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Wednesday, October 23, 2019

KEDRU

A program for piping and valves, with which all current water hammer problems in power stations, chemical plants and pipelines can be solved.


KEDRU calculates flow processes and pressure wave paths in interconnected piping systems e.g. for pipe breaks and quick opening/closing valves and flaps. The calculation program works according to the Euler type "explicit finite differences" method (division of calculation model into fixed zones, the medium flows through the zones). It is 1 1/2 dimensional, i.e. one-dimensional flow with cross-section changes.

The following are amongst the factors that can be taken into account in KEDRU:

  • Pipes with variable cross-section,
  • Pipe junctions,
  • Irreversible losses, both continuous pipe friction and flow losses in elbows, chokes, changes in cross-section, etc.
  • Phase change water – steam and steam – water.

The following are included as externally determined boundary conditions: Pressure and temperature as a function of time.

Mass flow and energy flow, for example, are also possible as a function of time.

The pipe flow can also be influenced by "internal" boundary conditions: Valves, flaps, own medium controlled behaviour.

Two important elements are:

  • The general water-steam state comparison and
  • the calculation of the flow in the valve (VALVES subprogram) taking into account the two-phase flow - also at critical flow.

The program makes a genuine calculation of the pressure waves, i.e. the elasticity and the inertia of the medium are taken into account. If at any point the speed of sound is exceeded in the calculation, the speed is limited to the speed of sound (critical mass flow, homogeneous model). Ultrasound could only occur in a diffuser, not in a normal piping system. 

Since 1996 KEDRU has been linked with the structural dynamics program EASYPIPE. Fluid-structural interactions can therefore be calculated. These have a significant influence on "soft" (low stiffness) piping systems filled with liquid.

Some interesting applications:

Checking of blowing-off experiments (BMFT experiments) with steam, water and steam-water transition, a good match was found between experimental and calculated results.

Checking of an experiment in Delft for fluid-structural interaction (FSI) showed an excellent match. A very good match was also found between calculated and measured results for time variations of pressures, moments and deformations at the TH high pressure feed system at the Gundremmingen nuclear power plant.

Analytical functional demonstration of the pressure container Si-valves in the YP system of the Mülheim-Kärlich nuclear power plant.

KEDRU was used to investigate many important water impinged, spring loaded Si-valves from the companies Sempell and Bopp & Reuther for stable behaviour during operation for the nuclear power plants of Stade, Philippsburg, Obrigheim and Unterweser. As is the case for blowing-off processes, 2 phase flow and critical flow can occur here.

For all boiling water reactors in Germany calculations in important systems such as feed-water, live steam, volume control, after-cooling, quick shut-off: Pipe breaks, pump shut down and failure, turbine emergency shut-down, penetration emergency shut-down, own and foreign medium controlled opening and closing of valves, quick shut-downs,...

Pump failure, change-over or cut-off in waste water and drinking water systems.

Opening and closing of valves and blow-outs in natural gas preparation plants and pipelines (stations): STEGAL, MIDAL.