Linear Flow Orifice Meter Designs for Pre-set Flow Rates
Introduction
The LFOM mimics the Sutro weir with a series of holes positioned vertically on a riser pipe. Due to the approximation, and rounding errors, it is currently assumed that several preset designs are more accurate than a program that accepts any plant flow rate. The pre-set designs will ensure the optimal orifice configuration. A common error is an orifice pattern of 1, 1, 0, 2, 1. This occurs because in the second row the number of holes requested was a fractional amount and then in the subsequent row the program calls for 1 and a fractional hole which rounds to two holes. Installation of a LFOM for a higher flow rate than necessary won't degrade the performance and it is a way to ensure quality in the design. Criteria by which the designs are evaluated include: maximum error, number of rows, and the presense of the rounding error.
Designs for Pre-Set Flow Rates
Flow Rate (L/min) | Max Error % | Pi_LfomOrifice(the number of rows) | LFOM Design | Notes |
---|---|---|---|---|
100 | 0.398 | 20 |
| |
200 | 0.14 | 20 |
| |
300 | 0.195 | 20 |
| |
400 | 0.109 | 20 | This design has the lowest area but the construction is difficult because there are excessive orifices to drill | |
400 | 0.293 | 10 | This has a higher error but is easier to construct | |
500 | 0.097 | 20 | This design has the lowest area but the construction is difficult because there are excessive orifices to drill | |
500 | 0.315 | 10 | This has a higher error but is easier to construct | |
700 | 0.046 | 20 | This design has the lowest area but the construction is difficult because there are excessive orifices to drill | |
700 | 0.325 | 10 | This has a higher error but is easier to construct | |
1000 | 0.049 | 20 | This design has the lowest area but the construction is difficult because there are excessive orifices to drill | |
1000 | 0.125 | 10 | This has a higher error but is easier to construct |
The Mathcad Entrance Tank Code was run for seven flow rates, three Pi_LfomOrifice values, and two initial values for the H.flowloc array. The excel spreadsheet with the original data is available here. The Entrance Tank Code is available through the SourceForge repository, a storage system. To access the code follow these folders: design repository -> Automated Design -> Design -> EntranceTank.