Thermodynamic Simulation of Steam Power Cycles using GUIMatLab Interfaces

Pedro F. Arce. Int. Journal of Engineering Research and Application www.ijera.com
ISSN : 2248-9622, Vol. 7, Issue 1, ( Part -3) January 2017, pp.88-93
www.ijera.com 88 | P a g e
Thermodynamic Simulation of Steam Power Cycles using GUI-
MatLab Interfaces
Pedro F. Arce, Nian F. Vieira
Chemical Engineering Department, School Engineering of Lorena, University of São Paulo, BRAZIL
ABSTRACT
Steam power cycles are constituted by a series of thermodynamic processes that aim convert the thermal energy
of a fluid in mechanical work, which can then be transformed into electrical energy. There are many types of
steam power cycles in the world, using various work fluids that may or may not undergo some change in their
thermodynamic state. The Rankine Cycle is a steam power cycle that use usually water as work fluid to move
turbines and produce work. Nowadays, this steam power cycle is the most used in thermoelectric plants to
produce electricity. This work aims the creation of a program in MatLab software with an interface (Graphical
Unit Interface, GUI) to simulate many configurations of Rankine cycles, providing to the user the values of the
main parameters of these processes, that is: required heat in the boiler; work generated in the turbine; required
work in the pumps and the thermal efficiency of the cycle. This program provides good results, showing that it
can be used to improve the functions of the equipments in these thermodynamic cycles and to support the
teaching disciplines of Applied Thermodynamic.
Keywords: Rankine Cycle, Water, Thermodynamic Simulation, GUI-MatLab
I. INTRODUCTION
Nowadays, the electrical energy is
increasingly needed to the humanity, providing the
action of many machines in homes and industry.
Thus, technologies to produce electricity are the
subject of many investments and improvements.
The most part of the electrical energy
generated in the world come from power plants,
which use coal, gas or uranium to heat a fluid
(usually water) and move turbines. After this,
mechanical work is converted into electricity.
To convert efficiently the energy of a fluid
in work, these power plants use thermodynamic
power cycles, which are constituted by many types
of equipments, such as pumps, turbines, boilers,
condensers, etc. There are many power cycles
available to serve this objective. However, the power
cycle most used today is the Rankine cycle.
The Rankine cycle is a steam power cycle
that uses the phase changes of the thermodynamic
state of water to move turbines and produce energy.
Ideally, this thermodynamic cycle is constituted by
four stages, which are:
 Isobaric heating in the boiler;
 Isentropic expansion in the turbine(s);
 Isobaric cooling in the condenser;
 Isentropic compression in the pump(s).
In these stages, water changes its
thermodynamic state of superheated steam until
compressed liquid, changing also their values of
enthalpy, entropy and specific volume [1-3].
With the current technology and the
development of new materials, the temperature and
the pressure of the water in the thermodynamic cycle
can reach more than 620,0 ºC and 300,0 bar,
respectively. For becoming the Rankine cycle more
efficient, many improvements can be used, just
modifying the basic structure of the thermodynamic
cycle to reduce the required heat or to produce more
work. To reduce the required heat, it is used
regenerators, in which a side current, that leaves the
turbine, is used to preheat the fluid, which later is
going to the boiler. To produce more work, it is used
reheating between the turbines, with the first turbine
having high values of pressure and the last turbine
low values of pressure. These improvements can be
used isolated or together, depending of the capacity
and the financial resources of the power plants [1-4].
To design properly the equipments of any
configuration of Rankine cycle, four parameters
should be analyzed, that are:
 Required heat in the boiler;
 Work generated in the turbine(s);
 Required work in the pump(s);
 Thermal efficiency of the cycle.
These parameters can be determinate in a
thermodynamic simulation of the process.
Nowadays, many computer programs are available
RESEARCH ARTICLE OPEN ACCESS

for this purpose, working with different ranges and
providing to the user simple configurations of
Rankine cycle. In this work, a friendly computer
program was developed to simulate several
configurations of Rankine cycles, by utilizing the
mass, energy and entropy balances in turbines,
pumps, boilers and condensers in ideal and real
situations. The criteria for predicting thermodynamic
properties, such as enthalpy and entropy, were taken
from previous work [5]. This friendly software can
also be used for teaching of Applied
Thermodynamics in undergraduate and graduate
courses.
II. METHODOLOGY
There are many ways to calculate the
thermodynamic properties of a fluid. The prediction
of thermodynamic properties can be made by using
cubic or non-cubic equations of state or
thermodynamic tables of a pure substance [6].
However, it is necessary, at least, the knowledge of
two thermodynamic properties of the system, first to
determinate the thermodynamic state and then to
determinate the other thermodynamic properties. In
previous work [5], the authors used these criteria to
predict thermodynamic properties of water for
several thermodynamic states: compressed liquid,
saturated liquid, liquid - vapor mixture, saturated
vapor, superheated steam, supercritical fluid.
Main parameters of a Rankine cycle, which
are calculated through the mass, energy and entropy
balances involving properties of water such as
enthalpy and entropy, require the determination of
these values to begin the calculation. Based on this,
the computer program requests to the user the values
of temperature and pressure in some stages of the
cycle. Temperature should be provide in ºC and its
valid range is between 50,0 and 800,0 ºC. Pressure
should be provide in bar and its valid range is
between 0,0002 and 500,0 bar. These values are
used to find the thermodynamic properties of water
through the internal algorithms of the computer
program. At the same time, the computer program
also requests the configuration of Rankine cycle that
user wants to simulate, among the six available ones,
such as:
1. Basic Rankine Cycle;
2. Regenerative Rankine Cycle;
3. Rankine Cycle with Reheating;
4. Rankine Cycle with Reheating and
Regeneration on the Low Pressure Turbine
(LPT);
Regeneration on the High Pressure Turbine
(HPT);
Regeneration on both turbines (LPT and HPT).
After these specifications, the computer
program runs the thermodynamic simulation of a
Rankine cycle and provides to the user the results of
the mains parameters: mechanical work produced by
turbine (WT), mechanical work provided to pump
(WP), Heat provided to the boiler (QB), and
efficiency of the Rankine cycle (η). The first three
parameters can be obtained through the first and
second laws of thermodynamic (open systems,
without loss of heat, steady state, disregarding the
kinetic and potential energies and reversible
conditions in all equipments) and the efficiency of
Rankine cycle is calculated from definition of a heat
engine. The following equations show how these
parameters are obtained:
(1)
(2)
(3)
(4)
In the interface developed with GUI-
MatLab, there is a figure that represents all the
configurations of Rankine cycles available in the
computer program, numbered according to the order
cited above. This image helps users for
understanding about the process. This image is
shown in Fig. 1.
The user also can decide the irreversibility
of the steam power cycle. The sources of
irreversibility in a cycle at real conditions may be
friction, pressure drops, etc. For this, the user can
choose between a cycle at ideal conditions (with an
isentropic efficiency of the equipments as 100% or
also called reversible process) or a cycle at real
conditions or also called irreversible process (with
an isentropic efficiency of the equipments being
chosen by the user).
In the cycles at real conditions, the values
of work in turbines and pumps are corrected
according to the following equations:
(5)
(6)
where EfT and EfP are the isentropic efficiencies of
turbine and pump, respectively.

Fig. 1: Configurations of Rankine cycle available in the computer program of this work: (1) Basic Rankine
Cycle, (2) Regenerative Rankine Cycle; (3) Rankine Cycle with Reheating; (4) Rankine Cycle with Reheating
and Regeneration on the Low Pressure Turbine; (5) Rankine Cycle with Reheating and Regeneration on the
High Pressure Turbine; (6) Rankine Cycle with Reheating and Regeneration on both turbines.
With all these options, it was created an
interface in GUI-MatLab to help the interaction
with the user. This interface is shown in Fig. 2.
III. RESULT AND DISCUSSION
Results obtained with the computer
program developed in this work were compared
with the other one that simulates Rankine cycles
and with examples of books of Applied
Thermodynamics.
Fig. 2: GUI-MatLab interface after a thermodynamic simulation

The computer program used for comparison
is a software available in internet [7]. This software
work in a range of pressure and temperature
appropriated for Rankine cycles. It software was
developed for four configurations of Rankine cycles,
that are: basic cycle, regenerative cycle, cycle with
reheating and cycle with reheating and regeneration
on the low-pressure turbine.
As this computer program doesn‟t have two
of the configurations that the computer program
developed in this work has, configurations 5 and 6
are compared with examples of literature [1,8].
Tables 1 to 6 present the results obtained
for all the configurations of Rankine cycle available
in the computer program of this work, where Ph
representing the pressure in the boiler (bar), Th is the
temperature in the boiler (ºC), Pc is the pressure in
the condenser (bar), Pm is the pressure in the
regenerator (bar), Pr representing the pressure in the
reheating (bar), Tr is the temperature in the reheating
(ºC) and η representing the thermal efficiency of the
cycle (%). Although both computer programs
provide the four main parameters of a steam power
cycle, only the thermal efficiency was used for
comparison between the sources, with a relative
error calculated for the following equation:
(7)
Six configurations of Rankine cycles were
analyzed. They are: basic, regenerative, with
reheating, with reheating and regeneration on the
low-pressure turbine, with reheating and
regeneration on the high-pressure turbine and with
reheating and regeneration on both turbines. Results
for the configurations are presented in Tables 1, 2, 3,
4, 5 and 6, respectively.
Table 1: Results for basic Rankine Cycle
Table 2: Results for regenerative Rankine cycle
Table 3: Results for Rankine cycle with reheating
Table 4: Results for Rankine cycle with reheating and regeneration in the low-pressure turbine

Table 5: Results for Rankine cycle with reheating and regeneration in the high-pressure turbine
Table 6: Results for Rankine cycle with reheating and regeneration in both turbines
Based on the previous tables, it is possible
to observe that the computer program developed in
this work provides results with more accuracy and
very similar to the results of the other computer [7]
and examples of books [1,8]. Relative errors
between the sources are smaller than 2,0% in all
configurations of Rankine cycles obtained by the
thermodynamic simulation in this work.
Analyzing the results and the input values
of pressure and temperature, it is observed that, at
moderate values of pressure and temperature, such
as 100,0 bar and 400,0ºC, the error between the
sources is small and less than 1,0%. The more the
values of pressure and temperature increase and the
closer they come to the critical point of water
(374,1ºC and 220,6 bar), relative errors increase.
This fact is due to differences in the reference states
used to analyze the thermodynamic properties of
water in this work and other researches. In previous
works for the prediction of thermodynamic
properties, authors obtained different values of
thermodynamic properties of fluid at different
reference states. Thus, each computer program uses
different tables of thermodynamic properties of
water to simulate its steam power cycles. At low
values of pressure, the difference is minimal.
However, at high values of pressure, the difference
between values of thermodynamic properties, such
as enthalpy and entropy, increases, causing relative
errors greater than 1,0%.
Besides, errors may also occur due to the
interpolation method used in the program code in
MatLab („spline‟) to predict the thermodynamic
properties of water. However, this source of error
isn‟t so big and the results continue being accurate.
It is worth mentioning that, in addition to
good accuracy, the computer program developed in
this work also have more configurations of Rankine
cycles than other computer programs and have the
option to choose between ideal and real conditions
(reversible and irreversible processes). In the
previous tables presented, all the results are obtained
assuming Rankine cycles operating under reversible
conditions, that is, turbines and pumps with 100% of
isentropic efficiency. Real conditions (irreversible
processes) were not explored because many
computer programs that simulating Rankine cycles
haven´t implemented that option.
The computer program developed in this
work can be downloaded from the following links:
 For users of MatLab:
https://www.dropbox.com/s/1xyzipmizvx7x0k/
Thermo_web.rar?dl=0
 For non-users of Matlab:
https://www.dropbox.com/s/13bqxff96anoaom/
Thermo_mcr.rar?dl=0
IV. CONCLUSION
It is possible conclude that, based on the
results, obtained by the computer program
developed in this work, have good accuracy, with
relative errors less than 2,0% in comparison with
other ones obtained of other sources. Besides, this
computer program also let to choose several
configurations of Rankine cycles than other
computer programs available online and provide to
the user the option to choose between ideal and real
conditions (reversible and irreversible processes,
respectively). Thus, the computer program can be
used to design equipments, simulate
thermodynamically Rankine cycles with water as
work fluid and becomes as a useful tool for teaching
in courses of Applied Thermodynamics.

LIST OF SYMBOLS
B: boiler
C: condenser
EfT: Isentropic Efficiency of the turbine(s) (%)
EfP: Isentropic Efficiency of the pump(s) (%)
E: Relative Error (%)
HPT: High-pressure Turbine
HPP : high-pressure pump
HPM : high-pressure mixer tank
Hin : inlet enthalpy (kJ/kg)
Hout : output enthalpy (kJ/kg)
IPP : intermediate-pressure pump
LPT: Low-pressure Turbine
LPP : low-pressure pump
LPM : low-pressure mixer tank
M : mixer tank
Ph: Pressure in the boiler (bar)
Pc: Pressure in the condenser (bar)
Pr: Pressure in reheating (bar)
Pm: Pressure in the mixer tank (bar)
P : pump
Pin : inlet pressure (bar)
Pout : output pressure (bar)
QB: Heat provided by the boiler (kJ/kg)
Th: Temperature in the boiler (°C)
Tr: Temperature in reheating (°C)
T : turbine
v : specific volume (m3
/kg)
WT: Mechanical Work produced in the turbine(s)
(kJ/kg)
WP: Mechanical Work required in the pump(s)
(kJ/kg)
η: Thermal Efficiency of the cycle (%)
ACKNOWLEDGEMENTS
N.V. Freire thanks the Chemical Engineering
Department of the Engineering School of Lorena,
University of São Paulo (USP) for the opportunity
given to him to get his scientific initiation and P.F.
Arce-Castillo thanks the “Fundação de Amparo à
Pesquisa do Estado de São Paulo (FAPESP)” the
financial aid through the research grant:
2015/05155-8.
REFERENCES
[1]. Y.A. Çengel, M.A. Boles, Termodinâmica
(Porto Alegre, Brazil : McGraw Hill
Publishers, 2013).
[2]. I. Granet, Termodinâmica e Energia Térmica
(Rio de Janeiro, Brazil : Prentice-Hall
Publishers, 1990).
[3]. C. Borgnakke, R.E. Sonntag, Fundamentos da
Termodinâmica (São Paulo, Brazil : Blucher
Publishers, 2013).
[4]. M.C. Potter, E.P. Scott, Termodinâmica (São
Paulo, Brazil : Thomson Learning, 2006).
[5]. P.F. Arce, N.V. Freire. Programming and
testing of a friendly GUI-MatLab software to
predict the thermodynamic properties of
water, International J. of Research in
Engineering and Technology, 5 (11), 2016,
52-57.
[6]. M.L. Michelsen, J.M. Mollerup,
Thermodynamic Models: Fundamentals &
Computational Aspects (Denmark: Tie Line
Publications, 2007).
[7]. http://www.engr.siu.edu/staff1/weston/thermo
/Rankine/ RankineCycles.html; accessed in
May 27, 2015.
[8]. G.H. Milton, Problemas Resueltos Examenes
- UNI y Otros (Lima, Perú: Ediciones Habich,
1986).

Thermodynamic Simulation of Steam Power Cycles using GUIMatLab Interfaces

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