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University of JohannesburgFaculty of Engineering and the Built Environment

Mining Department

MTLA411 (Ventilation)

Tutorial 4

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Required information:

Psychrometric charts as attached.

Learning points:

1. Air flowing down a mine shaft is subjected to the phenomenon of autocompression. As the air loses altitude, it becomes compressed andtherefore its temperature will increase. There is a gain in enthalpywithout the presence of an external source of heat. This is called anadiabatic process. The gain in enthalpy is taken as equal to the loss inpotential energy.

2. Auto compression is responsible for a significant rise in the tempera-ture of mine ventilating air

note the results of the calculations done in

this tutorial.

3. Geothermal heating (heat from rock) in tunnels can be estimated indifferent ways:

Heat flux expressed per meter length of tunnel (kW/m).Heat flux per m2 of tunnel wall (kW/m2).

Both methods will be used in this tutorial.

4. Fissure water can be a significant source of heat see problem 4. Toestimate the heat load of the water, the quantity and temperaturechange must be known.

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Problem 1(5 minutes)

A quantity of 200m3 /s enters a downcast shaft at a temperature of 14/22Cand a barometric pressure of 95kPa.

Estimate the air temperature at a depth of 2300m, given the following data:

A fissure in shaft increases the moisture content by 20%.Geothermal heating in the shaft is negligible.The barometric pressure @ -2300m is 115kPa.

Problem 2(5 minutes)

A heat wave in the area increases the air temperature to 24/29C and thepressure to 100kPa. What would the -2300m temperature be now (pressurehere is 120kPa).

Problem 3(10 minutes)

A section of a mine is ventilated with 80m3/s of ventilating air that leaves anunderground Bulk Air Cooler at a temperature of 5C (saturated) and flowsalong an Intake Airway, 2000m long and then enters a stope. The pressure is110kPa.

The heat load of the IAW is as follows:

Geothermal heat 1,95kW per meter of tunnelMachinery 700kWWater added to the air 10g/kg

What is the air temperature at the stope intake?

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Problem 4(20 minutes)

You are responsible for a mining production section that is 2600m deep onaverage. A quantity of 65m3/s of ventilating air is fed to the section through an

intake airway that is 1800m long, 3m wide and 3m high. The air enters thisairway at a temperature of 19/23C.

The geothermal heat load of the tunnel is 75W per square meter of tunnelwall.Machinery adds another 670kW of heat to the ventilating air.A quantity of 26liters/second of fissure water enters the airway at a tempera-ture of 35C and leaves it at a temperature of 26.The fissure also increases the moisture content by 3,5g/kg.The mean air pressure in the airway is 115kPa.

Estimate the temperature at the end of the airway.Would you, as the manager, be comfortable with this value?

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