Problem Statement

PRODUCT: AFT Arrow

MODEL FILE: AroVerify5.ARO

REFERENCE: Crane Co., Flow of Fluids Through Valves, Fittings, and Pipe, Technical Paper No. 410, Crane Co., Joliet, IL, 1988, Page 4-11, example 4-18

GAS: Natural Gas (mole fractions: 75% methane, 21% ethane, and 4% propane)

ASSUMPTIONS: Isothermal flow at 40 degrees F

RESULTS:

†        Crane’s calculation uses the “Simplified Compressible Flow Formula”

*        Crane uses the actual Weymouth and Panhandle equations. AFT Arrow does have these equations, but instead solves the governing mass and momentum equations over pipe sections. The AFT Arrow Weymouth and Panhandle solutions above were obtained using the Weymouth and Panhandle friction factor correlation options in AFT Arrow rather than the standard Darcy-Weisbach friction factor (as used in the first case above).

DISCUSSION:

The mixture properties for this example offer an opportunity to use the Chempak mixture capabilities. The problem statement does not say whether the fractions are on a mass or mole basis, but it does say in Crane that the mixture molecular weight is 20.1. This is consistent with mole fraction. AFT Arrow’s output indicates the molecular weight of the mixture is 20.11.

As noted above (*), AFT Arrow has optional friction factor models for Weymouth and Panhandle (see Crane, page 1-8 or AFT Arrow documentation). These were used for the second and third cases above. However, regardless of what friction factor model is used, AFT Arrow differs from any of the three methods above in that it directly solves the governing equations and it does so over pipe segments. In this model, the pipe was broken into 100 segments.

Since it can be easily demonstrated that AFT Arrow’s solution satisfies the mass and momentum equations for this pipe, and the solution differs from the Crane solutions, the Crane solutions do not offer a mass and/or momentum balance.

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