BENG1 INTRODUCTION to
THERMO-FLUIDS (THER 103)
TUTORIAL EXAMPLES in FIRST LAW CLOSED SYSTEMS (2)
(SSL conditions are 101.325 kPa, and 15°C)
1. 0.05 kg of CO2, molar
mass 44 kg/kmol, occupying a volume of 0.03 m3 at 102.5 kPa is
compressed reversibly until the pressure is 615 kPa. Calculate the initial temperature, and the
final temperature and work transfer:
(a) when the process
is according to the law pV1.31 = constant;
(b) when the process
is isothermal.
Assume CO2
to be a perfect gas. The Universal Gas Constant is 8.3143 kJ/kmol K.
[325.46 K; (a)
224.33 K; 5.24 kJ; (b) 325.46 K; 5.51 kJ]
2. A quantity of gas occupying 0.14 m3
at a pressure of 1.4 MPa and temperature of 300°C
is expanded adiabatically to 280 kPa.
If, for this gas, CV = 0.74 kJ/kgK and CP
= 1.04 kJ/kgK, determine:
(a) the mass of the
gas;
(b) the temperature
of the gas after expansion;
(c) the work done
during the expansion. [1.14 kg; 360.2 K;
-179.56 kJ]
3. A quantity of CO2,
initially occupying 0.10 m3 at pressure 101.3 kPa and temperature 27°C
is compressed according to the law pVn = constant, until it occupies 0.02 m3
at a pressure of 620kPa. Determine:
(a) the value of ‘n’;
(b) the change of
internal energy of the system;
(c) the heat transfer
to/from the system;
For CO2: CV
= 0.737 kJ/kgK. R = 0.189 kJ/kgK. [n = 1.1256;
8.852 kJ; -9.22 kJ]
4. A certain gas occupies 4 m3
at 110 kPa and 20°C.
It is compressed adiabatically in a closed system to a pressure of 690
kPa. Determine:
(a) the final
temperature
(b) the final volume
(c) the change in
internal energy of the gas.
The density of the
gas is 1.39 kg/m3 at 101.3 kPa and 0°C,
and the specific heat capacity at constant volume is 0.732 kJ/kgK.
[478.6K, 1.042 m3, 764.3 kJ]
5. Air at SSL conditions is
compressed to a pressure of 900 kPa before it is delivered to a reservoir. If
the compression process follows a law pV1.27 = constant determine:
(a) the specific work
transferred to the air during the compression process;
(b) the temperature
of the delivered air;
(c) the heat
transfer/kg of air delivered. [180.91 kJ/kg; 458.2 K; -58.37 kJ/kg]