Most extensively used thermodynamic fluid for heat power industry is water since it is cheap and easily available and has very good thermal and chemical properties. But thermodynamic properties of water in its different phases vary extensively with the variation in temperatures and pressures adding complexities. Important steam and water properties used in industry are pressure, temperature, enthalpy, entropy, quality, specific volume and also thermal conductivity, specific heat and viscosity.

Determination of those properties from basic formulae is cumbersome for regular engineering calculations due to computational complexities. For many years steam tables and charts have served industry and academics for finding out such properties. In steam tables, properties of steam and water are displayed in tables at certain intervals of temperature, pressure etc. Charts (graphs) or diagrams are of many types as in two-dimensional plane, only two major properties can be used as axes and others are shown as lines of constant values at different intervals. For example, in an enthalpy-entropy plane (generally called Mollier Diagram), constant pressure lines, constant temperature lines and constant specific volume lines are shown at different intervals. Charts like temperature-entropy, pressure-temperature, pressure-enthalpy, etc. are also available with different properties shown as constant lines. Both standard printed steam tables and charts give rationally accurate output but they usually require interpolation resulting in some inaccuracies, although small in nature. Software for steam and water properties has eliminated this accuracy problem and has minimized the use of steam tables and printed charts in the industry. However the use of charts (generally called Mollier diagrams) still continue to be important in academic world where understanding of the fundamentals and conception is of primary importance.

Software for steam and water properties and steam tables give property valuse at a particular point with input of at least two properties for that point and mostly helps in further calculations etc. but fall short of providing an insight regarding the relative position of the point in entire range. There comes the importance of the Mollier diagram. In Mollier diagram a point can be conveniently located in the desired plane and the consequence of change in input properties can clearly be understood giving a perfect insight rather than trading only with numbers. It also explains graphically how the phase of water changes with the change in their properties.

Handling big size Mollier diagram with proper resolution is burdensome and that indulges teachers, students and practicing engineers to restrict the diagram’s use in day-to-day computations even though they provide more insight. Under such circumstances the software for Mollier’s diagram has come as an advantage. It may sound little unusual to use software for generating a Mollier’s diagram, but it is true and very handy as well. It is a perfect blend of both the power of computer’s computational skills and graphic facilities. In fact the same steam and water properties software is opportunely used to generate the Mollier’s diagrams using a package that can handle both graphics and commutations.

There are many benefits of using the software for generation of Mollier’s diagrams. This eliminates the necessity of possessing and use of the printed diagrams. The diagram can be viewed right on the computer screen and that can be saved in a file and printed as per requirement. With the help of the software, diagrams can be created in interactive way to suit any range with as many constant line properties as desired. Any constant property line for any value can be drawn on the diagram totally eliminating the requirement of interpolation as usually required in printed diagrams. A point with two input parameters can be easily located interactively on the diagram giving comprehensible picture of its position in the entire range. The clarity of the diagram can be highly enhanced by using available many colors of the computer display. In the academic world the software can be extremely useful as it may greatly help academicians to explore, investigate and explain the nature of variation of the properties with respect to one another just by few commands. An example can divulge the supremacy of such software. We are aware that by using the software for steam/water properties or steam tables or printed Mollier diagrams, the properties of steam can be determined by providing two input parameters say like pressure and temperature. By using the software for Mollier diagram, the point can also be located on the diagram and all the properties may be obtained. But additional advantage can be taken by using the software to demonstrate that constant lines generated on the diagram using the input value of any property, say specific volume, passes through the point already located on the diagram. This decisively proves the correctness of the software and comprehensive understanding of the subject. Such methods assume vast importance in the teaching and academic field.

The Mollier’s diagram software is not widely available like steam and water properties software. Searching over the Internet reveals that only few of them make available all the options as described earlier. Some of them are linked with the steam and water properties software and display sketchy diagrams with only the saturation line and the facility to locate the specific point without the provision of printing. Some of them display pre-laded standard diagrams and only with the ability of locating the specific point. Only few of them provide total freedom of generating the fully tailor made diagrams as per user’s specific requirement using any value of user’s choice.

It can be summarized that there is high potential of using Mollier’s diagram software especially in institutions and academic world provided a proper one is chosen. It can be a substitute of printed diagrams and can be very helpful in conceptualization and regular use by professionals, students, teachers and academicians.

To know more on Mollier’s diagram software please visit

Source by Amit Bhaduri

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