When DP is not of interest, and it is only the system lag/holdup, you see separators being used instead of valves with volume. Adding volume to any of the simple methodologies is quite simple as described in Stuart's comment above. a valve with a CV is preferred to a pipe with detailed geometry because it is simpler (assuming it achieves the desired goals).Ģ - Do we need to capture lag? There are many reasons to capture lag, or holdup in the system, and it is the second most common parameter needed in dynamic models. Do we have a reference pressure drop/flow that can be used for a quick CV estimate? If not, Do we have an equivalent length (and size)? If not, Do we have detailed pipe geometry? Depending on the answer to these questions you try to select the simplest approach first, i.e. The key parameters for selection are: pressure drop, lag (holdup), dead time, phase slipġ - In many cases we need to capture pressure drop. The purpose of the model is the key to selecting the modelling approach.
This argument also applies to plant piping. Every attempt to add detail and complexity to a model has to be evaluated against the expected return. The key is to understand that having the ability to model something with more detail doesn't mean that it is good to do so.
Dynamic simulation opens up the ability to model the real world with a bit more reality. This post is a slightly modified copy of a post made by Mohamed Abouelhassan on LinkedIn in the Aspen HYSYS Dynamics users group.ĭynamic models should always be for "fit for purpose".