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Choose the right Steam and Water Properties Software

Water is the cheapest and most extensively used engineering fluid for transportation and conversion of heat energy. The importance of water and steam, water’s another phase, in heat power engineering and science assumes utmost importance. Steam is used as primary heat carrier in steam power plants and for heating duties not only because water is available in abundance or cheaply but also it is chemically very stable and for its excellent thermal properties.

It is known that at standard atmospheric pressure, liquid water changes its phase and gets converted to steam at about 100ºC upon addition of heat and transforms to solid ice at about 0ºC 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. However 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, which is not of much significance in heat power engineering, the steam and water phase themselves present a wide range of changing states providing enough complexities in determination of various properties at various states.

In heat power engineering, most 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 not very regularly. Intensive properties like pressure and temperature can be measured directly with instruments but most of the other extensive properties are required to be computed. Manual computation of derived properties call for reasonably complex and lengthy mathematical procedures and is generally not possible to follow in day-to-day engineering job.

Traditionally steam tables and Mollier daigram (graph showing thermodynamic properties of steam and water) prepared based on intensive and other calculated properties have served the industry for more than 100 years. Although steam tables and the diagram provides reasonably acceptable data, but it always remains difficult to get accurate output from the tables and the chart since interpolation error crops in, however minor they may be. It has been possible to overcome those difficulties to a great extent with the advent 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 tremendous work in formulating methods keeping electronic computing in view. In fact today, use software programs for computing steam and water properties based on IAPWS guidelines has become the industry standard.

It is not difficult to purchase or even download a free version of the steam and water properties software in these days of Internet. However one has to be vigilant in choosing the right one. Review of some of the software suggests that all them are not equally well designed. The first thing is to look for is to examine 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 options. The next thing is to look for as to whether the program allows the use of SI, English and customary American units. Accuracy is another aspect, which should be verified by the buyer by comparing the output 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. Modification of the program is a must as soon as IAWPS issues a change notice and unfortunately many sellers do not take prompt care to update their programs and inform their customers. Price is the final issue over which buyer will very naturally spend time and it is worth probing since for all most same set of features the price of steam properties software vary quite a lot. It is not the intent of this article to advertise for any particular program but a recent website is giving a free trial version and a full version at a very little price with many desired functionalities. However the interested buyer must scout for the right one and compare the value for money before making any decision. It is possible to get two solutions, if exists, with enthalpy and dryness fraction as input and the software must provide the same.

In conclusion it can be summarized that heat power engineering personnel using steam properties is encouraged to use a suitable PC based software and should evaluate that the program is based on IAWPS latest edition, provides maximum choice of input/output data and units’ features, accuracy as stated in IAWPS, updating options are available or not and finally the value for money.   

 

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