Q1. A perfect gas is cooled at constant pressure from a temperature of 1400℃ to a temperature of 1000℃. It is further cooled at constant volume until the temperature is 600℃, the change of specific entropy during this process is 1.202 kJ/kg K. After cooling, the gas is compressed isentropically back to the original pressure.
The temperature of the gas at the end of compression is 737℃.
(a) Sketch The sequence of process on pressure-volume and temperature-specific entropy diagrams. (4)
(b) Calculate EACH of the following:
(i) The values of Cv, γ, Cp and R for the gas; (4)
(ii) The change in specific entropy during the constant pressure process; (2)
(iii) The specific work transfer; (3)
(iv) The specific heat transfer. (3).
Q2. In an air standard dual combustion cycle 720 kJ/kg of heat is added at constant volume, the remaining 60 % of the total heat supply is added at constant pressure.
The minimum pressure and temperature in the cycle are 1.05 bar and 311 K respectively.
The volume compression ratio is 14 : 1.
(a) Sketch The cycle on pressure- Volume and Temperature-specific entropy diagrams. (4)
(i) The pressure and temperature at each point in the cycle; (6)
(ii) The specific work output; (3)
(iii) The Theoretical mean effective pressure. (3)
Note: for air γ = 1.4 and cp= 1.005 kJ⁄(kg K).
Q3.A gaseous fuel has a volumetric composition of 60% methane (CH4) and 40% ethane (C2H6) and is completely burned in 20% excess air.
The combustion gases are at a pressure and temperature of 3.346 bar and 400℃ respectively and are cooled at constant pressure to 100℃.
(a) Determine the combustion equation in kmols per kmol of fuel. (6)
(i) the mean value of Cp for the dry gas; (4)
(ii) the dew point temperature of the gas; (3)
(iii) the quantity of heat removed from the dry gas per kmol of fuel. (3)
Note: atomic mass relationships H = 1, C = 12, O = 16, N = 14
air contains 21% oxygen by volume
Values of Cp: CO2 = 1.113 kJ/kg K, O2 = 1.024 kJ/kg K, N2 = 1.091 kJ/kg K
Q4. Steam flows through a bank of 20 identical convergent divergent nozzles at the rate of 10 kg/s.
The steam enters each nozzle at 16 bar 400℃ with a negligible velocity and expands to an exit pressure of 3 bar.
Expansion in the convergent section is isentropic, whilst in the divergent section the specific entropy increases by 1%.
The nozzles are choked and at this condition, the critical pressure ratio is 0.5625.
Calculate EACH of the following:
(a) the degree of superheat of the steam at the throat; (5)
(b) the throat diameter of each nozzle; (5)
(c) the degree of superheat of the steam at exit; (3)
(d) the exit velocity. (3)
Q5. In a 50 % reaction turbine stage, the steam leaves the fixed blades with a velocity of 400 m/s, the blade speed ratio is 0.7332 and the fixed blade outlet angle is 35°.
The mean diameter of the blade ring is 800 mm.
(a) Sketch The velocity vector diagram, labelling ALL The velocities and angles. (5)
(i) The turbine rotor speed of rotation in rev/min; (3)
(ii) The blade inlet angle; (3)
(iii) The diagram efficiency. (5)
Q7. A combustion air heater has 100 tubes each of 2.5 m long in a single pass counter flow arrangement. Exhaust gas from the combustion process enters at 400℃ and heats 0.3334 kg/s of air from 25℃ to 170℃. The combustion air to fuel ratio is 20: 1 and the overall heat transfer coefficient is 6.391 W/m2K.
(a) Calculate EACH of the following:
(i) The outlet temperature of the exhaust gas; (5)
(ii) The log means temperature difference for the heater; (5)
(iii) The mean diameter of the heater tubes. (4)
(b) Sketch the heater temperature distribution (profile) diagram. (2)
Note: for air cp=1.005 kJ⁄(kg K)
for exhaust gas cp=1.15 kJ⁄(kg K).
Q8. In a single acting, single stage reciprocating compressor, air is compressed from free air conditions of 1 bar and 15℃ to 9 bars.
The clearance volume is 4 % of the swept volume.
Compression and expansion processes take place according to the law pV1.3 = constant.
Calculate EACH of the following for 1 kg of air delivered:
(a) The volumetric efficiency; (2)
(b) The delivery temperature; (2)
(c) The heat transferred during the compression process; (5)
(d) The heat transferred during the expansion process; (4)
(e) The network output. (3)
Q9. A freshwater cooling system discharges into an observation tank through a 50 mm diameter horizontal pipe.
The flow from the pipe strikes the centre of a flat square plate which is hinged at its upper edge.
The plate has a side length of 150 mm and uniform thickness.
During maintenance the original 1.5 kg plate was replaced with a new plate of the same dimensions but of mass 2 kg.
The effect of friction in the hinge may be ignored.
(a) Sketch the system of forces acting on the plate. (4)
(i)The mass flow rate when the 1.5 kg plate was at an angle of 30° to the vertical;(8)
(ii) The percentage change in mass flow when the 2 kg plate is now at an angle of 30° to the vertical. (4)
Username or email address *Required
Password *Required
Note: Entering wrong username in the login form will ban your IP address immediately. Entering wrong password multiple times will also ban your IP address temporarily.
Log in
Lost your password? Remember me
No account yet?
