GeoSteamNet: 1. Thermodynamic Data for Numerical Simulation of Steam Flow in a Pipeline Network of Geothermal System


Mahendra P. Verma

Key Words:

ActiveX control, SteamTablesGrid, StmTblGrd, Thermodynamic properties of water, IAPWS-95 formulation, Visual Basic, Excel 2007, fluid flow, pipeline


Stanford Geothermal Workshop







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Recent trend for programming thermodynamic data in a computer code is through ActiveX components; however, the iteration process in them makes the execution very slow. This intricacy is resolved with creating an ActiveX control StmTblGrd for the thermodynamic properties of water. First a grid (matrix) for a specified range of temperature (say 400 to 600 K with 40 segments) and pressure (say 100000 to 20000000 Pa with 40 segments) is created. Using the ActiveX component SteamTables the values of selected properties of water for each element (nodal point) of the 41x41 matrix are computed. The grid can be saved in a file for its reuse. A linear interpolation within an individual phase, vapor or liquid is implemented to calculate the properties at a given value of temperature and pressure.

In an Excel worksheet the enthalpy of one thousand random datasets for temperature and pressure is calculated using the ActiveX control StmTblGrd and component SteamTables. The uncertainty in the enthalpy calculated with StmTblGrd is within ±0.03%. The calculations were performed on a personal computer, which has a processor “Pentium(R) 4 CPU 3.2 GHz, RAM 1.0 GB” and Windows XP. The total execution time for the calculation with StmTblGrd is 0.3 s, while it is 60.0 s for SteamTables. The accuracy can be further improved by refining the grid.

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