Table 3.

Experimental results in human airflows

Authors	Type of human airflow	Metrology	Experimental method					Main results
(Duguid 1946)	Coughing, sneezing and Speaking	Microscope	Dye is introduced into the mouth Eosin or fluorescein powder is applied to the surfaces of the mouth, fauces and tip of the tongue The surface of a celluloid slide was targeted by the droplet-spray; Slide to mouth distance is 3 in. for speaking case, and 6 in. for coughing and sneezing cases A microscope is used to estimate droplet’s size					Ddiameters of droplets are between 2 and 100 $\mu m$
(Mahajan et al. 1994)	Coughing	Pneumotachograph "tusso-meter"	The pneumotachograph system consists of a mesh where the human is subjected to cough A rotameter is used to obtain the pressure differential of the air flow across the mesh Rotameter for air flows: (series tube size 47 k, Rotameter Manufacturing Co. Ltd, Croydon, England) up to 1100 L min−1					Significant correlations between the peak flow and the time engaged to complete this
(Papineni and Rosenthal, 1997)	Breathing, Coughing and Talking	Exhaled droplets are measured using a OPC (optical particle counter) and a AEM (analytical transmission electron microscope)						A majority of droplets were less than 1 μm

Authors	Type of human airflow	Metrology	Experimental method					Main results
			Illumination system	Image recording device	Samples	Tracer particles	Scale
[111]	Coughing in calm indoor environment	2D PIV	Plused Nd:YAG laser of New Wave (50 mJ/pulse, 15 Hz)	Kodac ES1.0, with the Nikon Micro lens of 60 mm (35 mm, F ¼ 5.6)	Time between recordings: 70 ms Time between laser pulses: 0.05 ms	Human droplets	Chamber (1.8 m × 1.8mx1.8 m) Size of field: 100 mm × 100 mm	Gravity effects is negligible on particles which diameters are less than 30 $\mu m$ Particles of 50–200 $\mu m$ in diameter are considerably induced by the gravity field Particles of more than 300 $\mu m$ in diameter are more affected by inertia than gravity
[103]	Coughing, Talking	Water-sensitive paper (WSP) and Microscope glass slides	WSP is covered by yellow paper that change in blue when reached by droplets of water					Respiratory droplet sizes and numbers The glass slide technique without food dye demonstrate significant potential

Authors	Type of human airflow	Metrology	Experimental method					Main results
			Illumination system	Image recording device	Samples	Tracer particles	Scale
(Chao et al., 2009)	Coughing, speaking	InterferometricMie Imaging	PulsedNd:YAG laser at 532 nm wavelength 30 mJ with a pulse width of 3–5 ns Thickness of laser sheet: about 1 mm	CCD camera (LaVision, ImagerIntense) Macrolens (Zeiss Makro-Planar T ∗ 2.8/100)	Resolution of 1376 × 1040 pixels A maximum framerate of 10/s	Transparent droplets	8.9 mm × 6.7 mm (W × H)	The average velocity of coughing is: 11.7 m/s (with a droplet size equal to 13.5 μm) 3.9 m/s for speaking (with a droplet size equal to 16 μm)
		2D PIV	PulsedNd:YAG laser at 532 nm wavelength 30 mJ with a pulse width of 3–5 ns Thickness of laser sheet: about 1 mm	CCD camera (LaVision, ImagerIntense) Lens(Nikkor50mm/f1.8D) with a 532 nm optical filter	Frequency of 5 pairs/s	LaVision, Aerosol Generator by means of a saline solution	5 mm × 60 mm (W × H)
[38]	Coughing	Spirometer + Photography	It is based on capillary tubes which provide the flowrate thanks to the to the measure of the pressure drop The cough flow rates are measured with a sampling rate of 330 Hz Moderate-speed photography at arate of 120 Hz The resolution is 1 Mega Pixel The smoke of a cigarette is employed to seed the fluid (particle size: 0.2$\mu m$)					The obtained flow rate could be represnted by gamma-probability-distribution functions Two succesive single coughs could represent a sequential cough
(Gupta et al., 2010)	Breathing and Talking	Spirometer to measure the flow rates	A spirometer is employed to obtain the flow rates at a sampling rate of 330 Hz The flow is snapped using moderate speed photography at 120 Hz The smoke of a cigarette is employed to seed the fluid The mouth opening areas are obtained thanks to the photography technic at 120 Hz					A sinusoidal function can represent the flow rates over time in case of breathing

Authors	Type of human airflow	Metrology	Experimental method					Main results
			Illumination system	Image recording device	Samples	Tracer particles	Scale
(VanSciver et al., 2011)	Coughing and Breathing	2D PIV	120 mJ Nd:YAG laser Wavelength of 532 nm Spherical lens f = 1000 mm Sheet thickness = 0.15 mm 117 mJ/pulse	TSI PIVCam 138 Model 630,047 camera Resolution: 1 K × 1 K Nikkor 60 mm focal length lens	Pulse separation time of 100 μs Image pair recorded each 0.267 s	Theatrical fog 1 μm in diameter	Enclosure of 120 cm in length, 76 cm in width, and 67 cm height	The cough impinge on the wall at a speed of 10 m/s The average velocity ranged from 1.15 to 28.8 m/s The average of overall maximum coughing velocity is 10.2 m/s
[84]	Coughing, Sneezing	Schlieren and Shadowgraph Imaging	Schlieren imaging technique based on refraction of light through a medium of different densities, A large astronomical telescope quality, having a diameter of 1 m and a radius of curvature equal to 10 m and a focal length of 5 m					Maximum propagation distance: 0.31–0.64 m for males and 0.16–0.55 m for females Maximum velocity: 3.2–14 m/s for males and 2.2–5.0 m/s for females Maximum 2-D area: 0.04–0.14 m2 for males and 0.010–0.11 m2 for females Maximum expansion rate: 0.25–1.4 m2/s for males and 0.15–0.55 m2/s for females

Authors	Type of human airflow	Metrology	Experimental method			Main results
			Illumination system	Image recording device	Samples
[85]	Sneezing and breathing	Shadowgraph imaging technique	Light beam generated by an LED light source placed at 10 m from the mirror	High-speed camera (Photron SA1.1, Dynamic Analysis System, Pte Ltd, Singapore) 1-m diameter, spherical, concave, f/5 mirror of astronomical reflector telescope quality (Cosmo Optics Inc., Middletown, NY)	500 Hz is case of breathing, and 2000 Hz in case of sneezing	The maximum distance travelled bu the flow was 0.6 m The maximum sneeze velocity was 4.5 m/s

Authors	Type of human airflow	Metrology	Experimental method					Main results
			Illumination system	Image recording device	Samples	Tracer particles	Scale
(Feng et al., 2015)	Breathing	2D PIV	Pegasus double-cavity Nd:YLF Laser Energy = 10 mJ Wavelength = 532 nm Sheet thickness = 0.5 mm	Dantec NanoSense MK III camera with a resolution of 1280 1024 pixels	3000 image pair at a sampling rate of 10 Hz	Theatrical fog 1 $\mu m$ in diameter	Measurement area: 103.9 mm × 83.1 mm	The entire process of breathing was described with quantitative data what could be used for validation data for CFD simulations

Authors	Type of human airflow	Metrology	Experimental method				Main results
			Illumination system	Image recording device	Samples	Tracer particles
[8]	Coughing, sneezing	Visualization	Light	High-speed imaging Cameras Phantom	Recording rate: 1000–4000 Hz Phantom high-speed video	Smoke generator	Underlined the multiphase dynamics of human airflows

Authors	Type of human airflow	Metrology	Experimental method			Main results
			Illumination system	Image recording device	Samples
[70, 74]	Sneezing and Coughing	High-speed videography	Liht	Monochrome cameras	1000 to 8000 fps	Observe the fluid fragmentation at the exit of the mouths

Authors	Type of human airflow	Metrology	Experimental method						Main results
			Illumination system	Image recording device	Samples	Tracer particles	Scale
[98, 102]	Coughing	2D PIV	3 W DPSS 532 nm laser projector (Ourslux Lighting Technology Co, Ltd) Sheet thickness = 3 mm	Canon 6D camera (24–105 mm focal lens)	50 frames per second	Glass beads (ρ = 2480 kg/m3) Three sizes: small (30–50 μm, Polysciences Inc., category no 18901–100), medium (210–250 μm, 18,902–100) and large (355–420 μm, 18,905– 100)	Water tank 1.5 m (length)  × 1 m (width)  × 1.2 m (height) in dimen- sion		Exit velocity profiles had negligible effect on the penetration Penetration distances ranged from 50.6–85.5D range The leading vortex had a strong impact in improving the droplets’ spread
(Zhang et al., 2019)	Coughing, breathing	Thermal manikin + Particles concentration	Aerosol generation device: Model 7388AGS Aerosol and Particle Technologies (size between 0.1 and 10 μm), The solute is: colorless, odorless and non-toxic Diisooctyl sebacate (DEHS), density = 914 kgm−3 The solvent is: isopropanol (C3H8O) with a mass fraction of 60% for the solute The ejection of aerosols take place from the nose of the manikin with a speed of 2.2 ± 0.1 m.s−1 in average The 1 μm aerosols concentration is monitored via TSI- Model 8530 monitors						Validation of CFD model

Authors	Type of human airflow	Metrology	Experimental method					Main results
			Illumination system	Image recording device	Samples	Tracer particles	Scale
[28]	Coughing	2D PIV	120 mJ / pulse, 532-nm Nd:YAG laser Sheet thickness = 1 mm	CCD Camera at a sampling rate of 15 Hz	Δt = 100 μs between two successive images Laser pulse delay: 400 μs PIV exposure times: 405 μs	Aerosolized titanium dioxide (TiO2) particles (Size between 0.15 and 0.47 μm)—69% of particles are between 0.34 and 0.43 μm)	Chamber of a 1.81 m × 1.81 m × 1.78 m enclosure	Validation of computational Fluid dynamics (CFD) models At the jet center, an average peak velocity of 1.2 m/s at an average jet spread angle of θ = 24° is obtained
		Hot-wire anemometry (HWA)	CTA unit, tungsten wire of 1.25 mm in length abd 5 μm in diameter Voltage measurements at 1 kHz

Authors	Type of human airflow	Metrology	Experimental method			Main results
			Illumination system	Image recording device	Samples
(Bahl et al., 2020)	Sneezing	PTV	Halogen light source Light sheet, A 5 mm wide and 80 mm long Sheet thickness of 25 ± 2 mm	High-speed monochrome camera (nac MEMRECAM HX-7 s)	Resolution of 1920 × 1080 pixels and a frame rate of 1500 frames-per-sec (fps)	- Less than 1% of ejected particles had velocities above 10 m/s − 80% of droplets had velocities below 5 m/s