Measuring flow rate with a throttle orifice plate – does the orifice plate itself alter the originally designed flow rate?

A throttle orifice plate is a commonly used device for measuring fluid flow rate; it works by utilizing an orifice plate installed in the middle of the pipe to induce changes in the fluid velocity, thereby enabling the measurement of flow rate. The design of orifice plates should take into account the properties of the fluid flowing in the pipeline, in order to accurately calculate the relationship between flow velocity and pressure drop and thus achieve the desired flow measurement results. If an inappropriate orvert plate is used or if it is not installed properly, the orvert plate itself may interfere with the flow rate, affecting the accuracy of the flow rate as intended in the original design. Therefore, it is very important to correctly select and install the appropriate orifice plate to ensure that the measured flow data are accurate and reliable. .

The flow velocity here at the orifice plate must be much higher than in other parts of the pipe, right? Is it because the cross-sectional area at the orifice plate is very small?

Changing a straight-through type flow meter to an orifice plate flow meter does not alter the original flow rate; only the pressure loss increases. The selection of throttling flow meters is based on calculations regarding the groove angle, as well as the size and number of orifices. If there is no accurate calculation and an inappropriate orifice plate is selected, it indeed can affect the flow rate specified in the original design. However, this only happens when the selection is incorrect; under normal circumstances, it does not alter the original design flow rate. What it does is increase the pressure loss in the pipeline, resulting in higher pressure losses. Just my personal opinion; discussions are welcome

The orifice plate will change the flow velocity (flow rate), but not the design flow rate. Orifice plates cause pressure loss in the pipeline; with all other pipeline conditions remaining unchanged, the flow rate in the pipeline decreases upon the installation of an orifice plate ； The design flow rate is a value determined after fully taking into account various pipeline resistances (including those caused by orifice plates, valves, elbows, pipe walls, and other such factors). .

A orifice plate only changes the flow velocity, not the flow rate. Based on this principle, when the valve is closed, the flow velocity increases but the flow rate remains unchanged; does this mean that valves cannot regulate the flow rate?

It will change the flow rate; otherwise, there would be no need for flow-limiting orifice plates. But this is on the condition that all other factors remain unchanged. In an ideal pipeline, the introduction of an orifice plate will result in a reduction in both the flow velocity and the flow rate, which in turn means that there will be a certain pressure loss. However, in practice, when the flow rate is restricted by an orifice plate, the process relies on adjusting valves, the power of pumps, and so on to achieve the desired flow rate.