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Q5. The steam condition at a stage in a 50% reaction turbine is 0.18 bar and 0.94 dry.

The stage develops a power of 1800 kW at a speed of 400 rev/min.

The mass flow of steam is 54 tonnes/hour.

The fixed blades have an exit angle of 21.5° and the axial velocity is 79% of the blade speed at the mean blade radius.

(a) Sketch the stage velocity vector diagram indicating the velocities. (3)

(b) Calculate EACH of the following:

(i) The mean diameter of the blade ring; (4)

(ii) The blade height; (4)

(iii) The diagram efficiency.(5)

Q6. A vapour compression refrigeration plant using ammonia is used is used to maintain the temperature of a cold room at -25℃ when the ambient conditions are 30℃.

The cold room bulkheads have an overall thermal conductivity of 0.5 W/m²K and a total surface area of 162 m².

The ammonia enters the compressor as a dry saturated vapour at -28℃ and leaves at a pressure and temperature of 9.134 bar and 122℃. It enters the expansion valve at a temperature of 22℃.

The two-cylinder single acting compressor has a bore of 76 mm and a stroke of 80 mm and runs at a speed of 320 rev/min.

(a) Sketch the cycle on a Temperature specific entropy diagram showing ALL the temperature. (3)

(b) Calculate EACH of the following:

(i) The cooling load; (2)

(ii) The cycle coefficient of performance;(4)

(iii) The Carnot cycle coefficient of performance when operating between the same pressure; (2)

(iv) The volumetric efficiency of the compressor. (5)

Q7. An annular water jacket surrounds a 200 mm mean diameter pipe carrying a hot gas, in a counter flow arrangement.

The hot gas enters the cooler with a velocity of 3 m/s and a temperature of 527℃, it leaves a temperature of 50℃.

The cooling water enters the cooler at 15℃ and has a flow rate of 900 kg/hour.

The wall thickness of the pipe may be ignored.

(a) Calculate EACH of the following:

(i) The rate of heat of transfer across the cooler; (2)

(ii) The exit temperature of the water;(2)

(iii) The log mean temperature difference; (4)

(iv) The length of the cooler. (5)

(b) Sketch the cooler temperature profile diagram. (3)

Notre: for cooling water C = 4.19 kJ/kg K

For the hot gas C_p = 1.169 kJ/kg K, specific volume = 1.493 m³/kg

The inner surface heat transfer coefficient = 0.2 kW/m² K

The outer surface heat transfer coefficient = 1.25 kW/m² K

Q8. A two-stage single acting reciprocating compressor is water cooled and runs at a speed of 240 rev/min. The pressure and temperature at the first stage inlet are 1 bar and 15℃ respectively. The second stage inlet conditions are 6 bar and 27℃.

The air leaves the machine at a pressure of 30 bar and temperature of 60℃.

The total mass of air in the low- pressure cylinder at the beginning of compression is 0.025 kg and the clearance ratio is 0.05. The polytropic index for all expansion and compression processes is 1.25. Calculate EACH of the following:

(a) the total indicated power; (8)

(b) the total heat removed per cycle from the cylinder;(5)

(c) the total heat removed per cycle by the coolers.(3)

Note: for air, γ = 1.4 , C_V = 0.7175  kJ⁄(kg K)

Q9. A centrifugal pump runs at 400 rev/min and delivers a liquid at the rate of 160 tonne per hour. The impeller diameter is 900 mm and at exit the blades are backward facing at an angle of 30° to the plane of rotation.

There is no whirl at inlet and the fluid has a constant radial velocity through the impeller. Suction is from a tank 1.2 m below the pump and delivery is to a tank 18.4 m above the pump.

The delivery pipe has an internal diameter of 200 mm, a length of 60 m and a friction factor coefficient of 0.06. Valves and bends in the system create a loss equivalent to an additional 24 m of pipeline. Suction line losses can be ignored.

Calculate EACH of the following:

a) The system total head; (7)

b) The pump power (2)

c) The width of the impeller at exit. (7)

Note: for the fluid, ρ = 900  kg⁄m³