {Basel}, address = {MDPI}, doi = {10.3390/jcm12041300}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20230208-49262}, pages = {20}, abstract = {Physical exercise demonstrates a special case of aerosol emission due to its associated elevated breathing rate. This can lead to a faster spread of airborne viruses and respiratory diseases. Therefore, this study investigates cross-infection risk during training. Twelve human subjects exercised on a cycle ergometer under three mask scenarios: no mask, surgical mask, and FFP2 mask. The emitted aerosols were measured in a grey room with a measurement setup equipped with an optical particle sensor. The spread of expired air was qualitatively and quantitatively assessed using schlieren imaging. Moreover, user satisfaction surveys were conducted to evaluate the comfort of wearing face masks during training. The results indicated that both surgical and FFP2 masks significantly reduced particles emission with a reduction efficiency of 87.1\% and 91.3\% of all particle sizes, respectively. However, compared to surgical masks, FFP2 masks provided a nearly tenfold greater reduction of the particle size range with long residence time in the air (0.3-0.5 μm). Furthermore, the investigated masks reduced exhalation spreading distances to less than 0.15 m and 0.1 m in the case of the surgical mask and FFP2 mask, respectively. User satisfaction solely differed with respect to perceived dyspnea between no mask and FFP2 mask conditions.}, subject = {Sport}, language = {en} }