TPWS
Thermodynamic
Properties of Water and Steam
by Howard Chao and Stella Unruh
Introduction
Properties
of water and steam are vital to the successful design and operation of most
industrial plants. The calculation of
the thermodynamic properties of water can be tedious and time consuming through
the use of steam tables and diagrams.
Furthermore, obtaining highly accurate and precise data by these methods
may be difficult if not impossible.
Therefore the need for computer programs capable of finding this data
quickly and accurately is great.
The
objective of this project was to create a robust program which provides values
for various thermodynamic properties of water and steam at a given temperature
and pressure with a built in unit converter.
In addition to providing an electronic steam table, these calculated properties
are continently stored in data structures for additional analysis and
processing. With these main features in
place, the code may be easily adapted and modified to suit advanced processes
and calculations.
The
thermodynamic properties of water and steam were calculated using the most recent standards (IF-97)
set forth by The International Association for
the Properties of Water and Steam (IAPWS).
The IAPWS IF-97 formulation covers the following range of validity
273.15 K ≤ T ≤
1073.15 K p ≤ 100 MPa
1073.15 K ≤ T ≤
2273.15 K p ≤ 10 MPa.
The
figure below depicts the five distinct regions which are covered by the IAPWS
IF-97 on the phase diagram for water.
For
each region a different generating function is used to calculate the properties
for points within that area. Regions 1,
2 and 5 are specifically covered by the specific Gibbs free energy (as a
function of temperature and pressure) while Region 3 is represented by the
specific Helmholtz free energy (as a function of temperature and density). For the purposes of our project, iterations
must be performed to determine the density of water corresponding to a given
pressure and temperature point in Region 3.
Region 4 corresponds to the liquid/vapor coexistence curve and
culminates at the critical point (647.096 K, 22.064 MPa). From the expressions for the free energies,
all of the relevant thermodynamic properties may be easily evaluated by taking
the appropriate partial derivatives.
[ Introduction | Matlab
Code | Program
Verification | Examples | Suggested Improvements | References ]