Study of the Human Breathing Flow Profile with Three Different

Ventilation Strategies

Inés OlmedoPeter 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

From nose

From mouth

No ventilation

Displacement ventilation

Mixing ventilation

2.5 seconds after exhalation

Measurements by Li Liu, HKU

Semianalytical ExpressionThe flow is partly a vortex ring, and partly an instantaneously turbulent jet

It appears earlier that the peakvelocity ux in the flow can be given by:

HUMAN EXHALATION FLOW

• Centre line velocities and concentration for a free jet

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 mouthc0, u0: peak values of the velocity and mean concentration at the mouth Kexp, Kc: proportionality constantsn1, n2: exponents

1

exp

n

oo

x

axK

uu

⋅=

2n

oc

Ro

Rx

axK

cccc

⋅=

−−

2

(1) (2)

• Velocity values at the mouth

Max velocity (u0): 4.74 m/s

Max mean value of concentration (c0): 6687 ppm

MEASUREMENTS

MEASUREMENTS

RESULTS• Centre line of the exhalation flow

DiscussionThe 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

Displacement Mixing Without ventilation

Kexp 7.5 4.48 4.50

Kc 10.76 6.30 8.45

n1 -0.64 -0.68 -0.66

n2 -0.63 -0.69 -0.43

• Proportionality constants of equations (1) and (2)

RESULTS

• Graphical representation of equations (1) and (2)

Discussion

Ro

Rx

o

x

cccc

uu

−−~

The identity between dimensionless velocity and dimensionlessconcentration is obvious from equations (1) and (2)

Earlier measurements show that coughing can be described with a similarequation 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!