Amayu Wakoya Gena (MSc) and Professor Conrad Voelker from the Professorship for Building Physics were already using the schlieren mirror in March to show how the air we breathe is spreading when we cough with and without covering our mouth and nose. The visualization attracted a great deal of media interest, particularly in light of the social distancing measures and obligation to wear a face mask due to the coronavirus pandemic. The experiment in the schlieren laboratory has now been repeated to test the effectiveness of the newly developed »BauhausUniVisor«.

Professor Andreas Mühlenberend – who developed the visor together with Assistant Professor Jason Reizner and Kristian Gohlke – was himself the test subject, standing before the test setup with a schlieren mirror and a high-resolution camera for the experiment. Different scenarios were tested, namely breathing, coughing and speaking. The expired air was visualized without his mouth and nose being covered, then again while only wearing the visor. The outcome: no exhalation clouds are visible outside the visor directly in front of the wearer, as the expired air is diverted downwards and upwards by the protective film in front of their face. In contrast, without the protective visor, the expired air spreads straight forward at different speeds and ranges.

It is important to note that the turbulence air above Professor Mühlenberend’s head and the rising air around his body  is due to human body heat (natural convection), which occurs independently of the air we breathe and is also visible in front of the schlieren mirror. The schlieren mirror test does not provide any information on distribution and quantity of the liquid droplets known as aerosols suspended in the air.

Despite the visor’s effect, which can be seen in the video, the experiment’s participants emphasize that it is still important to adhere to social distancing and all instructions issued by the health authorities and particularly to maintain an appropriate distance if you are experiencing coronavirus symptoms. 

About the schlieren imaging

The schlieren imaging is a technique for visualizing and measuring indoor airflow. The optical setup of the system enables to visualize the refractive index fluctuations in transparent media. For example, thermal convection currents. The setup essentially comprises a mirror with the precision of an astronomical telescope, a light source and a high-resolution camera.

About the »BauhausUniVisor«

The »BauhausUniVisor« that was tested has ergonomic advantages over a mask: breathing is not restricted (this is particularly important for individuals with pre-existing medical conditions), facial expressions are still visible (and social interaction thus preserved), wearers do not need to touch their faces to correct any slippage, glasses do not fog, and there is no increase in sweating (and consequently also no moisture formation on the skin or in the mouth area). These advantages should boost and make it easier for people to adopt hygiene precautions in their daily life.