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Software for Steam and Water properties
By Amit Bhaduri
Water is cheapest and extensively used engineering fluid for transportation and conversion of heat energy. Water is chemically very stable with excellent thermal properties and that is why it is used as primary heat carrier in steam power plants and for heating duties. The importance of water and steam in heat power engineering and science is undeniable.
At standard atmospheric pressure, water changes its phase and gets converted to steam at about 100º C upon addition of heat and transforms to solid ice at about 0º C upon rejection of heat. The steaming temperature, called saturation temperature, increases when the pressure is increased. Another phenomenon is that during steaming from liquid water, it passes through a mixed phase, called saturation zone, when both water and steam simultaneously exists till it gets fully converted to dry steam and during that period the temperature does not increase when the pressure is kept constant. Beyond the saturation zone, the temperature further increases at constant pressure.
The saturation phase phenomenon exists up to a certain point called critical point, and above the critical pressure and critical temperature range water directly gets converted to steam without passing through saturation zone. Hence living aside the ice phase of water, the steam and water phase themselves present a wide range of changing states and gives rise to complexities in determination of various properties at various stages.
In heat power engineering, commonly used intensive properties of steam and water are pressure and temperature and extensive properties like enthalpy, entropy, dryness fraction, specific volume, viscosity, isobaric and isochoric heat capacities and thermal conductivity. There are other properties also which are used as and when required but they are not very regularly used. Intensive properties like pressure and temperature can be measured directly with instruments but most of the other extensive properties are required to be calculated. Manual calculation of extensive properties requires reasonably complex and lengthy mathematical procedures and is usually not possible to follow in day-to-day engineering job.
Steam tables and Mollier daigram (graph showing thermodynamic properties of steam and water) prepared based on intensive and other extensive properties have served the industry for more than 100 years. Although steam tables and the diagram provides reasonably acceptable data still now, but it always remains difficult to get accurate output from the tables and the chart due to interpolation errors. It has been possible to overcome those difficulties to a good extent with the introduction of the personal computers. The International Association for the Properties of Water and Steam (IAPWS), the body responsible for providing the guideline for the calculation procedure, has done a formidable work in standardizing methods keeping electronic computer in consideration. In fact today, use software programs for calculating steam and water properties based on IAPWS procedures has become the engineering standard.
It is easy to procure or even download a free version of the steam and water properties software through the Internet. However one has to be careful in choosing the proper one. Review of some of them reveals that all are not equally good. The first thing is to look for is to check that the program can give output of all the relevant properties if any two of the properties like pressure, temperature, enthalpy, entropy and dryness fraction (and sometimes specific volume also) are given as input parameters. Many of the programs do not cover this full range of input and output options.
The next item is to check that the program accepts the use of SI, English and customary American units. Accuracy is key aspect, which should be verified by the buyer by using the figures given specifically for testing in IAPWS. Some programs do come with graphic features along with the basic numeric input/ output, but their use may be more relevant in classroom studies and research work. Continuous modification of the program is another aspect requires attention of the buyer as and when IAWPS issues a change notice and unfortunately many sellers do not take prompt care in this regard. Price is the final issue over which buyer must spend time. It is worth scouting since for same features the price of the software may vary quite a lot. The buyer must look for the right one and compare the price before taking any decision.
It can be summarized that heat power engineers using steam properties is seriously encouraged to use software and must evaluate that the program is based on IAWPS latest edition, provides maximum choice of input/output data and units' features, accuracy, updating options and finally the price.
To read more about steam and water properties you can visit www.steam-water-properties.com
About the Author
The author is a power plant engineer with more than 30 years experience in consulting engineering services and has developed quite a few engineering software for day-to-day use. He specialized on Software for steam and Water Properties.
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