Steel balls 12 mm in diameter are annealed by heating to
1150 K and then slowly cooling to 400 K in an air
environment for which T_∞ = 325 K and h = 20 W/m²⋅K.
Assuming the properties of the steel to be k = 40 W/m⋅K,  =
7800 kg/m³ and C_p = 600 J/kg⋅K, estimate the time required
for the cooling process.

The steady flow rate of steam through an adiabatic turbine is 2.5 kg/s . The steam at 600 ^oc and 10 bar enters the turbine through pipeline 10 cm in diameter. The steam exits the turbine through at pipeline 25 cm in diameter at a temperature 400 ^oc and pressure of 1 bar.

1. State the steady flow energy equation
2. At the inlet conditions of the turbine, obtain from steam tables

                The saturation temperature of steam at 10 bar

                 Specific volume

                 Specific internal energy

                 Specific enthalpy

Calculate

1. The degree of superheat
2. The cross sectional area of inlet pipeline
3. Inlet velocity

3. At the outlet conditions of the turbine, from the steam tables, read

The saturation temperature of steam at 1 bar

Specific volume

Specific internal energy

Specific enthalpy

Calculate

1. The degree of superheat
2. The cross sectional area of inlet pipeline
3. Inlet velocity

4. Calculate the change in enthalpy across turbine
5. Calculate the change in kinetic energy across the turbine
6. Calculate the work obtained from the turbine

The steady flow rate of steam through an adiabatic turbine is 2.5 kg/s . The steam at 600 ^oc and 10 bar enters the turbine through pipeline 10 cm in diameter. The steam exits the turbine through at pipeline 25 cm in diameter at a temperature 400 ^oc and pressure of 1 bar.

1. State the steady flow energy equation
2. At the inlet conditions of the turbine, obtain from steam tables

                The saturation temperature of steam at 10 bar

                 Specific volume

                 Specific internal energy

                 Specific enthalpy

Calculate

1. The degree of superheat
2. The cross sectional area of inlet pipeline
3. Inlet velocity

3. At the outlet conditions of the turbine, from the steam tables, read

The saturation temperature of steam at 1 bar

Specific volume

Specific internal energy

Specific enthalpy

Calculate

1. The degree of superheat
2. The cross sectional area of inlet pipeline
3. Inlet velocity

4. Calculate the change in enthalpy across turbine
5. Calculate the change in kinetic energy across the turbine
6. Calculate the work obtained from the turbine

A boiler operates at a constant pressure producing steam at a rate of 2520 kg/h with a specific enthalpy of 2700 kJ/kg . The specific enthalpy of feed water to the boiler is 280 kJ/kg . The outlet pipe of the boiler is at a height of 15 m about the inlet pipe. The inlet and outlet velocities of 15 m/s and 35 m/s respectively.

Calculate

1. Change in enthalpy
2. Change in potential energy
3. Change in kinetic energy
4. The heat energy used by boiler

If 75% of the heat energy supplied by the combustion of coal is used by the boiler in forming steam, and combustion of 1 kg of coal produces 28000 kJ of heat energy.

5. Heat supplied to the boiler by combustion of coal
6. The mass flow rate of consumption of coal

A medium-growth coniferous tree planted in an urban or suburban setting after being raised in a nursery for 1 year can sequester 10.5 Kg of CO₂ over a 10-year period of growth. If you lived in an average home in Australia, how many trees would you need to plant to remove the CO₂ you would produce from driving your car, using electricity in your home using natural gas heating for a period of 10 years?

In order to answer the question you may need to make use of the following data:

1. Average household energy use is 24 kWh per day.

2. 20% of household energy use is due to gas heating.

1. The calorific value of natural gas is 10 kWh/kg
2. Natural gas has specific carbon dioxide emissions of 0.2kgCO₂/kWh

3. The distance travelled by car per annum is 20,000 km

1. The car's fuel efficiency is 0.1 lt/km
2. The engine's efficiency is 20%.
3. The calorific value of petrol is 10 kWh/lt
4. Petrol has specific carbon dioxide emissions of 0.25 kgCO₂/kWh

4. Electricity if produced from coal

1. The power station and transmission efficiency is 35%
2. The  calorific value of coal is 8.4 kWh/kg
3. Coal  has specific carbon dioxide emissions of 0.34 kgCO₂/kWh

1. In the production of alternative and natural sweeteners from Stevia, the cleaned leaves at a rate of 875 kg/h are first passed through a mechanical sorter. 23.0% of the fresh feed are small leaves and can go straight to the drier. They are dried to 8.00% moisture, from the original 46.7% moisture. After drying, they are ground to a fine powder. The remaining large leaves are first fed to a grinder where the leaves are ground to a pulp. They are then fed to an extractor where hexane is also added to extract steviol glycosides, the “sweet component” of the stevia leaves. Fresh hexane at 27.2 kg/h is added to a recycled condensed hexane stream and is then fed to the extractor at 2.75 kg hexane per kg of ground stevia leaves. The exit stream of the extractor then passes through a filter where the filter cake (predominantly containing pulp) is separated from the liquid part of the stream (filtrate). The filtrate is then fed to a decanter where the hexane stream is separated from the aqueous stream. The aqueous stream is virtually pure water. The hexane stream is fed to an evaporator where all of the hexane is evaporated, leaving pure steviol glycosides. The evaporated hexane is then condensed and recycled back to the extractor. Given below are useful information for the composition of some streams and materials:
   1. Fresh Stevia leaves contain 46.7% moisture, 3.80% steviol glycosides, and the remainder is pulp.
   2. The filter cake is 92.4% pulp, the remainder is a mixture of hexane and steviol glycoside.
   3. Two final products are produced in the process: dried ground Stevia leaves and pure steviol glycoside.

Calculate the following:

1. Rate of production of the two final products in tons/year (assume that 1 year of operation is equal to 300 days of continuous operation)
2. Rate of hexane recycle (kg/h) and recycle ratio (recycled hexane/fresh hexane)

In the production of alternative and natural sweeteners from Stevia, the cleaned leaves at a rate of 875 kg/h are first passed through a mechanical sorter. 23.0% of the fresh feed are small leaves and can go straight to the drier. They are dried to 8.00% moisture, from the original 46.7% moisture. After drying, they are ground to a fine powder. The remaining large leaves are first fed to a grinder where the leaves are ground to a pulp. They are then fed to an extractor where hexane is also added to extract steviol glycosides, the “sweet component” of the stevia leaves. Fresh hexane at 27.2 kg/h is added to a recycled condensed hexane stream and is then fed to the extractor at 2.75 kg hexane per kg of ground stevia leaves. The exit stream of the extractor then passes through a filter where the filter cake (predominantly containing pulp) is separated from the liquid part of the stream (filtrate). The filtrate is then fed to a decanter where the hexane stream is separated from the aqueous stream. The aqueous stream is virtually pure water. The hexane stream is fed to an evaporator where all of the hexane is evaporated, leaving pure steviol glycosides. The evaporated hexane is then condensed and recycled back to the extractor. Some information for the composition of streams and materials are: Fresh Stevia leaves contain 46.7% moisture, 3.80% steviol glycosides, and the remainder is pulp; The filter cake is 92.4% pulp, the remainder is a mixture of hexane and steviol glycoside.; Two final products are produced in the process: dried ground Stevia leaves and pure steviol glycoside.
Find the following:
a. Complete diagram

b. Rate of production of the two final products in tons/year (assume that 1 yr. operation = 300 days of continuous operation)

c. Rate of hexane recycle (kg/h) and recycle ratio (recycled hexane/fresh hexane)

What is the significance of Bernoulli equation and Reynolds number in Fluid Mechanics?

1. Using pictures and/or diagrams describe and explain in detail the difference between conventional surface mining and solution mining. Ensure to include the advantages and disadvantages of both of these mining methods. (2.5 pages minimum.) (10 points)

A steam turbine expands steam from 70 bar, 300 °C, to 6.5 bar. The flow rate of steam is 2.5 kg/s and the turbine generates 500 kW of power.

a) Determine the temperature at the outlet.
b) Determine the efficiency of the turbine.
c) Determine the entropy generation.

1. Define BOD. Describe the measurement of BOD. Give an estimate of possible BOD values for the following three water types: pristine river, sewage and stormwater.

2. Classify microorganisms according to their source of energy and carbon. In your answer, define chemotroph, autotroph, heterotroph, phototroph, decomposer and producer.

3. In which class(es) are you likely to find algae, bacteria and fungi?

2. “Famine is a natural occurrence.” Explain what is wrong with this statement by drawing on examples of famines in two different world regions. 500 words

a) A natural draft cooling tower is used to cool the condenser of a 100 MW power plant. The water enters the tower at 40 °C at a rate of 80 kg/s. The range value of cooling tower is 15 °C. The water is cooled by air stream and the air entering the tower is at 1.01325 bar, 23°C and 60% relative humidity. The air leaves the tower as saturated at 32°C. According to the given data, using pyschrometric chart and steam table, determine the volumetric flow rate of air flowing into the cooling tower.

b) Describe briefly the definition and function of cooling tower fill material.