Frequently Asked Questions (FAQ)

Can AFT Impulse model transient cavitation?

Yes, AFT Impulse uses the Discrete Vapor Cavity Model or Discrete Gas Cavity Model.

Can AFT Impulse model gas transients?

No, AFT Impulse only models transients in liquid systems.

Can AFT Impulse model pump transients?

Yes. Pumps can be modeled as a prescribed speed transient or the speed can be calculated based on pump inertial characteristics.

Can AFT Impulse model transients cause by positive displacement pumps?

Yes, positive displacement pumps can be modeled as steady operation with periodic flow or during startups and shutdowns.

Can AFT Impulse model air (i.e., vacuum breaker) valves?

Yes, see the Air Valve junction topic.

Can AFT Impulse model pressure and flow control valves?

Yes, see the Control Valve junction topic.

Can pipes be modeled with varying elevation profiles?

Yes, users can assign an elevation profiles to individual pipes.

Can I specify maximum and minimum operating pressures?

Yes, AFT Impulse allows you to include these as "design alerts". Design alerts can be cross-plotted against pressure profiles.

What fluid properties are available in AFT Impulse?

AFT Impulse offers a standard set of properties for common fluids in the AFT Standard Fluids library. It also offers the NIST REFPROP library included with all AFT applications. Users can also utilize the optional Chempak data add-on which is a chemical property library of up to 700 fluids with mixing capability. Use the library as a stand-alone application with the Chempak Viewer or access the library from within Microsoft Excel with the Chempak Add-in.

Can AFT Impulse model non-newtonian fluid behavior or pulp and paper systems?

Yes, AFT Impulse offers Power Law and Bingham Plastic non-newtonian fluid models, and offers the Duffy method and Brecht & Heller for pulp and paper system modeling.

How does the steady-state solution capabilities in AFT Impulse differ from AFT Fathom?

The steady-state solver in AFT Impulse uses the same method as AFT Fathom. However, its purpose is different. AFT Fathom is a general purpose steady-state modeling tool. On the other hand, AFT Impulse uses steady-state only as it relates to waterhammer. Thus some capabilities found in AFT Fathom do not exist or are more limited in AFT Impulse. The most important differences are as follows: AFT Impulse does not model heat transfer. It does not have junctions for static elements like elbows, orifices, heat exchangers, etc., although these can still be modeled in AFT Impulse but through other methods such as Additional Losses in pipes or as General Components. AFT Impulse does not offer polynomial resistance curves except for General Components. AFT Impulse does not offer graphing of pump and system curves, which only have meaning for steady-state.

Does Impulse have the ability to model partially filled pipes?

Impulse can model partially filled pipes at the end of a flow path or run. This capability is primarily intended to handle the situation where a supply riser to a cooling tower or condenser, for example, partially drains when the system is not in operation.