Laminar and Non-Newtonian Corrections Panel

AFT Fathom uses the methods and correlations discussed for each viscosity model only to model frictional losses for pipes. Frictional losses due to pipe fittings or junction losses are modeled using the methods discussed on this page regardless of viscosity model.

It is generally believed that the pressure drop through valves, fittings, etc derive from the physics of bulk fluid motion, wall separation, turbulence, etc and hence are not affected by Non-Newtonian fluid behavior in turbulent flow. Thus, pressure loss due to pipe fittings or junction-specific losses during turbulent flow are modeled using the same methods employed for Newtonian flow.

During laminar flow, pipe fittings and junction losses may not be similar for both Newtonian and Non-Newtonian fluids. AFT Fathom offers two options to model these losses during laminar flow. The correction options are:

Use Adjusted Turbulent K Factor Method (ATKF) - derived from the Crane hydraulic handbook (Crane 1988Crane Co., Flow of Fluids Through Valves, Fittings, and Pipe, Technical Paper No. 410, Crane Co., Joliet, IL, 1988. ).
- Also Apply in Turbulent Region
- Use Improved Method
Use Non-Newtonian to Newtonian Pipe Friction Ratio Multiplier

Modifying Losses for Fittings and Junctions Interface

The options listed above to modify losses at fittings and junctions can be found on the Laminar and Non-Newtonian Corrections panel in the Fluids Properties group of the Analysis Setup, as shown in Figure 1 below.

The Laminar and Non-Newtonian Corrections panel in Analysis Setup.

Figure 1: Options to modify fitting and junction losses on the Laminar and Non-Newtonian Corrections panel

These corrections are off by default and "Apply Corrections" must be selected to access them. Users can select which correction method is applied and can select which junction types the loss model will be applied to. Fathom Default can be selected at any time to reset the selected junction types.

Non-Newtonian to Newtonian Pipe Friction Ratio Multiplier

One approach to modeling losses associated with fittings and junction losses is to assume that the ratio of those losses in a Non-Newtonian and Newtonian fluid is equivalent to the ratio of pipe friction in a Non-Newtonian and Newtonian fluid. One can write:

This approach uses the pipe friction at the adjacent upstream pipe and the uncorrected loss factor in a Newtonian fluid to model the losses associated with the fitting or junction for a Non-Newtonian fluid.