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Q1. In a non-flow process a gas initially expands from 10 bar, 0.005 m³ and 400 K to 3.75 bar and 0.009 m³ according to the law PV^γ = C. Then the gas expands polytropically to 0.024 m³, 1 bar and 192 K.

Calculate EACH of the following:

(a) the mass of the gas;(3)

(b) the temperature after the initial expansion;(2)

(c) the total work;(5)

(d) the total heat transfer if the change in internal energy in the polytypic process is – 1452.32 J;(3)

(e) the total change in entropy. (3)

Note: g = 1.67, n = 1.35, c_v = 443.18J/kg K, Molar mass = 28 kg/kmol

Q2. A compression ignition engine working on he ideal dual combustion cycle has a compression ratio of 16 :1. The pressure and temperature at the beginning of compression are 0.98 bar and 30℃ respectively.

The pressure and temperature at the completion of heat supply are 60 bar and 1300℃.

Determine EACH of the following:

(a) T₂,T₃ and Ts;(6)

(b) the net specific heat supplied and the net specific work;(8)

(c) the thermal efficiency. (2)

Note: For air g = 1.4 and c_p = 1.005 kJ/kg K, c_v = 0.718 kJ/kgK

Q3. A single acting, 2 -stage reciprocating air compressor is designed with some intercooling. The compressor has equal stage pressure ratios and delivers air from initial conditions of 0.95 bar and 285 K.

At the entrance to the second stage the temperature is 300 K. The index of both compression and expansion is 1.29 and it applies to both stages. The final delivery pressure is 12.90 bar.

a) Draw the p-V diagram of the compressor. (3)

b) Calculate EACH of the following:

i) The specific work required by the compressor; (10)

ii) The thermal efficiency. (3)

Note: For Air C_p = 1005 J/kgK, C_v = 718 J/kgK

Q5. A vapour compression cycle operates using R717. The refrigerant enters the compressor at 1.196 bar as dry saturated vapour. The refrigerant is isentropically compressed to 8.57 bar. The temperature at the outlet of the condenser is undercooled by 18 K.

(a) Calculate the enthalpy and temperature at the exit of the compressor. (6)

(b) Calculate the entropy at the entrance to the evaporator. (6)

(c) Draw the P-h and T-s graphs to represent the system. (4)

Q8. An impulse turbine has a nozzle at the entrance.

(a) Calculate the nozzle exit velocity if the change in enthalpy across the nozzle is 520 kJ/kg

(b) The turbine has a nozzle extrance angle 21°, the blade velocity is 400m/s and the blades are symmetrical and have an angle of 33.5°. if the blade velocity coefficient is 0.97 and the mass flow rate of the steam is 2.1 kg/s:

(i) sketch the blade velocity diagram for the turbine; (4)

(ii) calculate the diagram power. (9)

Q9. An olive oil centrifugal pump has an outer diameter of 650 mm and an outer blade width of 9.5 mm.

It runs at 475 rpm; the outlet radial velocity is 5.5 m/s and the outlet tangential velocity is 6.6 m/s.

(a) Sketch the velocity diagrams of the centrifugal pumps. (6)

(b) Calculate EACH of the following:

(i) The blade outlet angle;

(ii) The mass flow rate;

(iii) The power.

Note: ρ_{olive oil} = 920kg/m³