Verification Case 47
PRODUCT: AFT Fathom
TITLE: FthVerify47.fth
REFERENCE: James John, William Haberman, Introduction to Fluid Mechanics, 2nd Ed., 1980, Prentice-Hall, Page 178-179, Example 6.5
FLUID: Water at 20 deg. C (incorrectly stated as 25 deg. C)
ASSUMPTIONS: Use the K factors provided
RESULTS:
| Parameter | John & Haberman | AFT Fathom |
| Flow rate through pipe line (liter/sec) | 13.55* | 19.33 |
| Flow rate through pipe line (liter/sec) | 19.17** | 19.33 |
(*) Calculation error in text explained below
(**) Corrected flow rate calculation as explained below
DISCUSSION:
The K factors used by John & Haberman differ from Crane's and those in the AFT Fathom library. The model therefore uses the same K factors as used in the problem solution. The pipe lengths between fittings were not specified, and do not affect the results. The AFT Fathom assumed pipe lengths, with the total pipe length adding up to 250 m.
The problem statement is for water at 25 deg. C, but when the Reynolds number is calculated on page 179 the kinematic viscosity is that at 20 deg. C. Therefore the AFT Fathom model uses 20 deg. C water.
The results disagree significantly. A review of John & Haberman page 179 shows a calculation error. The text says the following:
which is incorrect. Solving the above equation by a hand calculator shows that
If the incorrect velocity is used the final flow rate in John & Haberman is significantly different that Fathom.
When using the corrected velocity the final flow rate in John & Haberman is much closer to the Fathom result.
Using the correct velocity results in the correct flow rate, which agrees closely with AFT Fathom.
