SOFTWARE FOR MOLLIER DIAGRAM

Water is the most extensively used thermodynamic fluid for heat power industry since it is cheap and easily available in abundance with excellent thermal and chemical properties. But thermodynamic properties of water vary substantially with changes in temperatures and pressures with added complexities of phase changes like water/steam/ice transformation. The most important steam and water properties used extensively in industry can be short listed as pressure, temperature, enthalpy, entropy, quality, specific volume and also thermal conductivity, specific heat and viscosity.

Quantitative determination of all those properties from fundamental formulae is ruled out in day-to-day engineering calculations due to obvious mathematical complexities. Traditionally steam tables and charts have served both industry and academics for finding out such properties. In steam tables, different properties of steam and water are tabulated in certain intervals of temperature, pressure etc. Charts (graphs) or diagrams can be of many types since in two-dimensional plane, two major properties can be used as axes and others are shown as lines of constant values at different intervals. Like 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. Other 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 reasonably accurate output but they usually call for interpolation resulting in some inaccuracies, whatever small they may be. Computer software for steam and water properties has eliminated this accuracy problem and has marginalized the use of printed steam tables and charts in the industry. However the study of charts (generally called Mollier diagrams) still remain very important in academic world where understanding of the fundamentals and conception is of primary importance.

Steam and water properties software and tables give property numbers at a particular point with input of at least two properties for that point and are mostly helpful in further calculations etc. but fail to provide an insight regarding the relative position of such point in entire range. Here comes the invaluable importance of the Mollier diagram. In Mollier diagram a particular point can be easily located in the desired plane and the effect of change in input properties can easily be understood very clearly giving a perfect perception rather than juggling with only numbers. It also demonstrates graphically how the phase of water changes with the change in properties.

It is true that carrying and handling big size Mollier diagram with good resolution is cumbersome and that forces teachers, students and practicing engineers to restrict the diagram’s use in real life computations even though they provide more insight. Of late the software for Mollier’s diagram has come as a boon. It may sound little offbeat to use software for generating a Mollier’s diagram, but believe me it is true and very handy. It is a perfect application of both the power of computer’s computational abilities and graphic abilities. In fact it is the same software, which is used to determine steam and water thermodynamic properties, is conveniently used to generate the Mollier’s diagrams using a package that can generate and display graphics as well.

The benefits of the software generated Mollier’s diagrams are manifold. Firstly this completely eliminates the need of carefully preserving and handling of the printed diagrams. The diagram can be viewed directly on the computer screen and the same can be saved in a file and printed as and when required. Using the software, diagrams can be generated in interactive tailor made fashion to suit any range with as many or as little constant line properties as required. Any constant property line for any specific value can be drawn on the diagram fully eliminating the need of interpolation as generally required in commercially available printed diagrams. Any point with two input parameters can be very easily located interactively on the diagram giving clear picture of its position in the entire range including possible two points, if exists, for enthalpy and quality as input. The clarity of the diagram can be greatly enhanced by using available many different colors of the computer display. In the teaching institutes and academic world the software can be very useful since it may greatly help teachers and students to explore, investigate and explain the nature of variation of the properties with respect to one another just by few clicks. One example can reveal the power of such software. We know that by using the steam/water properties software or steam tables or printed Mollier diagrams, all the properties of steam can be determined by providing two input parameters say like pressure and temperature. By using the Mollier diagram software, the point can be easily located on the diagram and all the properties can also be obtained. But added advantage can be taken using the software to demonstrate that constant line generated on the diagram using the input value of any property, say specific volume, passes through rtance in the teaching and academic field.

Unlike steam and water properties software, the Mollier’s diagram software are not available in so wide spread manner. Little probing over the Internet reveals that very few of them provide all the options as described earlier. Many of them are linked with the steam and water properties software and show sketchy diagrams with only the saturation line and the ability to locate the specific point without the facility of printing. Some of them display standard diagrams and only with the facility of locating the specific point. Very few of them provide compete freedom of generating the full tailor made diagram as per user’s specific requirement using any value of user’s choice.

In conclusion it can be summarized that there is high potential of using Mollier’s diagram software especially in institutions and academic world provided a right one is chosen. It can be conveniently used as a substitute of printed diagrams and can be very helpful in conceptualization and day-to-day use by professionals, students, teachers and academicians.

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