North American / Ninth U.S. Mine Ventilation

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MEASUREMENT OF AIRFLOW THROUGH REGULATORS AND
REAL TIME INTEGRATED MONITORING

• Stewart Gillies
• The University of Queensland

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Outline of Presentation

• Introduction
• Theory of Regulators
• Field Tests of Regulators
• UQEM Real Time Mine Ventilation System
• Trials of the UQEM System
• Conclusions

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THEORY OF MINE REGULATORS

• An artificial resistance (in the form of shock
  loss) or a large thin plate installed in a fluid
  conduit with an orifice.
• When a difference in pressure exists between the
  two sides fluid flows as shown.

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Mathematical Modelling of Regulators

• Irregularity in shape and symmetry and their
  positioning in roughly square or rectangular
  airways,
• Construction of the opening - louvres, sliding
  door, window or curtain or placement of drop
  boards, and
• Uncontrolled air leakage.

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C-Section (Drop Board Type) Regulator
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An Example of Louvre Regulator
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Derivation of Regulator Equation

• Bernoullis equation can be applied to both sides
  of the orifice to calculate the velocity and
  hence the airflow quantity.
• A correction must be made for the contraction of
  the jet at the vena contracta.
• Velocity at the orifice is obtained with the
  following equation

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Derivation of Regulator Equation (cont.)

• Airflow quantity through regulator is as follows.
• where Cc is the coefficient of contraction
  (Ac/Ar)
• Ar is orifice opening area
• N is the ratio of the orifice and airway
  cross
• sectional area, (Ar/A)
• Ps is the differential pressure across
  regulator
• ? is air density

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FIELD TESTS OF REGULATORS

• To verify airflow behaviour through a drop board
  regulator.
• Airflow quantity and pressure drop across the
  regulator were measured.
• Airflow quantity through the regulators can also
  be calculated in theory from pressure
  measurements.
• Results compared with measured values and the
  reasons for significant differences investigated.

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Comparison of measured and predicted Q
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Reasons for the differences in Quantities

• Error during measurement
• Small cross-sectional area
• No-symmetrical condition and shape
• Leakage occurs due to gaps or holes between
  boards, regulator frame and the airway walls.
• Airflow quantity can be expressed as follows to
  account for leakage.
• where Ql is the leakage quantity

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Airflow Paths in Regulator

• Regulators can be treated as a set of two
  parallel airways namely
• Regulator opening and
• Leakage paths

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Resistance of Regulator

• The total resistance of regulator (Rt) can be
  modelled to consist of the regulator opening
  resistance (Ro) and the leakage path resistance
  (Rl).
• The regulator opening resistance (Ro) can be
  calculated from the derived formula
• Where A is the airway cross sectional
  area.

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Resistance of Regulator

• When the regulator is in a fully closed
  condition, the air flows through the leakage path
  only with resistance Rl which can be empirically
  derived.

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Measured and Predicted Airflow Quantity
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Regulator Resistance vs Opening Area
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UQEM Regulator Characteristic Curves
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Plan of UQ Experimental MineShowing locations of
doors and sensors
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VENTSIM Real Time Simulations
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VENTSIM - Remote Station Database Interface
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VENTSIM - Airway Edit Interface
Input of Remote Station Number
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TRIALS OF THE UQEM SYSTEM

• Trial Scenarios
• The inclined shaft door was open, and the
  regulator in 116 level set on fully open.
• The inclined shaft door was open, and the
  regulator was set 1/5 open with 12 boards
• The inclined shaft door was open, and the
  regulator set on fully closed.

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Schematic of UQEM Ventilation System
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Accuracy of Trial Results

• Ventsim monitoring system predicts changes with
  reasonable accuracy although some differences in
  quantities were larger than 10.

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Constraints of the System Transition Time
The transient period in UQEM is short and
therefore is not of great significance in
interpreting the network system. However, in
large-scale mines, the period can be up to 10
minutes or more.
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Updating of Ventilation Simulation Models

• The trial demonstrated the importance and
  necessity of updating simulation models after
  changes.
• The three scenarios were examined for how the
  network reacted to the input of a real time fixed
  quantity in terms of maintenance of model
  accuracy without a change to the regulator/door
  R value
• Based on air quantity observations it is not
  necessary to make adjustment to the
  regulator/door R in the model as error is no
  more than 5.
• However when comparing the predicted pressure
  drops across regulators, significant need for
  adjustment was found.

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CONCLUSIONS

• Efforts to mathematically model some operating
  mine regulators have been described.
• Theoretical calculations to predict airflow
  quantity through regulators based on measured
  pressure drop are inadequate due to leakage,
  geometry etc.
• It is necessary to quantify the resistance of the
  leakage path based on regulator opening area and
  then recalculate the total resistance of the
  regulators.

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CONCLUSIONS Cont.

• An investigation was undertaken as to whether the
  Real Time Airflow Monitoring system can
  accurately detect changes in a ventilation
  network and identify constraints.
• The system was able to detect changes and to
  predict the changes accurately.
• Limitations caused by transient period delays
  have been examined.
• It is important to update the simulation models
  based on real time data.