Orifice plate flow meter
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Dear experts, why does a orifice plate flow meter require three measurement points? Are these three points needed solely for accurate measurement? Thank you
A orifice plate flow meter is a differential pressure flow measurement device with a high range ratio, consisting of a standard orifice plate in combination with a multi-parameter differential pressure transmitter (or separate differential pressure transmitter, temperature transmitter, and pressure transmitter). It can measure the flow rate of gases, steam, liquids, and natural gas, and is widely used in process control and measurement across industries such as petroleum, chemicals, metallurgy, power generation, heating, and water supply. Application range of orifice plate flow meters:
1. Nominal diameter: 15 mm ≤ DN ≤ 1200 mm
2. Nominal pressure: PN ≤ 40 MPa
3. Operating temperature: -50°C ≤ t ≤ 550°C
4. Range ratio: 1:10, 1:15
5. Accuracy: Class 0.5, Class 1
I. Overview of orifice plate flow meters
Throttle devices, also known as differential pressure flow meters, consist of a primary sensing element (throttle element) and secondary components (differential pressure transmitter and flow display instrument). They are widely used for measuring the flow rate of gases, steam, and liquids. These devices feature a simple structure, easy maintenance, stable performance, and reliability in operation.
The orifice plate throttle device uses standard throttle elements that can be manufactured directly in accordance with relevant standards: 1. National standard GB2624-81; 2. International standard ISO51673; 3. Standards issued by the Ministry of Chemical Industry, GJ516-87-HK06.
II. Working principle of orifice plate flow meters
When fluid filling a pipeline flows through the throttle device within it, a local constriction is created near the throttle element, resulting in an increase in flow velocity. This leads to a difference in static pressure on the upstream and downstream sides of the element. Given the known parameters, the relationship between differential pressure and flow rate can be derived using the principle of fluid continuity and Bernoulli’s equation, thereby allowing the flow rate to be determined. Its basic formulas are as follows:
c – Discharge coefficient, dimensionless
d – Diameter of the orifice or throat of the throttling element under operating conditions
D – Inner diameter of the upstream pipe under operating conditions
qm – Mass flow rate, Kg/s
qv – Volumetric flow rate, m³/s
ß – Diameter ratio d/D, dimensionless
Density of the fluid, Kg/m³
Coefficient of expandability, dimensionless
III. Structure of the orifice plate flow meter
Components of the throttling device:
Throttling elements: Standard orifice plates, standard nozzles, long-diameter nozzles, 1/4 circular orifice plates, double orifice plates, eccentric orifice plates, lunate orifice plates, conical inlet orifice plates, etc.
Pressure tapping devices: Annular chambers, pressure tapping flanges, clamping rings, pressure guide tubes, etc.
Connection flanges (**standard, various standards, and flanges from other design organizations), fasteners. Measurement tube: The installation requirements for orifice plate flow meters are that there should be 10D of straight pipe section in front and 5D behind the orifice plate. Therefore, when selecting an orifice plate flow meter, it is essential to choose one that is suitable for the specific conditions at the installation site. Application range of orifice plate flow meters: 1. Nominal diameter: 15 mm ≤ DN ≤ 1200 mm 2. Nominal pressure: PN ≤ 10 MPa 3. Operating temperature: –50°C ≤ t ≤ 550°C 4. Range ratio: 1:10, 1:15 5. Accuracy: Class 0.5, Class 1
1. Nominal diameter: 15 mm ≤ DN ≤ 1200 mm
2. Nominal pressure: PN ≤ 40 MPa
3. Operating temperature: -50°C ≤ t ≤ 550°C
4. Range ratio: 1:10, 1:15
5. Accuracy: Class 0.5, Class 1
I. Overview of orifice plate flow meters
Throttle devices, also known as differential pressure flow meters, consist of a primary sensing element (throttle element) and secondary components (differential pressure transmitter and flow display instrument). They are widely used for measuring the flow rate of gases, steam, and liquids. These devices feature a simple structure, easy maintenance, stable performance, and reliability in operation.
The orifice plate throttle device uses standard throttle elements that can be manufactured directly in accordance with relevant standards: 1. National standard GB2624-81; 2. International standard ISO51673; 3. Standards issued by the Ministry of Chemical Industry, GJ516-87-HK06.
II. Working principle of orifice plate flow meters
When fluid filling a pipeline flows through the throttle device within it, a local constriction is created near the throttle element, resulting in an increase in flow velocity. This leads to a difference in static pressure on the upstream and downstream sides of the element. Given the known parameters, the relationship between differential pressure and flow rate can be derived using the principle of fluid continuity and Bernoulli’s equation, thereby allowing the flow rate to be determined. Its basic formulas are as follows:
c – Discharge coefficient, dimensionless
d – Diameter of the orifice or throat of the throttling element under operating conditions
D – Inner diameter of the upstream pipe under operating conditions
qm – Mass flow rate, Kg/s
qv – Volumetric flow rate, m³/s
ß – Diameter ratio d/D, dimensionless
Density of the fluid, Kg/m³
Coefficient of expandability, dimensionless
III. Structure of the orifice plate flow meter
Components of the throttling device:
Throttling elements: Standard orifice plates, standard nozzles, long-diameter nozzles, 1/4 circular orifice plates, double orifice plates, eccentric orifice plates, lunate orifice plates, conical inlet orifice plates, etc.
Pressure tapping devices: Annular chambers, pressure tapping flanges, clamping rings, pressure guide tubes, etc.
Connection flanges (**standard, various standards, and flanges from other design organizations), fasteners. Measurement tube: The installation requirements for orifice plate flow meters are that there should be 10D of straight pipe section in front and 5D behind the orifice plate. Therefore, when selecting an orifice plate flow meter, it is essential to choose one that is suitable for the specific conditions at the installation site. Application range of orifice plate flow meters: 1. Nominal diameter: 15 mm ≤ DN ≤ 1200 mm 2. Nominal pressure: PN ≤ 10 MPa 3. Operating temperature: –50°C ≤ t ≤ 550°C 4. Range ratio: 1:10, 1:15 5. Accuracy: Class 0.5, Class 1
One measurement point is the orifice plate; one is for temperature, another for pressure. The latter two are used to provide temperature and pressure corrections, that is, to convert the data obtained from the orifice plate into a flow rate under standard conditions