Arch. Min. Sci., Vol. 53 (2008), No 2, p. 221–234

Arch. Min. Sci., Vol. 53 (2008), No 2, p. 221–234

Arch. Min. Sci., Vol. 53 (2008), No 2, p. 221–234
221
MARIAN BRANNY*, WIKTOR FILIPEK*
NUMERICAL SIMULATION OF VENTILATION OF BLIND DRIFTS WITH A FORCE- EXHAUST
OVERLAP SYSTEM IN THE CONDITION OF METHAN AND DUST HAZARDS
SYMULACJA NUMERYCZNA PRZEWIETRZANIA WYROBISK ŚLEPYCH SYSTEMEM WENTYLACJI
KOMBINOWANEJ W WARUNKACH ZAGROŻENIA METANOWEGO I PYŁOWEGO
This paper outlines a theoretical method of finding 3D velocity fields and methane and dust concentrations in the air in blind drifts with a force-exhaust overlap ventilation system incorporating a forcing
duct with a vortex duct and an auxiliary exhaust duct with the dust separator. The solution is supported
by equations and simulation programs utilizing the CFD approach. The air and methane mixture is
assumed to be an ideal and compressible gas, its motion is taken to be steady and the whole process is
assumed to be isothermal. Fresh air is assumed to be a three-component mixture of nitrogen, oxygen
and water vapour. The problem considered in this study is described with continuity equations, NavierStokes equations, k-ε model equations as well as transport equations of chemical species (components
of air-methan mixture).
Calculation data are presented in the form of velocity field images, streamlines and mass fractions of
CH4. Fig. 2 shows velocity distributions in the selected drift cross-sections in the considered flow region
(Fig. 1). The air vortex, generated by the vortex duct, moves towards the face head and in the direction of
the overlap zone. The actual division of the air stream depends on the ratio of air volume supplied to the
overlap zone to that supplied to the face region. The air jet leaving the dust separatpr installation produces
in its wake a zone of about 15 m, dominated by recirculation flow. Fig. 4 shows the distribution of mass
fractions of methane, assuming that methane should enter via the face region and via the belt-shaped section
in the floor, in the central part of the overlap zone. Apart from expected methane concentration levels near
the roof (in the face region), there are other methane concentration zones caused by flow obstacles, such as
continuous mining machines and forsing duct system here located near the side walls. This is associated
with the development of low-intensity airing zones, where methane concentrations are higher.
The flow of air-solid particles mixture is governed by the two-phase Euler- Lagrange’s model with
the gaseous continuous phase and a dispersed phase comprising solid (dust) particles. Apart from solving
the equations of mass, momentum and energy conservation for the continuous phase, the model utilizes
the trajectories of dispersed phase particles. It is assumed that dust is emitted from the face head surface.
Images of several hundred particles’ trajectories, originating in the face head section, are shown in Figs 5, 6.
Small ratio of air in the overlap zone helps contain the dust cloud in the face region. As the amounts of
air in the overlap zone increase, the highly dusted zone enlarges, too. Tables 1 and 2 summarize the dust
measurement and calculation data in the selected drift locations and the length of time that solid partic*
AGH UNIVERSITY OF SCIENCE & TECHNOLOGY, DEPARTMENT OF MINING AND GEOENGINEERING, AL. MICKIEWICZA 30, 30-059 KRAKOW, POLAND
222
les remain in the face zone. In qualitative terms, simulation data obtained using the Euler-Lagrange’s
two-phase flow model are consistent with the data quoted in literature and with practical observations.
A full quantitative analysis, however, would require us to find the degree of correspondence between the
simulation and experimental data.
Calculations are supported by the program FLUENT 6.1.
Keywords: unerground ventilation, CFD simulation, blind drifts ventilation
W artykule zaprezentowano teoretyczny sposób wyznaczania 3D pól prędkości przepływu, stężeń
metanu i pyłu w powietrzu w wyrobisku z kombinowanym systemem wentylacji, składającym się z zasadniczego lutniociągu tłoczącego zakończonego lutnią wirową oraz pomocniczego lutniociągu ssącego
z odpylaczem. Rozwiązywanie oparto o równania i programy symulacyjne stosowane w Numerycznej
Mechanice Płynów. Założono, że mieszanina powietrzno-metanowa jest gazem doskonałym i ściśliwym,
ruch mieszaniny jest ustalony zaś proces przebiega w warunkach izotermicznych. Przyjęto, że powietrze
świeże jest trójskładnikową mieszaniną azotu, tlenu i pary wodnej. Rozważany problem opisany jest
układem równań ciągłości, Naviera-Stokesa oraz równań modelu k-ε i transportu składników chemicznych
(składników mieszaniny powietrzno-metanowej).
Rezultaty obliczeń przedstawiono w postaci obrazów pól prędkości, linii prądu oraz rozkładów
udziałów masowych CH4. Dla przyjętego obszaru przepływu (rys. 1) na rys. 2 przedstawiono rozkłady
prędkości w wybranych przekrojach poprzecznych wyrobiska. Wir powietrzny, wytwarzany przez lutnię
wirową przemieszcza się zarówno w kierunku czoła przodka jak i w kierunku strefy zazębiania. Ilościowy podział strumienia powietrza zależy od stosunku strumienia objętości powietrza w strefie zazębiania
lutniociągów do strumienia objętości powietrza doprowadzonego do przodka. Ze strugą powietrza wypływającą z instalacji odpylającej związana jest strefa o długości około 15 m charakteryzująca się przepływem recyrkulacyjnym. Na rys. 5 przedstawiono rozkłady udziałów masowych metanu przy założeniu,
że metan dopływa przez powierzchnię czoła przodka oraz przez pas usytuowany na spągu w środkowej
części strefy zazębiania. Oprócz spodziewanych obszarów z przystropowymi nagromadzeniami metanu
(w pobliżu przodka) charakterystyczne są również te, które powodowane są obecnością w przepływie
przeszkód takich jak kombajn i lutniociąg tłoczący, w przykładzie ułożony na spągu chodnika w niedalekiej odległości od ociosu. Jest to związane z powstaniem stref o małej intensywności przewietrzania
a zarazem o podwyższonym stężeniu metanu.
Przepływ powietrze-cząstki stałe opisano przy pomocy modelu dwufazowego Eulera-Lagrange’a
z gazową fazą ciągłą i złożoną z cząstek stałych (pyłu) fazą rozproszoną. Oprócz rozwiązania układu
równań zachowania masy, pędu i energii dla fazy ciągłej w modelu tym wyznacza się trajektorie cząstek
fazy rozproszonej. Równanie ruchu, reprezentujące bilans sił działających na cząstkę stałą, zapisane we
współrzędnych Lagrange’a ma postać (1) zaś tory cząstek wyznaczane są z równania (2). Przyjęto, że pył
emitowany jest z powierzchni czoła przodka. Cząstki stałe mają kształt kulisty o średnicy 5×10–6 m, ich
gęstość wynosi 1400 kg/m3 zaś prędkość początkowa 5 m/s. Obraz kilkuset trajektorii cząstek stałych,
rozpoczynających się na płaszczyźnie czoła przodka przedstawiono na rys. 5 i 6. Przy małym udziale
powietrza w strefie zazębiania obłok pyłu skutecznie utrzymywany jest w strefie przodkowej. W miarę
zwiększania ilość powietrza płynącego przez strefę zazębiania powiększa się również strefa charakteryzująca się dużym zapyleniem powietrza. Model Lagrange’a umożliwia również określenie pola stężeń
pyłu. W tabelach 1 i 2 zestawiono wyniki pomiarów i obliczeń stężenia pyłu w wybranych miejscach
wyrobiska oraz czasu przebywania cząstek stałych w strefie przodka.
Wyniki symulacji numerycznej uzyskane w pracy są jakościowo zgodne z informacjami literaturowymi jak i obserwacjami z praktyki natomiast ocena ilościowa będzie możliwa dopiero po stwierdzeniu
stopnia zgodności wyników symulacji z danymi eksperymentalnymi.
Obliczenia wykonano przy pomocy programu FLUENT 6.1.
Słowa kluczowe: wentylacja kopalń, symulacja metodami CFD, przewietrzanie wyrobisk ślepych
223
1. Introduction
Currently employed mechanical rock mining methods are responsible for large
amounts of dust in blind drifts. Rock cutting with the use of cutting tools involves the
disintegration of solid rock, causing the emissions of tiny dust particles to the air, a portion of these remains in the form of suspended particulate. Regulations currently in force
require the use of dust separators in drivages where continuous miner are operated. In
the conditions of dust and methane hazard, such headings are often aired by an overlap
ventilation system, incorporating main forcing air duct and the auxiliary exhaust duct
with a dust separator installation. Overlap systems have become widespread recently,
particularly in long drifts at considerable depths (Krzykowski, 2005; Szlązak et al., 2003).
In gassy fields the main air duct must be complete with an swirl pipe. A directed air
stream leaving the vortex duct should prevent methane gathering in the roof regions
and contain the cloud of dust, produced by the continuous miner in the face head zone.
A short exhaust duct is typically equipped with a suction unit positioned over the continuous miner. An inlet to the dust removing installation should be as close to the face
head as possible – at the distance of up to 3 m from the cutting tool. Apart from ensuring
the minimal average flow velocities specified in relevant regulations, the flow rate of air
supplied to the face should exceed the dust separator efficiency by at least 20%. In drifts
with high methane concentrations – in excess of 2 m3CH4/min (Krzykowski, 2005) – this
fraction was maintained on the level of 50%. Typically, ventilation systems are designed
to match the target length of the whole drivage and hence the air jet in the overlap zone
shall be larger than nominal in a major part of the drift length. Increased amounts of air
in the overlap zone are responsible for enhanced dust levels in the zone behind the dust
separator. Overlap systems and their operating performance were extensively studied in
the works by (Krzykowski, 2005; Szlązak et al., 2003; Krause & Łukowicz, 1999) who
focused on analysis and interpretation of methane flow and dust measurement data.
The purpose of the present study is to predict the distributions of flow velocities
and methane and dust concentrations in drifts with an overlap ventilation system. The
solutions utilize the CFD simulation programs and equations. CFD modeling is widely
applied to solving a wide range of flow problems, including the flows of multi-phase
media. However, it is extremely difficult to establish how accurately the real flows are
emulated. In the case of mine headings and drifts, simulations data are typically compared
to the measured flow parameters in some cross-sections, sometimes they are related to
averaged values for the given cross-section, which is inadequate for full validation of
the model. This problem is thoroughly investigated in the monograph by J. Krawczyk
(2007). Recent research suggests that CFD models are able to emulate flow parameters
with a sufficient accuracy for practical applications (Wala, 2004; Sivester, 2002; Younh
et al., 2004).
The calculation procedure is supported by the program FLUENT 6.1.
224
2. Flow region
The flow region shown in Fig. 1 comprises a part of a blind drift 76 m in length, with
the cross-section area 15.8 m2. The main forcing duct 800 mm in diameter is complete
with a vortex duct with the slit length 10 m. The distance between the duct end and
the face head is 8 m. A short exhaust duct with a dust separator is shown as a cylinder
(air duct), 1000 mm in diameter. An inlet to the dust removing installation is located
over the continuous miner, at the distance of 3 m from the face head. The length of the
overlap zone equals 8 m. The continuous miner is represented by a rectangular prism
2 m × 1.5 m × 6.0 m.
intet to dust separator
vortex pipe
outlet from dust separator
face head
forcing duct
continuous miner
overlap zone
inflow of methan
inflow of methan
Fig. 1. Flow region
Rys. 1. Obszar przepływu
3. Mathematical model
Air-methane mixture is assumed to be an ideal, compressible gas so that Clapeyron’s
formula should be applicable. The motion of this mixture is steady and the whole process
is taken as isothermal. Fresh air is assumed to be a three-component mixture of nitrogen,
oxygen and water vapour. The local mass fraction of the i-th component is obtained by
solving the relevant transport equation.
A selection of an adequate CFD model is particularly difficult. Models used for most
practical applications are based on the Reynold’s averaging hypothesis and among this,
thouse based on the Boussineque’a hypothesis. In his doctoral dissertation S. Silvester
[12] reviews the current expertise in the area of CFD modeling, finally concluding that
the standard k-ε model (kinetic energy of turbulence- dissipation rate of kinetic energy of
turbulence) proves to be most adequate as it most accurately emulates the real flow parameters. This models has been in widespread use in industrial applications (Krawczyk, 2007;
Young, 2004; Branny, 2006; Silvester 2002, Wala et al., 2001; Hargraves & Lowndes,
2001; Konduri, 1997; Lipska, 1997; Ren et al., 1997). The problem considered here is
described with continuity equations, Navier–Stokes equations, k-ε model equations as
well as transport equations of chemical species. This model ought to be supplemented
225
by adding the description of dust particles’ motion, suspended in the air. An assumption is made that solid particles generated during rock cutting by a continuous miner
are liberated from the face head. The flow of air-solid particles mixture is governed by
a two-phase model with the gaseous continuous phase and dispersed phase comprising
solid (dust) particles. In fluid mechanics this method is referred to as Euler-Lagrange’s
method (Fluent, 2005). The continuous phase (air) is described with time-averaged continuity equations, Navier-Stokes equations and turbulence model equations whilst the
solutions for the dispersed phase consist in determining the trajectories of a large number
of particles in the computed velocity field. Underlying the model is an assumption that
a volumetric fraction of the dispersed phase should be small, accounting for no more
than 10% (Fluent, 2005). In the problem considered here the volumetric fraction of dust
is much below 1%. Apart from solving the equations of mass, momentum and energy
conservation for the continuous phase, the model enables us to find the trajectories of
dispersed phase particles. The equation of motion, expressing the balance of forces acting upon a solid particle, can be written in the Lagrange’s coordinates as:
d vsi
g (r - r )
= FDi (vi - vsi ) + i s
dt
r
(1)
where:
FDi (vi – vsi) — drag force per unit particle mass,
FDi = FDi (Re, dp, ρ, μ)
vsi — particle’s velocity component in the direction i,
vi — air velocity component in the direction i,
Re — Reynold’s number,
ρs, ρ — respective density of a solid particle and air,
dp — particle diameter,
μ — dynamic viscosity,
gi — gravity acceleration component in the direction i
Trajectories of solid particles are obtained from the equation:
d xi
= vsi
dt
(2)
Boundary conditions
– In the inlet opening (the slit in the vortex duct and the surface area of methane inflow
to the drift) mass flow rate of gas entering the area is taken as constant whilst the
amount of fresh air incoming to the slit is assumed to change along its length, as
evidenced by the vortex duct characteristic (Frydel & Krzykowski, 2003). Kinetic
energy of turbulence and energy dissipation rate are computed assuming the 10%
turbulence intensity at the inlet.
226
– At the outlet boundary constant static (gauge) pressure is assumed.
– The description of wall boundary conditions utilizes the classical wall function
model. In FLUENT program wall roughness are modeled by presetting the average
roughness dimension. According to (Hargreves & Lowndes, 2001), sufficiently
good results are reported in drifts and headings for the roughness height 0.05 m and
this value is used in further calculations. One has to bear in mind, however, that
the widely adopted wall function model (also recalled in the FLUENT program)
was initially developed to analyze surfaces much smoother than those encountered
in mine headings and drifts.
Boundary conditions for the dispersed phase involve the selection of emission sites
and determining the conditions under which they should collide with rigid walls.
– Solid particles with specified diameter, density and velocity are liberated from the
coalface.
– On reaching the outlet opening or the floor, a particle will vanish (i.e. leave the
region) or it will be captured.
– On colliding with the roof or side wall surfaces, a particle will elastically rebound.
4. Velocity field images
The forcing duct supplies 435 m3/min of air to the working face. The slit in the vortex
duct is 10 m in length and 60 mm in width. For the purpose of calculations, the slit is
divided into five segments, two meters in length. In each segment the mass flux of air
is obtained on the basis of velocity measurement data at the outlet from a vortex duct
(Frydel & Krzykowski, 2003) and the predetermined airflow rates. The dust separator
installation handles 272 m3/min of air, hence the air stream contribution in the overlap
zone is 0.37, which expresses the ratio of air volume flux in the overlap zone to that
supplied to the working face.
Fig. 2 presents velocity field images in the selected cross-sections of the blind drift,
featuring relatively large flow velocities near rigid walls- the roof, floor and side walls.
Flow velocity at the distance of 0.1 m from the roof, measured along the heading centerline alongside the vortex duct equals 1.5-4.3 m/s. The air jet leaving the dust separator installation produces in its wake the 15 m long zone where recirculation flows will
occur.
To highlight the distinctive properties of the flow, velocity field can be represented
in the form of streamlines. The image of streamlines originating in the slit of the vortex
duct and in the outlet of the auxiliary duct is shown in Fig. 3. A clearly visible air whirl,
generated by the vortex duct, by directing the air jet tangent to the site walls of working,
moves both towards the face head and in the direction of the overlap zone. The quantitative fraction of the air jet depends on the efficiency of the dust separator fan.
227
working face
a)
inlet to short exhaust ventube
Z
Y
X
b)
wortex duct
Z
Y
c)
X
outlet from dust separator
overlap zone
Z
Y
X
Fig. 2. Velocity field in the heading cross-section; a) – Zone stretching from the air jet outlet
in the forcing system to the face head, cross-sections taken at the distance of 7 m, 5 m and 2 m
from the head, b) – alongside the slit in the vortex duct, c) – zone of overlap and outlet
from the auxiliary duct, (counting from the left) at the distance of 15 m, 10 m, 5 m
from the auxiliary duct outlet and mid-length of the overlap zone
Rys. 2. Pole prędkości w przekrojach poprzecznych wyrobiska; a) – strefa od wylotu powietrza
z lutniociągu tłoczącego do czoła przodka, przekroje w odległości 7 m, 5 m i 2 m od czoła,
b) – na długości szczeliny wirowej, c) – strefa zazębiania i wylotu z lutniociągu pomocniczego,
licząc od lewej strony w odległości 15 m, 10 m i 5 m od wylotu z lutniociągu pomocniczego
oraz w połowie długości strefy zazębiania
228
intet to dust separator
outlet from dust separator
vortex pipe
continuous miner
overlap zone
Fig. 3. Streamlines originating in the slit of vortex duct and in the outlet of the auxiliary exhaust duct
Rys. 3. Obraz kilkudziesięciu linii prądu wychodzących z szczeliny lutni wirowej
oraz z otworu wylotowego lutniociągu pomocniczego
5. Methane concentration
The flow rate of methane liberated to the heading face is assumed to be 1.4 kg CH4/
min and beyond the face zone this level is taken as 0.4 kg CH4/min. It is further assumed
that methane enters the heading through the face head (1.4 kg CH4/min) and through the
belt-shaped section (0.5 m×2 m) in the floor, in the central part of the overlap zone. Fig. 4
shows distributions of mass fraction of methane in particular cross-sections of the drift:
1.50e-02
1.43e-02
1.35e-02
1.27e-02
1.20e-02
1.12e-02
inflow of methan
1.05e-02
intet to dust separator
9.75e-03
9.00e-03
8.25e-03
7.50e-03
6.75e-03
6.00e-03
5.25e-03
continuous miner
4.50e-03
vortex duct
3.75e-03
3.00e-03
overlap zone
overlap zone
2.25e-03
1.50e-03
7.50e-04
inflow of methan
Z
Y
X
0.00e-00
Fig. 4. Mass fraction of CH4 in particular cross-sections
Rys. 4. Rozkład udziałów masowych CH4 w przekrojach poprzecznych
229
in the middle of the overlap zone, at mid-point and at the end of the vortex duct and at
5 m, 3 m (exhaust fan inlet) and 1 m from the face head.
The highest methane concentration in the face region, accounting for 1-1.5% of the
mass fraction of CH4, is registered near the roof. Apart from near-roof regions where
higher methane concentrations levels are anticipated, there are other regions where such
elevated levels are due to the presence of flow obstacles, such as continuous miners or
the forcing duct, here laid on the floor. The presence of a continuous miner causes a zone
to be formed where flow velocities are low and methane concentrations higher. In the
overlap zone, at the point of assumed methane inflow to the drift, the highest methane
concentration levels will be registered in the drivage corner, near the intersection of the
floor and side wall planes. The airing of the area between the side wall and a forcing
duct is the least intensive. Methane concentration levels decidedly lower that in the face
region are registered at the point referred to as the coordinate of the exhaust fan inlet.
Near the continuous miner operator’s station (setback 5 m from the face) the maximal
mass fraction of CH4 approaches 0.3%. At distances in excess of 15 m from the dust
separator outlet, methane concentrations in drift cross-sections are uniform.
6. Dust emissions
Air jet contributions in the overlap zone would range from 30 to 70%, as reported by
(Krzykowski, 2005). It is well-known from literature that increased amounts of air in the
overlap zone lead to deterioration of efficiency of dust extraction. Further calculations
were performed to show whether this effect can be emulated under the assumptions
imposed by the Euler-Lagrange’s model.
It is assumed that dust emissions come from the face head. Particles are taken to be
spherical in shape, 5×10–6 m in diameter, their density is 1400 kg/m3, initial velocity:
5 m/s. Initial velocity was particularly hard to establish due to the scarcity of data from
literature. Calculations performed for initial velocity ranging from several to more than
ten m/s did not reveal any major influence of this parameter on particles’ trajectory images in qualitative terms. Three air fraction values in the overlap zones were considered:
32, 40 and 68%, the remaining parameters being unchanged. The image of numerous
particles’ trajectories, originating from the face head surface are shown in Figs 5 and 6.
When the fraction of air in the overlap zone is 32%, most trajectories tend to end at the
exhaust fan inlet, the remaining ones end on the floor surface. The dust cloud is therefore contained in the face region. As the amount of air flowing through the overlap zone
increases, the highly dusted zone will extend. It is reasonable to suppose that when the
fraction of air in the overlap zone is less than 50%, the cloud of dust is contained within
the area covering the blind drift section stretching from the face head to the vortex duct
(Fig. 5). For higher levels (in excess of 50%), dust levels increase both in the overlap
zone and in the outlet air jet (Fig. 6).
230
inlet to exhaust duct with dust separator
vortex duct
Fig 5. Particles’ trajectories originating on the face head, for 40% fraction of air in the overlap zone
Rys. 5. Trajektorie cząstek stałych rozpoczynających się na płaszczyźnie czoła przodka
przy 40% udziale strumienia powietrza w strefie zazębiania
exhaust duct with dust separator
inlet to exhaust duct
forcing duct system
Fig. 6. Particles’ trajectories originating on the face head, for 68% fraction of air in the overlap zone
Rys. 6. Trajektorie cząstek stałych rozpoczynających się na płaszczyźnie czoła przodka
przy 68% udziale strumienia powietrza w strefie zazębiania
The Lagrange’s model enables us to find the dust concentration fields. Each particle
moving along the specified trajectory is associated with an ‘extra’ mass, resulting from
the dust mass generated in unit time at the face head. This parameter (mass) is unknown,
hence the calculations utilize the measured data obtained in one gallery in the colliery
‘Borynia” (Krzykowski, 2005). Air was supplied to the face head by the forcing duct
(555 m3/min) and through the dust separator installation (278 m3/min), hence the fraction of air in the overlap zone was 50%. The measured concentration of respirable dust
fraction at the inlet to the exhaust fan is 106.49 mg/m3. The predicted concentration
level was similar – 99.36 mg/m3 – for the dust stream rate equal 500 mg/s of respirable
fraction produced during the continuous miner’s operation. Table 1 summarizes the
measured and computed data.
231
TABLE 1
Measured and predicted dust concentrations
TABLICA 1
Wyniki pomiarów i obliczeń stężenia pyłu
Measurements
of respirable
fraction
Site
Inlet to dust
separator installation
Dust concentration [mg/m3]
Calculations
weighted average for the cross-section
particle diameter 5×10–6 m
106.49
Operator’s
station
12.03
Overlap zone
14.27
99.36
4 m from the face
45.64
14.95
5 m from the face
11.93
6 m from the face
9.83
7 m from the face
0.38 in the centre of the overlap zone
Figs 7 and 8 show dust concentrations in two of the drift’s cross-sections. A numerically generated image of dust concentration reveals a strong heterogeneity, which proves
a major difficulty when the model is to be validated. The biggest difference between
the measured and predicted data is reported in the overlap zone. Computed dust concentrations, with air jet contribution less than 50%, are insignificant whilst observations
(Krzykowski, 2005; Szlązak et al., 2003) suggest that these should be similar to those
measured at the operator’s station. A visible increase of dust concentration in the overlap
zone in numerical simulation is reported for 60% air jet contributions.
Major determinants of the dust concentration levels include the period of time a particle remains in the particular zone. Trajectories of solid particles, particles’ status and
the time of their residence in a given zone are summarized in Table 2.
TABLE 2
Duration of solid particles’ residence in the face zone
TABLICA 2
Czas przebywania cząstek stałych w strefie przodka
Status
Captured by the dust separator
Deposited on the floor
Incomplete
Total number of particles
Number
of particles
9034
1523
3
10560
Residence in the face zone [s]
min
max
average
3.650e+000
2.159e+002
3.375e+001
7.972e–002
2.268e+002
2.395e+001
232
1.30e-03
1.23e-03
1.17e-03
1.11e-03
1.04e-03
inlet to the dust separator instalation
9.75e-04
9.10e-04
8.45e-04
7.80e-04
7.15e-04
6.50e-04
5.85e-04
5.20e-04
4.55e-04
3.90e-04
3.25e-04
2.60e-04
1.95e-04
Z
1.30e-04
6.50e-05
0.00e-00
Y
X
Fig. 7. Dust concentration (kg/m3) in the cross-section defined by the coordinate of the inlet
to the dust separator installation
Rys. 7. Stężenie pyłu w kg/m3 w przekroju poprzecznym wyrobiska określanym współrzędną wlotu
do instalacji odpylającej
Obviously, the shorter the particles’ residence in the face zone, the lower the dust
concentrations, no matter whether they are captured by the dust separator or deposited on
the floor. Out of the total dust emission (respirable fraction), about 86% of the mass flow
rate is directed to the dust speparator installation (0.0004277 kg/s), the remaining 14%
(0.00007211 kg/s) will be deposited on the floor. In the case of incomplete trajectories,
the calculation procedure was interrupted when the restraint was encountered limiting
the maximal admissible number of time steps.
7. Conclusions
At present CFD models are employed in solving local ventilation problems in mines,
particularly in the case of 2D or 3D flows. However, it is extremely difficult to prove
the reliability of numerical modeling, due to the lack of adequate measurement data.
233
1.80e-04
1.71e-04
1.62e-04
1.53e-04
1.44e-04
1.35e-04
1.26e-04
1.17e-04
1.08e-04
9.90e-05
9.00e-05
8.10e-05
7.20e-05
6.30e-05
5.40e-05
4.50e-05
3.60e-05
2.70e-054
Z
1.80e-05
9.00e-06
0.00e-00
Y
X
Fig. 8. Dust concentration (kg/m3) in the drift’s cross-section 5 m from the face head
Rys. 8. Stężenie pyłu w kg/m3 w przekroju poprzecznym wyrobiska w odległości 5 m
od czoła przodka
That difficulty arises due to technical problems and high costs of measurements, both in
laboratory conditions and in situ. The available measurement data is not comprehensive,
covering only selected parameters measured at the specified sites in the flow region. On
the other hand, many sources indicate sufficient reliability of CFD models, rendering
them adequate for practical applications.
Flow velocity fields and gas and dust concentrations obtained by numerical models
should be treated as the basis for comprehensive studies on the ventilation conditions.
In qualitative terms simulation data obtained using the Euler-Lagrange’s two-phase
model agree well with the results reported in literature and with practical observations.
The quantitative assessment shall be possible when the degree of correspondence is
established between the simulation and experimental data.
This study is supported through the statutory research no 11.11.100.193, financed
by the Ministry of Science and IT.
234
REFERENCES
B r a n n y M., 2006. Computer Simulation of Flow of Air and Methan Mixture in the Longwall-Return Crossing Zone.
Archives of Mining Sciences, vol. 51, Issue 1, p. 133-145.
FLUENT Inc. 2005. FLUENT 6.1 Documentation.
F r y d e l W., K r z y k o w s k i R., 2003. Lutnia wirowa WIR 630 w systemie wentylacji kobinowanej, Miesięcznik
WUG, nr 9/2003, Katowice, p. 27-29.
H a r g r e v e s D.M., L o w n d e s I.S., 2001. An Assesment of the Future Use of Computentional Fluid Dynamics for
Network Modeling. Proceedings of the 7th International Mine Ventilation Congress, Kraków, p. 547-553.
K a z i m i e r s k i Z., 2004. Podstawy Mechaniki Płynów i Metod Komputerowej Symulacji Przepływów. Politechnika
Łódzka.
K o n d u r i I.M., M c P h e r s o n M.J., T o p u z E., 1997. Experimental and Numerical Modelling of Jet Fans for Auxiliary Ventilation in Mines. Proceedings of the 6th International Mine Ventilation Congress, Pittsburg.
K r a u s e E., Ł u k o w i c z K., 1999. Kryteria bezpiecznego drążenia wyrobisk korytarzowych w polach metanowych
przy użyciu kombajnów z zastosowaniem wentylacji lutniowej kombinowanej z ssącym lutniociągiem pomocniczym
wyposażonym w odpylacz, Seria Instrukcje nr 10, GIG, Katowice.
K r a w c z y k J., 2007. Jedno i wielowymiarowe modele niestacjonarnych przepływów powietrza i gazów w wyrobiskach
kopalnianych. Przykłady zastosowań. Archives of Mining Sciences, seria: Monografie, nr 2.
K r z y k o w s k i R., 2005. Ocena skuteczności odpylania powietrza w wyrobiskach drążonych kombajnami w warunkach
zagrożenia metanowego, Praca Doktorska, AGH, Kraków.
L i p s k a B., 1997. Rezultaty badawcze ANEKSU 26 IEA w zakresie prognozowania przepływów wentylacyjnych.
Piąte Ogólnopolskie Sympozjum “Zastosowanie Mechaniki Płynów w Inżynierii Środowiska”, Gliwice-Wisła,
p. 199-213.
R e n T.X., E d w a r d s J.S., J o z e f o w i c z R.R., 1997. CFD Modelling of Methan Flow Around Longwall Faces.
Proceedings of the 6th International Mine Ventilation Congress. Pittsburg, p. 247-251.
S i l v e s t e r S.A., 2002. The Integration of CFD and VR Methods to Assist Auxiliary Ventilation Practice. PhD Thesis.
The University of Nottingham, Nottingham.
S z l ą z a k N., S z l ą z a k J., Tor A., 2003. Systemy przewietrzania wyrobisk ślepych, Monografia, Uczelniane Wydawnictwa Naukowo-Dydaktyczne AGH, Kraków.
W a l a A.M., S t o l t z J.R., J a c o b J.D., 2001. Numerical and Experimental Study of a Mine Face Ventilation System
for CFD Code Validation. Proceedings of the 7th International Mine Ventilation Congress, Kraków, p. 411-418.
Yo u n g T., 2004. CFD and Field Testing of a Naturally Ventilated Full-Scale Building. PhD Thesis. University of
Nottingham, Nottinghm.
Received: 18 December 2007