KB Final Flashcards
Review: What is quality control in mine ventilation in 3 points?
- Purification of air and removal of contaminants
- To keep non-particulate and particulate contaminant below thresholds
- Regulation of magnitude and direction of airflow
Review: What is the Re number?
It is a non-dimensional number to measure the ratio of inertia and viscous force. In a pipe, laminar (non-turbulent) if Re < 2000.
Review: What is a brattice?
An air curtain commonly used in underground mine to direct airflow to the mining face.
Review: What is the effect of placing a main fan in pull mode on the underground workings related to pressure?
The underground workings experience negative pressure. Sucking the air out.
Review: What is the effect of conveyance on pressure loss depending on the direction of the direction of the airflow and the direction of the skip/cage?
- Same direction decreases pressure loss due to conveyance
- Opposite direction increases pressure loss due to conveyance
Review: Describe the cause of shock losses in ventilation system?
Pressure loss due to due to changes in geometry or direction of airflow.
Review: In ventilation network describe the rules regarding series “circuit”.
Series:
* The pressure drops are additive (total pressure drop is the sum of individual pressure drops).
* The airflow rate is constant throughout the series components.
*
Review: In ventilation network describe the rules regarding para “circuit”.
Parallel:
* The airflow rates are additive (total airflow is the sum of individual airflows).
* The pressure drop is constant across the parallel components.
Review: Describe the stall region in fan characteristics curve.
Stall region in the fan characteristic curve is the unstable region typically located at the top-left of the curve. The fan operating point should not be located in this region as it is unstable, which can create resonance, vibration, noise, and low efficiency.
Review: Describe the process that occurs during ventilation commissioning.
In ventilation commissioning for the validation of a ventilation network model, the engineer needs to calibrate mine resistances based on the pressure and flow rate obtained from ventilation surveys.
Review: Give the formulas for conservation of mass, conservation of moisture and conservation of energy.
Review: Describe relative humidity.
Ratio of actual vapor pressure versus saturation vapor pressure.
Review: When does fog occur?
Fog forms when the air at higher humidity experiences a sudden pressure change to a higher (positive) pressure, such that the shift to the left in the saturation line causes the air to become supersaturated, leading to fog formation.
Review: Describe the effects of on temperature and humidity of coil cooling and spray cooling.
In coil cooling, temperature reduces and humidity decreases due to condensation.
Similarly, in spray cooling, temperature reduces but humidity increases due to the addition of water vapor.
Review: Compare dry and wet bulb temperature at 100% relative humidity.
They are the same.
Review: Explain auto-compression.
Air entering a mine through a shaft is compressed and heated as it flows downward. It occurs when the potential energy is converted to thermal energy.
Review: Describe the refrigeration process and its component and associated temperature vs. entropy chart.
Review: Describe the behaviour of dust particles based on their size.
The heavier and larger dust particle will settle more rapidly, while smaller dust particle will tend to remain airborne.
Section 5 Fans: 2 types of fans
- Centrifugal Fan
- Axial Fan.
Section 5 Fans: 3 types of centrifugal fans
- Paddle blade
- Forward Curved
- Backward Curved
Section 5 Fans: 3 types of axial fans + the most common
- Tube Axial
- Vane Axial (most common in mine)
- Propeller
Section 5 Fans: Name the design variables of centrifugal fans.
- Blade curvature
- Number of blades
- Inlet
- Impeller diameter
- Fan width
- Scroll
- Guide vane
Section 5 Fans: Explain the Axial Fan principle:
Air passes through the fan along flowpaths that are essentially aligned with the axis of rotation of the impeller and without changing their macro-direction. More commonly used in mines.
Section 5 Fans: Name the design variables of axial fans.
- Angle or pitch of blades
- Number of blades
- Number of stages
- Ratio of hub to impeller diameter
- Housing
Section 5 Fans: What does increasing the number of blades in a centrifugal fan do?
It yields an increase in the pressure and quantity of air discharges. However, after a certain number, it increases the friction losses and reduce the available area for airflow.
Section 5 Fans: What does the number of stages represent in axial fans?
It is the number of impellers, higher pressures can be obtained from impellers in series.
Section 5 Fans: Why the blade angle is changed in axial fans?
The angle can be adjusted to maintain efficiency at the desired airflow quantity.
Section 5 Fans: The fan operating point is the intersection between which curves?
Intersection between System characteristics curve and Fan characteristic curve
Section 5 Fans: What happens to total pressure and Q when 2 fans are in series?
The total pressure is the sum of both fans while the air quantity provided stays the same.
Section 5 Fans: What happens to total pressure and Q when 2 fans are in parallel?
The total pressure stays the same while the air quantity is the sum of both fans,
Section 5 Fans: Air compressibility
air density changes with pressure. Thus, accounting for compressibility is essential for accurate fan power estimation at higher pressures.
Section 5 Fans: Booster fans:
To enhance or maintain adequate airflow in areas of the mine that are difficult or uneconomic to ventilate by main fans, and To redistribute the pressure pattern such that air leakage is minimized.
Section 5 Fans: Auxiliary fans
Pass air through ducts to ventilate blind headings.
Section 5 Fans: Brattices
A partition used in a mine ventilation system to direct and regulate airflow.
Section 5 Fans: Which fan characteristic curve is for an axial fan and which for a centrifugal fan?
Left is centrifugal, Right is axial
Section 5 Fans: Which graph shows two fans in series and which is two fans in parallel?
Left is parallel, Right is series
Section 5 Fans: Explain the concept of Ventilation on Demand and how does it relate to Fan Laws?
VOD adjusts mine airflow in real-time based on current needs with the use of tags on personnel and equipment. These tags will communicate with receptors that will activate the required louvers and fans.
Fan Laws are fundamental to implementing VOD because they allow engineers to predict how changes in fan speed or system resistance will affect the ventilation system.
Section 4 Mine Ventilation Network : What is Kirchooff’s first law?
The mass flow entering a junction equals the mass flow leaving the junction.
Section 4 Mine Ventilation Network : What is Kirchooff’s second law and when is it used?
The algebraic sum of all pressure drops around a closed path in the network must be zero, having taken into account the effects of fans and ventilating pressures. Used when inspection of the network shows that it cannot be resolved into a series/parallel configuration.
Section 4 Mine Ventilation Network : What happens to Q and p in a series network?
The flowrate is the same but the pressure drop is different.
Section 4 Mine Ventilation Network : What happens to Q and p in a parallel network?
The sum of the flowrate in parallel branches should equal the total flowrat coming in. The pressure drop is the same through the network.
Section 4 Mine Ventilation Network : What is the Hardy Cross technique?
It is a numerical method for ventilation network analysis
Section 4 Mine Ventilation Network : What does the Hardy Cross Technique show?
It shows the system resistance curve for one single representative branch in a ventilation network. If the air flow, Q, is reversed then the frictional pressure drop, p, also becomes negative.
Section 2 Basic Principles : What is the Re number?
It is a non-dimensional number to measure the ratio of inertia and viscous force. In a pipe, laminar if Re < 2000.
Section 2 Basic Principles : State if the pressure in the mine is positive / greater than atm pressure for blowing fans, exhaust fans, push-pull fans
Blowing = higher than atm pressure, Exhaust = lower than atm pressure, Push-pull = neutral pressure
Section 2 Basic Principles : What is a passive regulator?
Simply a door fitted with one or more adjustable orifices.
Section 2 Basic Principles : What is an active regulation?
This implies the use of a booster fan to enhance the airflow through a part of the mine.
Section 2 Basic Principles : What does an antitropal airflow mean?
It is when airflow and transported rock move in opposite direction.
Section 2 Basic Principles : What does an homotropal airflow mean?
Airflow and transported rock move in the same direction.
Section 2 Basic Principles : What does an ascentional airflow mean?
Airflow moves upwards through inclined workings.
Section 2 Basic Principles : What does a descentional airflow mean?
Airflow moves downward through inclined workings
G*Section 3 Pressure Losses : List and explain three sources of pressure losses in the Mine Ventilation system.
- Friction losses are associated to the pressure loss due to the roughness of the airway, a smooth airway will have lower frictional losses compared to a rough one.
- Shock losses are related to the pressure loss caused by changes in kinetic energy due to alterations in geometry, changes in flow direction, obstructions, etc.
- Conveyance losses are linked to aerodynamic disturbances caused by the movement of the cage or skip in the shaft or UG equipment.
Section 7 Gasses and Dust : Underground gas concentrations are regulated based on Threshold Limit value (TLV). Explain how TLV relates to Time Weighted Average (TWA) and Short-Term Exposure Limit (STEL).
The TWA and STEL both have TLVs. They both have threshold values for contaminants exposure based on the duration and interval of exposure (8h or 15 min).
Section 7 Gasses and Dust : Define TLV
Refers to concentrations within which personnel may be exposed without known adverse effects to their health or safety.
Section 7 Gasses and Dust : Define TWA
Is the average concentration to which nearly all workers may be exposed over an 8h shift and 40h per week without any known adverse effects.
Section 7 Gasses and Dust : Define STEL:
Is a time-weighted average concentration occurring over a period of < 15 min.
Section 7 Gasses and Dust : What is the ceiling limit?
The concentration that should not be exceeded at any time.
Section 7 Gasses and Dust : Describe Methane gas characteristics
Its non-toxic but highly flammable. Density lower than the air, so it can form pools of gas at ceiling level.
G*Section 7 Gasses and Dust : Describe and give examples of methane control: before excavation, during excavation and after excavation:
- Before excavation: Pre-drainage; we predrill the methane by drilling a vertical hole through the seam, we pre drain the methane.
- During excavation: Fresh air ventilation, water spray, inert ventilation, scrubber ventilation. Fresh air ventilation to dilute the methane content, water spray which suppresses the dust and lower activation energy (spark point), inert ventilation blows inert gas to reduce explosion risk during an outburst, scrubber ventilation used when there is an outburst.
- After excavation: inertisation, post-drainage. Inertisation, you seal the cob and then inject with nitrogen or CO2, post-drainage used if methane content is high where you suck out the methane out.
Section 7 Gasses and Dust : Describe CO2 gas density:
Density higher than air, accumulates at floor.
Section 7 Gasses and Dust : Describe CO gas characteristics
Inodor, colorless, no taste. Density very close to air density, it mixes easily with air.
Section 7 Gasses and Dust : Describe SO2 gas characteristics
Acidic taste, burns the eyes and respiratory tracts. Highly soluble in water.
Section 7 Gasses and Dust : Describe Hydrogen suplhide (H2S) gas characteristics
Smell like bad eggs, narcotic effect on nervous system.
Section 7 Gasses and Dust : What is DPM composed of:
Combination of soot, unburned fuel and aldehydes, and is regarded as being the component of diesel exhaust that is most hazardous to health.
Section 7 Gasses and Dust : When are mine dusts formed?
Mineral dusts are formed whenever rock is broken by impact, abrasion, crushing, cutting, grinding or explosives. Loading operations, transportation, workshops.
Section 7 Gasses and Dust : Toxic dusts
Arsenic, Lead, Uranium, Silver, Nickel
Section 7 Gasses and Dust : Carcinogenic dusts
Radon, Asbestos fiber, Quartz particles, Arsenic, DPM.
Section 7 Gasses and Dust : Dust diseases
Pneumoconiosis, Silicosis, Asbestosis
G*Section 7 Gasses and Dust : 4 Dust control methods:
- Suppression: the prevention of dust becoming airborne. Ex: Pick face flushing and jet-assisted cutting, Water infusion, Wetting agent.
- Filtration and scrubbing: the removal of dust from the air. Ex: Water spray, Wet scruber, dry filters and separators, personal respirators.
- Dilution by airflow: reducing dust concentration. Ex: Auxiliary fan, brattice etc
- Isolation: separation of personnel from the higher concentrations of dust. Ex: Air curtain, barriers
Section 9 Cooling : What are the main factors that influence thermal inflow.
- Climate and season
- Geological factor
- Mining factor
- Auto-compression (constant relative to depth tho)
