Table 1.

The main measured parameters of the experimental studies on the characterization of human exhaled airflow

Measurement techniques		Article	Main findings					No. of subjects
			Measured parameters	Breathing	Coughing	Sneezing	Speaking
Global flow field	High‐speed visualization	Bourouiba et al 20	Duration (ms)		300	200		1
			Re		10 000	40 000
			Entrainment coef. (jet phase)		0.24 ± 0.02	0.13 ± 0.02
			Entrainment coef. (puff phase)		0.132 ± 0.06	0.055 ± 0.01
		Gupta et al 15	Nose opening area (cm2)	F: 1.16 ± 0.67 M: 1.20 ± 0.52				5
			Mouth opening area (cm2)	F: 0.56 ± 0.10 M: 0.71 ± 0.23			F: 1.80 ± 0.03 M: 1.80 ± 0.03
		Gupta et al 14	Mouth opening area (cm2)		F: 3.37 ± 1.40 M: 4.00 ± 0.95			5
	Schlieren photography	Xu et al 16	Propagation velocity (m/s)	Mouth: M: 0.2‐0.6
				F: 0.3‐0.8
		Tang et al 23	Propagation distance (m)	Nose: 0.60	0.7	0.6		20
				Mouth: 0.80
			Propagation velocity (m/s)	Nose: 1.40	5	4.5
				Mouth 1.30
			Propagation area (m2)	Nose: 0.11	0.2	0.2
				Mouth: 0.18
			Area expansion rate (m2/s)	Nose only: 0.16	1.5	2
				Mouth only: 0.17
		Tang et al 18	Propagation distance (m)		F: 0.16‐0.55 M: 0.31‐0.64			20
			Propagation velocity (m/s)		F: 2.20‐5.00 M: 3.20‐14.00
			Propagation area (m2)		F: 0.01‐0.11 M: 0.04‐0.14
			Area expansion rate (m2/s)		F: 0.15‐0.55 M: 0.25‐1.40
	Schlieren PIV’ velocimetry	Tang et al 18	Maximum air speed (m/s)		8.00			16
	Particle image velocimetry	Savory et al 28	Average of the spatially averaged maximum velocity after 1 m from mouth (m/s)		0.41			12
		Kwon et al 19	Average initial velocity (m/s)		M: 15.30		M: 4.07	26
					F: 10.60		F: 2.31
		VanSciver et al 25	Maximum velocity range (m/s)		1.15‐28.8			29
			Average max. velocity (m/s)		10.2 ± 6.7
			Location of max. velocity (mm)		67.8 ± 78
			Median velocity (m/s)		8.1
			Jet width at 50 mm from mouth (mm)		35.8 ± 27.9
		Chao et al 27	Maximum air velocity (m/s)		M: 13.2 F: 10.2		M: 4.6 F: 3.6	11
			Average initial air velocity (m/s)		10.2		3.9
		Zhu et al 26	Initial velocity (m/s)		11.2			3
Pointwise measurement		Xu et al 16	Thermal plume (m/s)	0.23				18
			Velocity at 3 mm from nose in standing position (m/s)	F: 1.63 M: 1.08
			Velocity at 3 mm from nose in Lying position (m/s)	F: 1.52 M: 1.82
			Centerline velocity (m/s)	Decay of centerline see Equation 1
			Exhaled air temperature (°C)	36‐32
		Xu et al 34	Relative humidity	80%				22
			Mean peak velocity at 3 mm from mouth (m/s)	F: 1.03 ± 0.51
				M: 0.81 ± 0.4
			Propagation distance (m)	0.3
			Turbulence intensity at 3 mm from mouth	41 ± 5%
		Gupta et al 15	Change of airflow rate over time (L/s)	Sine function			1.6	25
		Gupta et al 14	Change of airflow rate over time (L/s)		Combination of gamma probability distribution functions			25

Abbreviations: F, female; M, male.