Throttling device calculation
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There is an orifice plate flow meter being maintained on site; the fluid is demineralized water, the temperature is 20 degrees, the diameter is DN80, the maximum flow rate is 5 T, the normal flow rate is 3 T, and the operating gauge pressure is 700 kPa. Please help calculate what range should be selected for the accompanying differential pressure transmitter.
This post was last edited by hfrs on 2019-2-27 at 11:56. Based on a DN80 SCH40 pipe diameter, with a full-scale flow rate of 5 T/h, a differential pressure of 10 kPa, and b=0.328； 6kpa, b=0.371. It must not exceed 10 kPa; 6 kPa can be chosen. If the full-scale range is greater than 5 T/h, a larger value can be chosen. For example, select 6 T/h for the full-scale range and 10 kPa for the differential pressure range, with b=0.358.
There is a functional relationship among the orifice plate aperture, differential pressure value, and measurement range. 1. If the orifice plate is reselected, it can be recalculated. Under such operating conditions, a differential pressure value of 6 to 16 is acceptable. 2. If it is an existing orifice plate, reset the differential pressure value. Since the aperture has already been determined, back-calculation is required. There is a corresponding relationship between the range and the differential pressure value. Based on your description, it should fall under the second case, so reverse calculation is required. Set a reasonable range and differential pressure value, while also taking into account pressure loss and the relationship between the range ratios.
I used calculation software to determine that for DN80, assuming the density is that of water, the maximum load is 5 tons while the typical value is 3 tons. The optimal range for differential pressure is 0–1.6 kPa, with 580 Pa being the commonly used value. Did I make a calculation mistake, or is there an issue with the data selection? ?
1. As described by the poster, the range and differential pressure should be selected under the existing orifice plate. 2. Even when calculated using the new table, an orifice plate with a differential pressure of 1.6 KPA is certainly not suitable; any slight fluctuation causes the flow rate to vary greatly. The aperture ratio does not necessarily have to be around 0.5. It is recommended to choose a differential pressure of at least 6 for use with orifice plates.
I’ve learned it, I’ve learned it. There’s another question: many of the orifice plates we produce come out of the factory equipped with EJA differential pressure transmitters, meaning that the differential pressure values are all below 1 KPA. In such cases, can there still be significant fluctuations? I haven’t really seen any customers report such issues.
1. Generally, orifice plates are equipped with differential pressure transmitters, as the design recommends a differential pressure range of 6–60 kPa. Micro-differential pressure versions do exist as well; they are generally used for gas and steam at large diameters, such as in Venturi devices. Because the differential pressure value calculated for this type of table is very small. If you’re interested, you can look for similar books or consult the specification sheets of orifice plates from large design institutes; a differential pressure value of 10 to 40 is generally chosen.