GATE Mining Engineering Surface Environment, Mine Ventilation and Underground Hazards Flashcards

24 sample cards from the Surface Environment, Mine Ventilation and Underground Hazards deck

Sampled from the end of the deck, so these are different cards from the ones shown on the syllabus page.

1. What numerical method is standard for solving complex ventilation networks, and on what is it based?

   The Hardy Cross iterative method, applied to mesh equations. Each loop correction is $$\Delta Q=-\frac{\sum R Q|Q|}{2\sum R|Q|}$$ iterated until pressure imbalances around all meshes are negligibly small.

2. What is natural ventilation pressure (NVP) and what causes it?

   NVP is the pressure difference that drives airflow due to the density difference between the downcast and upcast air columns, created mainly by temperature (and humidity) differences. $$NVP=g\,H(\rho_{dc}-\rho_{uc})$$ for a shaft of height $H$.

3. Contrast forcing, exhausting and combined (push-pull) main mechanical ventilation systems.

   Forcing (blowing): fan at downcast pushes fresh air in, mine at above-atmospheric pressure. Exhausting: fan at upcast draws air out, mine below atmospheric (preferred in gassy mines to bleed strata gas). Combined: two fans, one forcing and one exhausting, giving near-atmospheric mine pressure and higher total head.

4. Give the fan total pressure relationship and the definition of fan static pressure.

   Fan total pressure $FTP=FSP+FVP$, where fan velocity pressure $FVP=\tfrac{1}{2}\rho v^{2}$ at outlet and fan static pressure $FSP=FTP-FVP$. FSP is the pressure available to overcome airway resistance.

5. Write the air-power (fan output power) and fan efficiency formulas.

   Air power $$P_{air}=Q\times p$$ (with $Q$ in m³/s and $p$ in Pa giving watts). Fan efficiency $\eta=\dfrac{P_{air}}{P_{shaft}}=\dfrac{Q\,p}{\text{input power}}$.

6. State the fan laws relating quantity, pressure and power to fan speed $N$ (fixed diameter and density).

   $$Q\propto N,\qquad p\propto N^{2},\qquad \text{Power}\propto N^{3}$$ Quantity varies directly, pressure with the square, and power with the cube of rotational speed.

7. Compare centrifugal and axial-flow mine fans.

   Centrifugal: flow leaves radially, develops high pressure, robust, lower speed, larger footprint, good for deep/high-resistance mines. Axial: flow stays parallel to axis, compact, high quantity at moderate pressure, reversible easily and blade-angle adjustable, higher speed; widely used as main and booster fans.

8. What is a fan operating point and how is it found?

   It is the intersection of the fan characteristic (pressure–quantity) curve with the mine resistance (system) curve $P=RQ^{2}$. The intersection gives the steady-state air quantity and pressure at which the fan operates in that mine.

9. What is auxiliary ventilation and where is it used?

   Auxiliary ventilation supplies air to blind headings/dead ends (development drivages, tunnels) not connected to the through (coursed) ventilation circuit, using a fan and ducting/brattice to carry air to and from the face.

10. Compare forcing, exhausting and overlap auxiliary ventilation systems.

    Forcing: duct fan blows fresh air to the face, fast face clearance, rigid or flexible duct, but contaminated air travels back along the heading. Exhausting: draws dust/gas/fumes directly from the face through a rigid duct, cleaner heading but slower throw. Overlap (combined): both a forcing and an exhausting line with overlap at the face — best dust and gas control.

11. What is a ventilation survey and what are its two principal measurements?

    A ventilation survey systematically measures the distribution of air in a mine to compute resistances and check the circuit. Its two key measurements are quantity (air velocity by anemometer × cross-section area $Q=vA$) and pressure (frictional pressure drop between stations, e.g. by gauge-and-tube or barometric/altimeter method).

12. Name the instruments used to measure air velocity, pressure drop and air quantity underground.

    Velocity: vane anemometer (and smoke tube for low velocities); Pressure: water/inclined-tube manometer or magnehelic gauge with the gauge-and-tube method, and precision aneroid barometer/altimeter for the barometric method; Quantity is derived as $Q=vA$.

13. What are the four classic sources of heat (heat load) in a deep underground mine?

    (1) Auto-compression and geothermal heat from strata (rock temperature rising with depth via geothermal gradient), (2) machinery and electromechanical equipment, (3) oxidation and chemical reactions (e.g. timber, sulphides), and (4) human metabolism, blasting, lights, and groundwater heat.

14. What is auto-compression of air in a downcast shaft and its approximate dry rate?

    As air descends a shaft it is compressed by its own weight, converting potential energy to heat and raising temperature even with no external heat input — about $0.98\,^{\circ}\text{C}$ per 100 m (the dry adiabatic lapse, $g/c_p$).

15. Define the geothermal gradient and geothermal step.

    Geothermal gradient = rate of rock temperature rise with depth (typically $\sim1\,^{\circ}\text{C}$ per 30–40 m). Geothermal step = depth increase per $1\,^{\circ}\text{C}$ rise (the reciprocal, typically 30–40 m/°C).

16. What two thermal indices are used to assess heat stress in mines?

    Effective Temperature (ET / Corrected Effective Temperature CET), combining dry-bulb, wet-bulb temperature and air velocity; and the Wet-Bulb Globe Temperature (WBGT) index, $WBGT=0.7t_{wb}+0.2t_g+0.1t_{db}$ for cases with solar load.

17. What is the role of psychrometry in the mine thermal environment, and what does a sling psychrometer measure?

    Psychrometry quantifies the heat and moisture content of mine air (humidity, enthalpy). A sling/whirling psychrometer gives the dry-bulb and wet-bulb temperatures, from which relative humidity, moisture content and the cooling power of the air are obtained.

18. Name the principal methods of air cooling (refrigeration) used in hot deep mines.

    Mechanical refrigeration using vapour-compression chiller plants (surface, underground or combined) supplying chilled water to bulk air coolers or spot coolers; ice-cooling (ice transport to underground melting dams); and increasing ventilation air quantity/velocity for evaporative cooling.

19. Classify the causes of mine fires into the two broad types.

    Open (active) fires — from external/exposed sources: electrical faults, friction (belt/rope), welding, blasting, explosives, smoking, hot machinery. Spontaneous (concealed) fires — self-heating from exothermic oxidation of coal/sulphides leading to spontaneous combustion (gob fires).

20. What ratios/indices are used to detect and assess the status of an underground fire?

    Graham's Ratio (CO make / O2 absorbed × 100) for spontaneous heating, the CO/CO2 ratio, the oxides-of-carbon ratio, and Young's/Jones-Trickett ratio for explosibility — all from sampling and analysis of mine-air gases.

21. What is a coal-dust explosion, and what is the function of stone dusting?

    Fine airborne coal dust can propagate or initiate an explosion (often triggered by a firedamp ignition) since dispersed coal dust is combustible. Stone dusting spreads incombustible rock dust (limestone) to dilute the coal dust below explosibility (statutorily the mixture must contain enough incombustible matter, typically ≥ 65–80%) so a flame cannot propagate.

22. Differentiate the explosibility behaviour and control of firedamp versus coal dust, and a device that limits propagation.

    Firedamp (CH4) is a gas explosive between ~5–14%; coal dust is a suspended solid that can explode over a wide range and sustain a travelling explosion. Stone-dust barriers or water (passive/triggered) barriers placed in roadways quench an advancing explosion flame and limit propagation.

23. What is inundation in a mine and what is the primary precaution against it?

    Inundation is the sudden inrush of water (or water-laden slurry/gas) into mine workings from old waterlogged workings, surface bodies, or aquifers. The primary precaution is maintaining statutory barriers/pillars against water bodies and advance boring (probe drilling) ahead of the face when approaching suspected water.

24. Name the two main classes of mine rescue breathing apparatus and how they differ.

    Self-Contained Self-Rescuer (SCSR) — a short-duration escape device (filter type converts CO to CO2, or chemical-oxygen type generates O2) for self-escape; and Self-Contained Breathing Apparatus (closed-circuit oxygen breathing apparatus, e.g. ~2-hour set) worn by trained rescue teams entering irrespirable atmospheres, recirculating breath through a CO2 scrubber and oxygen supply.

What this deck covers

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