Flow measurement is the process of determining the amount of material flowing through a system, usually a pipe or duct, using flowmeters such as orifice, turbine, venturi, ultrasonic, and electromagnetic. The type of flowmeter used depends on the properties of the substance being measured. Correction or compensation factors can be used to improve calculated flow measurements.
Flow measurement is the practice of determining the amount of material flowing through a specific system, usually a pipe or duct. This is typically achieved with an inline flowmeter. Flow measurement is used extensively in applications ranging from chemical plants to commercial air conditioning systems. The type of flowmeter required for any particular application will depend on the properties of the substance being measured.
The field of flow measurement is incredibly diverse and far-reaching, and is one of the central themes of studies of transport phenomena. Measuring the flow rate of a substance can be as simple as measuring the level change of a process vessel or as complicated as measuring the induced voltage across a conductive fluid moving in a magnetic field. While flow measurement usually refers to material in pipes or ducts, it can also refer to the flow of solids or the flow of material through systems such as traffic networks or riverbeds.
Direct measurement of the flow rate of a gas or liquid requires the use of a flowmeter. There are many types of flowmeters, including orifice meters, turbine meters, venturi meters, ultrasonic meters, and electromagnetic flowmeters, just to name a few. In most chemical process industries, orifice meters are the most popular type of flowmeter due to their simplicity and low cost.
Orifice meters and venturi meters work according to Bernoulli’s principle, or more specifically, the relationship between the flow rate of the material and the pressure drop that the material experiences across the meter. Turbine meters correlate the number of rotations that an internal turbine performs in a given period of time to the flow of fluid passing over the blades. Electromagnetic flowmeters use Faraday’s law to correlate fluid velocity with the voltage induced on a magnetic field in the fluid.
All of these flow measurement methods may be subject to limitations, depending on the nature of the fluid being measured. For example, an electromagnetic flowmeter will only work on an electrically conductive fluid. Gauges with moving parts, such as turbine gauges, are not recommended for abrasive or corrosive materials. Unusual systems may require unique or hybrid flowmeters and calculations.
The calculated flow measurements can be improved with the use of correction or compensation factors. These factors are often used to compensate for temperatures, pressures, and molecular weights that differ significantly from the fluid flow design basis. Compensation factors are often applied in distributed control system (DCS) calculations in a chemical process environment.
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