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Important Thermal Mass Flow Technology Terminology

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Mass Flow vs. Volumetric Flow

To avoid confusion when discussing flow or flow rate, it is important that the correct terms are used and that the concepts of flow rate, volume flow rate and mass flow rate are clearly understood. In general Flow Rate can be understood as the actual velocity (V) of the moving fluid, whereas Volumetric Flow Rate (Q) is expressed in units such as cubic feet, actual cubic feet, cubic meters, liters, cubic centimeters, etc., flowing through a cross sectional area (A) such as a pipe or duct. The formula Q = V x A represents Volumetric Flow Rate. Conversely Mass Flow Rate (M) shall be defined as the quantity of fluid delivered in pounds or grams per unit time. The formula M = ρ x A x V represents Mass Flow Rate. Density (ρ) has a great effect on compressible fluids such as gasses, whereas it has a minor effect on liquids.

Airflow Measurement Methods

Most flow meters are volumetric and infer mass flow through calculations derived by taking other physical process measurements such as absolute pressure, differential pressure, temperature and viscosity readings. Because of this method of obtaining a mass flow output they are known as inferential mass flow meters as opposed to direct mass flow measurement.

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