Rosales, Rey Jr. R.
BSME 4-1
Unit #4 – Heat Balance Problem
Set
Section I – Terminologies (20 pts).
Direction:
1. The thermodynamic cycle used in a
thermal power plant is:
A. Ericson
B. Brayton
C. Carnot
D. Rankine
2. Rankine cycle efficiency for fixed
steam temperature of any volume up
to critical temperature will be
maximum for steam pressure of:
A. Critical pressure
B. 200 kg/cm2
C. 100 kg/cm2
D. 203.5 kg/cm2
3. On which does the working pressure
of a boiler does not depend?
A. Tensile strength of shell
B. Thickness of shell
C. Factor of safety
D. Type of fuel being fired
4. A
simultaneous
generation
of
electricity and steam, or heat, in a
single power plant.
A. Gas turbine plant
B. Cogeneration
C. Waste heat recovery
D. Steam turbine-gas turbine plant
5. Consider a simple Rankine cycle fixed
boiler and condenser pressures. If the
cycle is modified with reheating,
A. The pump work input will
decrease
B. The turbine output work will
decrease
C. The moisture content at turbine
exit will decrease
D. The amount of heat rejected
will decrease
Problem Set #4
6. The conversion of older power plant
into combined cycle unit is called
A. Rehabilitation
B. Rejuvenation
C. Repowering
D. Converted status
7. An engineer want to increase the
temperature in the boiler but he want
that the pressure should remain the
same. What shall he do?
A. Superheat
B. Desuperheat
C. Saturate
D. Subcool
8. Which group contains processes that
are always part of any physically
realizable vapor power cycle?
A. Isentropic compression and
isentropic expansion
B. Isentropic compression
C. Adiabatic heat addition and
adiabatic heat extraction
D. Isobaric
vaporization
and
isobaric condensation
9. When the boiler pressure increases or
when the exhaust pressure decreases,
the amount of moisture:
A. Increases
B. Decreases
C. Constant
D. Zero
10. When the number of reheat stages in
a reheat cycle is increased, the
average temperature:
A. Increases
B. Decreases
C. Constant
D. zero
Section II – Problem Solving (80 pts).
Direction:
1. A simple rankine cycle operates
between superheated steam at 6 MPa,
600°C entering the turbine, and 10
kPa entering the pump. Determine the
maximum possible cycle thermal
efficiency. Draw the schematic and Ts
diagram.
2. Steam at 100 bar, 600°C is received by
a rankine engine and exhausts at 2
bar, ΔPE and ΔKE are negligible
a. For the ideal engine, find W, w,
e, and pm
b. For the actual engine, Mb =
84%, egen = 93%, and the driven
generator produces 30 MW.
Find Wk, ek, total throttle flow,
and estimate the exhaust
enthalpy h2’.
3. Draw a flow diagram of a Rankine
vapor cycle steam power plant. Steam
engine drives 150-kW generator of
90% electrical efficiency; steam rate.
6.7 kg/bhp-hr; steam pressure, 1
034.6 kPag; 55.6°SH; exhaust to
condenser at 15.2 cmHg abs; no
feedwater heating. Motor driven
boiler feed pump. Find
a. eR
b. etb
c. ec
4. Consider the ideal regenerative cycle.
Steam enters the turbine at 275
N/cm2, 320°C. Condenser pressure is
137 N/cm2. Steam is exhausted at 64
N/cm2 and 9.8 N/cm2 for purposes of
heating the feedwater. The feedwater
heaters are open heaters, and the
feedwater leaves at the temperature
of the condensing steam. The
appropriate pumps are used for the
water leaving the condenser and the
two feedwater heaters. Determine the
thermal efficiency and the net work
obtained per kg steam.
5. A reheat cycle with two stages of
reheating is executed, with steam
expanding initially from 10 MPa and
540°C. The two reheating pressures
are 4 MPa and 1 MPa, and the steam
leaves each reheater at 540°C.
Condensation occurs at 60°C where hf
= 251 and hB = 268 kJ/kg. Sketch the
T-s diagram. For the ideal cycle, and 1
kg/s of steam, find
a. QA
b. eth