Calculate the air mass flow rate in the shaft the rate at

Question

1. Given the ventilation circuit and resistances shown in the figure below, determine the distribution of airflow. Assume that the fan pressure remains constant at 2000 Pa and that there is no natural ventilation.

2. The following measurements were made at the top and bottom of a vertical downcast shaft:

	Top	Bottom
Temperature	17.7/15.78 C	25.83/20.50 C
Pressure	100.77 kPa	114.07 kPa
Elevation	0.0 m	-1,108.5 m
Airflow rate	-	500 m3/s

Calculate the air mass flow rate in the shaft; the rate at which moisture is evaporated into the airstream and the rate at which heat is added to the shaft. The shaft is circular with a diameter of 7.5 m. The moisture enters the shaft at a temperature of 20°C at a point 400m from the top of the shaft.

3. In a production area the speed of the ventilation airflow is 1 m/s. Calculate the rate of heat transfer from a work-person with an average body diameter of 200mm. Assume that the work-person has a skin area of 1.5 m² and an average skin temperature of 35°C. It can also be assumed that the condition of the ventilation air is 31°C dry bulb, 29°C wet bulb and has an atmospheric pressure of 100 kPa. (Assume convective heat transfer coefficient hc = 9.5 W/m²°C)

4. A steel pipe has an internal diameter of 150mm and an outside diameter of 160mm. The pipe carries water at a temperature of 10°C flowing at a velocity of 0.5 m/s. The air surrounding the pipe has a dry bulb temperature of 27°C. The air flow's over the pipe with a velocity of 3 m/s. If the pipe is covered by insulation of 30mm thickness with a thermal conductivity of 0.035 W/m°, determine:

(a) The UA factor for 1m length of insulated pipe,
(b) The rate of heat gain by the water per m of pipe
(c) The temperature of the inner and outer surfaces of the pipe and the temperature of the outer surface of the insulation
(Note ksteel = 45 W/m°C, hc inside pipe = 1400 W/m²°C, hc outside insulation = 18 W/m²°C and radiative heat transfer coefficient outside insulation hr = 6.1 W/m²°C)

5. Water enters the condenser of a refrigeration plant at 35°C and leaves at 41°C. The condensing temperature of the refrigerant is 45°C. Determine the log mean temperature difference and the arithmetic temperature difference.

6. A basic vapour compression refrigeration system is using refrigerant R12 .The evaporator temperature is 0°C and the condenser temperature is 55°C .The isentropic efficiency of the compressor is 80%. Observations made on the chilled water circuit to the evaporator indicate that the cooling duty is 2800 kW. Assuming the refrigerant enters the compressor as a saturated vapour and leaves the condenser as a saturated liquid detail the necessary calculations and then plot the cycle on the R12 pressure/specific enthalpy diagram provided. Also calculate:

(a) The power input to the compressor;
(b) The rate of heat removal in the condenser;
(c) The actual coefficient of performance;
(d) The Carnot COP;
(e) The cycle efficiency.

Discuss briefly how the COP of this plant might be improved and illustrate the benefits by providing a freehand sketch of the modified refrigeration cycle on a appropriate property diagram.

7. With respect to a mine refrigeration system define the following terms
(a) Carnot COP
(b) Actual COP
(c) LMTD
(d) Sub cooling
(e) Water efficiency
(f) Air efficiency
(g) Thermal Capacity Ratio
(h) Factor of Merit

8. The following measurements were made during a routine check of an underground cooling tower.
Air circuit: Quantity 220m³/s
Barometric pressure 110 kPa
Inlet temperature dry bulb 34°C, wet bulb 29°C Outlet temperature dry bulb 41°C, wet bulb 41°C

Water Circuit Flow rate 500 l/s
Temperature in 44°C Temperature out 36°C

Determine the following performance characteristics of the tower
a. Duty
b. Water efficiency
c. Thermal Capacity Ratio
d. Factor of merit

9.
a. What is your understanding of ventilation on demand and what relevance does it have for the mining industry?
b. A mine is proposing to trial a ventilation on demand system in a development area which is 750 m in length and a 5.5 x 5.5 m heading. The shift breakdown of tasks occurring in the heading are as follows:

Activity	Equipment
0-20 mins	CAT LHD 350 kW
20mins to 2 hours	Drilling 2 boom jumbo 250 kW
2-3 hours charging	ANFO loader 100kW IT 150 kW
3-4        hours         blasting including fume clearance	none
4-5 hours mucking	CAT LHD
5-6 hours scaling	2 boom jumbo using high pressure water jets
6-7 hours shotcreting	150 kW shotcreter
7-8.5    hours    idle    curing time	none
8.5-10         hours         bolt installation	Drill jumbo
10-11 hours	Service upgrade, 150 kW IT
11-12 hours shift change	none

For diesel sources the required minimum flow rate is 5 m³/s per 100 kW of installed power. When drilling, scaling and bolting the jumbo is powered by electrical power. Minimum airflow velocity is 0.5 m/s. Blasting undertaken using ANFO, you will need to determine the clearance time and associated airflow rate using the method taught in the mine ventilation course, assuming an average advance of 4m per round.

How much power can be saved by moving to ventilation on demand from the normal peak ventilation requirement methodology? If the fan efficiency is 85% and electrical power costs $ 0.5 per kWhr what is the potential cost saving?

Any assumptions used should be stated in your answer.

Advanced Mine Ventilation

Purpose

The purposes of this exercise are to:

1. Test the ventilation knowledge of the student in a real mine situation
2. To introduce the student to mine ventilation planning
3. To employ the knowledge gained in lectures, undertaking other assessed work and the students own research to solve a ventilation problem
4. To show the changes with time in a mine ventilation network
5. To enable the student to use mine ventilation software.

Task

The following sections describe a proposed mechanised block caving operation; at each stage students are to develop a suitable ventilation system for the project. It can be assumed that the surface RL is 1000m above datum, the undercut level is 500m above datum, the production level 475 m above datum and the transport level 425m above datum.

Stage 1 Surface connections

The initial stage of the project involves the development of the key surface connections as illustrated in figure 1. To the west a 1 in 7 switchback decline is to be developed acting as the primary intake to the mine, horizontal curve sections (180°) are to be developed every 50m descent from the surface with an internal radius of 20m. In the middle of the decline footprint a 3m diameter raise is to be developed to surface, acting as a second means of egress and as a return airway during the decline development, this raise will act as a second intake system once through ventilation has been established on all levels with the 6 m diameter main return and haulage shaft located at the East of the proposed mining area. At all stages in this project all drives are 5m x 5m in dimension and shotcreted to a minimum thickness of 50mm.

Shaft sinking is undertaken by traditional drill and blast techniques

Decline development using drill and blast, using 1 drill jumbo (electro- hydraulic), 1 diesel LHD rated at 300 kW, two 60 tonne diesel trucks rated at 450kW each.

Stage 2: Development of through ventilation at each level

This stage involves driving the main drives from the East to the west of the ore body. The eventual designs for the undercut and production levels are shown in figures 3 and 4. The transport level consists of a single main drive from the decline/raise bore to the main shaft under the production level south drive. Ore passes between these two levels number 4 and are 2.5m in diameter.

Equipment in the undercut level at this stage comprises of 2 drill jumbo (electro-hydraulic), 2 diesel LHD rated at 300 kW, four 60 tonne diesel trucks rated at 450kW each. On the production level 2 drill jumbo (electro-hydraulic), 2 diesel LHD rated at 300 kW, four 60 tonne diesel trucks rated at 450kW each. On the transport level 1 drill jumbo (electro-hydraulic), 1 diesel LHD rated at 300 kW, two 60 tonne diesel trucks rated at 450kW each.

Stage 3: Undercut and Production level development

During this stage the cross cuts from the south to the North drives are to be developed on both levels. On the undercut level these are spaced centreline to centreline by 15m, and by 30m on the production level. The ore pass entries are also to be developed on the production level at this stage.

Equipment consists of 4 drill jumbo (electro-hydraulic), 4 diesel LHD rated at 300 kW, eight 60 tonne diesel trucks rated at 450kW each on each of these levels.

Stage 4: Production

At this stage the undercut has been blasted and caving initiated, the draw bells between the undercut and production levels created and full cave production initiated. At this stage 16 300 kW rated LHD's are in operation on the production level and a conveyor operating in the transport level.

Requirements

For diesel loading the following standard should be applied, 0.05 m³/s per kW of rated power.

Maximum air velocity in main decline 6 m/s, in Production areas 2 m/s, in the shaft 20 m/s.

The mine does not have any indications of methane or radon gas and at 500m depth the virgin rock temperature is 32°C. Surface climate is similar to Ballarat.

Attachment:- Civil.rar