An orifice plate meter is the most common flow measurement device. A constricting orifice is placed between two flanges, as shown in Figure M15-4. As the fluid “speeds up” through the orifice, the pressure drops. The volumetric flow rate is related to the pressure drop across the orifice. As shown in the motivating example, a DP cell is typically used to measure the pressure drop; here, we use a manometer for illustrative purposes.
The equation for flow through an orifice is (McCabe and Smith, 1976)
where vo is the average velocity through the orifice;
β is the ratio of orifice to pipe ...