Mine Ventilation

Heat Load, Thermal Environment & Air Cooling

Why deep mines get hot, how to quantify the sensible heat the air must remove, and the refrigeration duty that keeps workings within legal limits.

PART 1

Topic Breakdown & Traps

The Engineering Principle

As mines deepen, virgin rock temperature rises with the geothermal gradient (typically

\sim 1^{\circ} C

per 30–40 m), and autocompression heats descending air. Heat sources include the strata, machinery, oxidation, men and lights. The ventilating air removes heat as sensible heat (temperature rise of the air) and latent heat (moisture pick-up). The sensible-heat balance

Q = \overset{m}{˙} c_{p} Δ T

sets the airflow or cooling needed to hold the workplace within the statutory wet-bulb limit. When ventilation alone cannot cope, mechanical refrigeration / spot coolers supply the extra cooling duty.

The Core Formula Matrix

Sensible heat removed by air:

Q = \overset{m}{˙} c_{p} Δ T

(

\overset{m}{˙}

= mass flow,

c_{p} \approx 1.005 kJ/kg\cdotK

for dry air)

Mass flow from volume flow:

\overset{m}{˙} = ρ Q_{v}

(air density

ρ \approx 1.2 kg/m^{3}

)

Virgin rock temperature:

T_{r} = T_{s u r f a ce} + g_{g eo} (H - H_{0})

(

g_{g eo}

= geothermal gradient)

Refrigeration duty:

Q_{r e f} = Q_{h e a t, t o t a l} - Q_{ai r}

(cooling that ventilation cannot remove).

The ‘IIT Traps’

⚠
**Use mass flow, not volume flow, in $Q = \overset{m}{˙} c_{p} Δ T$ .** Convert $Q_{v}$ via $\overset{m}{˙} = ρ Q_{v}$ first.
⚠
** $c_{p}$ in kJ/kg·K gives $Q$ in kW** when $\overset{m}{˙}$ is kg/s and $Δ T$ in K — keep the units aligned.
⚠
Wet-bulb temperature, not dry-bulb, governs heat stress. Humidity (latent heat) matters as much as temperature.
⚠
Autocompression heats *downcast* air even with no other source — about $1^{\circ} C$ per 100 m of descent.

PART 2

Progressive 3-Tier Question Suite

Q1BASIC1 Mark · MCQ

The statutory index used to assess heat stress on miners is primarily the:

Q2MEDIUM2 Marks · NAT

Air flows through a working at

50 kg/s

. It enters at

2 4^{\circ} C

and leaves at

3 0^{\circ} C

. Taking

c_{p} = 1.005 kJ/kg\cdotK

, the sensible heat picked up is ______ kW. (Round to the nearest whole number.)

Q3HARD2 Marks · NAT

A working generates a total heat load of

400 kW

. The ventilating air (

30 kg/s

c_{p} = 1.005 kJ/kg\cdotK

) is allowed a temperature rise of only

8 K

. The refrigeration duty required is ______ kW. (Round to the nearest whole number.)