Airborne Dust Capture and Induced Airflow of Various 

Spray Nozzle Designs 

Douglas Pollock and John Organiscak 

NIOSH, Respiratory Hazards Control Branch, Pittsburgh, Pennsylvania, USA 

Disclaimer: The findings and conclusions in this article are those of 

the authors, and do not necessarily represent the views of the National 

Institute for Occupational Safety and Health. 

Water spray characteristics, including droplet size and velocity, 

airborne dust capture potential, and induced airflow quantity for 

various spray nozzle designs were evaluated to provide basic information for improving spray applications. Water droplet size and 

velocity characteristics were initially measured by a Phase Doppler 

Particle Analyzer (PDPA) for hollow cone, full cone, flat fan, and 

air atomized spray nozzles at similar operating parameters. Airflow 

inducement and dust capture experiments were also conducted under the same operating parameters to examine any salient features 

of the spray nozzle type, droplet characteristics, induced airflow, 

and airborne dust capture. 

Test results indicate that there are trade offs between airflow inducement and dust capture efficiency. A spray nozzle with a wider 

discharge angle was observed to induce more airflow, but at reduced 

dust capture efficiencies. Increasing spray nozzle fluid pressure(s) 

generally reduced water droplet sizes with concurrent increases in 

droplet velocity, airflow inducement, and airborne dust capture. 

Placing a three-sided barrier around the spray nozzles normally 

reduced spray air induction and increased dust capture efficiency. 

A direct relationship between airborne dust capture efficiency and 

spray input power normalized per unit of airflow induced was observed. This information can be utilized to improve the performance of water sprays for reducing airborne dust levels. 

INTRODUCTION 

Water spray dust suppression systems have made significant 

contributions toward reducing the industry average respirable 

dust exposure of underground coal miners over an 8-hour shift 

from over 6 mg/m3 in 1969 to below 2 mg/m3 today, which 

is the standard set by the Federal Mine Safety and Health 

Administration (MSHA) (NIOSH 1995). However, despite 

this success, the former Bureau of Mines identified a point of 

diminishing ,returns for existing mine spray systems operating 

at higher supply parameters (pressure and quantity) (Schroeder 

et al. 1986; Colinet et al. 1991). It was also shown that these 

spray systems are probably not adequately providing the dust 

control needed for meeting lower permissible exposure levels 

(PEL) enforced by MSHA when silica exceeds 5%(Organiscak 

et al. 1990). MSHA's coal mine dust PEL is a reduced Mining 

Research Establishment (MRE) equivalent respirable dust 

standard of (10 s %quartz) mg/m3 when there is more than 5% 

quartz present in the dust sample, as determined by MSHA's 

P7 infrared method (US CFR 2004; Parobeck and Tomb 2000). 

MSHA's metal/nonmetal mine PEL is a reduced dust standard 

of (10 s (%quartz + 2)) mg/m3 for respirable dust containing at 

least 1 percent quartz, as determined by NIOSH's X-ray method 

(US CFR 2004; Parobeck and Tomb 2000). The percentage of 

airborne coal mine dust samples taken between 1990 and 1999 

that exceeds the 2.0 mg/m3 respirable coal PEL was 8.6%. The 

percentage of airborne dust samples taken between 1990 and 

1999 that exceed the respirable quartz and resulting reduced 

PEL for coal, metal, and nonmetallic mining were 30.196, 

12.4%, and 7.0%, respectively (NIOSH 2003). 

Previous water spray studies have shown differences in airborne respirable dust removal rates for various spray nozzle designs in an enclosed mixing chamber (McCoy et al. 1985). The 

air-atomized and hollow cone nozzles had higher rates of dust 

removal per unit of water flow, while the full cone and ffat fan had 

lower removal rates per unit of water flow (USBM 1982). Spray 

nozzle dust removal rates per unit of water were also found to 

directly increase with nozzle operating pressures in the confined 

dust chamber and were recognized to be a product of increased 

droplet velocity and reduced droplet size. 

While high water pressure is advantageous for confined spray 

dust capture, it can be detrimental to dust capture with unconfined water spray systems commonly used on mining machinery. Laboratory and underground research has shown that as the 

number of spray nozzles and the water pressure are increased 

for unconfined spray systems, the dust capture effectiveness per 

gallon of water is reduced (Schroeder et al. 1986). The improved 

dust capture from smaller higher velocity droplets at higher 

spray pressures is offset by the additional dilution from spray 

induced airflow in the unconfined space (reduced residence time 

or droplet dust interaction). This research also found that operating unconfined water sprays at high pressures can cause undesirable localized air turbulence, pushing contaminated dusty 
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Theoretical models reveal that water spray airborne dust capture efficiency is directly proportional to the relative velocity difference between spray droplets and dust particles and 

is inversely proportional to droplet diameters (Calvert 1977; 

Cheng 1973). Cheng modeled that irrespective of droplet velocity 150-μm, 200-μm, and 300-μm diameter droplets have a relative optimum capture efficiency (mostly inertial impaction) on 

1-μm, 2-μm, and 3-μm particles, respectively. The current study 

experimentally examined the effects of spray nozzle design on 

droplet characteristics, airflow induction, and airborne dust capture efficiency. 

SPRAY NOZZLE TYPE AND WATER DROPLET 

CHARACTERISTICS 

To increase the understanding of air inducement and airborne 

dust capture of different spray nozzle designs, spray droplet sizes 

and velocities were sampled by using a state-of-the-art laser instrument. NIOSH contracted the measurement of spray nozzle 

droplet characteristics to the Spray Systems Technology Center 

(Carnegie Mellon University (CMU), Mechanical Engineering 

is capable of measuring the size and velocity of water droplet

as they pass through the micron-size probe volume of intersect

ing laser beams. The measurements are based on the principle

of light scattering interferometry with an off-axis receiving len

projecting scattered light onto multiple photo detectors. Each 

detector produces a Doppler burst signal with the frequency 

proportional to the droplet velocity and the phase shift between 

the detectors proportional to the droplet size. The PDPA at CMU 

measured droplet velocities in two directions or axes. A descrip

tion of the experimental set up and measurements made on spray 

nozzles can be found in Gemci et al. (2003). 

The spray nozzles were mounted on a traversing mechanism 

so multiple points in the spray pattern could be sampled fo

droplet characteristics. The spray droplet pattern was sampled 

at 3 to 4 equally spaced points along a sectional plane 30.48 cm 

and 60.96 cm perpendicular to the nozzle flow centerline. Th

spacing of the droplet sampling points varied from 1.27 to 5.08 

cm to accommodate various spray pattern angles. The spray pat

tern was sampled on one side of the nozzle centerline, assuming 

to be representative of similar radial regions along the plane

Table 1 shows the nozzle designs that were studied for drople

TABLE 1
 

Spray nozzles and operating parameters studied
 

Spray nozzle Nozzle Performance Spray nozzle droplet 

designation type specifications measurement parameters 

∗Spraying Systems UniJet Single Fluid Hollow Cone 81◦ Spray Angle @ 552 kPa & 552 & 1103 kPa @ 30.48 cm 

Nozzle No. TTD6-45 81◦ HC 3.14 lpm & 60.96 cm Plane 

Distances from Nozzle 

Spraying Systems UniJet Single Fluid Hollow Cone 33◦ Spray Angle @ 552 kPa & 552 & 1103 kPa @ 30.48 cm 

Nozzle No. TTD4-46 33◦ HC 2.95 lpm & 60.96 cm Plane 

Distances from Nozzle 

Spraying Systems FullJet Single Fluid Full Cone 59◦ Spray Angle @ 552 kPa & 552 & 1103 kPa @ 30.48 cm 

Nozzle No. GG3 GG FC 2.99 lpm & 60.96 cm Plane 

Distances from Nozzle 

Spraying Systems UniJet Single Fluid Flat Spray 31◦ Spray Angle @ 552 kPa & 552 & 1103 kPa @ 30.48 cm 

Nozzle No. TT2506 25◦ FF 3.22 lpm & 60.96 cm Plane 

Distances from Nozzle 

Spraying Systems UniJet Single Fluid Flat Spray 56◦ Spray Angle @ 552 kPa & 552 & 1103 kPa @ 30.48 cm 

Nozzle No. TT5006 50◦ FF 3.22 lpm & 60.96 cm Plane 

Distances from Nozzle 

Spraying Systems Air Twin Fluid Full Cone 20◦ Spray Angle @ Air 345 kPa 172 kPa air/water & 345 kPa 

Atomizing Nozzle No. & 150 lpm, Water 276 kPa & air/water @ 1& 2 ft Plane 

J-SU22 SU22 Fluid Cap 1.77 lpm Distances from Nozzle 

60100, Air Cap 1401110 

Spraying Systems Air Twin Fluid Full Cone 21◦ Spray Angle @ Air 303 kPa 172 kPa air/water & 345 kPa 

Atomizing Nozzle No. & 160 lpm Water 275 kPa & air/water @ 30.48 cm & 

J-SU42 SU42 Fluid 1.77 lpm 60.96 cm Plane Distances 

Cap100150, Air Cap1891125 from Nozzle 

∗Mention of any company name or product does not constitute endorsement by the National Institute for Occupational Safety and Health. 
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characteristics by CMU and for air inducement and airborne dust 

capture by NIOSH. The nozzles chosen for this study are common in the mining industry. Single fluid nozzle designs tested 

were hollow-cone, full-cone, and flat spray patterns, and they 

were selected to achieve similar water flow rates at the same operating pressures. Several two-fluid or air-atomizing nozzles in a 

full cone pattern were also tested. Their water consumption and 

operating pressures were considerably less than the single-fluid 

nozzles. Figure 1 shows the types of nozzles tested. 

FIG. 1. Spray nozzles tested. 

All the spray nozzle designs were sampled at two fluid pressures with water being the medium of droplet formation to examine the droplet characteristics with respect to fluid pressure. 

Figure 2 shows the Sauter Mean Diameter (SMD) and mean 

droplet velocity (parallel to the nozzle axis) measurement results 

for the second nozzle listed in the table (33◦ hollow-cone spray) 

one foot away from the nozzle. SMD represents the mean diameter ratio of total droplet volume to total droplet surface area 

of the water droplets sampled. The actual droplet sample measurements were made at the points connected by the solid lines, 

FIG. 2. Spray droplet characteristics 30.48 cm away from the 33◦ HollowCone Nozzle. SMD curves are the darker lines. The lighter lines represent the 

mean droplet velocity. Line thickness represents the water pressure differences. 

which were asymmetrically projected to the other side of th

spray centerline. 

Figure 2 illustrates that this hollow-cone spray nozzle gener

ates smaller water droplets (as defined by SMD) near the cente

of the hollow cone spray pattern, with larger droplet sizes gen

erated away from the nozzle centerline. In contrast, the mea

droplet velocities (parallel to the nozzle axis) are the highest a

the spray pattern center with lower droplet velocities generate

away from nozzle centerline. Another salient feature observe

from these spray droplet characteristics is that higher water spra

pressures consistently decrease SMDs and increase mean drople

velocities across the spray pattern. The other spray nozzles teste

(full cone, flat fan, and air-atomizing) also exhibited relativel

higher droplet velocities at the center of the spray pattern, bu

differed from the hollow cone nozzle by having relatively large

droplet sizes located at the center of the spray pattern. A concis

comparison of the different spray nozzle test data is illustrate

in Figures 3 and 4. 

Figures 3 and 4 show the range of water droplet SMDs an

mean velocities measured across all the spray patterns at bot

planar distances from the nozzle and operating pressures as spec

ified in Table 1. P1 represents the lower test pressure (552 kP

water nozzles and 172 kPa air-atomized nozzles) and P2 rep

resents the higher test pressure (1,103 kPa water nozzles an

345 kPa air-atomizing nozzles) for each nozzle. The vertica

lines within each bar range represent the average centerlin

SMD and mean velocity for both planar distances measured

As these figures show, higher spray nozzle fluid pressure gen

erally reduces droplet sizes (SMD) and increases mean drople

velocities within the spray pattern. It is also evident from thes

figures that there are different droplet characteristics with regar

to nozzle design or type. The hollow cone nozzles, especially th

wider angle nozzle, tend to generate smaller and slower velocit

droplets, while the flat fan nozzles tend to generate larger drople

sizes at moderate velocities. On the other hand, the full con
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FIG. 3. Sauter Mean Diameter ranges measured within various nozzle spray patterns. The vertical line in each SMD range bar indicates the average centerlin

SMD for both planar distances measured. 

FIG. 4. Mean droplet velocity ranges measured within various nozzle spray patterns. The vertical line in each velocity range bar indicates the average centerlin

mean velocity for both planar distances measured. 

(water only and air-atomizing) nozzles tend to generate droplet 

size ranges between the hollow-cone and flat fan spray nozzles, 

with noticeably higher mean droplet velocities generated from 

the air-atomizing sprays. These general spray droplet characteristics are useful for understanding the differences in sprayinduced air movement and dust capture effectiveness, which are 

measured and discussed below. 

SPRAY INDUCEMENT AIR MEASUREMENTS 

An open-ended test duct was constructed from plywood to 

determine the airflow quantity generated by each spray configu

ration in a some what unrestrictive spray environment. The duc

dimensions were 91.44 cm wide by 91.44 cm high by 121.92 cm 

long. The test spray nozzle was mounted 20.32 cm from th

opening on the centerline axis. A hot-wire anemometer with 
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statistical capabilities (VelociCalc model 8346 manufactured by 

TSI Incorporated, Shoreview, MN) was used to take air velocity 

measurements along a nine-point traverse just upstream of the 

spray nozzle inside the duct as shown in Figure 5. Each spray 

nozzle was tested in the test duct to determine the airflow rate 

induced by the spray. Water pressures were set similar to droplet 

measurements at 552 kPa and 1,103 kPa while air velocity measurements were taken. For the air-atomizing sprays (Spraying 

Systems No. J-SU22 and No. J-SU42), the water/air pressures 

were set at 172 kPa and 345 kPa. 

FIG. 5. Air velocity test duct. 

Spray barriers were constructed and mounted under the 

sprays and flow measurements were taken with the same pressures as listed above. The barrier arrangements consisted of platforms that were 30.48 cm wide × 15.24 cm long, 30.48 cm wide 

× 30.48 cm long, 15.24 cm wide × 91.44 cm long, and 30.48 cm 

wide × 91.44 cm long, with removable sides mounted 15.24 

cm and 5.08 cm under the spray centerline. The barrier sides 

were the same dimensions as the corresponding platform (see 

Figure 6). 

FIG. 6. Air velocity test duct with barriers. 

Induced air flow measurements were taken for all spray type

while varying the water pressure, barrier size, and location unde

the spray centerline and installing sides on the barrier. Pressur

versus induced airflow curves were generated for each scenari

and the data from the airflow curves was utilized in the dust cap

ture experiments for the efficiency calculations of the sprays

More specifically, the airflow curves generated from the bar

rier arrangements were analyzed to determine the most advan

tageous arrangement for the dust capture tests. 

It should be noted that the airflow inducement measurement

were utilized for ranking purposes only. To accurately measur

the airflow within this cross section of duct, it would have to b

approximately 10 m long upstream of the spray. Due to spac

limitations and purpose for these measurements, the test duc

utilized for these airflow ratings was sufficient for this work. Th

relative low power provided by the nozzles at the test pressure

would have to overcome the additional restriction from stati

pressure losses associated with a 10 m duct. The purpose of thi

portion of the study was to investigate the relative performance o

the individual spray nozzles under similar operating condition

in a somewhat unrestrictive spray environment. 

LABORATORY DUST CAPTURE EXPERIMENTS 

The spray dust capture efficiency testing was conducted in 

2.44 m high by 2.44 m wide by 2.44 m deep dust chamber. Dus

chamber experiments were conducted for each water spray bot

with and without barrier arrangements to determine the captur

efficiency for each arrangement. Dust was introduced into th

chamber by an air inductor until the concentration reached 

desired ceiling. A 1.1 m3/s mixing fan in the chamber was used t

disperse the injected dust throughout the chamber before the tes

Airborne dust capture efficiency of the sprays was determine

by the removal rate of a known concentration of dust in a know

volume of the chamber over the application time period. Th
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dC 

V = −C(Q + F) dt 

Which is solved and reduces to: 

 −V C 

F = ηQI = ln − Q t Co

Where: 

C–Final Dust Concentration, mg/m3 

Co–Initial Dust Concentration, mg/m3 

Q–Ventilation flow through Test Chamber added from compressed air in air-atomizing sprays, m3/s 

V–Fixed Volume of Test Chamber, m3 

t–Time, s 

F–Dust Removal Mechanism(s), m3/s 

η Q ́–Spray Dust Removal or Cleaned Airflow Rate, m3/s 

Q ́–Ventilation Flow through Spray Induction, m3/s 

η–Dust Capture Efficiency,% 

The dust removal rate (F = ηQ) was primarily the only  ́

mechanism of significance assumed during water spray testing 

with an additional air dilution mechanism occurring inside the 

chamber (Q) during air-atomizing testing. 

For each test, Keystone Mineral Black 325 BA (Keystone 

Filler and Manufacturing Co., Muncy, PA) was introduced to 

reach a level of just over 100 mg/m3 measured by an instantaneous, real-time aerosol monitor (RAM-1, MIE, Inc., Bedford, 

MA). The Keystone Mineral Black 325 BA is bituminous coal 

dust with a size distribution of 100% less than 44 μm and 65% 

less than 10 μm. The RAM-1 was operated at 2.0 L/min with 

a Dorr-Oliver 10 mm nylon cyclone to measure the respirable 

size fraction of dust. When the instantaneous, real-time concentration naturally decayed to 100 mg/m3, two personal MSA coal 

mine dust samplers were run for a 3-minute interval to determine 

the initial average respirable gravimetric dust concentration for 

calibrating the RAM-1 dust concentration at the beginning of the 

spray decay (Co). The MSA coal mine dust sampler consisted 

of a MSA Elf personal pump calibrated to 2.0 L/min, which was 

connected to a Dorr-Oliver 10-mm nylon cyclone to capture the 

respirable fraction of the airborne dust on a MSA coal mine preweighed filter cassette. After the 3-minute interval, the spray 

was operated for a time period required to reduce the RAM-1 

dust concentration to around 30 mg/m3. At this point, the water supply to the spray was shut off and another set of personal 

MSA coal mine dust samplers were run for a 10-minute period 

to determine the final average respirable gravimetric dust concentration for calibrating the RAM-1 dust concentration (C) at 

the end of the spray decay. 

The spray dust capture efficiency performance configurations 

tested in the chamber were conducted by using the same water 

pressures used while testing the air flow characteristics in the 

open-ended test duct. This allowed the testing of the sprays a

the predetermined air flow rate of the sprays (Q ́). For the ai

atomizing nozzles (Spraying Systems No. J-SU22 and No. J

SU42), the water/air pressures were set at 172 kPa and 345 kPa

Three repetitions were randomly conducted for each spray a

each pressure. During the testing, data (RAM-1 concentration

water pressure, and water flow rate) was continuously recorded 

using a Telog model 3307 data acquisition system (Telog Instru

ments, Inc., Victor, NY). 

A testing series was then randomly repeated after placing 

barrier around the spray, which consisted of a plywood channe

30.48 cm wide by 91.44 cm long with 30.48 cm sides, approxi

mately 15.24 cm below the centerline of the spray (see Figure 7)

This barrier arrangement was chosen based on the larger rang

of airflow changes observed during airflow velocity testing. Th

airflow quantity changes encountered using this barrier arrange

ment typically increased by 0.236 m3/sec. From the increase in 

water pressure. The dust capture testing was performed in th

same method as the unconfined sprays. 

FIG. 7. Three-sided barrier set-up. 

Background dust removal mechanisms of the dust chambe

itself were also tested and showed that there was about 1% re

moval efficiency. This was determined by thoroughly wetting 

the interior of the dust chamber, injecting the dust, and mixing 

with the 1.1 m3/s mixing fan (no spray operating) over the sam

time length of time that the spray tests were performed. Afte

three replications were conducted, the background dust chambe

removal mechanisms were considered negligible in these spray 

efficiency determinations. 

AIRFLOW INDUCEMENT AND DUST CAPTURE 

RESULTS 

Figures 8 and 9 show the average spray nozzle test results fo

the airflow induced and dust capture efficiency in the unconfined 
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and barrier configurations, respectively. Variations in dust 

capture experiments are shown by standard deviations (three 

test repetitions). 

Analyzing the sprays according to airflow inducement shows 

that the 81◦ HC (Spraying Systems UniJet Nozzle No.TTD6-45) 

was the best air mover with the air atomizing nozzles (Spraying 

Systems Air Atomizing Nozzles No. J-SU22 and No. J-SU42) 

at the lower end of the airflow inducement scale. The discharge 

angle in the unconfined spray tests seemed to have a direct association with the airflow induced. The discharge angles of th

sprays specified in Table 1 can be compared to the airflow in

ducement (Q ́) shown in Figure 8. The larger angled water sprays

such as the 81◦HC, 50◦ Flat Fan, 59◦ Full Cone (GG FC), and th

33◦ HC sprays, induced higher airflows as compared to the 25

Flat Fan water spray and air-atomizing nozzles with discharg

angles of around 20◦. These airflow induction effects can be at

tributed to the larger spray discharge angle, which acts to mov

a larger cross-sectional area of air. Also, the wider angle spra

FIG. 8. Dust capture efficiency and airflow for unconfined sprays. 

FIG. 9. Dust capture efficiency and airflow for sprays with barriers. 
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nozzles tended to generate smaller water droplets with more airto-droplet surface area interaction. The 81◦ HC spray appeared 

to generate the smallest droplet sizes at the lowest droplet velocities and was the best spray nozzle for moving air as compared 

to the other sprays. The narrow angle, full cone, air-atomizing 

sprays had noticeably less air induction than the other sprays, but 

also had less water mass flow rates for droplet-to-air momentum 

transfer. 

Figures 8 and 9 also show a direct relationship between water 

pressure and air flow quantity. If the pressure to the spray increases, the airflow rate increases. An increase of water pressure 

results in an increase of droplet velocity and a decrease in droplet 

size (see Figures 3 and 4). Smaller and faster droplets impart their 

increased kinetic energy to the air, inducing more airflow. The 

addition of the three-sided barrier around the spray decreased the 

airflow mostly on the wider angled sprays (greater than 25o), as 

seen in Figure 9. This can be attributed to the droplets colliding 

with the barrier sides, and thus losing their energy. Increasing 

the pressure to the water spray also increases the dust capture 

efficiency with the exception of the air-atomizing SU22 and 

SU42 sprays during the testing with the three-sided barrier. A 

slight air-atomizing dust capture efficiency decrease was only 

observed for spray fluid pressure increases on the three-sided 

barrier tests. This reduced efficiency was accompanied by relatively higher induced airflows achieved with the barrier when 

using the narrower angle, air-atomizing nozzles. 

The dust capture efficiency of the spray types appears to compare inversely to the airflow inducement. When the airflow inducement is high, the airborne dust capture efficiency appears 

to be low. While high airflow inducement may redirect the dust 

cloud by acting as a spray fan to sweep the dust cloud away 

from the area, the relatively lower velocity difference between 

the droplet and the air stream likely diminishes droplet/dust impaction processes in dust removal. Sprays seem to have either 

high air-moving characteristics or dust removal capability. Ther

are sprays such as the flat fan sprays that offer medium air move

ment and dust removal capability, as shown in Figure 8. Figur

9 also shows that barrier configurations inversely changed spray 

airflow and dust capture measurements. 

The average spray power input during the dust experiment

was normalized by the airflow induction previously measured 

in the duct at those spray conditions to examine the dust captur

efficiency of all of the sprays in more comprehensive terms. Th

power input is the product of the water flow rate and the wate

pressure delivered to the spray. In the case of the air-atomizing 

sprays, the power input is the sum of the water power input plu

the air power input to the spray. The water and compressed ai

equations used to determine the power input can be found in th

appendix (Glover 1996). The average dust capture efficiency 

relationship to the airflow normalized spray power inputs ar

shown in Figure 10. 

FIG. 10. Spray power and efficiency relationship. 

Figure 10 indicates that a general direct logarithmic relation

ship exists between the spray power per airflow induced and th

capture efficiency during the spray testing. It also illustrates th

trade-offs of dust capture efficiency versus airflow inducement

A spray operating at relatively higher power input per airflow 

inducement has high dust capture efficiency. On the other hand

sprays operating at the lower end of the chart have relatively 

lower power input per airflow inducement. These spray type

are more air movers than dust capturers, and, therefore, the dus

capture efficiency is low. Figure 10 also shows a similar dus

capture effect with the barrier. The barrier commonly reduce

airflow induction, which usually results in an increase in dus

capture efficiency. These trade-offs exist when a spray is im

peded by the barrier; there is a reduction in airflow, but a sligh

increase in dust capture efficiency. 

The operation of the air-atomizing nozzles requires not only 

water but also compressed air to atomize the fluid. Figure 10 
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shows the efficiency of the atomizing nozzles comes with the 

cost of power input by the water plus the large power input to 

compress the air to atomize the water. 

Table 2 lists the spray nozzle power per airflow values for 

nozzle design comparison purposes. The values were calculated using the airflow inducement measurements, water and air 

pressures and water flow rates measured throughout the testing. 

While the spray power can be more accurately determined from 

pressures and fluid flow rates taken with calibrated instruments, 

the spray inducement air measurements had some known inaccuracies from using a short test duct. However, these spray induced 

airflow measurements were made under similar test conditions 

and expected to provide relatively good comparisons between 

sprays. 

Spray 

nozzle 

designation 

Spray power per 

airflow (W/m3/s) 

unconfined P1 P2 

Spray power per 

airflow (W/m3/s) 

barrier P1 P2 

81◦ HC 

33◦ HC 

GG FC 

25◦ FF 

50◦ FF 

SU22 

SU42 

47 

65 

73 

129 

49 

108 

119 

249 

83 

136 

1030 

1804 

1129 

1983 

84 

131 

101 

133 

55 

132 

134 

210 

134 

176 

1057 

1471 

963 

1254 

CONCLUSIONS 

Laboratory testing of several water spray nozzle designs show 

that water supply pressure, spray design, and barriers near the 

spray can affect the airflow inducement and dust capture efficiency of the spray. Increasing water pressure to the sprays 

reduces water droplet sizes and increases the droplet velocities, 

the airflow induction for both unconfined and barrier spray arrangements and the dust capture efficiency of the spray with the 

exception of the air-atomizing SU22 and SU42 sprays with the 

three-sided barrier. 

The spray nozzle designs with the wider nozzle angles tend 

to reduce water droplet sizes and droplet velocities. The flat fan 

nozzles tend to produce the largest water droplet sizes and the airatomizing sprays tend to generate the highest droplet velocities. 

Spray designs with a large discharge angle will induce higher 

airflows compared to sprays with smaller discharge angles op

erate high airflow inducement tend to have low dust captur

efficiency, while sprays with high dust capture efficiency tend t

have low airflow inducement. Barriers placed around the spra

will reduce the airflow induction of the spray while increasin

the dust capture efficiency of the spray. 

Lastly, a direct relationship was also observed between spra

power input per unit airflow versus dust capture efficiency. Th

sprays with the air moving capability were poor performers fo

dust capture efficiency, and those with poor airflow inducemen

had high dust capture efficiency. Also, the addition of barrier

caused a reduction in airflow rate and an increase in efficiency

Based upon the information of spray nozzle performanc

characteristics obtained through this testing, NIOSH is devel

oping water-powered scrubbers and spray systems to be teste

for dust control performance in multiple mining applications. 

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APPENDIX

This appendix contains fluid power equations (at standard

barometric pressure and air density).

Spray Power per airflow (Psprays/Q’):

Spray power (Psprays) per airflow for conventional sprays is

equal to (pwater)(Qwater)/Q'

where

pwateris the gage pressure (Pascals),

Qwateris the water flow rate (m3/sec) and

Q’ is the ventilation flow through spray induction (m3/s).

For the air-atomizing sprays, Psprays=Pwater+Pair

where

Pwater is the hydraulic power (watts) = ((pwater)(Qwater))

and

Pair is the theoretical power (watts) to compress the air at

standard conditions.

 0.283 pair Pair = 357,943(Qair) + 1 − 1

101,353

where

pair is the gage pressure of the air to the nozzle in Pascals

and

Qair is the atomizing air flow rate to the nozzle in m3/sec.