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Q1) A gas in a cylinder is heated at constant volume from a temperature of 387℃ to 568℃ and then further heated at constant pressure to 827℃.

The change in specific entropy in the first process is 0.182  kJ/kgK.

After the heating processes the gas expands isentropically to 10 times V1 and a temperature of 17℃.

(a) Sketch PV and Ts diagrams to show the process; (2)

(b) Calculate EACH of the following:

(i) C_V, C_P and ɣ; (9)

(ii) the change is specific entropy in the constant pressure process; (2)

(iii) the specific work in the isentropic process. (3)

Q2) In an air standard dual combustion cycle, the initial volume compression ratio is 13/1.

The maximum and minimum temperatures are 1500 K and 300 K, respectively.

The maximum and minimum pressure are respectively 67 bar and 1.13 bar.

(a) Sketch the processes on p-V and T-s diagrams: (2)

(b) Calculate EACH of the following:

(i) the temperature at all points; (10)

(ii) the thermal efficiency; (2)

(iii) the mean effective pressure. (2)

Note:

For air ɣ = 1.4 and C_p = 1.005  kJ/kgK, C_v = 0.718  kJ/kgK.

Q3) A single acting single stage air compressor runs at 300 rpm and has a clearance volume equal to 7% of the swept volume.

The compressor delivers 50 m³ of air per hour measured at 1.013 bar and 0℃.

The suction pressure and temperature are 0.98 bar and 23℃ (T₁ and T₄) respectively, and the discharge pressure and temperature are 6.6 bar and 170℃ (T₂ and T₃), respectively.

(a) Sketch the cycle on a pressure – volume diagram. (2)

(b) Calculate EACH of the following:

(i) the volume induced per cycle; (5)

(ii) the swept volume; (4)

(iii) the index of compression; (3)

(iv) the indicated power; (2)

Note: For C_p = 1.005 kJ/kgK  C_v = 0.718 kJ/kgK

Q5) A vapour compression refrigeration system operates between the pressures of 4.625 bar and 8.053 bar.

R717 refrigerant enters the compressor dry saturated and is isentropically compressed. Upon leaving the condenser it is undercooled by 6 k. The mass flow rate is 0.8 .

(a) Sketch the cycle on pressure – specific enthalpy and Temperature – specific entropy diagrams. (2)

(b) Calculate EACH of the following:

(i) The dryness fraction of the refrigerant entering the evaporator; (3)

(ii) The temperature leaving the compressor; (5)

(iii) The compressor power. (4)

(c) Explain the application of intermediate liquid cooling; (2)

Q6) An LNG carrier has five spherical tanks each of diameter 36m. They contain liquefied gas at a temperature of -163℃. The tanks are insulated with 60 cm thickness of material of fibre glass with a thermal conductivity of 0.04 W/mK

The outside surface heat transfer coefficient is 8  W/(m² k)  and the outside air temperature is 29℃.

(a) Calculate the total rate of heat gain. (7)

(b) Find the external surface temperature. (4)

(c) Calculate the total percentage mass evaporated each day. (5)

NOTE: r = 1000 kg/m³   Latent heat of evaporation is 515 kJ/kg

Q7) Butane (C₄H₁₀) is burned with 12% excess air.

(a) Analyze the percentage of dry products by volume. (14)

(b) Define the HCV. (2)

Q8) An impulse turbine has a nozzle at the entrance angle is 16°, the blade velocity is 360 m/s, and the blades are symmetrical and have an angle of 34°.

If the blade velocity coefficient is 0.94 and the mass flowrate of the steam is 1.67 kg/s.

(a) Calculate the nozzle exit velocity if the change in enthalpy across the nozzle is 490 kJ/kg.(2)

(b) Sketch a blade velocity diagram labelling all significant angles and velocities. (3)

(c) Using Fig Q8, calculate the diagram power. (11)

Q9) A bend of constant cross – sectional area which turns through 75 degrees is fitted in a horizontal section of 600mm diameter fresh water – cooling system.

The cooling system pressure is 3 bar and the flowrate is 0.85 m³/s. The pressure loss due to each bend is negligible.

Calculate EACH of the following:

(a) the net force acting on the axis ox; (6)

(b) the net force acting on the axis oy; (6)

(c) the magnitude of the resultant force acting on the bend; (2)

(d) the direction of the resultant force. (2)