BENG1 INTRODUCTION to
THERMO-FLUIDS (THER 103)
TUTORIAL EXAMPLES in SFEE APPLICATIONS
(SSL conditions are 101.325 kPa, and 15°C)
1. Air
flows steadily through a tubular heater of constant cross-section. The initial temperature and pressure of the
air are 15°C and 125 kPa respectively and the velocity of entry is 25 m/s. The exit conditions are 60°C and 100 kPa.
If the heater is horizontal and the air mass flow rate is 18 kg/s, find:
(a) the cross-sectional area of the heater
(b) the rate of heat transfer to the air
For air: R = 0.287 kJ/kgK;
Cp = 1.005 kJ/kgK [0.476 m²; 820.2 kW]
2. A
fluid ‘A’ with a specific enthalpy of 2260 kJ/kg flows steadily into a mixing
tank at a rate of 0.75 kg/s. A second
fluid ‘B’ with a specific enthalpy of 160 kJ/kg also flows into the
tank at a steady rate. During mixing,
heat is lost to the surroundings at 1260 kJ/min. If the specific enthalpy of the fluid mixture
flowing from the tank is 1040 kJ/kg, calculate the rate of flow of fluid
‘B’. [1.016
kg/s]
3. Air
enters a centrifugal compressor at 1 bar and leaves at 2.1 bar. During the passage of the air through the
compressor, the specific internal energy of the air increases by 56 kJ/kg, and
the specific volume decreases from 0.825 m3/kg to 0.5 m3/kg. Assuming that the flow is adiabatic and that
the changes in kinetic energy are negligible, calculate the power required to
drive the compressor when the air flow rate is 135 kg/min. [176.6 kW]
4. A
steam turbine uses 3.6 tonne of steam per hour.
At inlet to the turbine the steam has a velocity of 27.5 m/s, and a
specific enthalpy of 3000 kJ/kg. The
steam leaves the turbine with a velocity of 182.5 m/s and a specific enthalpy
of 2220 kJ/kg. If the process is
adiabatic, calculate the power output of the turbine.
5. The
following data refer to a gas nozzle :-
|
Section |
p (bar) |
v (m³/kg) |
u (kJ/kg) |
|
Inlet |
4.8 |
0.520 |
725 |
|
Intermediate |
2.6 |
0. 825 |
620 |
|
Outlet |
1.0 |
1.750 |
510 |
It may be assumed that the inlet velocity is negligible, and that the process
is adiabatic. If the area of flow at the
intermediate section is 645 mm2, calculate the rate of gas flow
through the nozzle and the required outlet area.
6. Fluid
at 10.35 bar having a specific volume of 0.18 m3/kg is throttled to
a pressure of 1 bar. If the specific
volume of the fluid after throttling is 0.107m3/kg, calculate the
change in specific internal energy during the process.
7. A
nozzle is supplied with steam having a specific enthalpy of 2780 kJ/kg at a
flow rate of 9.1 kg/min. At outlet from
the nozzle the velocity of the steam is 1070 m/s. Assuming that the inlet velocity of the steam
is negligible and that the process is adiabatic, determine:
(a) the specific enthalpy of the steam at the
nozzle exit.
(b) the outlet area, if the final specific
volume of the steam is 18.75 m3/kg.
8. Steam
with specific enthalpy of 2400 kJ/kg flows at the rate of 0.4 kg/s into a small
condenser and leaves as condensate with specific enthalpy of 160 kJ/kg. The specific volume of the incoming steam is
18.5 m3/kg and the diameter of the inlet pipe is 300 mm. The condenser is supplied with cooling water
which enters at 10oC and leaves at 20oC. Calculate the velocity of steam entering the
condenser and the mass flow rate of cooling water, assuming negligible velocity
at exit for the condensate. Neglect heat
transfer to surroundings and take specific heat of cooling water as 4.185
kJ/kgK.
9. A simple
steam plant has the following data:
Location Pressure Temp/Quality
Leaving
boiler 30
bar 300 oC
Entering
turbine 28
bar 275 oC
Leaving
turbine/entering condenser 0.1
bar 0.9
Leaving
condenser/entering pump 0.1
bar 45.8 oC
If the
specific work input to the feed pump is 6.2 kJ/kg, determine the following/kg:
(a) heat transfer
in the line between boiler and turbine
(b) turbine work
(c) heat
transfer in condenser
(d) heat transfer
in boiler
[60.1
kJ/kg (loss), 588.0 kJ/kg, 2153.6 kJ/kg (loss), 2795.5 kJ/kg]