Vacuum Simulation Tools
There are a number of specialist simulation software tools available to the vacuum fraternity.
PumpCalc is a simulation package for “simple systems” (i.e. those that consist of a chamber, a foreline and a pump set), with the “pressure” time from pump output to the chamber being small enough so that speed and conductance are approximately constant. Whilst PumpCalc is best suited for simple systems, it can still be used on more complex systems, if symmetry can be used to simplify the entirety.
TransCalc is a network-based computational simulation software package for the design of vacuum systems. TransCalc is based upon duct-flow prediction techniques which provide a solution across all pressure ranges (including turbulent, compressable and transitional flow). Compared to steady-state models, TransCalc uses fewer primary assumptions about the system, calculates pipe flows based on whole-system throughput and, furthermore, modifies pressures by conserving throughput over a short time interval.
Pascal is a smart simulation tool enables the engineering of a flow-optimisation pump system using empirical data gained from existing pumps, which is coupled with data from the components required to complete the vacuum system, and then through simulation allows the study of three-dimensional molecular flow through the whole unit. Then, by using existing CAD data the simulation software can calculate the characteristics of the entire vacuum system, allowing flow engineering to be optimised.
MolFlow is a Monte-Carlo simulator package developed at CERN, which provides insight into the behaviour of vacuum systems. MolFlow can show the distribution of the number of gas bounces, the flight distance and the flight time of test particles.
VacSim is a PC-based software simulation package which uses the hermetic capture of a vacuum system and is able to predict/calculate how the system pressure varies with time, throughput volumes, pump speed and oil back-streaming. VacSim is able to produce pump-down curves, show the impact of bakeout regimes, illustrate the impact of (construction) material and demonstrate what difference a pump change will make.
VacSim is perhaps not as sophisticated as some vacuum simulation packages but makes up for this by its inherent simplicity and its ease-of-use.
COMSOL can trace its development from 1986 at the Royal Institute of Technology in Stockholm, Sweden. It is used for vacuum system simulation including those used in semi-conductor processing, particle acceleration and mass spectrometers. Small channel applications (such as shale gas exploration and gas flow in nano-porous materials) can also be simulated.
ANSYS is a stress analysis CAD-type finite element (FE) analysis software package that provides a multi-coloured graphic image that can assist in the balancing of rotors, seismic simulation, model analysis, non-linear stress (i.e. creep and/or fatigue modelling), all of which are important in ensuring product reliability and safety. In addition to traditional stress analysis, ANSYS also has a thermal capability that provides a visual model of thermal distortion in pump components, evaluates cooling (thus highlighting cool spots which can lead to condensation), and enables multi-physics modelling (by coupling stress and magnetic analysis).
