inhalability of micron particles through the nose and

7/31/2019 Inhalability of Micron Particles Through the Nose And

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Introduction

Inhalation o toxic airborne contaminants such as asbes-tos, acid mist, smoke, and diesel umes is a requentoccurrence or those working in the manuacturing andprocessing industries. In more recent times, the outbreako viruses (SARS [severe acute respiratory syndrome],equine lu, swine lu, bird lu) is a consequence o thetransportation o viral particles ound in the airstreams.Although viruses usually exist on a nano scale, they areusually transported with water molecules rom sneezingor coughing. he impact o inhaling such inected water-

based particles has led to chaotic situations in 2004 orthe outbreak o SARS and 2009 o the swine lu. Airborneparticles enter the body through the nose or mouth, lead-ing to deposition within the respiratory system, whichin turn has many potential health risks. he respiratorysystem has its own physiological deensive reactionsto the presence o airborne particulates. For example,

high biurcation angles in the lung airways, mucocili-ary action in ciliated wall regions that trap and removethe particles, and 90 curvatures in the airway geometryound at the nostril inlet, at the nasopharynx, and at theoropharynx. Despite these natural deences, airborneparticulates, especially low-Stokes-numbered particlesand nano-scaled particles, oten become entrained inthe airlow and deposit deep into the respiratory system,causing serious health problems. Studies o deposition inthe respiratory system have been previously studied bythe authors (Inthavong et al., 2008a, 2008b), among other

researchers (Balashazy et al., 2003; Crowder et al., 2002;Kleinstreuer & Zhang 2003). hese studies were exclu-sively limited to the internal respiratory system (noseand lung airways).

In contrast, micron particles tend to deposit in thenasal cavity. Deposition eciency in the nasal cavityunder dierent inhalation ow rates has been extensively

(Received 30 July 2009; revised 27 August 2009; accepted 28 August 2009)

ISSN 0895-8378 print/ISSN 1091-7691 online 2010 Inorma UK Ltd

DOI: 10.3109/08958370903295204 http://www.inormahealthcare.com/iht

R E S E A R C H A R T I C L E

Inhalability of micron particles through the nose and

mouthCamby Mei King Se, Kiao Inthavong, and Jiyuan u

School of Aerospace, Mechanical and Manufacturing Engineering, RMIT University, Bundoora, Victoria, Australia

AbstractAspiration eciencies rom nose and mouth inhalations are investigated at low and high inhalation rates byusing the commercial Computational Fluid Dynamics (CFD) sotware CFX 11. A realistic human head with detailedacial eatures was constructed. Facial eatures were matched to represent the 50th percentile o a human male,aged between 20 and 65 years old, based on anthropometric data. The constant reestream velocity was 0.2 ms1,

normal to the ace, and inhalation rates through the mouth and nose were 15 liters per minute (LPM) or lightbreathing and 40 LPM or heavy breathing. It was ound that the ow feld in the near breathing region exhib-ited vertical direction caused by the presence o the torso where the airstream diverges as it ows around andover the body. The critical area concept was used as a tool to determine the aspiration eciency o particles.Comparisons between critical areas or the nose and mouth inhalations show similar geometric properties suchas the areas shape, and its vertical distance location on the x-zplane located aty= 80 cm upstream. The criticalarea sizes were ound to be slightly larger or the mouth inhalation mainly due to the larger mouth area and alsothe aligned orientation o the mouth to the upstream ow, whereas the nose is perpendicular to the upstreamow. This study was undertaken to establish the ow feld in the near breathing region that will help to charac-terize the ow and particle feld or initial boundary conditions leading to a more holistic modeling approach orespiration through the internal nasal cavity and mouth.

Keywords: Aspiration eciency; computational fuid dynamics; particle inhalability

Inhalation Toxicology, 2010; 22(4): 287300

Address for Correspondence: Pro. Jiyuan u, School o Aerospace, Mechanical and Manuacturing Engineering, RMI University, PO Box 71, Bundoora Vic 3083,Australia. el: +61-3-9925 6191; Fax: +61-3-9925 6108; E-mail:[email protected]
mailto:[email protected]:[email protected]


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288 C. M. K. Se et al.

investigated (Inthavong, 2006; Inthavong et al., 2006,2009b; Shi et al., 2008; Guilmette et al., 1994; Zwartz &Guilmette 2001). However, external conditions, such asairow feld, and particle inhalability were not consid-ered in any particular detail. For example, the inhalationo wood dust through the nasal cavity was simulated (ianet al., 2007) by injecting particles rom a particle size dis-

tribution defned rom settled particles on the ground(Chung et al., 2000) rather than a particle size distribution(PSD) suspended in the breathing region o the worker.With this consideration, the inhalable PSD can be defnedthat presents a more realistic initial boundary conditionor uture deposition studies in the respiratory system.Applying such experimental PSD neglects the impact oinhalation and the surrounding reestream airow onparticle inhalation through the mouth or nose. Troughan integrated modeling approach presented in this study,the results will contribute towards a more realistic modelor inhalation and toxicological studies.

Tereore in this study, Computational Fluid Dynamics(CFD) modeling is used to visualize and compare theeects o nose and mouth inhalations o airborne particles.Te inhalability o airborne particles rom a contaminantsource upstream is evaluated to determine the risk itcan pose to a person exposed to the particles. A three-dimensional humanoid was created with emphasis onrealistic acial eatures that included detailed mouth andnose. A holistic approach incorporating the external envi-ronment such as the ow feld and contaminant source,coupled with human actors that include the humanoidbody shape, acial eatures, and inhalation through the noseand mouth, are considered. Results such as the aspiration

eciency can be quantifed, which provides the basis oinitial boundary conditions or internal nasal cavity andlung airway particle deposition studies.

Aspiration eciency

Particle inhalability or aspiration eciency has been meas-ured as the raction o particles that are inhaled throughthe nose or mouth during breathing (Vincent, 1999). Basedon the experimental studies byVincent and Mark (1982),Ogden and Birkett (1977), and Armbruster and Breuer(1982), a sampling criterion or the Inhalable ParticulateMatter (IPM) o orientation-averaged mouth inhalation

and wind speed o 0.4 ms

1

or below was developed:

(1)

where dae

is the aerodynamic diameter o the particle. Teinhalability measurements made by Ogden and Birkett(1977) and Armbruster and Breuer (1982) used a manne-quin head with inhalation only, whereas those made byVincent and Mark (1982) used a mannequin that inhaledthrough the mouth and exhaled through the nose.Comparisons o these results do not show any detect-able dierences in the results that can be attributed to the

exhalation pattern. It is important to note that the IPMcurve is limited to wind velocities between 1 and 4 m/s, par-ticles with aerodynamic diameters no larger than 100 m(due to the requirement o maintaining uniorm concentra-tions o large aerosols), orientation averaged, and or mouthinhalation only. Tese limitations make the IPM curve lackgenerality and does not allow or direct applications to

dierent conditions such as the nasal breathing or lowerenvironmental wind speeds. Te diculties in obtaining auniorm suspension o large particles at low velocities, andthe costs associated with experimental studies perormedin large wind tunnels have lead to CFD simulations as analternative. Early studies began with simple geometricshapes acting as surrogates or the human body. For exam-ple Ingham and Hildyard (1991) used an infnitely long cyl-inder to represent the body, Erdal and Esmen (1995) useda hemispherical top or the head placed on a cylinder thatrepresented the body, and Hyun and Kleinstreuer (2001)used a sphere as the head o mannequin. In all cases, an

oval opening was used to represent the mouth o the sur-rogate bodies. Studies byAnthony et al. (2005) ound thatusing simplifed body and acial eatures was inadequate.In their study, a mannequin with detailed acial eatureswas compared with a cylindrical human orm having anoval opening or the mouth. It was ound that a cylindri-cal orm inhaled more particles through the mouth whencompared to an adult-size mannequin, particularly oracing-the-wind orientation. Inhalation through the nosewas not studied. It was also ound that the aspiration e-ciency decreased due to the projection o the anatomicalmannequins acial eatures in ront o the mouth opening.Facial eatures resulted in a reduction o the horizontal

velocity upstream rom the nose, although this was limitedto 10 mm in ront o the nose tip. Similar fndings were alsoobtained in a study on an child-size mannequin under-taken byHeist et al. (2003).

Methods

Geometric modeling

In this study, a realistic human head was generated as anIGES fle rom FaceGEN Modeller (Singularity InversionInc., 2007) sotware, based on photographic images takenrom a male volunteer. Te three-dimensional (3D) head

contained detailed acial eatures, such as shaped eyes,nose, mouth, and ears. Te IGES fle contained the suraceand volume inormation, which was then exported intoICEM CFD (Ansys Inc., 2007) or CFD mesh construction(Figure 1). Slight modifcations were made to the compu-tational model where possible, to allow the model dimen-sions to represent the 50th percentile o a human male,aged between 20 and 65 years old, based on anthropomet-ric data oilley (1993) (see able 1). Te opening o themouth has maximum dimensions o 2 cm wide and 0.5 cmhigh, resulting in a total area o 5.49 cm2, which compares

with 2.2 cm2 in Dunnet and Ingham (1988) and 7.1 cm2 inHsu and Switt (1999).


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exertion in the workplace environment, respectively(Snyer, 1975). Assuming inhalation and exhalation timesare shared equally during an inhalation cycle, these two

inhalation rates correspond to tidal volumes o about 500and 1200 L, respectively.

Te inlet velocity corresponds to Reinlet

= 16,433 at theinlet. Te modeling assumptions applied or the CFD sim-ulations include ully turbulent isothermal, incompress-ible ow. Te isothermal assumption was used to allowdirect velocity profle comparisons with the experimentaldata oAnthony et al. (2005), which used a mannequinwithout any heat ux. Te k- turbulence model, which isa robust, low computational cost model, has been widelyused in 3D simulations o personal exposure to contami-nant sources in ventilated rooms (Brohus & Nielsen, 1996;Brohus, 1997; Zhu et al., 2005). However, the standardk- model is a poor predictor o ow separation (Durbin,1995). Te Re-Normalisation Group (RNG) k- modelused in Hyun and Kleinstreuer (2001) and Bird (2005) orthe simulation o inhaled indoor pollutants is also used inthis study. In addition, reported results have shown muchbetter ow separation and reattachment or the RNG k-model (Speziale & Tangam, 1992), which is an expectedow eature o the ow passing over the head.

Te steady, incompressible turbulent Navier-Stokesequations were used to model the airow. Te continuityand momentum equations are given in Equations (2) and(3), respectively.

(2)

(3)

wheret=ck2/ and ij is the Kronecker delta, ij = 1 ii=jand

ij= 0 iij.

Te RNG k- model equations can be cast in Equation (4)and (5).

(4)

(5)

where P U U U U U k

c

k t

T

t kb= + ( ) ( ) + +

=

m m r

sm

2

33

0 09

P

. , kk RNG RNG

RMG

C

C

= = =

=

1 00 1 30 1 92

1 42

2

1

. . .

.

, , ,

, in which

se e

e hf

ffP

CRNG

k

RNG

h

hm

hh

bh

r e=

+( )=

14 38

1 3

.and

o resolve the boundary layer in the near wall regions, theScalable Wall Function (Menter & Esch 2001) was used. Teuid ow equations (Equations 25) were solved in ANSYSCFX v11.0 using a segregated solver with an implicit ormu-lation. Te pressure-velocity coupling was resolved by theSIMPLEC algorithm. Te convective terms o the transportequations were all discretised using second-order-upwindscheme in order to obtain suciently accurate solutions. Inaddition, the residual values o the governing equations andthe transport equations were all set to converge at 10 5 orbelow or all simulation cases.

Particle phase modeling

Individual representative particles are tracked sepa-

rately through the ow feld in a Lagrangian approach.Te equation o motion or each particle is given inEquation (6):

(6)

where mip is the mass o particle, m d

P P P=

pr

6

3 , andAF

is theeective cross section.

Te drag orce acting on the particle, FD, is given by

(7)

Table 2. Dynamic similarity matching or the present study with the

study oAnthony et al. (2005).

Dimension Anthony et al. (2005) Present study

Refreestream

1909 1909

Characteristic length (cm)

(head hydraulic diameter)

9.6 14.0

Vfree

(ms1) 0.30 0.20

Reinhale 1590 1590Characteristic length (cm)

(mouth equivalent diameter)

8.87 9.87

Mouth area (cm2) 0.618 104 5.49 104

Inhalation velocity (ms1) 2.700 1.816

Table 3. Inhaling mass ow rate or each scenario.

Nasal inhalation* Oral inhalation

15 LPM 40 LPM 15 LPM 40 LPM

Inhaling mass

ow rate

(E-4 m3s1)

4.97 13.33 4.97 13.33

*Assume the inhalation velocity through each nostril shares equally.

Table 4. Aspiration eciency or various inhalation rates against

diferent particle sizes.

Inhalation

Aspiration eciency, AE

1m 5m 10m 20m 40m 80m 140m

Nasal 15 LPM 0.86 0.81 0.80 0.78 0.77 0.70 0.00

40 LPM 0.85 0.83 0.82 0.81 0.78 0.62 0.00

Oral 15 LPM 0.89 0.89 0.89 0.88 0.88 0.80 0.00

40 LPM 0.92 0.91 0.87 0.83 0.83 0.78 0.00


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Inhalability of micron particles 291

whereas the buoyancy orce due to gravity, FB

, is given as

(8)

where UF, U

P,

F, and

Pare uid (air) velocity, particle

velocity, uid density, and particle density, respectively.Te drag coecient, C

D, is evaluated rom an

experimental-ftted expression given by Schiller andNaumann (1933) in Equation (9), which considered the lim-iting behavior in the inertial regime.

CD p= +( )

maxRe

. Re , ..24

1 0 15 0 440 687 (9)

where the Reynolds number o particle is defned asEquation (10)

(10)

Te new particle velocity is then calculated by usingEquation (11), which is the analytical solution toEquation (6).

u u u ut

Ft

p fluid p

old

fluid

p

T

p

= + +( )

+

exp

exp

d

t

td

t1

(11)

where p

=pd2

p/18

g, which is the particle relaxation time

and F is the total orce.Te particle displacement is calculated using orward

Euler integration in Equation (10), o the particle velocityupi

old , over a timestep t.

(12)

In the orward integration, the particle velocity calculated atthe start o the timestep is assumed to prevail over the entirestep. At the end o the timestep, the new particle velocity istaken rom Equation (11).

One-way coupling is assumed between the air and par-ticle ow felds and the interaction between particles isalso neglected because the particle ow is dilute (i.e., thevolume raction o the particles is less than 10%). S

iis the

additional orces that may include the rotation orce, pres-sure gradient orce, virtual mass eect, and Basset orce.Contaminant aerosols in the micron size range such asacid mist, asbestos, and wood dust are typically ar denserthan air, causing terms that depend on the density ratio,such as those in S

i, to be negligibly small. Te turbulent

dispersion o the particle tracking is modeled through theeddy interaction model where the particle is assumed tobe always within a single turbulent eddy and each eddyhas a characteristic uctuating velocityu

P, lietime

eand

length le. Te uctuating velocity or that eddy is added

to the local mean uid velocity in Equation (11) to obtainthe instantaneous uid velocity. Te turbulence scales aredefned as

(13)

(14)

(15)

where is a normally distributed random number, and kis the local turbulent kinetic energy. Further details o themodel is ound in the ANSYS CFX documentation (AnsysInc., 2006).

Inhalability and critical area

Te aspiration eciency is defned as the ratio o the inhaledparticle concentration (C) to the ambient reestream particleconcentration (C

o)

(16)

Te inhaled concentration, C, can be expressed as thenumber o particles inhaled (N

n) per volume,A

nV

nt,

(17)

whereAn

is the inhalation area, Vn

is the average inhalationvelocity, and tis the time.

Experimental and numerical studies assume a uniormparticle concentration upstream o the humanoid, becausethe velocity feld is unaected by the presence o the per-son. Over any upstream cross-sectional area, the particleconcentration is the ratio o the number o particles inthe reestream, N

C, to the volume o air through the cross-

sectional area, which is the product o the cross-sectionalarea (A

C), the average velocity through the cross-section

(VC), and time (t):

(18)

Te aspiration eciency is evaluated based on the particlesthat are actually inhaled, which obviates the need simulateparticle releases that are uniormly distributed across theentire inlet. Te original locations o the inhaled particlescan be determined by looking up the particle statisticsrom the Lagrangian tracking. A map can then be createdon the release (x-zplane at y = 80 cm) showing only theparticles that are inhaled, and the enclosed region ormsthe cross-sectional area A

C. A

Cis termed the critical area

in Anthony and Flynn (2006b), which represents a region


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o inhalable particles upstream rom the humanoid. Byapplying the critical area concept N

C = N

n, the aspiration

eciency becomes

(19)

Grid and particle number independence

Te generated mesh surrounding the body was graduallymade coarse toward the surrounding walls. Grid refne-ments at suraces, and the level o coarsening towardsthe walls, were changed to increase the number o cellsin the model. Tree dierent models o 480,000, 1.2 mil-lion, and 2.6 million cells were created and tested or gridindependence through velocity profles taken along a lineat x = 0 cm, y = 1.7 cm, upstream o the mouth in the x-zplane, which cuts through the centerline o the humanoid(Figure 3). Te grid was considered converged or 1.2 mil-lion cells where velocities along a profle exhibited


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show the larger streamtubes or the inhalation rate o 40LPM, which are apparent rom the increase in the criticalinhalation areas ound in Figure 7. he entrained 1-mparticle ollows the liting upstream low ield where thelocation o the critical area is below the mouth in the ver-tical direction. Particles within the inhaled streamtubes

approaching the mouth are accelerated and depart romthe low ield due to the mouth inhalation, eventuallyexiting through the mouth. he particle sizes o 80 and140 m, which are signiicantly aected by gravitationalsettling, show trajectories originating much higher verti-cally in relation to the mouth. he trajectory o the parti-cles is linear until they reach the mouth inhalation whereacceleration towards the mouth occurs. his linearitymeans that the location o the critical area or large par-ticles can be easily identiied or a given upstream dis-tance. he urther upstream the distance, the higher thevertical distance needs to be or the particles to descendtowards the mouth. Particles that lay just outside o the

streamtubes that did not get inhaled were impacted onthe ace and their trajectory ceased. hereore any parti-cle bounce that may occur with solid particulates was notconsidered in this study.

Critical areas and particle inhalation

Te inhalability o particles with aerodynamic diameterso 1, 5, 10, 20, 40, and 80m released 80 cm upstream othe humanoid were studied in a acing-the-wind scenario.Tere were our cases that involved nasal and oral inhala-tion or the two inhalation rates o 15 and 40 LPM.

Figure 7 and Figure 8 show critical areas or all theparticles on one graph, which was only possible by com-pressing the Vertical Distance (cm) axis. It can be seenor all cases that gravitational settling becomes dominantor 40- and 80-m particles, where the critical areas arelocated above the mouth position o z = 0 cm. In con-trast, the vertical distances or the 110-m particlesare ound at similar locations at 0 < z < 15 cm, which is

(a)

3

2.5

2

1.5

Vertical

Distance(cm)

10.5

0

0.5

1

1.5

2

2.5

3

5 4 3

Horizontal Distance (cm)

2 1.5 1

(b)

3

2.5

2

1.5

VerticalDistance(cm)

1

0.5

0

0.5

1

1.5

2

2.5

3

5 4 3


2 1.5 1

(c)

3

2.5

2

1.5


1

0.5

0

0.5

1

1.5

2

2.5

3

5 4 3


2 1.5 1

Figure 4. Velocity vector plots or (a) CFD oral inhalation and (b) PIV experimental measurements rom Anthony et al. (2005). (c) CFD nasal

inhalation.


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actually below the mouth location. his implies that thesmaller particles are entrained and dependent on the

low ield where the velocity vectors in Figure 4 showan upward low in the near breathing region caused bylow separation as it passes over the humanoid. In thisstudy, there is an absence o any additional ventilationsystem and the acing-the-wind scenario low ield is ahorizontal low deined by the inlet-outlet conditions. Itcan be imagined that in more realistic conditions wherethe low ield may not necessarily be a horizontal low butcontain low-velocity recirculation, low separation, andwake lows, entrained small particles become more haz-ardous as they loat through the open spaces and exhibitlonger residence times. his leads to greater exposureto the harmul particles or the occupant and a greater

reliance on local and general ventilation is needed orsmaller particles. Larger particles become less dangerousbecause inhalation will only occur when the contaminantsource is located above the humanoid, up to z = 70 cmabove the mouth.

Comparisons between critical areas or the nose andmouth inhalations show similar geometric properties suchas the teardrop shape, and its vertical distance location onthe x-zplane located at y = 80 cm upstream. Tis similar-

ity may be attributed to the normalization o inhalationvelocities or the nose and mouth in order to achieve equalvolume ow rates o 15 and 40 LPM. Te critical area sizesare ound to be slightly larger or the mouth inhalation,mainly due to the larger mouth area and also the alignedorientation o the mouth to the upstream ow, whereas thenose is perpendicular to the upstream ow. Te ow felddirectly in the breathing region is inuenced more by thehigher inhalation rate o the nose, but this eect is in turnhindered by the smaller cross-sectional area o the nostrilsand even urther aected by the nostrils perpendicularalignment in relation to the ow feld. Te vertical align-

ment o the nostrils is an anatomical eature o the nose thatcan be thought o as an evolutionary deence mechanismthat reduces the ability to inhale larger diameter airborneparticles.

Comparisons between inhalation rates show anincrease in the critical areas with increasing inhalationrates. Te width o the critical area nearly doubles in size.An increase in the critical area height is also ound butthis is not as signifcant as the width increase, especiallyor the smaller particles where the gravitational settlingis not signifcant. Whereas the trajectory o the particle isderived rom the orce balance in Equation (6), the poten-tial or the particle to be entrained in the ow feld can be

Normalized Velocity()


0 0.2 0.4 0.6 0.8 1 1.2 1.4

Normalized Velocity()

0 0.2 0.4 0.6 0.8 1 1.2 1.4

3

2

1

0

1

2

3


3

2

1

0

1

2

3PIV (1cm)Oral Breathing(1cm)

PIV(1.5cm)

Oral Breathing(1.5cm)

(b)(a)

Figure 5. Velocity between the PIV measurements and the numerical results at (a) y = 1 cm rom the mouth and (b) y = 1.5 cm rom the mouth at the

midsagittal plane (x = 0 cm).

(a) 1 m - 15LPM (b) 18 m - 15LPM

(c) 1 m - 40LPM (d) 80 m - 40LPM

Figure 6. rajectory o inhaled particles released aty= 80 cm upstream

or 1-m and 80-m particles or mouth inhalation.


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determined through the particle Stokes number, which isthe ratio o the particle relaxation time

pto the system

response time s:

(20)

Te increase in inhalation and thereore Uin Equation (20)leads to an increase in the system response time. Tisreduces the particle Stokes number and enhances thelikelihood o the particle to entrain in the inhaled owstreamlines.

Uncompressed critical areas or 1- and 80-m particlesare shown in Figure 9, which reveals the true shape o theupstream inhalable contaminant source. Te two contrast-ing particle sizes are shown to reect the inuence o theparticle Stokes number and gravitational settling underthe higher inhalation rate o 40 LPM. Both critical areas

or 1- and 80-m particles resemble a teardrop shape butopposite in their vertical orientation. For 1-m particles,the critical area is located below the nostril openings atz = 1.5 cm, where the thicker end o the teardrop shapeis at the top. Gravitational settling is insignifcant or the1-m particle and its ight path is dependent on the ow

feld, which is slightly directed upwards as seen in the vec-tor plots oFigure 4. For 80-m particles, the eect o thelow indoor velocity ow feld is less signifcant whereasthe gravitational settling becomes important. As a result,the vertical distance o the critical area is relatively higher,reaching up to z= 70 cm above the mouth opening. Teteardrop shape o the critical area has the thicker endat the bottom where the majority o the particles aretransported across the ow feld 80 cm horizontally and70 cm downwards towards the nostril openings. Withheavier particles, the contaminant source location needsto be even higher or the same horizontal distance awayrom the humanoid. Te authors also simulated 140-m

20

10

0

10

20

30

40

50

60

70

4.0 2.0 0.0 2.0 4.0 4.0 2.0 0.0 2.0 4.0

Horizontal x-axis (cm)

VerticalDistancez-axis(cm)

20

10

0

10

20

30

40

50

60

70



Symbol

1

5

10

20

40

80

Particle(m)

Figure 7. Scaled critical areas or diferent particle sizes or mouth inhalation at (a) 15 LPM and (b) 40 LPM.


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particles to test this idea, which ound that rom thesame release plane, no particles reached the humanoid.Instead, gravitational settling became dominant or the140-m particles, which orced the particles to all to the

ground much earlier. Further testing ound that or inha-lation to occur, the 140-m particles had to be released at

y= 65 cm or approximately fve head diameters upstreamo the humanoid.

20

10

0

10

20

30

40

50

60

70

20

10

0

10

20

30

40

50

60

70

4.0 2.0 0.0 2.0 4.0



4.0 2.0 0.0 2.0 4.0



Symbol

1

5

10

20

40

80

Particle(m)

Figure 8. Scaled critical areas or diferent particle sizes or nose inhalation at (a) 15 LPM and (b) 40 LPM.

54

56

58

60

62

64

66

68

70

72

74

Horizontal Distance(cm)



0 2 4 6 8 10

2

4

6

8

10

12

14

16

1810 8 6 4 2

Horizontal Distance(cm)

0 2 4 6 8 1010 8 6 4 2

0

2

1 m 80 m

Figure 9. Uncompressed critical area o nose inhalation at 40 LPM or particle sizes o 1m and 80m.


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Aspiration eciency

Te aspiration eciency (AE) or acing-the-wind ori-entation or mouth inhalation is given in Figure 10 aswell as able 4, which shows a general decrease o AEwith increasing particle size. Increased inhalation rom15LPM to 40LPM produced an increase in the AE. Te140-m particles were also included but no particles were

inhaled when released rom the upstream distance oy =80 cm at a mouth inhalation rate o 15 LPM. Te resultsare based on the assumption that the particle contami-nant source is within the computational domain verticalheight, which is z = 154 cm above the mouth, and therelease point located at y = 80 cm. I the vertical heightwithin the computational domain was to extend urther,it was thought that the 140-m particles would be ableto achieve some inhalation. Te authors tested shorterupstream distances and ound that no inhalation occurredor the 140-m particles even at a very close distanceoy= 10 cm.

Comparisons o the aspiration eciency are madewith Kennedy and Hinds (2002) and Anthony and Flynn(2006b). Additional comparisons with the orientationaverage were not made, as the CFD results are aimed atinvestigating the worst-case scenario. In the applicationo the AE results or risk management, the worst-casescenario must be used and to account or variabilities.Furthermore, actors o saety should be urther appliedwhen setting saety measures such as worker exposurelimits and design and layout o workspace. Te compari-sons with the experimental data o Kennedy and Hinds(2002) show a underprediction or smaller particles. Teexperimental data used realistic breathing conditions

or a tidal volume inhalation o 20 LPM, which producesa peak velocity much greater than an averaged steadyow. Te higher peak velocity leads to an increase in thesmaller particle AE.

Comparisons with the numerical data o Anthonyand Flynn (2006b) also show an underprediction;

however, both have similar profles. Te AE does notchange greatly or aerodynamic diameters between 1and 70 m, but a large drop in the AE is ound or aero-dynamic diameters greater than 70 m. Te numeri-cal data rom Anthony and Flynn (2006b) were alsoobtained under a steady-state inhalation, whereasthe established IPM curve has been established rom

unsteady breathing with an orientation average, onlytested under reestream velocities between 1 and 4 ms1.Tereore or lower reestream velocities, which are com-mon in indoor environments, the IPM curve may notbe suitable as a tool or determining the risk o particleinhalation.

he only recorded AE or nose inhalation is rom thework oKennedy and Hinds (2002), which is used to com-pare the numerical results o this paper (Figure 11). heAE trend is similar to the numerical results or the mouthinhalation where the AE does not change greatly oraerodynamic diameters between 1 and 70 m, but a

large drop in the AE is ound or aerodynamic diametersgreater than 70 m. In the experimental work oKennedyand Hinds (2002), nose inhalability drops rom nearly100% or 7-m particles to less than 10% or particlesbetween 50 and 80 m. he inhalability or particleslarger than 80 m increases, but this trend is thought tobe unclear in the experiment because o large variabili-ties. here are some dierences between the numericalresults and the experimental data. For particle sizebetween 1 and 70 m, the higher peak velocity romunsteady inhalation leads to an increase in the AE.his eect is not signiicant or larger particles, whichare prone to gravitational settling. It was shown in the

particle trajectories section that the contaminantsource o larger particles needed to be above the inha-lation region due to gravitational settling and or largerparticles a minimum height was needed in order toachieve any particle inhalation. he experimental oKennedy and Hinds (2002) set up the aerosol delivery

0

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1

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Aerodynamic Diameter (micron)

AspirationEffic

iency

Mouth 15LPM

Mouth 40LPM

Kennedy & Hinds(2002) - Mouth Inhalation

Anthony & Flynn (2006)

Figure 10. Aspiration eciency or mouth inhalation under acing-the-

wind condition.

0

0.2

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0 20 40 60 80 100 120 140

Aerodynamic Diameter (micron)

Aspiration

Effic

iency

Nose 15LPM

Nose 40LPM

Kennedy & Hinds(2002) -

Nose Inhalation

Figure 11. Aspiration eciency or nasal inhalation under acing-the-

wind condition.


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maniold approximately 170 cm upstream. his longerdistance prevents the larger particles rom being trans-ported the entire distance and instead the particles settleto the ground.

Applications

In the design and layout o a workspace, particularly

manuacturing, and in a previous case study by the authors(Inthavong et al., 2009), a wood-turning workstation, thelocation o a contaminant source was not studied. Teresult rom this work is a numerical representation o par-ticles being transported downstream rom all locationsrom a plane. Te work was aimed at providing insight intothe inhalability o particles under the worst-case scenarioto identiy the particles and its location that were inhaled,rom upstream. Te critical area not only identifes thecontribution o a particle to the inhalability, but it alsoprovides a means or prevention o particle inhalation. Forexample, particle sizes between 1 and 20m tend to be

inhaled below the level o nostrils or mouth, whereas orparticles larger than 40m, inhalation occurred or parti-cles above the nostrils or mouth. Identiying the inhalabil-ity o a particle rom a contaminant source provides useulinormation or allocating aerosol-generating machinery toavoid inhalation o those undesirable aerosols. In addition,lower inhalability may be achieved with nasal breathing.Te implication here is that a workers exertion becomes

important when exposed to harmul aerosols. Breathingat normal or low exertion is normally through the nose,whereas heavy exertion leads to oral-nasal breathing andin some cases may even be wholly oral breathing. Underthis type o exertion, a worker will be subjected to dierentlevels o exposure to the inhalability o particles. Tereore,when setting the exposure time a worker is allowed to be

under, one must consider the type o inhalation that willoccur given the type o work that the worker is enduring.

Te results rom this study also contribute towards aholistic modeling approach through the aspiration e-ciency, which can be converted into an inhalable particlesize distribution (PSD). Tis can be calculated by multi-plying the particle size distribution by its correspondingaspiration eciency. From the measured PSD o settledparticles by Chung et al. (2000), the inhalable PSDs orpine and oak dust or oral breathing and nasal breathingare given in Figure 12 and Figure 13, respectively. Fouradditional particle sizes (2, 3, 15, and 24m) had been

studied to cover more particle sizes or oak dusts. It isound that the inhalable PSD through either the mouth ornostrils generally gives lower values than the experimen-tal PSD. Te raction reduced more signifcantly aboutthe mean particle size o pine and oak dusts. Because theinhalability has taken into consideration the inhalationrate, wind speed, and dimension o openings, the inhal-able PSDs presented can be applied as initial boundary

0

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Inhalable particle size distribution

(PSD) through mouth

Experimental PSD0

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0 5 10 15 20 25

(b) Oak Dust( = 930 kg/m3)(a) Pine Dust( = 560 kg/m3)


(PSD) through mouth

Experimental PSD

Figure 12. Inhalable particle distribution (PSD) through mouth and ideal PSD or (a) pine and (b) oak dusts.

0

0.02

0.04

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(b) Oak Dust( = 930 kg/m3)

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(PSD) through nostrils

Experimental PSD


(PSD) through nostrils

Experimental PSD

(a) Pine Dust ( =560 kg/m3)

Figure 13. Inhalable particle distribution (PSD) through nostrils and ideal PSD or (a) pine and (b) oak dusts.


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conditions or respiratory particle deposition studies. Inaddition, any normalized PSD using the aerodynamicdiameter can be used in conjunction with the aspirationeciency to provide an inhalable PSD.

Conclusion

Aspiration eciency through the nostrils and mouth atlow velocity environments was investigated using CFDtechniques. Particle transport was simulated with a three-dimensional humanoid with detailed acial eatures.Velocity vectors in the y-z plane at the centerline o thehumanoid were compared with the experimental datareported byAnthony et al. (2005) to ensure confdencein the results. Te ow feld in the near breathing regionshows slight vertical direction caused by the presence othe torso, where the airstream diverges as it ows past thebody. Te critical area concept was used as a tool to deter-mine the aspiration eciency o particles. At any plane

normal to the acing mannequin upstream, there existsa region (area) o particles that are inhaled. Tis regionor critical area on a plane is ound at varying vertical dis-tance in relation to the mouth. Smaller Stokes numberparticles that are entrained in the ow exhibit a criticalarea located at a vertical distance below the mouth due tothe ow feld vectors directed having an upwards direc-tion. Te critical area or larger Stokes number particlesis ound at a vertical distance higher than the mouth dueto gravitational settling. With even heavier particles, thecontaminant source location needs to be increasinglyhigher or the same upstream release distance rom thehumanoid. Comparisons between critical areas or thenose and mouth inhalations show similar geometricproperties such as the teardrop shape, and its verticaldistance location on the x-z plane located at y = 70 cmupstream. Te critical area sizes were ound to be slightlylarger or the mouth inhalation, mainly due to the largermouth area and also the aligned orientation o the mouthto the upstream ow, whereas the nose is perpendicularto the upstream ow. Te AE does not change greatlyor aerodynamic diameters between 1 and 70 m, but alarge drop in the AE is ound or aerodynamic diametersgreater than 70 m. Tis is in contrast to the establishedIPM curve, which shows a rapid drop in AE or smaller

particles and a plateau or aerodynamic diameters greaterthan 70m. Tis studys inhalability curve along withthose o the Anthony and Flynn (2006b) and Kennedyand Hinds (2002) studies showed signifcant deviationrom the IPM sampling criterion. Te source o the di-erence is unknown, but may be related to dierencesin experimental/computational set up. Te results orthe nose data were generated computationally and werecompared with one set o experimental results. No otherdata or nose inhalation exist and it is anticipated thatthese results can be used or comparisons in uture workwhere transient inhalation conditions can be simulated.Tis study was undertaken to establish the ow feld in

the near breathing region, which will help to characterizethe ow feld and particle feld or initial boundary con-ditions, leading to a more holistic modeling approach orespiration through the nasal cavity and mouth. Refnedmodels to include unsteady ows and dierent orienta-tions will be urther conducted.

Declaration of interest

Te fndings and conclusions in this report are those o theauthors and do not necessarily represent the views o theAustralian Research Council and RMI University. Te fnan-cial support provided by the Australian Research Council(project ID LP0989452) and by RMI University through anEmerging Research Grant are grateully acknowledged.

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inhalability of micron particles through the nose and

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