Valery Ochkov, Vsevolod Znamenskiy (Moscow Power Engineering Institute)
In this article the technology of cloud computing is described, based on the use of references to web-functions, purposed for calculation of different power engineering working substances properties.
Thermal engineering calculations demand knowledge of thermodynamic and physical properties of working substances. If such calculations are conducted manually, it is enough to have at hand corresponding tables  of properties of specific working substance. But computer calculations (which are conducted more often nowadays) demand special program functions, which return specific values of properties of working substances of power cycles depending on parameters of the cycle – temperature, pressure, specific enthalpy, specific entropy, density, etc.
One of the most widespread and convenient programs on properties of working substances of power engineering (water and water steam, air and smoke gases) is program WaterSteamPro [2, 3]. After downloading this program from a site www.wsp.ru and its installation on the computer, user can utilize corresponding functions on properties of working substances in his engineering calculations. It will be said about this program in greater details in the end of this article.
But downloading functions from Internet sites or installation from disks onto user’s computer has one essential lack consisting in the following.
Programs for computers, and in particular, programs for calculation of thermo physical properties of individual substances and their mixes are continuously improved. It is connected with the development of new formulations, that contain directions for calculating specific properties of concrete substances, or that in existing programs errors and inaccuracies are corrected, and the area of their application extends, their characteristics (speed, volume of occupied memory of the computer, etc.) improve. Users of such programs often do not keep up with these changes and work with out-of-date versions. But this isn’t the biggest trouble. The trouble comes when user changes his computer and / or an operating system on it. That often leads to that old programs cannot be installed or cease to work on new or updated computers.
In this connection, and also taking into account the fact that now almost all computers on which engineering, and in particular thermal calculations, are conducted, have a permanent access to the Internet, the new technology of work with functions on thermal and physical properties of working substances of power systems has been offered by the authors of the given article, based not on downloading, but on references to the functions, stored on different sites on the Internet.
The mentioned reference book on thermo physical properties of working substances of power systems is supplemented with a site which is placed on a calculation server of the Moscow Power Engineering Institute (MPEI - www.trie.ru) – see fig. 1. Along with other open, interactive network reference books useful for thermal and power engineers .
Fig. 1. Moscow Power Engineering Institute calculation server.
On the reference book’s site on thermo physical properties of working substances of power systems, separate areas of the IAPWS-IF97 formulation (see a footnote 2) were selected, on which properties of water and water steam are calculated:
1. Liquid phase (water)
2. Gaseous phase (steam)
3. Near critical point region
4. Saturation line
5. High temperature region (800 – 2000°Ñ)
If a visitor of the site, shown on fig. 1, for example needs to specify properties of water steam, he can click on the reference selected on fig. 1, and pass to the -page of a site, shown on fig. 2. On this web-page there are new references, that lead to: IAPWS-IF97 formulation description, "live" calculation on given formulation where the site visitor can change the initial data (pressure and temperature) and receive not only result of calculation (parameters of water steam at pressure and temperature preset values), but also all intermediate values, and the set point on ð – Ò diagram.
Fig. 2. Site on properties of water steam
From the site, shown on fig. 2, it is also possible to download corresponding functions for engineering calculator Mathcad (Mathcad 14, 15 and Mathcad Prime are supported) and to insert them in users thermal engineering calculations.
Engineering calculator Mathcad is a very convenient tool for the solution of thermal engineering problems . In the environment of Mathcad, record of formulas is conducted in the natural notation; it is possible to use measure units for the control over correctness of calculations and for more convenient display of their results. In Mathcad it is very simple to display results of calculations in the form of graphs and diagrams.
These and other useful qualities of Mathcad package have made it one of the most popular tools of the solution of technical problems on the computer.
In the environment of Mathcad there is a convenient tool - reference to other Mathcad-document, which variables and functions become visible in the Mathcad-document in which the corresponding reference is done. It is possible to do such reference on Mathcad-documents (files with expansion *.mcd, *.mcdz, *.xmcd, *.xmcdz, *.mcdx and *.mcdxz) which is stored not only, on a workstation or in a local computer network, but also on Internet sites. It opens ample opportunities for realization of a new technology of use of the functions stored on sites of the Internet without downloading them on the user’s computer.
If, during the solution of thermal engineering problems in the environment of Mathcad, it is necessary, that the functions returning thermodynamic properties of working substance, in particular, of water and water steam, became visible in the user’s document, it is necessary to execute several simple steps, displayed on fig. 3 and 4.
Fig. 3. Getting URL of the reference to Mathcad file
Fig. 4. Insert of the reference to Mathcad function into algorithm
On fig. 3 it is shown, how by clicking of the mouse right button on the reference selected on fig. 2, it is possible through the description of properties of the reference to receive the URL of the given function in the Internet and to insert it (reference) into the thermal engineering calculation (fig. 4). Thus it is possible to make visible all functions necessary for given calculation – for calculation of the thermal efficiency of the thermodynamic cycle for example, the beginning of which is shown on fig. 4, and the end on fig. 5.
Fig. 5. Rankin cycle computation, using references to functions on properties of water and water steam, stored on the Internet
On fig. 5 also displayed Internet sites where user can find corresponding Mathcad functions, that are referred to, in the given algorithm and which are necessary for the calculations on properties of water and water steam.
The user at his desire can click a mouse on any reference, shown on fig. 5, download and open the given Mathcad-file containing corresponding function, to check correctness of the calculation in it. This document can be kept on a workstation (on the computer) or in a local computer network of an organization and can be referred to its new place of storage – not on the Internet (in "clouds"), but on the users local place. It is done in the event that connection with the Internet is not quite reliable or limited. But in this case it is better to download at once, on the computer or into a local network of the organization, all functions on properties of working substances of power system, by addressing to the site WaterSteamPro (www.wsp.ru), – see fig. 6.
Fig. 6 One of the web-pages of WaterSteamPro site
After downloading and installing the program WaterSteamPro on a separate computer or in a local network, functions with prefixes wsp (water and water steam) and wspg (gases and their mixes) will be built in the environment of Mathcad, returning thermal and physical properties of working substances of power systems and many other functions useful in thermal engineering calculations.
Fig. 7. The example of thermal engineering calculation, using software package “WaterSteamPro”
So on fig. 7 it is possible to see that after enabling Mathcad functions of the software package WaterSteamPro it is not necessary to define areas of IAPWS-IF97 formulation in which calculation is conducted – see for example functions wspH1PT (area 1 – water) and wspH2PT (area 2 – water steam), on fig. 5. WaterSteamPro package itself will define this area automatically – see function wspHPT on fig. 7 and its description in a dialogue window “insert function”. Besides, on fig. 7 it is possible to see the work of the function returning specific enthalpy in dependence not from specified values of pressure and temperature, but from conditions of expansion of water steam in the turbine – see second dialogue window on fig. 7. On the basis of program WaterSteamPro the considerable quantity of thermal engineering calculations is created by MPEI and published on the MPEI (TU) calculation server.
Technologies of references and downloading, described in given article, have their advantages and disadvantages. The compromise (intermediate) technology is an installation on the computer or a local network of the program WaterSteamPro and its regular updating. If thermal engineering calculations are conducted on computers with a reliable connection to the Internet it is possible to apply the technology of the references described in this article. The technology of references to Internet functions opens to users a wide set of other useful thermal engineering functions placed on MPEI (TU) calculation server.
The given work is carried out within the bounds of the project MPEI (TU) - National Research University: «Information support of power engineering, power efficiency and power economy (IT EEE) - creation of the centre on thermal and physical properties of substances and decisions for power engineering».
1. Ochkov V.F. A New Reference Book for Power Engineers (9th conference on Power System Engineering, Thermodynamics & Fluid Flow - ES 2010, June 17 - 18, 2010, Pilsen, Czech Republic.
2. Alexandrov A.A., Ochkov V.F., Orlov K.A. Steam Tables and Diagrams on Mathcad Calculation Server for Personal Computers, Pocket Computers and Smart Phones // Proceedings of the 15th International Conference of the Property of Water and Steam, Berlin/Germany, September 7–11, 2008.
3. Ochkov V.F., Alexandrov A.A., Orlov K.A., Ochkov A.V. Thermodynamic Cycles: Calculations on the Internet // Proceedings of the 7-th Conference «Power System Engineering, Thermodynamics & Fluid Flow», June 26-27, 2008, Pilsen, Czech Republic, pp. 165-173
 And they can be conducted practically in any program environments: tabular processor Excel, engineering calculator Mathcad, the programming language of technical calculations Matlab, programming languages C, BASIC, Pascal, FORTRAN, etc.
 For example if we speak about water and water steam, the basic working body of power engineering, such formulations are developed and approved by The International Association for the Properties of Water and Steam (IAPWS) – see www.iapws.org.
 It is possible to create such a function separately from the package and publish it on the site, shown on fig. 1, but it will be rather bulky.