Mining · Course

Mine ventilation: airflow, network and dilution

Read a simplified ventilation network, balance two branches, limit leakage and connect airflow, pressure, energy and tracer dilution.

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Scientific principles

Airflow Q passes through area A at mean velocity v. A fan provides a pressure difference; roadways, doors and ducts create resistance. The operating point is the intersection of the fan curve and network curve. Increasing the speed setting can increase airflow and power demand.

Two parallel branches share a pressure difference but carry different flows according to their resistances. A regulating door increases local resistance and redistributes air. Leakage creates an additional path: fan flow is therefore not the same as useful airflow at working faces. Intake and return air must be distinguished.

Dilution compares tracer emission with the airflow receiving it. The proposed balance assumes perfect mixing, constant emission and steady state; it does not represent a gas pocket, fire or dust cloud. At zero airflow, the steady-state concentration is undefined: show a no-ventilation condition, not a reassuring value.

Compare velocity, pressure and power at different settings, then discuss the trade-offs. Displayed resistances and targets are synthetic. The model ignores heat, humidity, variable density, natural ventilation and transients; no result certifies breathability or compliance of a real atmosphere, which require measurements and specialist assessment.

Equations, units and conditions

Q = v × A

Q: airflow in m³/s; v: mean velocity in m/s; A: cross-sectional area in m².

Section-average measurement; a point reading may not represent the entire section.

Δp = R × Q²

Δp: pressure loss in Pa; R: resistance in Pa·s²/m⁶; Q: m³/s.

Fixed resistance and simplified turbulent flow; R must not be negative.

R_parallèle = 1 / (Σ 1/√R_i)²

R_i: branch resistances; R_parallèle: equivalent resistance in the same unit.

Branches connect the same two nodes, with strictly positive resistance; add common series resistances separately.

Q = √(P0 × n² / (R_réseau + K))

P0: shutoff pressure in Pa at reference speed; n: relative speed; K: fan-curve coefficient; Q: m³/s.

Synthetic curve Δp_fan = P0 × n² − K × Q²; this is not a manufacturer curve.

P_électrique = Δp × Q / (1000 × η)

P_électrique: kW; Δp: Pa; Q: m³/s; η: overall efficiency between 0 and 1.

Simplified balance; use pressure supplied to the entire network and total airflow.

C_sortie = C_entrée + G / Q

In the simulation: G is a mass emission in mg/s; Q is in m³/s; C is in mg/m³. For a volumetric emission G in m³/s, C would be a volume fraction and ppm = C × 10⁶. Do not mix the two conventions.

Strictly positive Q, dilute tracer, perfect mixing and steady state; no universal regulatory threshold is inferred.

Applications

Two-workplace network

Distribute flow between branches and observe the effect of doors.

Leak between intake and return

Compare total and useful airflow before and after reducing leakage.

Educational monitoring

Read velocity, pressure, power and fictional tracer concentration.

What to observe in the simulation

Change fan speed, doors and leakage. Check airflow conservation at the node, loss of useful air through a short circuit and its effect on the tracer. Export settings and limitations in the report; compare an educational target without declaring the air safe.