NUREG/CR-4321

LA-10478-MS

RI

Full-Scale Measurements

of Smoke Transport and Deposition

in Ventilation System Ductwork

R. A. Martin

D. L. Fenton*

Manuscript submitted: June 1985

Date published: July 1985

Prepared for

Division of Risk Analysis

Office of Nuclear Regulatory Research

US Nuclear Regulatory Commission

Washington, DC 20555

NRC FIN No. A7029

Consultant at Los Alamos. New Mexico State University, Las Cruces, NM 88003.

Lo's Los Alamos National Laboratory

Los Alamos, New Mexico 87545

FULL-SCALE MEASUREMENTS OF SMOKE TRANSPORT

AND DEPOSITION IN VENTILATION SYSTEM DUCTWORK

by

R. A. Martin and D. L. Fenton

ABSTRACT

This study is part of an effort to obtain experimental

data in support of the fire accident analysis computer code

FIRAC, which was developed at the Los Alamos National Laboratory. FIRAC can predict the transient movement of aerosolized or gaseous material throughout the complex ventilation systems-of-nuclear fuel cycle facilities. We conducted

a preliminary set of full-scale material depletion/modification experiments to help assess the accuracy of the code's

aerosol depletion model. Such tests were performed under

realistic conditions using real combustion products in fullsized ducts at typical airflow rates. To produce a combustion aerosol, we burned both polystyrene and polymethyl methacrylate, the most and least smoky fuels typically found in

fuel cycle plants, under varied ventilation (oxygen-lean and

oxygen-rich) conditions.

Aerosol mass depos.ition, size,,and concentration measurements were performed. We found that as much as -25% of

polystyrene smoke mass and as little as 2% of the polymethyl

methacrylate generated at the entrance to a 15.2-m duct is

deposited on the duct walls. We also compared our experimental results with.theoretical equations currently used in

FIRAC.

I. INTRODUCTION

A. Background

The Los Alamos National Laboratory is participating in a nuclear fuel cycle facility safety analysis program whose objective is to develop user-oriented

tools for making better estimates of accident-induced radioactive aerosol release or source-term characteristics at a facility's atmospheric boundary. 1' 2

These tools are intended to improve current safety analysis review techniques.

1
The plants being considered in this program include fuel fabrication, fuel reprocessing, waste solidification, fuel storage, and UF6 production facilities.

The types of accidents being considered include fires, explosions, spills, equipment failures, criticalities, and tornadoes.

Los Alamos developed the fire accident analysis computer code FIRAC to help

evaluate the consequences of fire accidents in fuel cycle plants. 3 FIRAC was

designed to predict transient fire-induced flows, temperatures, and material

transport within facilities. FIRAC can model an interconnected network of rooms

and typical ventilation system components such as ducts, fans, dampers, and protective high-efficiency particulate air (HEPA) filters.

The objective of the material transport portion of FIRAC is to estimate the

movement of material (aerosol or gas) in an interconnected'network of ventilation system components representing a given~fuel cycle facility. Using this

material transport capability, the code can calculatematerial concentrations

and mass flow rates at any location in the network.. Furthermore, the code will

perform these transport calculations for various gas-dynamic transients. It

solves the entire network for transient flow and in so doing.takes into account

system interactions.

A generalized treatment of material transport under fire-induced accident

conditions could become very complex because several different types of materials could be transported. Also, more than one phase could be involved (including solids, liquids, and gases with phase transitions), and-chemical reactions

leading to the formation of new species could occur during, transport. Further,

for each type of material there Will be a size distribution that varies with

time and position depending on the relative importance of effects such as homogeneous nucleation, coagulation (material interaction), diffusion (both by

Brownian motion and turbulence), and gravitational sedimentation. We know of

no codes that can model transient flow-induced material transport in a network

system subject to the possibility of all of these complications, and the transport portion of the FIRAC code does not include this level of generality either.

However, this version of the code does provide a simple material transport capability. The material. transp-ort components of FIRAC consist of

1. material characteristics,

2. transport initiation,

3. convective transport,.

2
4. aerosol depletion, and

5. filtration.

These components are described in more detail in Refs. 3--5. Here we are primarily concerned with item 4, aerosol depletion.

Although it can be thought that aerosol losses because of deposition

(item 4) are insignificant, a previous study indicated that such losses can be

appreciable in terms of mass percentage. Qualitative cascade impactor measurements in the downstream duct of full-sized compartment fire tests at Lawerence

Livermore National Laboratory (LLNL) have indicated that as much as 60% of combustion product aerosol mass can be removed by deposition in a relatively short

6 3 (-9.7-m-long) duct. 6 In case of a fire in a nuclear facility, the presence

of combustion products poses a threat to the HEPA filters. A reduction

in smoke concentration because of deposition can delay filter plugging. Because

4 deposition depends on size, it can modify the size distribution function of

the smoke reaching the filters.

Further, in fuel cycle facilities under fire accident conditions, the smoke

(solid and liquid aerosol) could be contaminated with radioactive material. In

this case it becomes important to know where hazardous material is deposited and

how much is deposited within the plant ventilation system. -A reduction in airborne material concentrations will reduce the quantity of radioactive material

accumulating on the HEPA filters and passing through them. We are particularly

interested in the location and concentration of radioactive material in the respirable size range, namely, about 0 to 15 pm. This time- and location-dependent

concentration will change continually because of deposition and material interaction (coagulation).

*Thus, there is a need to check'the accuracy of the deposition equations

available in the literature. Some of these deposition equations currently are

being used to compute unsteady material depletion in FIRAC and other Los Alamos

accident analysis computer codes. 1,4 The actual equations being used in FIRAC

and suggested improvements to the code are discussed in Sec. II. However, such

expressions have been confirmed only in small flow facilities using ideal aerosols. Thus, at this stage of computer code development, we have relatively

little confidence in the predictions of deposition losses for combustion

aerosols.

3
B. Purpose of this Study

The current study is part of a Los Alamos effort to obtain experimental data

in support of FIRAC computer code development and verification.l'3' This study

deals specifically with material transport area 4 listed above, aerosol depletion. Our purpose was to conduct a preliminary set of full-scale material depletion/modification experiments to obtain data on aerosol mass deposition, size,

and concentration variations. In this study we performed such tests under realistic conditions using real combustion products (particulate and gaseous, including water vapor) in full-sized ducts at typical airflow rates. To produce

a combustion aerosol we burned polystyrene (PS); and polymethyl methacrylate

(PMMA), the most and least smoky fuels, respectively, typically found in nuclear

fuel cycle facilities. We are unaware of adequate data of this kind in the

available literature.

With such depletion/modification data we can help answer three questions

for realistic fire conditions.

1. How important is deposition; that is, how much material accumulates on

the walls?

2. How much change in smoke characteristics (concentration and size distribution) can occur over reasonable duct lengths?

3. Are our idealized equations from the literature giving us reasonable,

and preferably conservative, quantitative estimates of deposition?

C. Scope of the Study

A survey of combustible materials in fuel cycle facilities produced the

typical fuel mixture composition given in Table 1.2 The composition percentages listed for these six materials represent a rough average for the facilities

surveyed. They are likely to buIrn under both oxygen-rich and oxygen-starved

(over- and under-ventilated) conditions to produce particulate material, water

vapor, and gaseous combustion ploducts.

A special test facility was needed to obtain smoke deposition/modification

data. We needed a facility in which some of the materials in Table I (or a mixture of materials) could be burned under controlled conditions so as to produce

variable efficiencies. The burn products had to be introduced into as long a

duct as practical to enhance deposition and aerosol concentration changes for

better resolution. We also needed to simulate rapid diffusion (mixing) of the

smoke plume to make an upstream, centerline smoke concentration measurement.

4
TABLE I

TYPICAL FUEL MIXTURE COMPOSITION 2

Component Composition (dgI

Polymethylmethacrylate 45

Cellulosic 26

Elastomer 18

Polyvinyl Chloride 8

Hydraulic Fluids 2

Polystyrene 1

Finally, we needed special experimental apparatus suitable for making surface

measurements of total aerosol mass deposition.

A test facility was constructed by New Mexico State University (NMSU) and

Los Alamos on the NMSU campus at Las Cruces, New Mexico. It had the dual purpose of allowing for the current studies and allowing for studies of HEPA filter

plugging response to simulated fire accidents. 7--912 The facility described

in Refs. 8 and 12 was modified to facilitate the current aerosol deposition/-

modification experiments. The major modifications included

1. coupling to a specially designed combustion chamber,

2. the design and installation of a biplanar grid of round tubes to promote turbulent mixing,

3. the construction of a metal hot duct, and

4. adding extra ductwork to bring the test section length for deposition

up to -15.24 m.

The proposed deposition/modification test series included a matrix of two

pure materials (PS and PMMA) burned at two mass-burning (or smoke-generating)

rates, high and low. The two materials were selected from Table I. Although

PS is not found in as large proportions in nuclear fuel cycle facilities as is

PMMA, PS is the most severe smoke producer in Table I. On the other hand, PMMA

produces relatively low quantities of smoke per the amount of mass burned.

Thus, by selecting these two fuels we attempted to bracket the extremes of smoke

generation (the mass fraction of solid or liquid fuel that converts to smoke)

expected in plants. For liquid PS and PMMA burned at over-ventilated conditions, Tewarson13 experimentally measured smoke mass fractions (Y = m /m s = ms/ub) and got 0.33 and 0.021, respectively, where both the soot and low vapor pressure

5
liquids are included in the aerosolized combustion products or "smoke." The

quantities ms and mb are mass. of smoke produced and mass of fuel burned, respectively.

A special combustor was designed and manufactured by Battelle Pacific Northwest Laboratory (PNL) to burn the fuels and control the~burning.efficiency. The

two mass burning rates were achieved by controlling the inlet air supply rate.

Each burning rate was repeated two times for a total of four tests. The repetitions were used to assess the reproducibility of our test results. Appropriate

instrumentation was set up and calibrated to obtain the following measurements.

1. Ambient pressure and temperature

2. Average or bulk volumetric airflow rate in the duct

3. Air temperature at four locations

4. Relative humidity

5. Fuel mass burning rate

6. Smoke mass concentration using cascade impactors at two locations on

the duct centerline (downstream of the mixing grid and 13.9 m further

downstream)

7. Smoke size distribution using eight-stage cascade impactors to obtain

the mass median aerodynamic diameter and geometric standard deviation

(for.a log-normally distributed aerosol)

8. Total mass deposition at one downstream location but on three surfaces

(ceiling, one side wall, and floor) at the 13.9 m downstream mass concentration measurement location (See item 6.)

We emphasize that the current study was useful but highly preliminary.

Only a limited number of measurements have been made to date. Also, although

much care was taken in the experimental procedures, relatively crude equipment

was used to collect smoke deposits. Consequently, our deposition results must

be viewed as qualitative. However, as we will discuss in Sec. IV, we believe

that our deposition measurements are conservative and useful as such.

II. AEROSOL DEPOSITION THEORY

A. Existing FIRAC Capability

Because the flow Reynolds number will be greater than about 2100 for all

cases of interest here (airflow in nuclear fuel cycle facilities), the flow always will be turbulent. We will assume that all flows are fully developed so

that boundary layer or duct velocity profile shapes are constant with distance.

6
However, this will be true-in most cases only sufficiently far. downstream from.

the inlets (20 to 50.hydraulic diameters).

Under these conditions, not all of the material that is made *airborne at

the location of material transport initiation will survive convective transport

to the filtration system's or facility's boundary. Depending on the aerosol

aerodynamic characteristics and passage geometry, there may be a sizable reduction in aerosol concentration. As such, an enclosure or duct acts as an aerosol

filter.

A user can calculate the aerosol losses caused by gravitational sedimentation in rooms, cells, and horizontal, rectangular ducts in the current version

of FIRAC. 3 The deposition module can be turned on for horizontal ducts and

rooms and turned off for vertical ducts by adjusting input flags. Aerosol depletion for any number of species and/or size distributions can be calculated

throughout the network during transient flow. The theory is based on quasisteady-state settling, with the terminal settling velocity corrected by the

Cunningham slip factor. The flow in ducts and rooms is assumed to be well-mixed

so that the aerosol concentration is uniform within the volume. More detail and

references are discussed below. The user supplies only the aerosol diameter and

density to this model. The aerosols may consist of sol.id particles or liquid

droplets.

Future versions of the material transport module will account for combined

molecular and turbulent diffusion as well as for aerosol interactions, but the

current version is restricted to gravitational sedimentation. The particle flux

iJ resulting from gravitational sedimentation is14

Jp = Upnp , (1)

p upsnp

where Jp is particles per unit area per unit time, ups is the terminal settling

velocity, and n is the local aerosol number concentration in particles per

unit volume for the homogeneous aerosol. If we multiply both sides of Eq. (1)

by the homogeneous particulate mass mp (assuming that we know this quantity

or can calculate it from a measured aerosol size and mass density), then

J'= Upp ', -(2)

7
where the units of J are mass per unit area per unit time and op = n m

p pp is the aerosol mass concentration per unit volume. The terminal settling velocity is calculated from14

u - _pdpgC (3) ps 

(3

18P

where

Pp = aerosol density,

d = aerosol particle diameter, P

g = gravitational acceleration,

C = Cunningham slip correction factor, and

= fluid dynamic viscosity.

The code input variables for material depletion are p and dp. These variables

p p*

may be assumed by the user. We recommend that the user select aerodynamic diameter with the unit density or Stokes diameter with the material bulk density.

This selection was discussed earlier in this section. To calculate the slip

14 correction factor, the code uses

C = 1 + 2L/dp [A1 + A2 exp(- A3 DDp/L) , (4)

where L is the gas molecular mean free path and the A's are dimensionless constants based on experimental measurements of small particle drag. The code uses

L = 0.065 pm

A1 = 1.257

A2 = 0.400

A3 = 0.550

g = 981 cm/s2, and

= 0.0001781 g/cm-s

where L, v, and g are taken at standard sea-level conditions.

8
We know P from the'material transport mass balance calculation for the

previous time step for.each node (.volume or duct). Then, knowing ups and the

projected floor area for sedimentation A, we can compute the sink (or mass loss)

term using Eq. (2),

md= -J'A = - UpspA (5)

which has the units grams per second. Because aerosol depletion is a sink term,

we have used a minus sign in Eq. (5). Aerosol depletion by sedimentation may

be selected for all volumes and ducts and is calculated in the same manner.

B. Future Improvements to FIRAC

Aerosols moving through passages that are horizontal (or not exactly vertical) can be deposited because of gravitational settling. However, a number

of other processes that can cause aerosol depletion and contribute to a material

transport sink term should be considered.1 4 2 0 Particles that Come sufficiently close to surfaces can be intercepted mechanically and stuck. Particles with

enough inertia can deviate from the flow streamlines, impact, and stick to rough

elements, obstacles, or bends. Particles less than about 1 um in size can be

transported to surfaces by both turbulent (eddy) and molecular (Brownian) diffusion. Particles greater'than about 1 um in size and being transported parallel

to surfaces can be deposited because of the fluctuating velocity components normal to the surface (turbulent inertial deposition). Lower flow velocities enhance deposition caused by molecular diffusion and sedimentation'; Unless the

surfaces are sticky, the net rate of deposition will depend on the relative

rates of transport and reentrainment. Except for fibrous particles or very

light particles, interception may be neglected because particles large enough

to be intercepted will most likely be deposited as a result of inertial effects

or sedimentation.

Under certain conditions, other effects may become important for the small-,

est particles. These effects include thermophoresis, diffusiophoresis, and photophoresis migration, which are discussed in Refs. 14 and 17. Tney are believed

to be relatively unimportant here compared with other effects.

9
.Friedlander's book provides an excellent'introduction to deposition by

convective diffus'ion and inertial deposition. Here the'concept of a particle

transfer coefficient k is introduced such that

p

Jp k p np (6)

where Jp is the particle deposition flux (particles per square centimetersecond) at a given location in a tube and np is the local average particle number concentration (particles.per cubic centimeter) in the mainstream at that

cross section. Thus, the transfer coefficient k P has units of centimeters per

second and may be considered an effective deposition velocity. Experimental

measurements of k for liquid droplets and solid particles were obtained for

turbulent flow in vertical tubes at Reynolds numbers up to 50-000. 2122 Several theories for predicting k for turbulent deposition are based on the diffusion free-flight model. Particles are assumed to be transported by turbulent

diffusion to within one stopping distance from the wall, at which point the particles make a. free flight to the wall. The stopping dilstance is

S= VTp- p d2 /18P , (7)

p pp p pp

where T is the particle relaxation time and vp is the assumed free-flight p,

velocity.

Beal 2 3 has developed an analytical method for predicting K for turbulent

p

flow in vertical tubes. Beal's method combines the:approaches taken in'Ref. 21

and Ref. 24 and applies them to particles ranging from molecular size to about

100 Pm. This theory accounts for the deposition mechanisms of Brownian and turbulent diffusion and turbulent inertial deposition but not gravitational settling. Beal's approach is to integrate the particle flux equation,

dn Jp= (D p+ cp d-y 8

10
across the concentration boundary layer. Here D is the particle coefficient

p of molecular diffusion and e is the particle eddy diffusivity (both have units P

of square centimeters per second). In the derivative, y represents distance in

centimeters perpendicular to the surface. In his paper, Beal 2 3 states his assumptions for D and c in specific regions of the turbulent boundary layer

and derives equations for k *

The authors of Ref. 25 have developed a method for predicting k for tur- P

bulent flow in horizontal tubes. This method applies to particles with a size

greater than about 1 pm because it accounts for the deposition mechanisms of

turbulent diffusion and gravitational settling but does not account for Brownian

diffusion. Reference 25 also considers the effect of pipe wall roughness and

provides experimental verification for particles with sizes from about 1 to

4 Pm.

The equations for k, presented in Refs. 23 and 25 were incorporated into'

a computer code called DUCT that estimates aerosol depletion under steady flow

conditions in a given duct segment. We propose to include these equations as an

improvement to the aerosol depletion modules in the Los Alamos tornado and explosion accident analysis codes TORAC26 and EXPAC,27 respectively, as well as

FIRAC. 3 (See also Refs. 1 and 4,.)

Experimental data are needed to check aerosol depletion calculations for

losses encountered in fuel cycle facilities, particularly for fire conditions,

and such data are being sought in the current fuel cycle safety program. Another area needing improvement is accounting for the effects of other ventilation

system components (besides filters) on aerosol removal. The other components

include blowers, dampers, bends, and flow restrictions.

C. Calculation of Integrated Material Losses Because of Sedimentation in a Duct

Equation (1) predicts the local flux of particles falling onto a horizontal

unit surface area per unit time. We use the term "local" because to use Eq. (1)

(in principle), we must know the aerosal concentration close to the surface.

This local concentration of aerosol supplies particles for deposition. This is

not a serious problem because turbulence effectively mixes the aerosol at a given duct cross-section except for a relatively thin (but important) region near 14

the duct walls. We also use the term local to remind ourselves that the aerosol concentration can change in the streamwise direction as well as in the

transverse directions at a given duct cross-section. Further, to use Eq. (3)

II
to calculate the sedimentation transfer coefficient :(settling velocity) ups,

we must assume either that our aerosol is monodisperse (d =.constant) and'homogeneous (pp = constant) or that our real aerosol can be adequately characterized by its median aerodynamic equivalent size (even though some variation in

size and density exists from particle to particle). We have measured the mass

median aerodynamic diameter (MMAD) of smoke using cascade impactors and found

that the proper value of density for us to use in Eq. (3) is p p 1.0 g/cm3 .

(See Ref. 19.)

How can we calculate the total loss of aerosol material because of deposition that occurs from the inlet to the exit of a duct? For steady-state conditions, we expect this loss to be a function of the volume of aerosol-laden air

that moves through the duct and the difference in concentration from inlet to

outlet in a given time interval. Thus, by conservation of mass (or conservation

of number of particles) we expect

Np (particles in) - (particles out) , (9)

where N is the total number of particles left behind in the duct (a loss, or

p

sink, term). Equation (9) may be written as

N = NpoQat - nQAt = (n po-n p)QAt , (10a)

where n 0 and n are the duct upstream (at the source) and downstream particle number concentrations, respectively; Q is the constant air volumetric flow

rate; and At is the time interval over which deposition takes place. We assume

that npo is greater than np.

For clarity, we will develop the simple expression for the concentration

ratio, n p/n = Pp/Ppo' corresponding to deposition from an aerosol moving in

a rectangular duct. This equation is given and discussed in Refs. 17 and 28.

However, we follow the reasoning given by Fuchs15 to derive the equation for

a duct with a circular cross section. Consider an aerosol flowing in a con12
stant-area rectangular duct of height h and width w and assume that we know

enough about the aerosol and the flow properties to calculate ups using

Eq. (3). Assume further-that the airflow-is fully developed andturbulent and

moves at bulk velocity U. Finally, assume that downstream distance is measured

in x direction with np = npo given at x = 0. We are interested in calculating

n at a downstream location x = L.

Our attention now is focused on a segment of duct of length Ax with crosssectional dimensions w by h. The projected area for vertical settling of particles in Ax is wax. We also know that the well-mixed volume of aerosol-laden

air in the segment is hwAx. Therefore, using Eq. (1), the number of particles

depositing onto area wax in time At = Ax/U is using Eq. (2)

AN = J (area)(At) = n u (WAX)(Ax/U) . (lOb)

p p p PS

If we let Anp be the incremental change in concentration of particles per

unit volume of air in the segment, then

An + AN /hwAx = n u w (Ax) 2 /hwAxU

p p p ps.

Because Anp = np2 -np1 <0 for Ax = X2 -xI >0, we can write

-An /Ax = n u /Uh

P, p pp

or, in differential form (in the limit as AX goes to zero),

dnp/dx = -npupS/Uh . (I1)

13
Nhis is a simple first-order ordinary differential equation for. the variationof n with x. The known boundary conditionis np= nn when x.= 0. Separating P p0

the variables in Eq. (11) we get

dnp/np -(Ups/Uh)dx

Integrating

fnn

using the dummy variables np and x', we have

dx

dn I n P 1- (uIp Uh) dx

so

n

n np

nop

= -Upsx /Uh

and

in (np/npo) -upsx/Uh

Finally,

n p/nPO = e-(upsx/Uh) (12)

Equation (12) gives the reduction in number concentration from npo to np in

distance x down the duct. Thus, for constant, known values of ups, h, and U,

14
the concentration falls off exponentially :from its initial. values. Notice from

Eq. (12) that increasing u and x will enhance sedimentation, as will decreasing U and h.

As we can now calculate the local concentration n at x from Eq. (12), we P

can calculate the deposition flux at x using Eq. (1) to be

j ... U.n. ="u ne(Upsx/Uh) (13)

Using Eq. (13) we can calculate the integrated'or total parti'culate-deposition

rate (in units..of particles/s) up to x = L as

SptotA Jpwdx L u psnpo e -(U n PO 1 1 

where A is the duct floor area. Q = hwU is the duct flow rate in Eq. (14), and

n Q = n hwU is the aerosol source strength in units of particles per second.

PO

For a time interval At, the total number of particles deposited in the duct may

be calculated using Eqs. (14) and (12) and will be

Np =J ttAAt = (np-n p)QAt .,(15)

Equation (15) gives the same result as Eq. (10), which followed from our'heuristic thinking. For homogeneous particles of mass mp, Eq. (15) gives the total

mass deposition,

md = mp N p= (p - p )QAt., (16)

15
and Eq. (12) gives the mass concentration ratio,

ppp =e(ups x/Uh) (17)

for any streamwise duct location x.

The FIRAC code makes a numerical approximation 'to the reduction in concentration because of sedimentation by using Eq. (5) directly if the duct lengths

and computational time increments are sufficiently small. However, for longer

ducts and/or sufficiently large or heavy materials (high us) for Wh'ich conPS

centration changes could exceed about 10% per time step, FIRAC can use Eq. (16)

and Eq. (17) in combination. See Refs. 3--5 for more information on FIRAC material transport calculations.

III. EXPERIMENTAL APPARATUS

The existing HEPA filter loading facility was modified to accomodate the

requirements associated with combustion aerosol generation and deposition and

filter plugging. The original filter loading facility is described in Ref. 8

and Ref. 12. Specifically, the modifications included the addition of approximately 7.4 m of straight duct upstream from the test filter location. The experimental apparatus consisted of the air handling equipment and associated instrumentation for characterizing the combustion products and smoke transport,

and special apparatus for measuring smoke deposition in the duct.

A. Air Handling Equipment

The airflow equipment is shown in Fig. 1, which also gives the dimensions

at the air supply and test section ends of the system. The distance from the

burner inlet to the upstream side of the test section was 20.3 m. The maximum

volumetric airflow rate through the system was 2040 m 3/h. The wood ducts were

constructed from 1.9-cm-thick plywood and reinforced with 5.1- by 5.1- by 0.63-cm

angle iron. The metal ducts were made of 20-gauge galvanized sheet steel reinforced with angle iron. The ductwork was 0.61 by 0.61 m square except for those

locations where transitions were used and the flow rate was measured.
Adjustable cone

By-pass

exhaust duct isolator Prefilter

0.15 m 0.29 m

I'219 1I-* I -14 -2.438m 10-4 - 2.438 m0.635 m 0.61 m 0.61 m .

Fig. 1.

Wind tunnel system - upstream section (plan view).

The fan was an axial-vane type manufactured by the Joy Corporation. The

nominal rated airflow was 4080.m 3/h and was driven by a 5.7-kW Dyna Corporation

electric motor operating at 1720 rpm. The fan assemblytwas enclosed in a wood

box with an adjustable door that served as a variable inlet. The air flowing

into the box first was cleaned by a furnace filter and subsequently was cleaned

by a HEPA filter (prefilter) downstream from the fan in the duct. All transitions were gradual in their geometric configuration; the wall angles measured

from the horizontal centerline were all less than 70.

Immediately downstream from the HEPA filter prefilter, 2.4 m of stainlesssteel duct was installed to facilitate addition of the test fuel burner or combustor. At the downstream edge of this steel duct, a turbulence mixing grid was

added to disperse the combustion products over the duct airflow. The grid was

composed of 2.2-cm-o.d. copper tubing spaced approximately 5.08 cm apart center

to center. Furthermore, steady-state conditions prevailed in the duct within

1 min.

A Dwyer inclined manometer capable of a 0.005-cm-w.g. resolution was used

to measure the centerline velocity pressure sensed by a pitot-static probe in

the circular cross-section duct downstream from the HEPA filter test section.

Horizontal and vertical traverses across the circular duct yielded velocity profiles that were used to calculate the volumetric airflow rate. A centerline

17
coefficient that relates the volumetric airflow rate to the centerline velocity

then was determined. Repeating these calculations for the volumetric flows expected in a typical HEPA filter plugging test then relates the centerline velocity of volumetric airflow rate. Figure 2 shows the centerline coefficient as a

function of volumetric flow where the coefficient is seen to vary slightly over

the tested flows. The equation shown in Fig. 2 giving the centerline coefficient was used to determine all the volumetric airflows.

Air temperature measurements were made at five positions. The inlet and

outlet dry and wet bulb temperatures-were measured with a psychrometer. Copperconstantan (type T) thermocouples were used to measure the temperature of the

airflow at the branch section upstream and downstream of the HEPA filter and the

ambient temperature. A Series 2000 Thermocouple Digital Temperature Indicator

was used to monitor the thermocouples, which were accurate to + 0.5 0C at the

95% confidence level.

B. Test Fuel Combustion

The test fuels, PS and PMMA, were burned in a special solid fuel combustor

designed by PNL. Figure 3 is an assembly drawing of the combustor. The burner

was positioned on the underside of the stainless-steel duct immediately downstream from'the HEPA prefilter and secured by a flanged steel pipe section using

eight 0.79-cm-diam bolts.

HEPA filter

,--Support frame

Exhaust duct

Flexible ducts Transition duct

Flow straighteners Pitot tube

.73 m

Static pressure ports• -Static priessure ports T

2. 0.61 m 2 2 914m

0.29 m

L 7.87 m

Fig. 2.

Wind tunnel system - downstream section (plan view).

18
-ONTROL VALVE

L- THERýIOLE

MNULA

WREEN

FILTER

Fig. 3.

Assembly drawing of the test fuel combustor.

'The combustor includes a cup holder where the fuel was contained and heated. The chamber walls provide the capability for combustion in a positive pressure atmosphere (duct interior). Fuel preheat temperatures were nominally 500%C

and were achieved using a 400-W electrical ring heater controlled by a Chromalox

on-off temperature controller. The flame was diffusion controlled, and the burning rate was regulated by adjusting the airflow rate to the combustor by means

of a valve and rotameter. A gate valve at the top of the burner (under the

stainless-steel duct) was maintained inwthe full-open position after the fire

was started,

C. Combustion Product Characterization

The characterization of the combustion products included only the particulate constituents. The particulate products were not monitored continuously,

but rather intermittent samples were taken and analyzed.

19
Particulate mass concentrations (milligrams per cubic meter) were determined with Anderson Mark III stainless-steel in-stack inertial impactors incorporating straight nozzles. These impactors also measure aerodynamic particle

diameter (based on unit density Spheres) through seven stages of particle collection and a back-up filter. Pre-impactors for use in conjunction with the

impactors were determined unnecessary for this application. Real-time particle

sizing equipment also was used. The units used here were a Royco Model 225 Optical Aerosol Particle Counter and a Thermal Systems Model 3030 Electrical Mobility Analyzer. The real-time equipment was less suitable in this experiment

because the particle size characteristics and mass concentration varied with the

burn time. Because about 1--3 min of cycling time was required by each particle

counter, the actual aerosol characteristics could not be resolved. In contrast,

the inertial impactors were operated in such a manner (nozzle diameter and sampling time) to sample over the entire fuel burn--up to 20 min. For this reason,

the impactor size data are considered pertinent to the duct wall particle deposition problem.

D. Smoke Deposition Measurement

The duct wall particulate mass deposition rate was measured approximately

I hydraulic duct diameter upstream from the HEPA filter. The technique employed

used a Nuclepore filter (polycarabonate, 0.03 pm and 47 mm in diameter) secured

to a specially designed back plate. The Nuclepore filter was kept in place by

a ring of brass shim-stock that in turn was held onto the back plate by a vacuum

as seen in Fig. 4. A drawback of this technique is the possibility for air leaks

around the edge of the shim-stock that would necessarily alter the particulate

deposition onto the Nuclepore filter. This potential problem was not resolved

fully in this-investigation. The gravimetric weight gain of the Nuclepore filter indicated the quantity of particulate deposition. A Sartorius Model 2007

Automatic Analytical Balance capable of mass resolutions of 0.1 mg was used in

all the gravimetric analyses. We performed this wall deposition study to estimate the quantity of particle loss by transport within the duct.

IV. EXPERIMENTAL PROCEDURES

The systematic procedures associated with our smoke transport and deposition experiments are outlined below.

20
DIA., 12 HOLES, EQUALLY SPACED

NUCLEPORE FILTER DIA = 47.. DETAIL: SHIM STOCK

'N

VACUUM'L PORE FILTER DEPSITION SUBSTRATE HOLDER

6/24/82

ALL DIMENSIONS IN CENTIMETERS

Fig. 4.

Assembly drawing of the deposition substrate holder.

1. The test fuel cups were weighed when empty and when loaded with the

PS fuel sample such that the mass was known for determination of the

apparent burning rate. These cups next were placed on a hot plate

with the temperature automatically controlled to 500°C.

2. All substrates were preweighed (Nuclepore filters for the deposition

sites and the specially cut glass fiber filters for the inertial impactors) on an analytical balance, and the impactors were loaded.

3. The deposition substrates and impactors were transported to the airflow facility and installed.

4. The test fuel cup ring heater within the combustor was switched on,

and the Chromolox on-off controller was adjusted to 500 0C. Approximately 40 min were required for the cup to achieve the set temperature. During this time, the fan prefilter was changed, all electronic instruments were rechecked, and the pressure manometers were

adjusted for correct zeros.

5. The airflow facility fan was turned on.

6. Barometric pressure was recorded and corrected to temperature and local elevation.

21
7. The airflow-adjusting door located at the fan box was "adjusted to

yield the desired velocity pressure (volumetric airflow) measured in

the circular cross-section duct downstream from the test HEPA filter.

8. Temperatures at the inlet, at the branch (downstream from combustor),

upstream from the test HEPA filter,;downstream from the HEPA filter,

and at the exit were recorded. The static pressure drop across the

filters also was recorded.

9. Impactor sampling at near isokinetic conditions was performed and

then test fuel combustion was initiated.

10. The airflow facility fan was turned off to start the fire. The fuel

test cup was placed inside the combuster in the cup holder, and the

top gate valve was opened slightly. No air was supplied to the combuster, which allowed vapors to accumulate in the volume above the

cup. After5--lO min, the igniter coil was energized electrically.

(Fuel vapor ignition occurred most consistently in this manner.)

After combustion was initiated, the top gate valve was changed to

full open and the combustion airflow adjusted to the required level

(4.7 x 10-4 or 18.9 x 10-4 m3 Is) on the rotameter by means of a

valve.

11, The airflow facility fan was switched on. Thermocouple temperature

measurements were recorded.

12, The data acquisition process involved the following items.

# The time at which the flame first appeared was recorded.

a The time at which the flame disappeared was recorded.

* After flame disappearance, the top gate valve was closed and the

inlet and exit dry and wet bulb temperatures and velocity pressure in the circular cross-section duct were recorded,

13. When all the test fuel was consumed, the airflow facility fan was

-turned off. Next, the impactors were shutdown and removed. Finally, the deposition substrates were removed and placed in plastic

petri dishes for transport back to the laboratory,

14. All substrates were final weighed on the analytical ,balance, and the

measurements were recorded. The inertial impactors were washed and

.readied for the next test..r

22
V. TESt RESULTS AND DISCUSSION

A. Physical Characterization of Smoke Particles

With the procedures given in the earlier section and with special instrumentation, the PS and PMMA combustion aerosols were characterized physically

during the particulate deposition tests. Results were obtained From the inertial impactors located at the duct centerline--one approximately 4.9 m downstream from the burner and the second immediately upstream from the test HEPA

filter. The distance between the impactors was 13.9 m. The impactors provided

both overall particle mass concentration and size distribution by equivalent

aerodynamic diameter. The purpose of the two simultaneous measurements was to

determine the amount of reduction of airborne particulate mass as a result of

duct wall' deposition and the change in aerosol concentration.

The PS particle size distributions are shown in Fig. 5. The particulate

mass concentration data' in conjunction with the mass burning rate, imply an

important feature associated with PS combustion. This feature is that the total particulate mass concentration measured near the HEPA filter is proportional to the mass burning rate. This is established by ratioing the average high

burning rate to the average low burning rate and obtaining the value of 2.0.

Calculating the corresponding ratio for average total particulate mass concentrations gives 2.3. The correspondence (deviation from-mean less than 7%)

implies a constant soot fraction for under-ventilated conditions. Figure 5

also shows that the particle size distribution is nearly the same for particles

less than 2.0 pm for the high and low mass burning rates. However, for particles greater than 2.0 um in diameter, there is a significantly greater relative

number of particles at the higher burning rate compared with the lower burning

rate. Additionally, the aerodynamic mean particle diameter varies from about

1.5 to 2.5 um as seen in Fig. 5.

The corresponding particle size data for ?MMA is shown in Fig. 6 as obtained from the impactors. In contrast to the PS combustion data, the ratios

obtained for the fuel burning rates (under-ventilated divided by over-ventilated) and the downstream particulate mass concentrations are 1.0 and 3.6, respectively. There, with PMMA combustion at these different combustion conditions, the soot fraction is not constant. Further examination of Fig. 6 does

not reveal any discernible features regarding the size distribution other than

the mean aerodynamic diameter, which is significantly smaller than that of PS

combustion (about 0.7 to 1.0 um).

23
99.99 99.99

LB, U=Low Burn. Upstream

LB, D -Low Burn, Downstream

HB, U - High Burn, Upstream

W HB, D - High Burn, Downstream W

N 0N

99.0 0 99.0 .

W o *0 Wo 4

90.0'. - n 0. Z 2

I- m I--

2 I U) Jp

wJ 50.0 -J 51 L p

tSL U 50.0 go 0 HB, U, pp- 0.0045 g/m3

0 W 0 HB, D, p,- 0.0038 g/m 3

W o 4 LB, U. pp 0.0154g/m3

10.0 . LBH r, 0, 0.0 150g/ 3

> 0 LB, U, ppa 0.0526 g/m3 > 0. HE, U, pH = 0.0051 g/rm3

0 LB, D, pp= 0.0594 g/m 3 0 NB, 0, pp - 0.0048 g/m3

0, HeN, U;, Ppp 0.2030 gus .. * LB, U, Ppp' 0.0202 g/m3

.0 E> NB. D, pp5 0.I1420 g/m 3 0 LB. D, pp 0.0 157 g/m 3

) LB. U, p, p= 0.061 g/m3 1.0LB, U= High Burn, Upstream

0 L, Dp 5 Ig/mHN, .0B D -igh Burn. Downstream

0 HB, D, p,= 0. 1570 g/m3 LB, DU= Low Burn, Downstream

0.01 0.01 I I

0.1 1.0 10.0 100.0 0.1 1.0 10.0 100.0

AERODYNAMIC PARTICLE DIAMETER (MJrm) AERODYNAMIC PARTICLE DIAMETER (MJrm)

Fig. 5. Fig. 6.

Polystryene combustion smoke Polymethyl methacrylate combustion

particle size distribution, smoke particle size distribution.

The effect of the 13.9-m transport length on duct centerline particulate

mass concentration is summarized in Table II. The last two columns provided

the calculation for- p/Ppo' the particulate mass concentration ratio. at the

two impactors, for the experiments and the theory based on only gravitational

settling [Eq. (17)]. Note that the averages of each of the four conditions are

predicted by the theory with an error of less than 10% (based on averages) with

the exception of the PS low burning rate condition, where the experimental result should be rejected.

Going back to Fig. 5, the change in particle size with transport along the

13.9-m length can be observed. With the exception of the larger (greater than

2.0 um) particles, no clear shift in size distribution occurs. However, with

these PS particles, the upstream size distribution by aerodynamic diameter relative to the corresponding downstream data of the same test.suggests an average

particle size reduction of about 1 um.

24
TABLE II

VARIATION OF PARTICULATE M.SS CONCENTRATION BY TRANSPORTa

Fuel Combustion Condition

PS

PS

PS

PS

PM?4A

P 14A

PMMA

P 144A

high

high

low

low

Mass Concentration

ppo(g/m3

0.2027

0.1765

0.0526

0.0685

Mass Concentration

ppo(glm

3

)

0.1415

0.1566

0.0594

0.0681

( lto

Po_______. ' )heo.

0.70

0.89

1.13

0.99

0.84

0.94

0.97

0.78

0.81

0.89

0.83

0.84

0.89

0.75

0.75

0.86

over-ventilated

over-ventilated

over-ventilated

over-ventilated

0.0045

0.0051

0.0154

0.0202

0.0038

0.0048

0.0150

0.0157

aDuct length (from impactor-to-impactor) was 13.9 m.

Figures 7 and 8 show the volumes of soot particles generated by the burner for the two fuels as measured by an optical particle counter (Royco Model

225/518). The main features to note are the large variations of soot particle

10-2

B

10-3

z

0

II2

Ld

U

I- 0 L• unRt

12

10-

0] LOW Burn Rate

t, .ih High Burn r Rate

0 High Burn Rate

io-6

0 5 10 15 20 25 30 35

FUEL BURN TIME (minutes)

Fig. 7.

Variation of particulate volume concentration for polystryene combustion

smoke during fuel sample burns.

E

O

z

0

Iz

U

U)

2

o IO-5

{_j

U

0

0

00

o

O O0 Loe Burn Rate

0- Low Burn Rate

* High Burn Rate

* High Burn Rnte

IU

0 5 10, 15 20 25 30

FUEL BURN TIME (minutes)

35

Fig. 8.

Variation of particulate volume concentration for polymethyl methacrylate combustion smoke during fuel sample burns.

25
output rates and the variation from burn to, burn under the same conditions.

Additionally, peak volumetric output rates for the PS and PMMA fuels vary by

more than an order of magnitude.

B. Smoke Particle Wall Deposition

Table III summarizes the numerical data obtained during the duct wall deposition tests. In these tests, the accumulated particulate mass on the HEPA

filters and the actual particulate mass deposits at the duct wall were measured

in addition to the physical characteristics of the airborne particles as already

described. The values reported for the duct volumetric flow rate are arithmetic averages of the flow at the initiation and conclusion of each test.

First, the experimental deposition results are given in Table IV. The important operational conditions are given in order to identify each test. Under

the columns labeled as "Experimental Data," the experimental results alone are

presented where the final result is a particulate mass ratio, md/mb, and is the

mass deposited on duct walls divided by the mass of unburned fuel. The mass

deposited on the walls, md, is given by

md Ysmb-mf , (18)

where mf is the accumulated particulate mass on the HEPA filter for the fuel

burned. This ratio identifies that portion of the fuel mass that was deposited

on the walls. This calculation assumes the appropriate constant value of YS

(0.33 for PS and 0.021 for PMMA) regardless of the burning condition. This experimental mass-balance technique was not sufficiently sensitive to discern wall

mass deposition at the under-ventilated PMMA burn rate.

Applying the gravitational settling theory requires calculating two variables related to the combustion particles. These are the particle settling

velocity, ups, and the upstream particulate mass concentration, ppob' at the

burner. Because the quantity mpJp is the particulate mass flux, using Eq. (1)

gives

mJ mpJ Us= __p__p = p (19)

mpnp pp

26
Fuel Typ

PS

PS

PS

P S

PMMA

P MMA

Burn

Condition

1.7 m3 /h Combustion Air

Low Burn Rate,

Underventilated

1.7 m

3 /h Combustion Air

Low Burn Rate,

Underventilated

6.8 m3 /h Combustion Air

High Burn Rate,

Underventilated

6.8m3 /h Combustion Air

High Burn Rate,

Underventilated

3.4 m

3 /h Combustion Air

Low Burn Rate,

Underventilated

3.4 m3

/h Combustion Air

Low Burn Rate,

Underventilated

8.5 m

3 /h Combustion Air

High Burn Rate,

Overventilated

8.5 m3 /h Combustion Air

High Burn Rate,

Overventilated

Fuel Mass

burned (g)

200.7

250.0

250.0

250.3

.600.5

600.0

1000.3

1000.0

Total Test

Time (min)

21.9

29.7

14.35

13.60

50.1

52.4

81.9

85.6

TABLE III

DUCT WALL DEPOSITION EXPERIMENTAL DATA

Fuel Mass Upstream

Burn Rate, Volumetric Duct Impactor Conc.

L AirFlow Rate A min Q (m3 1h) m

9.16 1642 0.0526

8.96 1470.. 0.0685

17.42 1589 0.2027

18.40 1439 0.1765

12.0 1607 0.0154

11.48 1448 0.0202

12.26 1700 0.0045

11.70 1530 0.0051

Downstream

Impactor Conc.

_9

m

0.0594

0.0681

0.1415

0.1566

0.0150

0.0157

0.0038,

0.0048

Accumulated

HEPA Mass

Gain (g)

i4.76

32.3

71.02

65.0

22.9

13.0

5.43

5.64

Wall Nuclepore

Filter Mass Deposit

(m ) TOP Side Bottom

0.2 0.2 1.1

0.1 0.1 0.8

0.2 0.3 1.5

0.2 0.4 1.4

0.1 0.1 0.4

0.0 0.1 0.8

0.1 0.1 0.4

0.0 0.1 0.3
O\0

TABLE IV

EXPERIMENTAL DEPOSITION RESULTS USING GRAVITATIONAL SETTLING THEORY

Gravitational Settling Theory Experimental Data

Fuel

Type

PS

PS

PS

PS

PWA

PMM

P 14A

PMMA

Burn

Condition

Low

Low

High

,High

Low

Low

High

High

Fuel Mass

Burned, mb(g)

200.7

250.0

250.0

250.3

600.5

600.0

1000.3

1000.0

/mpJpA

\mh

2.66

1.43

5.53

5.44

Ups

m

44.8

21.0

39.1

34.7

(poc)

1. 10X10-1

1.21x1901

2.17x1-1

2. 53x1O-1

9.42xlo9. 96x 10-3

9'.06x 10-s3

9. 66x 10- 3

Accumulated

HEPA Mass

Gain, mf (g)

14.8

32.3

71.0

65.0

22.9

13.0

5.43

5.64

mdg

17.8

13.4

20.4

20.0

m b

0'.0887

0.0536

0.0816

0.0799

Total Mass

Accounted

(g)

32.6

45.7

91.4

85.0

25.2

17.2

13.2

11.0

Apparent

Soot

Fraction

ysa

0.16

0.18

0.37

0.34

0.042

0.029

0.013

0.011

Vbys

66.2

82.5

82.5

82.6

12.6

12.6

21.0

21.0

md= Ysmb -mf

51.4

50.2

11.5

17.6

-10.3

-0.4

15.6

15.4

md

mb

0.256

0.201

0.046

0.070

0.0156

0.0154

0.422 28.1

0.808 51.5

0.258 67.9

0.185 38.5

2.31 0.00385

4.24 0.00707

7.76 0.00776

5.21 0.00531
where p is the duct centerline particulate mass concentration and was measured at the downstream impactor. The particulate mass wall flux also was measured at the downstream impactor, and thus the Ups calculated here is the downstream value. In this analysis, the ups values are assumed to be constant over

the duct length. Values of ups on the mean aerodynamic particle diameter as

determined by the impactors-are on the order of 1 m/m or less for the two fuels.

Because these values for ups do not reflect the realistic values shown in

Table IV as determined above, the mean aerodynamic particle diameter was not

used and thus not recommended for particle deposition calculations associated

with combustion aerosols.

The second variable, Ppob' is obtained.from

P pob= ' (20)

where Q is the duct volumetric airflow rate (cubic meters per hour). Finally,

modifying Eq. (14) gives the. particulate mass deposit considering only

gravitational settling:

mdg = 1ptj-e .j At *, (21)

where L is the straight duct length between the burner and downstream impactor

(19.63 m) and At is the test duration (in hours). The results from Eq. (21)

and the mass ratio indg/mib are given in Table IV.

Comparing the predicted and experimental PS combustion aerosol deposition

quantities suggests that, within a factor of 2 or 3, the values of mdg/mb agree.

This level of agreement weakly supports the gravitational settling theory.

Additionally, the calculated or apparent PS soot fraction, Ysa' is within 12%

of the 0.33 value at the high burn rate tests, thus indicating the correctness

of Ys for the PS fuel at these conditions. For the low burn rate conditions,

the Y values are significantly lower than the assumed Y value of 0.33.

sa as

Already argued is the consistency of Y based on the fuel mass burn rates and

5

29
downstream particle concentrations. Consequently, the gravitational settling

theory underestimates the mass deposit for the.PS low burn rate conditions.

With the PMMA tests-, comparisions can be made only for the over-ventilated combustion condition; md is negative for the under-ventilated conditions. -Again,

.the mass ratios and soot fractions agreeto a factor of 3 or less..-However,

the consistency of Y data suggests.that Y is indeed different for the two

sa s

conditions--by a factor of at least 2 for these experiments.

Gravitational settling is accompanied by other deposition mechanisms in a

horizontal duct and include turbulent diffusion, inertial impaction, and electrostatic effects. For the horizontal straight duct used in these experiments,

inertial and electrostatic effects were not significant.* To use the wall particulate mass flux measurements made in the vertical and top walls of the duct

at the downstream impactor, an expression for the deposited particulate mass

flux by turbulent diffusion must be developed regarding the flux measurements

made. Rewriting Eq. (6) and incorporating the four sides of the duct (bottom,

top, and two sides), we have

4

Jp =np i= k.+(K pi (2p PS ptt(22) k + ) 

where k is the particle mass transfer coefficient for turbulent diffusion (cenp

timeters per second) and the subscripts s,t, and I refer to the sides, top,

and lower surface, respectively. Proceeding as before with gravitational settling alone, the downstream to upstream particle number concentration ratio assuming constant kpi is

n p e [ 7 ] (23)

n

po

*For long and complex duct.geometrics, both particle inertial and elecrostatic

effects are likely important.

30
and after integration over the duct area,.the particulate mass deposit is given•

by

Mdt =p [ 42e_ýw e 7- At (24)

resulting only from turbulent diffusion.

Table V summarizes the results of the particulate deposition experiments

adding turbulent diffusion to the gravitational settling calculation. In these

calculations, the mass flux measured at the duct bottom wall is separated into

two parts-gravitational settling and turbulent diffusion. The diffusion portion is determined roughly by averaging the side and top particulate mass flux

deposition rates. The gravitational portion then is assumed as the remainder.

In Table V, the values of k are calculated from the particulate flux measurements as

m J

k pi =_ipi (25)

pp.

p

for a specific wall of the duct. Under the heading "Theoretical Prediction,"

the values resulting from the sum of gravitational and diffusion deposition are

given. With.the consideration of these two mechanisms, the PS deposition tests

indicate that the theory underestimates for the low burn rate and overestimates

for the high burn rate total duct wall deposit. With PMMA tests, the combined

theory does fairly well in that agreement is within 50%. Additionally, gravitational settling alone (corrected for diffusion) predicts the actual deposit

to within 15% of the PS high burn rate data. However, the PS low burn rate

deposition data remains unexplained.

In any event, the deposition rates predicted by theory are not fully embraced by the experimental data. Fwo reasons for this are the preliminary and

thus relatively crude nature of the particle deposition experiments and the

simplistic theoretical model used at present in FIRAC. Additionally, because

the mean particle diameters determined by the impactors are much too small, the

31:
TABLE V

EXPERIMENTAL DEPOSITION RESULTS USING TURBULENT DIFFUSION AND GRAVITATIONAL SETTLING THEORY

Gravitational Settling Turbulent Diffusion

Bottom Wall

Nuclepore Filter mpip poc k k

F Mass Deposit for pm p Us - m kpt kpb m d m m d Fuel Burn Burn Mass Only Gravitational m dn m dt d ind Type Condition Burned, mb(g) Settling (mg) h _+-- ( m g( Setln (mg)m-- (g) g ~ g x

PS Low 200.7 0.9 2.17 36.5 1.10x10- 1 14.9 8.13 8.13 8.13 14.6 29.5 0.14700 51.4 0.256

PS Low 250.0 0.7 1.25 18.4 1.21x0- 1 11.8 2.61 2.61 2.61 7.31 18.9 0.0756 50.2 0.201

PS High 250.0 1.2 4.42 31.2 2.17x10-1 16.7 7.85 5.21 7.85 16.8 33.5 0.134 11.5. 0.046

PS High 250.3 1.1 4.27 27.3 2.53x101- 16.2 9.96 4.97 7.47 20.7 .369 0.147 17.6 0;070

PMMA Low 600.5 0.3 0.317 21.1 9.42x0- 3 1.78 7.07 7.07 7lO7 2.50 4.28 0.00713

PMMA Low 600.0 0.7 0.0707 45.0 9.96x0- 3 3.79 6.43 0.00 6.43 14.5 18.3 0.0305

PMMA High 1000.3 0.3 0.194 51.1 9.06x10- 3 6.16 17.0 17.0 17.0 9.15 15.3 0.0153 15.6 0.0156

PMMA High 1000.0 0.2 0.124 25.8 9. 66x10- 3 3.72 12.9 0.00 12.9 26.9 30.6 0.0306 15.4 0.0154
gravitational settling theory current'y used in FIRAC is not conservative but

rather significantly underpredicts the actual particulatemass deposition rates,

by the combustion aerosols tested. Successful particle deposition studies in

which theory and experimental results are mutually supportive will require improved theoretical developments incorporating additional deposition mechanisms

and improved experimental techniques and procedures.

IV. CONCLUSIONS AND RECOMMENDATIONS

We developed the following conclusions from experimental work involving

the combustion products of PS and PMMA fuel.

1. Particulate mass deposition is an important feature associated with

the flow of combustion products and, even for short duct lengths (31

.hydraulic diameters), may reach 25% of the unburned fuel as with PS.

2. Physical changes associated with the transport of the particulate combustion products include a 10 to 30% reduction in mass concentration.

and a small (41-um) reduction in particle size only observable for the

PS combustion particles with an aerodynamic diameter greater than

.2.0 Pm.

Comparisons of the experimental results with the theory incorporating

gravitational settling provide some checks but cannot be considered

supportive. Extending the theory to include turbulent diffusion and

gravitational settling provides improvement for one experimental condition-over-ventilated PMMA combustion-but worsens the agreement for

the high PS burn rate condition.

4. The experimental techniques used in this effort are not sufficiently

sensitive to Verify the deposition models described.

Because HEPA filter plugging rates and efficiencies depend on the airborne

particulate mass and size distributions arriving at the filter, deposition is

an important consideration. The experimental work performed here establishes

some support for the theory developed and used in FIRAC. However, improved

experiments directed at the deposition problem alone are required to establish

.the important deposition mechanisms that should be included in the FIRAC code.

33
ACKNOWLEDGMENT

The au-thors acknowledge 'the assistance of M. V. Gunaji' of NMSU who operated the PNL compustor, ran the test facility, and-made numerous measurements.

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(July 1979), submitted to Second World Filtration Congress.(London,

September 18--20, 1979.).

34
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35
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36
:.DISTRIBUTION

Copies

Nuclear Regulatory Commission, RI, Laurel, Maryland 173

Technical Information Center, Oak Ridge, Tennessee 2

Los Alamos National Laboratory, Los Alamos, New Mexico 40

37

N•C FORM 3W . U.S. NUCLEAR REGULATORY COMMISSION 1. REPORT NUMBER (Assigned by TIDC add Vol. No., if any)

(2-841

NRC20 1. 02BLIOGRAPHIC SHEET NUREG/CR-4321

3201,3202 BI DATA LA-10478-MS SEE INSTRUCTIONS ON THE REVERSE.:.

2. TITLE AND SUBTITLE 3. LEAVE BLANK

Full-Scale Measurements of Smoke Transport and

Deposition in Ventilation System Ductwork

4. DATE REPORT COMPLETED

MONTH YEAR

B AUTHOR(S) June 1985

R. A. Martin and D. L. Fenton 6. DATE REPORT ISSUED

MONTH : EAR

July 1985

7. PERFORMING ORGANIZATION NAME AND MAILING ADDRESS (Include Zin Code) B. PROJECT/TASK/WORK UNIT NUMBER

Los Alamos National Laboratory 9. FIN OR GRANT NUMBER

Los Alamos, NM 87545 A7029

10. SPONSORING ORGANIZATION NAME AND MAILING ADDRESS (Include Zip Code) 11a. TYPE OF REPORT

Division of Risk Analysis Informal

Office of Nuclear Regulatory Research b._PERODCOVRED________dotes

U.S. Nuclear Regulatory Commission

Washington, DC 20555

12. SUPPLEMENTARY NOTES

13. ABSTRACT (200 words or/ess)

This study is part of an effort to obtain experimental data in support of the fire

accident analysis computer code FIRAC, which was developed at the Los Alamos National

Laboratory. FIRAC can predict the transient movement of aerosolized or gaseous material

throughout the complex ventilation systems of nuclear fuel cycle facilities. We conducted

a preliminary set of full-scale material depletion/modification experiments to helpasses•

the accuracy of the code's aerosol depletion model. Such tests were performed under

realistic conditions using real combustion products in full-sized ducts at typical airflow rates. To produce a combustion aerosol, we burned both polystyrene and polymethyl

methacrylate, the most and least smoky fuels typically found in fuel cycle plants, under

varied ventilation (oxygen-lean and oxygen-rich) conditions.

Aerosol mass deposition, size, and concentration measurements were performed.

We found that as much as %25% of polystyrene smoke mass and as little as 2% of the poly- methyl methacrylate generated at the entrance to a 15.2-m duct is deposited on the

duct walls.ý We also compared our experimental results with theoretical equations

currently used in FIRAC.

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STATEMENT

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