Vacuum simulation (or modelling) is an essential part of vacuum system design. It is now a well-established practice and is primarily concerned with the prediction and calculation of how vacuum pumps and systems will perform in specific scenarios.
These simulations enable engineers to identify anomalies in the design stage and acquire the right components, rather than building a vacuum system that later needs to be redesigned.
Of course, for accurate vacuum system calculation – the right information needs to be fed into the simulation exercise. System dimensions, leak-rates, gas throughputs, construction materials, vapour/gas to be pumped, target pressures, internal fixture design, hazardous substances involved – there are a plethora of things that need to be considered and accounted for, and this list is by no means exhaustive.
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However, the fundamental benefit of vacuum system calculation is that it can all be done without purchasing components or assembling any kind of system. With this approach, engineers can save a considerable amount of time, effort and money.
That said, vacuum system calculation is not without its drawbacks – and while slight variations in testing parameters will have minimal effects on simpler vacuum systems, in more complex systems these disparities and errors can be significant. Everything from starting pressure and throughput through to the type of pump used and its operating pressure.
There must also be an appreciation for the simple fact that nothing is better than the real thing. The simulation will outline obvious system imperfections, allowing the engineer to readily resolve them. Results will not be completely reflective of performance or conditions; experience allows a ‘semi-empirical’ approach.
Getting past the CHALLENGES
Overcoming these issues is possible but does require compromise with more complex vacuum systems. Removing pipes, valves and complex switches before running the simulation – for example – can help to produce ‘satisfactory’ results. Once you have a baseline for reporting, you can begin to re-insert removed components (or complexities) to fix your model and calculations.
Another example is potential lubricant contamination. These add another complexity due to filters being required to remove them – reducing the effective capacity of the pumping unit.
These are just a few examples of how additional elements can influence pump capability and simulation results.
Vacuum system calculation in the future
Modern vacuum systems need highly developed components that operate exactly to specification – at all parts of the vacuum spectrum. Using the right software, it’s entirely possible to obtain performance parameters and match components to produce bespoke vacuum systems.
Moreover, the gap between results obtained from simulation when compared to actual results, is ever narrowing. As simulation models become all-encompassing and more sophisticated, this gap will only get smaller.
Positive vs Negative Pressure in Vacuum System
There are two ways to express pressure: absolute and gauge. The absolute pressure is the actual pressure relative to a perfect vacuum (zero pressure) whereas gauge pressure is that relative to atmospheric pressure. A positive gauge pressure is measured when the pressure is above local atmospheric pressure and negative gauge pressure is when the pressure is below local atmospheric pressure. The typical negative pressure range is 0 to -1 bar. It should be noted that local atmospheric pressure may change. If it below 1 bar absolute then -1 bar will not be achieved and if it is above 1 bar then -1 bar gauge will not be a perfect vacuum.
The complexity of these new and more sophisticated vacuum systems presents a challenge for the vacuum engineer. And that’s where we can help.
Whether you’re working in the Research and Development field or otherwise, you need a vacuum system that is safe to operate, highly reliable and built to meet your operational requirements.
Our team of experts at Vacuum Science World have decades of experience in the design, modelling and specification of vacuum systems and can deliver free tailored recommendations.
If you are interested in finding out more, please have a look at our vacuum systems design page here.
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