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Mass flow rate is defined by the limit [3] [4] ˙ = =, i.e., the flow of mass m through a surface per unit time t. The overdot on the m is Newton's notation for a time derivative . Since mass is a scalar quantity, the mass flow rate (the time derivative of mass) is also a scalar quantity.
The mass flow rate is the mass of the fluid traveling past a fixed point per unit time. The mass flow meter does not measure the volume per unit time (e.g. cubic meters per second) passing through the device; it measures the mass per unit time (e.g. kilograms per second) flowing through the device. Volumetric flow rate is the mass flow rate ...
Mathematically, mass flux is defined as the limit =, where = = is the mass current (flow of mass m per unit time t) and A is the area through which the mass flows.. For mass flux as a vector j m, the surface integral of it over a surface S, followed by an integral over the time duration t 1 to t 2, gives the total amount of mass flowing through the surface in that time (t 2 − t 1): = ^.
Sonar flowmeters have the capacity of measuring the velocity of liquids or gases non-intrusively within the pipe and then leverage this velocity measurement into a flow rate by using the cross-sectional area of the pipe and the line pressure and temperature. The principle behind this flow measurement is the use of underwater acoustics.
The examples are here for gas flow, but the same meter types can be used on liquids as well, with similar turndown ratios. Note that meter manufacturers state their products' turndown ratios—a specific product may have a turndown ratio that varies from the list below. [citation needed] A thermal mass flow meter has a turndown ratio of 1000:1.
Many mass flow controllers (MFC) which combine a mass flow meter, electronics and a valve are based on this design. Furthermore, a thermal mass flow meter can be built by measuring temperature differential across a silicon-based MEMS chip. Both types measure fluid mass flow rate by means of the heat convected from a heated surface to the ...
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The mass is normally measured with a scale or balance; the volume may be measured directly (from the geometry of the object) or by the displacement of a fluid. To determine the density of a liquid or a gas, a hydrometer, a dasymeter or a Coriolis flow meter may be used, respectively.