ChE Thermo - Tarik Flashcards
Self-ignition would occur in the engine using
certain brand of petrol if the temperature due to compression reached 350°C. Calculate the highest ratio of compression that may be used to avoid pre-ignition if the law of compression is
PV1.3 = c
PV1.4 = c
Calculate the final pressure in each case. Assuming inlet conditions of 27°C and 1 bar.
[Answers: 11.36, 6.19, 23.5 bar, 12.8 bar]
Calculate the density of Ethane at 171 bar and 458K; assume for Ethane:
TC = 305 K
PC = 48.80 bar
R = 319.3 J/kg-K
a) Assume it behaves as a perfect gas.
b) Using the compressibility chart.
[Answers: 117 kg/m3
, 146 kg/m3]
Find the specific volume for H2O at 10 MPa and 500°C using:
a) Compressibility chart;
b) Steam tables
[Answers: 0.032 m3/kg; 0.03279 m3/kg]
Determine the pressure of water vapour at 300°C, if its specific volume is 0.2579 m3
/kg, using the following method:
a) Ideal gas equation
b) Van-der-Waals equation
[Answer: 1.025 MPa; 1.006 MPa]
An unknown gas has a mass of 1.5 kg contained in a bottle of volume 1.17 m3 while at a temperature of 300K, and a pressure of 200 kPa. Determine the ideal gas constant and deduce the gas?
[Answer: R = 520 J/kg-K; M = Ro/R = 15.99]
A 6 m3 tank contains helium at 400K is evacuated form atmospheric pressure of 100 kPa to a final pressure of 2.5 kPa. Determine
a) The mass of helium remaining in the tank;
b) The mass of helium pumped out;
c) If the temperature of the remaining helium falls to 10°C, what is the pressure in kPa?
[Answer: 0.018 kg; 0.704 kg; 1763 Pa]
A motorist equips his automobile tyres with a relief-
type valve so that the pressure inside the tyre will never exceed 220 kPa (gauge). He starts the trip with a pressure of 200 kPa (gauge) and a temperature of 23°C in the tyres. During the long drive the temperature of the air in the tyres reaches 83°C. each tyre contains 0.11 kg of air. Determine:
a) the mass of air escaping each tyre;
b) the pressure of the air inside the tyre when the temperature returns to 23°C.
[Answer: 0.0094 kg; 183 kPa]
300 kg/minute of steam at 3 MPa and 400°C is supplied to a steam turbine. Determine the potential heat released from steam if it is condensed at constant pressure. Can you deduce the specific heat of the steam under this condition?
T ⍴ = 3.00 Mpa (233.90°C)
v u h s
Sat. 0.06668 2604.1 2804.2 6.1869
225
250 0.07058 2644.0 2855.8 6.2872
300 0.08114 2750.1 2993.5 6.5390
350 0.09053 2843.7 3115.3 6.7248
400 0.09936 2932.8 3230.9 6.9212
450 0.10787 3020.4 3344.0 7.0834
500 0.11619 3108.0 3456.5 7.2338
[Answer: Q = 2133.5 kW; Cp = 4.009 kJ/kg-K]
Self-ignition would occur in an engine using certain brand of petrol if the temperature due to compression reaches 350°C; when the inlet condition is 1 bar, 27°C.
Calculate the highest compression ratio possible in order to avoid self-ignition, if the compression is according to
a) Adiabatic, with index of 1.4; and
b) Polytropic, with index of 1.3.
[Answer: 6.2; 11.4]
The gas in an internal combustion engine, initially at a temperature of 1270°C; expands polytropically to five times its initial volume and one-eight its initial pressure. Calculate:
a) The index of expansion, n, and
b) The final temperature
[Answer: 1.292; 698K]
Determine using Steam Tables, the volume
occupied by 2 kg of steam at 500 kPa, under the following conditions and specify the state of steam.
a) Pure liquid state
b) When it is in a pure vapour state
c) 20% moisture content
d) 20% dry
[Answer: 0.00218 m3; 0.7498 m3; 0.557 m3;
0.152 m3]
The model ‘6SE-TCA3 Perkins’ diesel engine have a stroke of 190 mm and a bore of 160 mm. If its clearance volume is 5% of the swept volume, determine the pressure and temperature at the end of compression when the inlet condition is 1 bar, 27°C. Assume n = 1.38
[Answer: 67.2 bar; 956K]
