Transient fluid flow

Normal fluid flow calculations assume that the system is at steady state. That is, there is a flow of a fluid in the pipes which is steady, occurring at a fixed rate. Most chemical engineering design is done at steady state conditions. Modern simulation programs can simulate dynamic situations, assessing how the plant operation and conditions will change as things change like production rate, raw materials composition, deterioriating plant item performance, etc. However they will not usually assess rapidly changing situations, such as can happen when flowrates change suddenly. This might be caused by a pump tripping, or a valve suddenly closing due to a fault.

Such transient events can generate very high pressures inside the pipes, risking their rupture and product loss of containment. Also, forces can be set up on pipe bends which can risk breaking the pipe supports, sometimes resulting in the rupture of the pipe and others supported nearby.

Assessment of these situations by modelling the transient events is a specialised subject. I have been involved with such assessments for many years, using state-of-the-art software such as –

  1. Pipenet (see
  2. Flowmaster (see
  3. HiTrans (see

Several other software packages exist, such as Wanda, Hammer, and Fathom. These are well respected, but I’ve not used them.

Personally I have found that the three named programs work well and are fairly easy to use, although significant learning is needed for them all. My preference for solving difficult transient flow problems is Pipenet. For simple, inexpensive simulations, HiTrans works well.

For a paper on transient fluid flow simulation, click here – (to be inserted)