Study of the
Human Breathing
Flow Profile with
Three Different
Ventilation
Strategies
Inés Olmedo
Peter V. Nielsen
Manuel Ruiz de Adana
STUDY OF THE HUMAN BREATHING EXHALATION
• Full scale test room
• Thermal manikin with breathing function
• Two ventilation distribution systems
• Without ventilation
TEST ROOM AND MANIKIN
• Test room dimensions: 4.1 m x 3.2 m x 2.7m
• Thermal load of the manikin: 94W
BREATHING PARAMETERS
•Exhalation through the
mouth
•Inhalation through the
nose
•Exhalation rate: 11 l/min
(0.75 l/exhalation)
•Exhalation temperature:
34oC
Breathing – Smoke experiment
2.5 seconds after exhalation
No
ventilation
Displacement
ventilation
Mixing
ventilation
From mouth
From nose
Measurements by Li Liu, HKU
Semianalytical Expression
The flow is partly a vortex ring, and partly an instantaneously turbulent jet
It appears earlier
that the peak
velocity ux in the
flow can be given by:
HUMAN EXHALATION FLOW
• Centre line velocities and concentration for a free jet
 x 
ux

= K exp ⋅ 
 a 
uo
 o
 x 
cx − cR

= Kc ⋅ 
 a 
co − c R
 o
n1
(1)
n2
(2)
2
a0: area of the mouth (123 mm )
x: horizontal distance (m)
ux, cx: peak values of the velocity and mean concentration at a
distance x from the mouth
c0, u0: peak values of the velocity and mean concentration at the
mouth
Kexp, Kc: proportionality constants
n1, n2: exponents
MEASUREMENTS
• Velocity values at the mouth
Max velocity (u0):
4.74 m/s
Max mean value of
concentration (c0):
6687 ppm
MEASUREMENTS
RESULTS
• Centre line of the exhalation flow
Discussion
The influence of the ventilation system on the exhalation flow is especially
the effect of the surrounding temperature and vertical temperature gradient
The exhalation temperature of 34 oC generates the upward direction of the flow.
The level of the exhalation temperature is partly a compensation for the effect
of humidity
The entrainment is probably reduced in the displacement flow because of a
vertical temperature gradient
RESULTS
• Proportionality constants of equations (1) and (2)
Displacement
Mixing
7.5
4.48
Without
ventilation
4.50
Kc
10.76
6.30
8.45
n1
-0.64
-0.68
-0.66
n2
-0.63
-0.69
-0.43
Kexp
RESULTS
• Graphical representation of equations (1) and (2)
Discussion
The identity between dimensionless velocity and dimensionless
concentration is obvious from equations (1) and (2)
u x c x − cR
~
uo co − cR
Earlier measurements show that coughing can be described with a similar
equation with Kexp ~ 7.4, (Nielsen et al. 2009)
The coughing will therefore be dissolved like breathing, and only the level
of initial realise of bacteria or viruses and the ability of a cough to
penetrate a long distance are an important problem
THANK YOU!