Page 176 - Fundamentals of Magnetic Thermonuclear Reactor Design

Superconducting Magnet Systems Chapter | 5 157

Such modelling strategy is dictated by a number of factors including the
following:

l Complexity of ITER cryogenic circuits that includes hundreds of compo-
nents of various functionality (conductors, feeders, collectors, cryogenic
lines, valves, LHe baths, heat exchangers, cryogenic pumps, compressors,
etc.);
l Necessity to allow for 3D heat transfer in the windings;
l Coupled electromagnetic and thermal effects inherent in the tokamak opera-
tion; and
l Pulsed character of heat release in the magnets, with the peak-to-peak heat
power variations comparable to an average heat load, making it necessary to
account for the cryoplant’s dynamic response.
With regard to these factors, a special modelling technique has been devel-
oped utilising an integrated set of mathematical models to simulate the typical
components of magnet and cryogenic systems. The basic models are integrated
via thermal and hydraulic links forming a generalised model for consistent ther-
mal–hydraulic analysis.
This technique has been implemented in the Vincenta and Venecia codes
[25,26] intended to predict the transient behaviour of complex superconducting
MS. Venecia has evolved from Vincenta and offers optimised computational
algorithms, an extended set of basic models and augmentable database of most
conventional cryogenic fluids, which now includes the single- and two-phase
helium (HeI and HeII), hydrogen, nitrogen, argon and neon. Different coolants
can be used within a single computational model simultaneously.
The developed computation techniques and new code enable a comprehen-
sive thermal–hydraulic analysis of SC magnets for fusion reactors, as well as
other devices employing SC coils (e.g. magnetic resonance imaging, magnets of
elementary particle accelerators, particle detectors, electrical power generators
and electrical engines).
Extended functionality of the Venecia thermal–hydraulic code enables
predictive and parametric simulations of modern cryogenic systems for low-
and high-temperature superconductivity applications and a range of coolant
fluids.

A.5.1.1 Venecia Basic Models and Modelling Technique

Basic mathematical models are used to simulate the typical components of
magnet and cryogenic systems. Each basic model is associated with a set of
properties to provide an adequate description of the component to cover typi-
cal operating conditions. To ensure a reliable thermal–hydraulic simulation, a
numerical model should obviously reflect all the key factors influencing the
solution. Consistency of the generated model calls for a good user’s expertise
and knowledge of the problem.