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 |
This design has the lowest error but the construction is difficult because there are excessive orifices to drill |
|
100 |
0.545 |
10 |
This has a higher error but is easier to construct |
|
200 |
0.14 |
20 |
This design has the lowest error but the construction is difficult because there are excessive orifices to drill |
|
200 |
0.718 |
10 |
This has a higher error but is easier to construct |
|
300 |
0.195 |
20 |
This design has the lowest error but the construction is difficult because there are excessive orifices to drill |
|
300 |
0.684 |
10 |
This has a higher error but is easier to construct |
|
400 |
0.109 |
20 |
This design has the lowest error 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 error 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 error 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 error 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.