BENG2 APPLIED THERMODYNAMICS
(THER 205)
TUTORIAL EXAMPLES : REVISION OF FIRST LAW PRINCIPLES
1. A motor vehicle tyre is inflated to 45 psig on
a 15ºC day. Assuming its volume remains constant, calculate the increase in
pressure due to high speed motorway driving when the temperature rises to
35ºC. [440.18
kPa (abs) or 49.15 psig]
2. Calculate the gross work*, the final
temperature, and the amount of heat transfer required to compress 1m³ of air
initially at SSL conditions# to a pressure of 7.9 bar absolute, if the
compression process is carried out:
(a) isothermally [208.09 kJ; 15ºC; -208.09 kJ]
(b) polytropically (n = 1.27); [205.45 kJ; 172.7ºC; -66.26 kJ]
(c) adiabatically. [202.19 kJ; 244.9ºC; 0 kJ]
3. The total volume of a gas mixture is 204 m³
at a pressure of 102kPa and a temperature of 20ºC. What is the partial pressure
of the Oxygen if the gas mixture consists (by volume) of 15% O2; 73% N2 and the
remainder CO2. How much Oxygen (in kg) is present? [15.3 kPa; 40.97 kg]
4. An engine using air as its working medium
compresses it adiabatically; heats it isobarically then cools it isochorically.
Sketch the
cycle on p-V co-ordinates and determine the net work per cycle if:
Vmin= 0.24 litres; Vmax = 2.67 litres; p1 = 101.325
kPa; T1 = 20ºC.
Determine
also the maximum cycle temperature.
[ -6.084 kJ ; 8271.5 ºC]
5. A steam turbine uses steam with specific
enthalpy at input equal to 2776.2 kJ/kg. If the measured specific enthalpy of
the steam at exit is found to be 2506.8 kJ/kg and the measured steam mass flow
is 3.341 kg/min, what shaft power is being produced by the turbine. [15.0 kW]
* Work transfer and Heat
transfer IN to a system are
positive.
# SSL = Standard Sea Level
conditions - viz. 101.325 kPa and 15ºC.