Plenary Speech:

Modeling and stability analyses of natural circulation steam generators

Prof. Heimo Walter
Institute for Thermodynamics and Energy Conversion
Vienna University of Technology
Getreidemarkt 9, A-1060 Vienna, AUSTRIA
E-mail: heimo.walter@tuwien.ac.at
Web site: http://www.ite.tuwien.ac.at

 

Abstract: Natural circulation systems have a wide range of applications such as e. g. power cycles or industrial heating processes. Working media in process facilities or power plants are operated in either single phase or multiphase condition. Water and steam are the most widely used working media. Multiphase flow has a stronger tendency towards unstable behavior than single phase flow. These so-called fluid-dynamic instabilities can manifest themselves e. g. in the form of pressure drop or mass flow fluctuations, or fluctuations of the wall temperatures. The instabilities can cause vibrations of plant components, a non-uniform mass flow distribution in the tube bank. They can accelerate the initiation of a boiling crisis, which is characterized by a sudden rise of surface temperature due to the drop of the heat transfer coefficient, and a non-uniform heat flux or a difficult measurement and control of system parameters. Thermo-hydraulic oscillations and flow instabilities can influence the operation and the control of the plant in a negative way and therefore they are undesirable. To avoid such instable flow conditions it is necessary to know the dynamic behavior of the steam generator already in the phase of the boiler design. The paper discusses the modeling as well as the stability analyses of natural circulation systems. In the first part of the paper a short description of the theoretical background of the computer code used for the numerical simulation of the natural circulation boilers will be presented. For solving the partial differential equations of the conservation laws for the working fluid the two finite volume algorithms SIMPLER and PISO are used. The computer code is suitable for the calculation of a boiler with a different number of pressure stages. In the second part of the article the fundamentals of the analyses of the static flow instability, namely the reverse flow, will be described and the results of a stability analyses on two different boiler designs will be presented. The investigation was carried out for two different boiler designs. Both boilers are analysed under hot start-up conditions. It can be shown that design possibilities exits to influence the stability of the boilers by changing the geometry.

 

Brief Biography of the Speaker:
Heimo Walter is a mechanical engineer. He obtained the Master degree in 1992 at the Vienna University of Technology. From 1994 to 2007 he was a University-Assistant at the institute for Thermodynamics and Energy Conversion at the Vienna University of Technology. 2001 PhD in Mechanical Engineering at the Vienna University of Technology. He is since Feb. 2007 assistent professor at the institute for Thermodynamics and Energy Conversion at the Vienna University of Technology. In Nov. 2007 he earned Dr. hab. degree with the thesis: "A contribution to the static and dynamic stability of natural circulation steam generators" at the Vienna University of Technology.
Since June 2007 - Editorial board member of the journals: Open Mechanical Engineering Journal; Open Mechanical Engineering Reviews and Open Mechanical Engineering Letters.
Since 2006 Member of ASME-American Society of Mechanical Engineering and Member of WSEAS - World Scientific and Engineering Academy and Society