outflow side. At depths exceeding 30 ft, the inflow was
entrained by the higher velocity outflow, which then pro-
ceeded toward the last open crosscut.

Also, the largest quantity of inflow air to the return
sides occurred at a distance of 50 ft from the fan. This
distance agreed with the initial assessment by researchers
regarding the position of the eddy zone. Therefore, it ap-
peared that strong inflow existed to a point roughly 50 ft
from the fan outlet. At greater distances, the jet stream
was greatly diminished and most likely characterized by
weaker, nondirected flow.

These anemometer surveys provided some insight into
the flow patterns in the heading. However, because of low
and erratic air velocities near the face, tracer gas surveys
were conducted to obtain more accurate estimates of these
flow quantities.

TRACER GAS SURVEYS

The tracer gas used in this study was sulfur hexafluoride
(SF,). This gas is safe, odorless, not found naturally, and
detectable at low concentrations (10° ppm). To find the
effectiveness of a jet in ventilating a known volume, V, SF,
is released uniformly throughout the volume. It has been
shown (10) that the SF, concentration, C, at any time, t,
decays exponentially as

C= CeO, (0))

where Q is the amount of fresh air entering the volume,
V, and C, is the initial concentration of SF, A plot of
concentration versus time on semilog paper gives a straight
line with a slope equal to -Q/V. The slope is written as
the following relationship, where C, and C, are concen-
trations along the slope line at t, and t,.

-O/V = In(Cy/Cy)/(t - ). @

Knowing the slope of the best fit line and the volume of
the heading, the quantity of fresh air, Q, can be calculated.
More complete descriptions of tracer gas studies are found
in Thimons and Kissell (10).

For this test, a single sampling line was hung at the face
area; the line was positioned in the middle of the heading,
1 ft from the face and 1 ft from the top. To begin the
test, 10 cm? of SF, was released throughout the heading.
Uniform mixing was achieved by pulsing the jet fan on and
off. Samples were then collected every minute for 3 min
from this face location to establish a baseline reading.
With the check curtain in place, the jet fan was turned on.
Samples were then drawn from this location every 30 s for
5 min. The check curtain was then quickly removed and
samples were again drawn every 30 s for 5 min.

Assuming the volume of the gallery to be 10,080 ft? (16
by 7 by 90 ft), a uniform release of 10 cm? of SF, would
lead to an initial concentration at the face of 0.035 ppm.
This figure closely agrees with the initial values shown in
figure 10. These results also reveal that without jet fan
operation the decay curve is essentially flat, indicating that
very little air reached the face area, When the fan was
turned on, the SF, concentration decreased, indicating that
fresh air was reaching the face area.

The amount of fresh air reaching the face was calcu-
lated from equation 2 by multiplying the slope of the
semilog plot by the value of (-V). In this case, the volume,
V, was the volume of the eddy zone situated between the
limit of jet penetration and the face area, The eddy zone
was 40 ft deep, 16 ft wide, and 7 ft high, or 4,500 ft’.
Using a slope equal to -0.482 yielded a fresh air quanti-
ty, Q, of 2,200 cfm (fig. 10). This value represented the
amount of fresh air moving at this location and not the
total airflow. The total flow would undoubtedly be greater
because of entrainment.

Five minutes after the fan was turned on (8 min af-
ter test start), the curtain was removed, The effects of
this action were quickly apparent. Because of increases
in recirculation at the fan, the slope of the decay curve

[ol p++ T T TT 7
\ Slope ¥ 0.000 q
— a
r \ssione =-0482 |
ford N
E ‘,
& ' R Si
2 NS lope = -0.221
6 | Awe J
N N
1o3 E J
r Curtain up t Curtain |
Fa ]
Hoff +—_—_ Fan on ————*
lo4 1 1 bot

o 2 4 6 8 10 12 14
TIME, min

Figure 10.—Decay curve of initial tracer gas test.


UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT

cubic foot per minute L/min iter per minute
cubic centimeter min minute

foot mL milliliter

cubic foot pet percent
horsepower ppm part per million

inch s second



80 Velocity near roof
(130) Velocity near floor

KEY

— Airflow toward face

= Airflow away from face

DISTANCE FROM FAN, ft

T T T T
OF 560 - +350 > 80 ° 4
. (1,750) —> (680) (130) (64)
- 440 — +320 = 60 °
- 2F Fan (1,330) — (650)—+ (140) 0 7
o alone \
z L 400 — +470 ° ° J
4 vet PN93— (740) —> (110) (a)
t angle oN 430 + 160 0
wy 6 (340) \ (760) (200)—* 0 J
— 340 \ +440 160 — +60
2 8r (280) (540) — = (60) (0) 7
= 520 +460 170 — °
i iof (450) (470) (110) (0) 7
8 L = 550 \ 7480 ° ° J
z '2 (360) (350) + (0) (0)
E +510 530 ° 70 —
Q l4F (330) Vo 1140) (eo 7
~
L = 530 SION = 160 ° 4
16 776590) 1340) SN 1130) (0)
1 nN
° 10 30 50 70
DISTANCE FROM FAN, ft
Figure 4.—Velocity readings (feet per minute) using fan alone.
KEY
80 Velocity near roof —> Airflow toward face
(130) Velocity near floor + Airflow away from face
T T T T
L 350 — + 270 170 70
_~ Of GE 4,765= (520) rf) 038)
= Fan \ 210 — 770 — + 250 150 —»
- 2PF and \ (860) (1,180) (960) + = (70) 4
o nozzle \
pd — 130 670 — + 300 180 —
oe  4P ZK (840) (730) (800) — (250) —
t ott § 240 200+ +290 130 —
a «6fane \ (190) (600) — (580) (60) J
2 — “290. + 290 + 290 170 —
z= 8F = (2507 ~~ (0) (450) (100) —
fe — 340 — BOTT = 3202 === =150 =.
a 10F = (240) = (390) = (220) (100)
8 -— 420 = 700 = 340 — 80
Z lap = (370) = (510) (160) +0120) J
EB | = 490 - 740 + 400 = 180
Z '4 = (320) — (560) (380) (140
a = 340 =— 870 = 440 so |
16 L340) = (760) 10) = 1120)
° 10 30 50 70

Figure 5.—Velocity readings (feet per minute) using fan plus nozzle.


INTRODUCTION

A number of factors have been responsible, in part, for
the increasing productivity of continuous mining sections
over the past decade (7). One of these is the increasing
use of extended cutting. In extended cutting, the con-
tinuous miner advances from 20 to 40 ft, rather than the
usual 10 to 20 ft. Distances beyond 40 ft are rare because
of limitations of ventilation systems, roof control methods,
shuttle car haulage, and operator visibility. Extended
cutting results in more time spent in actual mining and less
time spent in tramming the miner between entries. How-
ever, many questions concerning the safety of extended
cutting remain unanswered.

Several ventilation techniques have been used in con-
junction with extended cutting systems. These techniques
include machine-mounted scrubbers, sprayfan systems, im-
proved sprayfan systems, and extensible line curtains, To
date, face ventilation systems for extended cuts have been
adaptations of conventional practices, in which tubing or
brattice is maintained within 40 ft of the working face.

It is quite likely that the advantages of extended cutting
can be enhanced by cutting from crosscut to crosscut
where cut depths could exceed 100 ft. Cut depths of this
magnitude would require ventilation techniques quite dif-
ferent from existing designs with the ability to supply
sufficient quantities of air to remote face areas.

One possible method is to use a jet fan to ventilate very
deep cuts. A jet fan is simply a freestanding fan that uses
little or no ducting to direct the ventilation flow to the
face. In very deep cutting situations, this is a distinct
advantage. With any ducted ventilation system, tubing or
curtain would have to be handled remotely because there
would be no workers near the face area (2).

The jet fan is usually placed on the upstream corner of
the last open crosscut. The fan projects a high-velocity jet
of air that expands by entraining the surrounding air into
its stream. The jet expands until, ideally, the fresh air is
flowing to the face in half the crosscut and returning as
contaminated air through the other half (fig. 1). Through
entrainment of the surrounding air, a jet fan can deliver a
volume much greater than its rated capacity. This in-
creased volume improves mixing of the contaminated air.
A recent study found that entrainment ratios averaged 4:1;
that is, entrained volumes were four times as large as the
fan output (3). The total volumetric flow moving to the
face was then five times the fan’s output.

Jet fans have been used traditionally to ventilate faces
in metal-nonmetal operations with large cross-sectional en-
tries. In one instance, a large jet fan (55 in, 100,000 cfm)
adequately ventilated a face 300 ft distant (4). In another

‘Italic numbers in parentheses refer to items in the list of references
at the end of this report,

instance, a smaller fan (29 in, 20,000 cfm) adequately ven-
tilated a 150-ft heading in a large copper operation (5).

Despite the apparent appeal of jet fans for ventilating
faces, a number of questions remain regarding their
effectiveness in coal mining operations (2). One concern
in jet fan use is the recirculation of contaminated air,
which arises when contaminated return air finds its way in-
to the fan inlet. Dust and gas concentrations at the face
may not decrease, but may actually increase because the
intake air is contaminated (6). Although recirculation of
contaminated air is a potentially serious problem, it can be
easily controlled by mounting a length of rigid ducting on
the fan inlet and pointing this ductwork into the fresh air.
Recirculation can also be controlled by extending a check
curtain from the jet fan side of the entry to a point
midway across the entry and draping it on top of the fan.
Either measure ensures that contaminated air is unable to
find its way into the fan inlet.

Another concern is the limit of effective ventilation or
penetration distance of the jet flow. At this point, the flow
ceases to move toward the face and begins to move away
from this area. This depth limit depends upon the velocity
and integrity of the air jet, that is, the coherence of the jet
downwind of the fan outlet. It also depends on the char-
acteristics of the entry, such as its size and roughness. A
very rough surface could detach the jet from the rib, thus
reducing effective penetration.

Penetration distance of a jet in a large opening in-
creases, however, if the fan is placed against one rib (7).
In this configuration, the rib permits the formation of only
a half-jet so that the total jet energy acts on only half the
jet. Experimental results indicated that the penetration
distance was effectively doubled by restricting jet expansion
in this manner (8).

Intake air

a
* ia re
§ ¢

Return air

—

Outflow

Figure 1.—Idealized Jet flow in entry showing Inflow and
outflow.



JET FAN VENTILATION IN VERY DEEP CUTS—A
PRELIMINARY ANALYSIS

By Gerrit V. R. Goodman,’ Charles D. Taylor,? and Edward D. Thimons?

ABSTRACT

Future coal mining systems will be able to cut from crosscut to crosscut where advances could exceed
100 ft. However, limitations arise when ventilating such mining systems. In deep advance mining, there
would be no workers at the face to advance ventilation tubing or curtain manually. Traditional methods
also provide no means for maintaining face ventilation after the miner backs away from the face. U.S.
Bureau of Mines research is studying means to provide effective ventilation at cut depths beyond the
current limit of 40 ft.

Several innovative ventilation schemes are currently being considered. One such method is the use
of a jet fan to ventilate a deep cut. A jet fan is simply a freestanding fan using little or no ducting to
direct the ventilation flow.

Jet fan testing in a 90-ft entry revealed that higher exit velocities and greater penetration depth
occurred when various configurations were used to confine and direct the air flow. Additional testing
also indicated that 2,200 cfm of fresh air was delivered to the face.90 ft distant when a check curtain
was used to limit entrainment around the fan. Without this curtain, this quantity dropped to only 1,000
cfm.

This testing indicated that a jet fan was capable of providing ventilation to a distant face area. It also
highlighted potential problems, such as recirculation at the fan and reentrainment in the jet flow.
Despite these potential problems, jet fans may be adequate for ventilating cuts exceeding 40 ft.

‘Mining engineer.

Industrial hygienist.

3Supervisory physical scientist.

Pittsburgh Research Center, U.S. Bureau of Mines, Pittsburgh, PA.


FAN ALONE

FAN PLUS INJECTOR TUBE

FAN PLUS NOZZLE

‘Ome fins

FAN PLUS FLOW EXTENDER

Figure 3.—Fan configurations used during testing.

the fan were much more predictable, with well-defined
boundaries between the inflow and outflow airstreams,
Beyond a distance of 50 ft from the fan, however, the flow
in the heading was extremely erratic, characterized by
numerous eddies and airflow reversals,

The data in figure 4 show the velocity readings in the
heading when ventilating with the fan alone, The jet
angles at various distances from the fan also were also
determined from these data. The velocity readings taken
near the floor, as opposed to those near the roof, were
used to determine jet angle, because the fan was blowing
closer to the floor than the roof.

At a distance of 10 ft, the airflow direction changed
from inflow to outflow (positive to negative) roughly 5 ft
from the rib when using the fan alone. This corresponded
to an expansion of 26°. At a distance of 30 ft from the
fan, the jet expanded to a width of 14 ft. This cor-
responded to a jet angle of 25°. At a distance of 50 ft, the
jet flow became nonuniform and, hence, very unstable. As

evidenced by the data in figure 4, the jet detached from
the rib and began to move into the center of the heading.
A "fishtail" flow pattern developed, with return flow
forming along the left and right ribs, This resulted in a
loss of jet integrity and, hence, a smaller penetration of the
heading. Smoke tubes revealed a maximum penetration to
approximately 60 ft from the fan.

Flow along the roof of the heading was directed toward
the face to a distance of 10 ft. At distances of 30 and
50 ft, the flow at the roof began to move away from the
face. The flow at 70 ft was almost nonexistent.

A similar test was conducted using the jet fan plus
conical nozzle to ventilate the heading. The results in fig-
ure 5 indicate several major differences. The first was the
increased coherence of the jet flow as evidenced by the jet
angles. At distances of 30 and 50 ft from the fan, the jet
angle ranged from 10° to 15°, The smaller jet angle result-
ed in increased jet velocities at these distances compared
with velocities from the fan used alone. At a distance of


IRI] 9399 | REPORT OF INVESTIGATIONS/1992

Jet Fan Ventilation in Very Deep
Cuts—A Preliminary Analysis

By Gerrit V. R. Goodman, Charles D. Taylor,
and Edward D. Thimons

__ UNITED STATES DEPARTMENT OF THE INTERIOR

BUREAU OF MINES


80 Velocity near roof
(130) Velocity near floor

KEY

— Airflow toward face
+ Airflow away from face

T T
830

T T

L 220 > 200-- +80 |
_ ? a, (2,850) — (1,540) > (50) = (110)
tem MEO BBS BT eB
a extender AMNESO) ,260) —> (740) + = (120)
=z L 907. 670 — ° ° |
4 J +1150) ~~G10— (770)—* (130)
ft [vet angle «259 240-270 +180
4 6 + (340) + (270) SS, (570) = (110) 7
= 230 +210 NL 210 - EO
5 8r (190) (0) “BI See TM (70) —
& — 320 = 460 — 320 (90 —
wy OP = (280) = (420) (150) (oo) J
Z job = 260 = 530 = 380 200 — |
2 (400) — (500) (220) (60)
5 oat = 270 = 690 + 390 so |
2 = (280) (650) (420) (80) —*
i6b = 200 = 660 = 390 120 + |
210) = (720) +1380) (70)
fe} ie) 30 50 70
DISTANCE FROM FAN, ft _

Figure 7.—Velocity readings (feet per minute) using fan plus extender.

A reasonable explanation is that the increased flow from
the injector (9,300 cfm) simply increased turbulence in the
heading. This turbulence resulted in increased eddying,
which decreased penetration depth. This hypothesis was
verified by reducing the output volume using the inlet vane
controller. While using the fan plus injector and setting
the controller to 9,300 cfm, the penetration depth re-
mained about 50 ft. As the flow was reduced to 8,900 cfm
and then to 5,600 cfm, the penetration depth did not
change appreciably.

To better define the flow patterns in the heading,
several additional analyses were conducted. To avoid

ANALYSIS OF JET FAN PI

ANEMOMETER SURVEYS

Anemometer traverses were conducted to determine the
quantity of air flowing to the face at various distances from
the fan. By using smoke tubes, the jet angle could be eas-
ily approximated. Traverses were then conducted in both
the inflow and outflow jet streams at distances of 10, 30,
50, and 70 ft from the fan. The flow beyond 70 ft was dif-
ficult to detect with the instruments, To quantify the
amount of recirculation into the fan inlet, readings were

repetition, only one fan configuration was selected for
these additional tests. The flow extender fan configuration
was selected because of its cohesive jet flow. Although the
injector configuration performed similarly, this setup was
considered to be too cumbersome to use in actual practice.

In the previous series of tests, there were insufficient
data to conclude that the helical fins in the flow extender
led to cohesive jet flow. It is likely that the characteristics
of the jet flow were influenced by both the presence of the
helical fins and the confining action of the extender tube.

LUS FLOW EXTENDER

also taken near the inlet, All readings were taken using
a standard vane-type anemometer mounted on a slender
rod.

Using these anemometer readings, a ventilation circuit
was constructed that indicated the average flow at various
distances from the fan outlet. The flows in the inflow and
outflow jet streams were balanced by introducing entrain-
ment quantities, However, entrainment in the heading was
not a point-type phenomenon, but rather a continuous flow
of air between the inflow and outflow airstreams.


80 Velocity near roof
(130) Velocity near floor

KEY

— Airflow toward face
+ Airflow away from face

T
47

T T
> = 250

T
140 —

DISTANCE FROM FAN, ft

T
L ‘0 340
, ? oq (2,260) (1,030) —> (720) (90)—
= ak ond 312 400+ = 240 80 +
a injector L760) (1,000) > (820)—> (90) —
z L 220 ty. 470 > 200 100 —+
4 Jet ange (210) Ny (8900+ (640) (150)—>
tL vet angle ° NC 190 = 160 50 —
Wj 6 (260) (550) (450)—> (270) —>
.
= 310 + 370 = 150 Q
= 8 (250) (OPS ti60)—» (0)
= 290 +270 = T60 ~ O OET
e lor (320) 0) (0) (0)
oS lob + 370 330 = 180 160
Zz 12 (290) (220) (0) +{60)
Boab = 380 = 340 = 180 =130
2 '4 +-(200) (210) (420) (50)
16+ = 380 — 360 +270 fo}
(280) (340) (380) (80)
° 10 30 50 70

Figure 6.—Velocity readings (feet per minute) using fan plus injector.

70 ft from the fan, the jet flow detached from the rib with
the inflow situated in the region 4 to 8 ft from the rib,
Outflow was present in the other areas. For this fan com-
bination, penetration was approximately 70 ft from the fan.

For the fan plus conical nozzle, flow along the roof of
the gallery extended to 70 ft from the fan, At a distance
of 50 ft, the flow reversed and began moving away from
the face. At 70 ft, inflow was present at the roof near the
center of the heading, with return flow present at the ribs,

Velocity readings were also taken for the jet fan plus
injector (fig. 6) and for the fan plus flow extender (fig. 7).
The results for both configurations were quite similar and
indicated a very well established jet flow, even to depths
exceeding 50 ft. Definition of the jet stream led to very
high velocities throughout most of the flow regime. The
jet angles averaged roughly 13° at depths of 50 ft. Ef
fective penetrations in both cases averaged roughly 50 ft,
although a small positive flow was still present at a dis-
tance of 70 ft when using the fan plus injector. Using an
average penetration distance of 50 ft, this left a 40-ft eddy
zone located between the limit of jet penetration and the
face area.

The presence of eddy zones in face ventilation has been
discussed in detail by Kissell and Bielicki (9). These zones
were found to be poorly ventilated, compared with the rest

of the face area, and as such were often characterized by
nonuniform airflow.

In the current study, the important factors were limited
to jet velocity, jet flow coherence, and penetration depth.
Of all the fan configurations investigated, the jet fan with-
out any nozzle exhibited the lowest jet velocities, poorest
jet flow coherence, and the smallest penetration. The rel-
atively large jet angle of 23° to 26° led to a rapid extin-
guishment of the jet flow at distances beyond 50 ft from
the fan.

Ventilating the heading with the fan plus conical nozzle
produced better results. The improvements most likely
arose from the constriction of the airflow at the nozzle.
Similar results have been noted by Krause (8), who found
that a simple conical nozzle reduced the angle of expan-
sion of the jet stream. Krause also concluded that a jet
with a small expansion angle would have a greater pene-
tration than one with a large expansion angle (8). Al-
though these comments were only applied to air jets in
very large openings, a similar effect can be seen in these
results, When the flow was confined by a nozzle, injector,
or flow extender, the penetration depth was increased.

Only small differences in penetration were seen among
the nozzle, injector, and flow extender fan configurations
despite the increased flow volume from the injector tube.


Previous work has shown that jet fans are well suited
for ventilating large entries in metal-nonmetal operations.
However, the feasibility of jet fan ventilation in smaller
coal mine entries has never been fully investigated. There-
fore, the U.S, Bureau of Mines conducted testing to deter-
mine if a jet fan could provide adequate ventilation for

very deep cuts in coal mine operations. This testing was
seen as the first step toward the development of ventilation
schemes compatible with future crosscut-to-crosscut min-
ing systems. This research was performed in support of
the Bureau’s mission to ensure the continued health and
safety of miners.

JET FAN TESTING

Jet fan testing was done in an L-shaped gallery. A
40-hp Joy Series 1000° vane axial fan (23,25 in diameter,
13,500 cfm) was used to pull air into the gallery through
two access doors in one end of the building (fig. 2). A
curtain was erected to draw this air across the entrance to
a 90-ft wing of the building. This wing was 16 ft wide and
7 ft high, and it was used to simulate a blind coal mine
heading. Air passing by this heading simulated airflow in
a last open crosscut. With the main fan operating, roughly
13,500 cfm flowed into the gallery and then behind the
return curtain.

An 18-in-diameter vane axial fan rated at 6,800 cfm was
used as the jet fan. Airflow was regulated using an inlet
vane controller mounted on the intake of the fan. During
testing, the fan was positioned against the left rib in the
upstream corner of the last open crosscut to blow into the
90-ft heading. The centerline of the fan outlet was 2 ft off
the floor. Various fan and nozzle configurations were

Reference to specific products does not imply endorsement by the
US. Bureau of Mines.

40-hp gallery fan

tos"

tested to evaluate their effectiveness in ventilating a face
90 ft distant.

Point velocity readings were made during fan testing.
These measurements were made at specific locations
within the gallery: 10, 30, 50, and 70 ft from the fan outlet
and at 2-ft intervals across the width of the gallery. At
these locations, readings were taken 2 ft and 6 ft off the
floor. The number and location of these readings were
necessary to define the complex nature of the jet flow in
this 90-ft heading. Digital vane-type anemometers (model
AN-8600) manufactured by Material Control, Inc., were
used to determine the velocity readings at each point.

The penetration depth and expansion angle of the jet
flow were also examined and recorded during testing using
smoke tubes. The depth of penetration was the location
at which the smoke ceased to move toward the face, The
expansion or jet angle was the angle at which the air-
stream expanded after leaving the fan. It was along this
line that considerable mixing occurred between the high-
velocity and low-velocity airstreams, Near the fan, out-
flowing air was entrained into the higher velocity inflowing
airstream. At greater distances from the fan, the inflow
was entrained into the outflow airstream.

During testing, several different fan configurations were
investigated (fig. 3). The first configuration was simply the
fan by itself with no tubing or nozzles used. The second
was the fan plus a conical nozzle. This nozzle was 16.5 in
long with an outlet diameter that was reduced from 18 to
14.5 in. In the third configuration, the fan was positioned
to blow into a 10-ft length of 24-in-diameter rigid tubing.
The tubing was positioned 12 in downstream from the fan
outlet to allow additional air entrainment at the fan outlet:
Analysis of this “injector” arrangement using an equal-area
pitot tube traverse revealed that the total fan output was
increased to 9,300 cfm. This represents nearly a 40-pct
increase in volume flow due to entrainment of air into the
24-in-diameter tube.

The final fan configuration was an 18-in-diameter, 48-
in-long “flow extender" mounted on the fan outlet. This
extender had a set of helical fins welded on the inside to
impart a slight spinning action to the airflow.

Flow velocity measurements were made for each of
these different fan configurations. In general, flows near


CONTENTS

Analysis of jet fan plus flow extender...
Anemometer surveys
Tracer gas surveys ....

Discussion and conclusion .

References ..

ILLUSTRATIONS

Idealized jet flow in entry showing inflow and outflow
. Jet fan gallery showing test setup .....
Fan configurations used during testing .
Velocity readings using fan alone . . .
Velocity readings using fan plus nozzle .
Velocity readings using fan plus injector
Velocity readings using fan plus extender .
Balanced ventilation network using fan plus extender . .
Balanced ventilation network using fan plus extender and check curtain .
Decay curve of initial tracer gas test..........
Tracer gas test results ............. eeseees

PEP PAAMVAYNE

aw

1. Results of constant flow tracer gas test ..........0. eee eee nna eee eee n ee eeee

z

BB ewrauene

10


10

decreased to -0.221, showing that less fresh air was reach-
ing the eddy zone at the face. In fact, the amount of fresh
air dropped to 1,000 cfm after removing the curtain.

Although this test did provide a preliminary estimate of
the airflow reaching the face area, the calculations in equa-
tion 2 involved an estimate of the value of the eddy zone
volume, V. Because it was not possible to directly meas-
ure this volume, further confirmation of its size was
necessary,

Tn this test, SF, was released into the gallery at a con-
stant rate while samples were taken at specified time in-
tervals. The concentration, C, measured at any point is
equal to the ratio G/Q, where G and Q are the flow rates
of SF, and fresh air, respectively,

Three sampling lines were hung in the gallery. One
Tine was hung behind the return curtain leading to the
main gallery fan, The line was positioned in the middle of
the return airstream and 1 ft from the top. The remaining
sampling locations were positioned at the face 5 ft from
the left rib and 5 ft from the right rib, These lines were
hung 1 ft from the face and 1 ft from the roof. Samples
were again drawn through these lines at 1.7 L/min and
collected in 20-mL evacuated containers.

To begin the test, 1,000 ppm SF, was released at the
gallery face at a constant flow rate of 0.5 cfm. Samples
were taken at the two face locations every 15 min for
60 min with the jet fan off to establish a baseline. With
the check curtain in place, the jet fan was then turned on.
Samples were taken from all three locations every 15 min
for 90 min. The check curtain was then removed with
samples again drawn every 15 min for 90 min, The results
of the sampling are indicated in figure 11,

To determine the quantity of fresh air reaching the left
and right sides of the face area, it was necessary to find
the values of G and C at each face location, The value
of G was assumed to be constant throughout the test at
(1,000 x 10)(0.50 cfm) = 500 x 10* cfm, The value of
C was simply the average concentration at each sample
location.

As shown in table 1, the average fresh airflows reaching
the face with the curtain up and with the curtain down
were 2,000 cfm and 890 cfm, respectively. These average
airflows were very close to the values of 2,200 cfm and
1,000 cfm calculated from equation 2, The close agree-
ment of these values affirms that the eddy zone starts
about 40 ft from the face. The agreement also suggests
that the volume, V, in equation 2 should be the eddy zone
volume rather than the total volume of the heading, as
reported by Matta, Thimons, and Kissell (5). Using the

total heading volume for the value of V overestimates the
amount of fresh air entering that volume,

Table 1.—Results of constant flow tracer gas test

(Gas flow rate, 500 x 10% cfm; average retum
concentration, 0.05 ppm)

Average face = Fresh alr

Tost concentration, flowrate, FVE
ppm etm

200 0.02

3,800 38

2,000 20

170 02

1,600 6

800 09

FVE —_Face ventilation effectiveness.

During this final testing, several trends became appar-
ent. First, the presence of the check curtain across the fan
had a measurable effect on the quantity of fresh air reach-
ing the face area, This finding was consistent with results
from the initial tracer gas survey. Second, there was con-
siderable variation in the airflow along the face, where the
tight (off-fan) side was much better ventilated than the left
(fan) side. This variation indicates that the jet flow de-
tached from the left rib and moved to the right side of the
face. The fan side of the face received significantly less
fresh air than the off-fan side.

Although this testing was conducted without any in-
place mining equipment, it is possible that the airflow im-
balance would also be present at the face area during cut-
ting. In this case, the left side of the face could experience
dangerous gas concentrations, Therefore, sprayfan and
scrubber systems must be designed to hold the jet stream
along the fan-side rib until it reaches the face. Testing will
be necessary to determine the proper capacity and orienta-
tion of these sprayfan and scrubber systems.

Jet fan effectiveness can be assessed by measuring the
quantity of fresh air reaching the face area, However, a
more desirable means is to calculate the face ventilation
effectiveness (FVE). FVE is the ratio of the gas concen-
tration in the return to the concentration at the face.
From the last tracer gas test, the average return concentra-
tion was 0.05 ppm SF, (fig. 11). Using the average face
concentrations given in table 1, the FVE values were cal-
culated. These values also reveal the imbalance in airflow
at the face area, with the right side better ventilated (high-
er FVE) than the left side (lower FVE).


DISCUSSION AND CONCLUSION

This report describes research by the Bureau to define
and characterize the flow in a 90-ft heading ventilated by
a jet fan. Several fan configurations were investigated: a
fan without any ductwork, a fan plus conical nozzle, a fan
plus 10-ft injector tube, and a fan plus 4-ft flow extender.

First, digital anemometers were used to determine point
velocities at various locations throughout the test gallery.
The results indicate that the highest jet velocities arose
when using the fan plus flow extender. This configuration
translated into a more cohesive jet stream and greater
penetration depth. Jet angles averaged 13° at a depth of
50 ft from the fan. Measurable penetration was roughly
70 ft. In general, fan configurations using some type of
constrictive device on the fan outlet exhibited more con-
fined jet flows, lower jet angles, higher jet velocities, and
greater penetrations. In contrast, the jet fan without any
ductwork resulted in a jet angle of 25° at 30 ft and a pene-
tration of only 60 ft.

Tracer gas was then used to provide detailed informa-
tion on the flow characteristics in the jet stream. The fan
plus flow extender was selected for this test. To improve
flow conditions near the face area, a check curtain was
installed over the jet fan. Then, samples were taken of the
flows with and without the check curtain. Calculations
made using samples taken with the curtain up showed that
2,200 cfm of fresh air was delivered to the face area 90 ft

from the fan, With the curtain removed, the fresh airflow
at the face was reduced to 1,000 cfm.

Although this test did provide an indication of the fresh
air quantity flowing to the face, the calculations relied
upon a volume value that was not independently confirm-
ed. Thus, another SF, test was conducted to verify its size.
The results of this test confirmed the initial finding that
this volume, or eddy zone, began 40 ft from the face.
From these data, face ventilation effectiveness values also
were calculated. These values revealed that the right side
of the face was better ventilated than the left side. This
indicated that the jet flow possibly detached from the left
tib before hitting the right side of the face.

This testing has revealed that a jet fan may be feasible
for ventilating cut depths greater than 40 ft. The results
indicated that an average of 2,000 cfm existed at a depth
of 90 ft from the fan. Although this is less than the
3,000-cfm minimum required by Federal law, greater quan-
tities were found closer to the fan. This fan configuration,
although not presently suitable for 90-ft cuts, would likely
be effective in cut depths less than 90 ft.

The feasibility of jet fan ventilation may be improved
through the presence of in-place equipment. It is like-
ly that machine-mounted scrubbers or sprayfans would
force the jet stream against the fan-side rib, enabling it
to sweep the face. Such effects will be studied in future
investigations.

REFERENCES

1. Suboleski, S. C, and RH. King. Estimating Technology's Impact
on Underground Coal Productivity. Min. Eng. (Littleton, CO), v. 42,
1990, pp. 1159-1164.

2. Goodman, G. V. R, C. D. Taylor, and E. F, Divers. Ventila-
tion Schemes Permit Deep Advance. Coal Mag, v. 95, Oct. 1990,
pp. $0-53.

3. Dunn, M. F,, F. S. Kendorski, M, O. Rahim, and A. Mukherjee.
Testing Jet Fans in Metal/Nonmetal Mines With Large Cross-Sectional
Airways (contract J0318015, Engineer's International, Inc.). BuMines
OFR 106-84, 1983, 132 pp; NTIS PB 84-196393,

4, Thimons, E. D., C. E. Brechtel, M. B. Adam, and J. F. T. Aga-
pito. Face Ventilation for Oil Shale Mining. BuMines IC 9118, 1986,
2 pp.

% US.OP0: te1—s11-c10NeeNE

5. Matta, J. E., E. D, Thimons, and F. N. Kissell. Jet Fan Effective-
ness as Measured With SF, Tracer Gas. BuMines RI 8310, 1978, 14 pp.

6. Campbell, J.A.L. The Recirculation Hoax. Paper in Proceedings
of Third U.S. Mine Ventilation Symposium. PA State Univ., University
Park, PA, 1987, pp. 24-29.

7. McElroy, G. E. The Role of Air Jets In Mine Ventilation. Trans.
AIME, v. 163, 1945, pp. 399-414,

8 Krause, D, Free Jets in Auxiliary Ventilation. Neue Bergbautech.,
v2, No. 1, 1972, pp. 44-52.

9. Kissell, FN and R. J. Bielicki, Ventilation Eddy Zones at a
Model Coal Mine Working Face. BuMines RI 7991, 1974, 14 pp.

10. Thimons, E. D., and F. N. Kissell, Tracer Gas as an Aid in Mine

Ventilation Analysis. BuMines RI 7917, 1974, 17 pp.

INT.BU.OF MINES,PGH.,PA 29492


Library of Congress Cataloging in Publication Data:

Goodman, Gerrit V. R.

Jet fan ventilation in very deep cuts—a preliminary analysis / by Gerrit V.R.
Goodman, Charles D. Taylor, and Edward D. Thimons.

P. cm. — (Report of investigations; 9399)

Supt. of Docs. no.: 1 28.23:9399.

Includes bibliographical references (p. 12).

1. Mine ventilation—Equipment and supplies—Testing. 2. Fans (Machinery)—

Testing. I. Taylor, Charles D. (Charles Darrell), 1946- . Il. Thimons, Edward D.

III. Title. IV. Series: Report of investigations (United States. Bureau of Mines);
9399,

TN23.U43_  [TN303] 622 s—dc20 [622’.42] 91-34688 CIP



Report of Investigations 9399

Jet Fan Ventilation in Very Deep
Cuts—A Preliminary Analysis

By Gerrit V. R. Goodman, Charles D. Taylor,
and Edward D. Thimons

UNITED STATES DEPARTMENT OF THE INTERIOR
Manuel Lujan, Jr., Secretary

BUREAU OF MINES
T S Ary, Director


The balanced network is shown in figure &4 for the
flow extender fan configuration. The network indicated
that 2,400 cfm reached a distance of 70 ft from the fan.
These data also showed that a flow of 20,200 cfm was
Present at a distance of 10 ft. With the fan rated at
6,800 cfm, this meant that 13,400 cfm came from other
sources, namely entrainment of fresh air from the last
open crosscut (3,400 cfm) and reentrainment of the flow
passing down the return side of the entry (10,000 cfm) as
shown in figure 8B. A flow of 3,400 cfm was also recircu-
lated into the fan inlet. At 10 ft from the fan, 10,000 cfm
of the 20,200 cfm, or roughly 50 pet, was reentrained

A
70r 2,400 cfm 2,400 cfm
14900 cfm
co
z SOP 16,400 cfm 16,400 cfm
z
=
io}
£ 30} 26,100 ctm 26,100 cfm
8 5,900 cfm
Zz
=<
D 10F 20,200 cfm} — 19.000 ctm 20200 cfm
S .
6,800 cfm
ol
>
13,400 10,000 6,600 cfm 13,400 efm
cfm cfm
KEY
* Entrained flow
¥* Recirculated
Jet
8 ‘flow
Reentrained flow. tt t
Extender. ay
Fan. 47 ¥
Entrained flow a iF
Fresh airflow amp $
Figure 8.—Balanced ventilation network using fan plus
extender. A, Network diagram; B, airflow directions through

gallery.

from the return side. At a distance of 30 ft, an additional
5,900 cfm was reentrained. The total reentrained flow of
15,900 cfm represented over 60 pct of the total flow of
26,100 cfm.

As previously explained, a potentially serious problem
can arise if recirculation causes contaminated air to enter
the fan inlet. To reduce this recirculation, a check curtain
was hung from the left rib to a point 8 ft across the head-
ing. It was also draped across the fan housing. The pres-
ence of this curtain resulted in dramatic changes in the jet
flow (fig. 94). Although the check curtain eliminated re-
circulation, it also reduced the quantity of fresh air en-
trained around the fan and into the jet flow (fig. 9B). It
is conceivable that the reduced jet flow simply reduced the
eddying in the gallery and, hence, increased the efficiency
of the fan to ventilate the face. Figures 84 and 94 show
that flow traveled from the outflow side to the inflow side
in the first 30 ft. In this region, the lower velocity outflow
was entrained by the higher velocity inflow. As the inflow
quantity increased, its velocity decreased relative to the

Q
5,700 cfm 5,700 cfm
18,700 cfm,

A
70,

z
E SOF 24,400 cfm 24,400 cfm
3 d Q
&
us OF 25,500 cfm 25,500 cfm
oO
2 o o
=z
Q
S 10F 13,100 cfm 13,100 cfm
o d
Ob 6800 cfm ® Fan 6,800 cfm
13,400 cfm 6,600 cfm 13,400 cfm

° merges yt ‘
Extender. v a

vi

Return
flow

‘Check
curtain

Fresh airflow a>

Figure 9.—Balanced ventilation network using fan plus
extender and check curtain. A, Network diagram; B, airflow
directions through gallery.


102

T T T 7
5 i Curtain_J
F+—Curtain up—>t—- down

Fan ot Fan on—>te-Fan on—
e
lolF 1
e
° 4
e e
e |

€ e

a e

a q

. a e 4

é ew *4

9 L J
L . J

KEY 4
i © Face (left side)
© Return

1O'r q

I 5° ° ° 9° *o j

r ° 4
10° l l L °

0 60 120 180 240

TIME, min

+ curtain oe 4
Lar ton on-eteFan on—+

KEY
7 © Face (right side)
e

q

ry e4

¢

L e 4

)
L e 4
eee
ofre

0 60 120 180 240

TIME, min

Figure 11.—Tracer gas test results,