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VENTILATION AND CLIMATE SIMULATION OF DEVELOPMENT ENDS IN METAL MINES

Davood Bahrami, University of Nevada, Reno, Reno, NV.

Pedram Rostami, University of Nevada, Reno, Reno, NV.

George Danko, University of Nevada, Reno, Reno, NV.

Abstract

It is important to study the mine ventilation systems in

order to better design and control the working environment

in deep underground mines. With increasing depth, heat,

and humidity, worker performance may be reduced and the

safety of the workers must take special attention.

The purpose of this paper is to apply a development-

end ventilation model to a real underground mining

scenario at the Lucky Friday Mine in Idaho, USA. Two

models and field measurements from the mine are used for

comparison, MULTIFLUX (MF) (Danko 2008) and Kduct

(Gao and Inoue, 2002).

The MF development-end model template has already

been benchmarked against the measurement data from two

UK coal mines in previous studies (Danko et al., 2010a;

Danko et al., 2010b). The present study is another test of

MF application in a metal mine.

The results of the study show a reasonable agreement

between the MF model and the measurements, provided

that the heat transport between the freshly mined ore and

the air is incorporated in the model.

Introduction

The number of mines suffering heat problems due to

the increasing depth of the working area is growing. It is

well known that high temperature and humidity in an

underground working area may result in loss of productivity

and impairment of workers. A properly controlled

environment and a well-implemented ventilation system

model must be maintained in underground mines.

Many studies have been made to control the climate

conditions in underground mines but most of them are

based on through airflow in a single airway. Only a few

models (Gao and Inoue, 2002; Danko et al., 2010a; Danko

et al., 2010b) are available for applications in development-

ends with local ventilation.

The purpose of this study is to model and simulate a

development-end scenario using mine input data and

measurements from the Lucky Friday Mine. Two mine

ventilation and climate simulation programs, MF and Kduct

are employed for comparison with mine data to simulate the

ventilation network and calculate the unknown parameters

such as temperature and humidity.

First, the MF program (Danko 2008), developed at the

University of Nevada, Reno, USA is used as it is pursued

for wide-spread mine ventilation and climate predictions in

underground mines. The MF model takes into account the

air flow field in the drift and the auxiliary air duct;

simultaneous heat and humidity transport from the drift

wall; heat and mass exchange between the air in the drift,

the ducts and freshly mined rock as well as the evaporation

of process water and/or condensation of vapor as governed

by the psychometric conditions. The MF software is a

qualified software (Danko, 2008), for ventilation and

climate studies for high level nuclear waste repositories.

MF has been used in mining applications to compare it to

CLIMSIM (CLIMSIM 1997), as well as other mine

ventilation applications for development-ends (Danko et al.,

2010a; Danko et al., 2010b).

Second, the Kduct (Gao and Inoue, 2002), is also used,

since it is specifically developed for development-end

applications by Gao and Inoue at the Kyushu University,

Japan. The Kduct model has similar capabilities to those of

MF, however, it does not include heat and moisture

transport from the transportation of the mined ore.

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Model parameters and airway configuration

Input data for the simulation was received via personal

communication from the Lucky Friday Mine (Mousset,

2010). The dead-end development includes a 153m long

airway, 3.65m by 3.65m in cross section. A flexible duct

delivers fresh cooled air to the end of the drift. The air is

needed to clean out the dust from the production area by the

drill and blast operation, and to reduce the air temperature

for the miners. Figure 1 shows the schematic arrangements

of the development-end in this study. A single air duct is

used with a fan located 3m from the inlet to blow fresh air

to the face. The axial fan produces 11.8 (m3/s) airflow at

30% assumed power efficiency. The cooler is located 6m

from the inlet and has the capacity of 175.85KW (50 tonR)

of cooling power. The relative humidity of the air at the

inlet is calculated to be 100 %, based on wet-bulb and dry-

bulb temperatures.

Input Data

The input data used in the model configuration are

shown in Table 1. The nominal power ratings of 175kW

and 45kW for the cooler and the fan respectively, would

result in a colder air temperature entering the duct than that

of the drift. This would cause far too strong cooling effect

for the model to handle and to match the temperature at the

face and the exit. It was necessary to evaluate the

parameters manually after the cooler as the input for the air

duct.

Due to the fact that the efficiency of each unit is

unknown, the nominal values for the fan and the cooler

power cannot be used as the input values of the model.

Since no measurements were taken for the actual fan and

cooler power, the dry-bulb and wet-bulb temperatures after

the cooler were back-calculated manually, fitting the MF

model by trial and error to the measurements of the dry-

bulb and wet-bulb temperatures at the exit of the air duct.

The back-calculated dry-bulb and wet-bulb

temperatures after the cooler (i.e., the inlet value at the

beginning of the air duct) were 21.7 °C and 20.4 °C,

respectively.

No visible wetness was reported from the mine, but

judging from the measured values of wet-bulb at the inlet

being lower than the exit wet-bulb temperature, moisture

transport is expected and included in the model.

The Airflow, Thermal, and Humidity Model

The MF program is designed to be used in subsurface

openings such as a nuclear waste repository or an

underground mine with or without development-ends. The

model can be used for coupled, time-dependent thermal-

hydrologic and ventilation calculations. The software

allows for complex calculations for large-scale systems. MF

is composed of two main domains: (1) the geological rock

formation and (2) subsurface airway systems. The two main

domains are coupled iteratively in the MF program.

Table 1. Input parameters for the Kduct and MF model.

Airway

Length (m) 153

Grade (%) 16

Cross section (m2) 3.65x3.65

Surface are (m2) 13.4

Perimeter (m) 14.6

Inlet air Temperature (°C) 18

Relative Humidity (%) 100

Fan

Distance from the Entrance (m)

3

Flow(m3/s) 11.8

Power (kW) 44.74 (60 hp)

Cooler

Distance from the Entrance (m)

6

Flow(L/min) 284

Cooling Capacity (kW) 175 (50 tonR)

Duct Diameter (m) 1.07

Length (m) 132

Pressure Surface (kPa) 90.12

Section (kPa) 108.3

Rock

Virgin Rock Temperature(VTR) (°C)

50 (47.2*)

Thermal Conductivity (W/mK)

3.13

Density (kg/m3) 2670

Mining advance rate for material transport rate

Advance rate (m/day) 3.0**

Wet-bulb (WB)and Dry-bulb (DB) Temperature at the Face (measured)

DB (°C) 23.8

WB (°C) 21.11

Wet-bulb(WB) and Dry-bulb(DB) Temperature at the Entrance\Exit of duct (measured)

DB (°C) entrance 18.88

DB (°C) after fan and cooler

21.7***

WB (°C) entrance 18.88

WB (°C) after fan and cooler 20.4***

DB (°C) exit 22.7

WB (°C) exit 20.55

Wet-bulb(WB) and Dry-bulb(DB) Temperature at the exit (measured) ****

DB (°C) exit 29.4

WB (°C) exit 23.8

* Originally given as 47.2 °C, the VRT had to be modified, see discussion

section. **

Heat transport form the freshly mined ore to the air is included in the thermal

model. The material transport flow rate from the drift advance rate is 1 kg/s

per day ***

Back calculated temperatures, using the MF by trial and error. ****

These parameters were not explicitly needed for the modeling process;

however since the exit wet-bulb temperature was higher than that of the wet -

bulb at the inlet; moisture transport was expected and included in the model.

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Figure 1. General schematic of the development-end with the airflow pattern

Figure 2.Discretization of rock mass domain around the airway in NUFT

-40 -30 -20 -10 0 10 20 30 40-40

-30

-20

-10

0

10

20

30

40

Ventilation

Raise Cooler

Exit

Fan

Bulk

Head

Model Domain

131m

3.6m

3.6m

Drill and Blast

Face

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Figure 3.Heat and moisture fluxes from the strata to the interface elements of the drift.

In the rock mass domain, strata heat flow is modeled

with the NTCF (Numerical Transport Code

Functionalization) module (Danko, 2006). The NTCF

process uses a Porous Media Hydrothermal Code (PMHC)

to model the heat and moisture flow in the rock mass

around the airway. The PMHC model calculates the heat

and/or moisture flux for specific temperature and/or

humidity variations on any surface of the airway. NUFT

(Non-equilibrium, Unsaturated-saturated Flow and

Transport) (Nitao, 2000) is used as a PMHC in the present

paper. The rock mass model domain, shown in Figure 2, is

set up as a separate task. The relevant transport

connections in this study are shown in Figure 3. A

schematic illustration of the coupled processes in the cross-

section of a drift and on the rock-air interface is also shown.

In the drift air space, a numerical model is used in the

form of a lumped-parameter, Computational Fluid Dynamic

(CFD) solver for air, heat, and moisture transport. Heat and

moisture fluxes qh and qm are the input from NTCF, and

temperature and pressure are the output from CFD. The

heat and moisture fluxes are balanced at the common

surface temperature and partial vapor pressure at each drift

wall surface node and time instant t for the solution of the

time-dependent problem.

MF Model Definition

The first step in model preparation in MF is to discretize

the in-drift domain into a number of axial divisions and

define the elements and the transport processes in each

section between the elements. As shown in Figure 4,

discretization with the intervals of 1 meter spacing is

established in the airway and the air duct. Note that the

meshing is shown only at the two ends and left out in the

mid-section of the drift for clarity. The airflow affects the transport of heat and moisture in

two ways, first, by providing a direct means of transport

expressed in capacitive, and convection transport

connections in the CFD sub-models for heat and moisture

transport, second, by affecting the heat and mass transport

coefficients between the solid surfaces and moving fluid.

Heat and moisture transport connections are defined

between the nodes along the flow lines in the airway and

the duct, as well as between the nodes in the return flow

line and the solid surfaces. Further connections are

established between solid surface elements for modeling

heat radiation. As a result, the in-drift model domain has a

total of 1647 nodes for the air, the heat and the moisture

networks.

Air Node

Heat and moisture fluxqh, qm

Coupling

surface q

h (t) wall moisture flux

qm (t) wall heat flux

Wall Node

Tw (t) wall temperature

dependent p

w (t) wall partial vapor

pressure

Heat

convection

Heat

convection

Heat

convection

Moisture

convection

Duct thermal

radiation

qh (t) wall moisture flux

qm (t) wall heat flux

qm (t) wall heat flux q

h (t) wall moisture flux

Air Duct

Heat

convection

Mined Ore

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Figure 4.Thermal, moisture and airflow connections in the airway.

The MF model input data conform to those given in

Table1. In addition, the following internal data were used.

Wetness factor on the drift wall in the MF: 85%.

Heat transport connection for the material transport

based on 3m advancement per day is 1.0 kg/s of ore

transport with enhanced surface exposure of 13m2 per

meter of drift.

Heat transport coefficient between the transported

material and the air in the drift: internally calculated,

equal to that on the drift wall.

Kduct Model Definition

The Kduct program is designed specifically for

development-end applications. Figure 5 shows the model

interface and the input parameters given in mixed units.

These values follow the input data in Table 1. The Kduct

model includes a fan and a cooler but it was impossible to

use the nominal power rating of these units as input and

have reasonable output results from the model.

Generally speaking, the data entry for the model should

use the actual power input for the fan and the fan’s

hydraulic and electric motor efficiencies in order to model

the temperature rise across it. Similarly, the

thermodynamic and heat/moisture transport within the

cooler should be correctly modeled in order to predict the

air temperate and humidity leaving the unit.

There is simply not enough number of parameters to

enter into the Kduct model for defining the processes in the

fan and the cooler. After some unsuccessful attempts to run

the Kduct model with meaningful results, the fan and the

cooler were left out of the model. The dry-bulb and the

wet-bulb temperatures at the duct inlet after the cooler were

used as explained in the Input Data section.

Results

The results from MF and Kduct are shown together in

Figures 6 and 7 for the dry-bulb and wet-bulb temperatures.

At the beginning of the air duct (inlet) for the MF model,

the dry-bulb temperature starts at 21.7 °C. The air heats up

in the duct, and the temperature reaches 22.8 °C at the duct

exit and 23.5°C at the face. Prediction for the temperature

of the returned air in the drift at the exit is 29.1°C.

The dry-bulb temperature for the Kduct at the duct inlet

point is also kept at 21.7 °C. The temperature increases to

22 °C at the end of the duct. At the face, the temperature is

22.5 °C, and at the drift exit point the temperature is 24.6

°C. The results of MF are in good agreement with mine

measurement data.

Face

Wall Node

Air Node in the

Drift

Air Node in the

Duct

1m

6

Figure 5. K-duct model input parameters.

Figure 7 summarizes the predictions for wet-bulb

temperatures. The MF simulation results for the wet-bulb

temperature is 20.4 °C at the inlet of the duct and 20.5 °C at

the exit of the air duct. Due to exposure to the hot face, the

temperature increases to 21.0 °C. The predicted temperature

at the drift exit is 23.5 °C.

The Kduct wet-bulb temperature prediction rises from

20.25°C at the duct inlet to 20.6°C at the exit of the duct.

Temperatures at the face and the drift exit are 20.6°C and

21.7°C, respectively.

Discussion

Since the actual fan and cooler power were not

available, the temperatures after the cooler had to be back-

calculated using the dry-bulb and wet-bulb temperatures at

the exit of the air duct. The dry-bulb and wet bulb

temperatures from this calculation had to be used as input to

the air duct in order to start the model calculations.

There is reasonable agreement between the predicted

wet-bulb and dry-bulb temperature values from MF and

those of the measurement data received from the mine. The

MF model includes thermal and moisture transport

processes from the transportation of the freshly mined ore

in the drift. These transport processes have been included in

the previous studies (Danko et al., 2010a; Danko et al.,

2010b) as a realistic transport assumption, and good

agreement was obtained between measurement and

simulation. The heat exchange from material transportation

process is not included in the Kduct model. For this reason,

i.e., missing thermal connections, the Kduct predictions are

neither in agreement with the measurement data nor with

the predicted values from the MF model.

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Figure 6.Dry-bulb temperature predictions in the air duct and the drift.

Figure 7. Wet-bulb temperature predictions in the air duct and the drift.

0 20 40 60 80 100 120 140 16018

20

22

24

26

28

30

Distance, ( m )

Tem

pera

ture

, (

oC

)

MULTIFLUX

Kduct

measuement

0 20 40 60 80 100 120 140 16018

19

20

21

22

23

24

Distance, ( m )

Tem

pera

ture

, (

oC

)

MULTIFLUX

Kduct

measuement

Drift Exit

Drift

Face

Air Duct

Airway Inlet

Drift

Face

Air Duct

Duct Inlet, calibrated

Drift Exit

Airway Inlet

Duct Inlet, calibrated

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The virgin rock temperature of 50 °C (used in both

models), is 2.8 °C more than what was originally received

from the mine. Liberty was taken to make this temperature

increase for better matching the models to measurement

data. We consider that uncertainty should be expected from

temperature measurements of about ±4 °C RMS error in an

operating mine, with temporal thermal variation, (UNR,

2010).

The Kduct model input parameters can be tuned to

obtain agreement with the measurements from the mine

only by using extreme input parameters such as 11W/m-K

for the rock mass thermal conductivity, a rather unrealistic

value for any rock type in an underground mine. For this

reason the simulation results with this high rock thermal

conductivity are not included in this paper.

Concluding Remarks

A development-end modeling exercise is presented to a

real underground mining scenario at the Lucky Friday

Mine in Idaho, USA. Two models, MF and Kduct, as

well as field measurements from the mine are used for

comparison.

The MF model incorporates the simulation of the air

flow field in the drift and the auxiliary air duct;

simultaneous heat and moisture transport from the drift

wall; heat and mass exchange between the air in the

drift, the ducts and the freshly mined ore; as well as the

evaporation of process water and/or condensation of

vapor as governed by the psychometric conditions.

The Kduct model has similar capabilities to those of

MF, however, it does not include heat and moisture

transport from the transportation of the mined ore. The

model cannot be matched with mine data without using

an extreme value for heat conductivity of the strata.

Excellent match was obtained by MF, if a model

element for thermal and moisture transport of the

freshly mined ore, being transported in the airway, is

included.

Acknowledgement

The research fund from NIOSH, USA, under grant

number 200-2009-30157 is gratefully acknowledged. The

permission of using NUFT from the Lawrence Livermore

National Laboratory is thankfully appreciated. We

thankfully acknowledge Dr. Pierre Mousset-Jones for

providing the measurements data from the Lucky Friday

Mine and personal communications with the mine.

References

1. Danko, G., (2006). “Functional or Operator

Representation of Numerical Heat and Mass Transport

Models.” ASME Journal of Heat Transfer, Vol.128,

pp.162-175.

2. Danko, G., (2008). “MULTIFLUX V5.0 software

Documentation Qualification Documents.” Software

Tracking Number; 1002-5.0-00, Software Management

Office, Berkeley National Laboratory.

3. Danko, G and Bahrami D., (2008). “Application of

MULIFLUX for Air, Heat and Moisture Flow

Simulations.” 12th

U.S/North America mine Ventilation

Symposium 2008, Reno, NV Jun 9-11, 2008, pp. 267-

274.

4. Danko, G., Bahrami, D. and Gunda, R., (2010a).

“Simultaneous Ventilation, Power and Cooling Supply

with Compressed Air.” Proceedings Extracting the

Science: A Century of Mining Research, (Ed. Jurgen

Brune), SME Annual Meeting and Exhibition, Phoenix,

AZ, 2010 pp. 463-477.

5. Danko, G., Bahrami, D. and Gunda, R. (2010b).

“Simulation of ventilation and climate conditions in

development-end applications.” Proceedings of the

13th U.S'/North American Mine Ventilation Congress

Symposium, 2010 Sudbury, Ontario, Canada.

6. Gao, K. Uchino & M. Inoue Fukuoka, Japan (2002).

“Modeling of thermal environment conditions in

developing roadway.” Earth Resources Engineering

Dept. Kyushu University.

7. Mousset-Jones P (2010). Personal communications

including those with mine personnel at the Lucky

Friday Mine.

8. Nitao, J. (2000). “NUFT, Flow and Transport code

V3.0s.” Software Configuration Management, Yucca

Mountain Project – STN: 10088-3.0S-00. Prepared at

the Lawrence Livermore National Laboratory.

9. UNR (University of Nevada, Reno), (2010). “Safety,

Health, and Ventilation Cost Optimization with

Simulation and Control.” Phase 1 report, prepared for

NIOSH under grant number 200-2009-30157.