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What is a Mass Flow Meter?

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  • Written By: Paul Scott
  • Edited By: R. Halprin
  • Last Modified Date: 18 November 2016
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A mass flow meter is a device used to measure the flow of a fluid or gas passing through a tube in a fixed time. Mass flow in this sense refers to the weight and not the volume of the substance. Mass flow measurement is used in a variety of scientific and industry applications and is achieved with one of two common types of mass flow meters: the inertial or coriolis meter and the thermal mass flow meter.

Mass flow, not be confused with volumetric flow, is a measurement of fluid or gas mass past a fixed point in a specific time frame. The standard unit of measure for mass flow is pounds per second or kilograms per second rather than gallons or liters per second. These measurements are made with one of two different types of mass flow meter. The first makes use of a natural phenomenon known as the coriolis effect to measure mass flow. The second type makes use of the principles of thermal transfer.

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The coriolis or inertial mass flow meter utilizes fluid flowing through an arrangement of tubes which are subjected to an induced semi-circular vibratory force. The resultant coriolis effect leads to the oscillation in different parts of the tube arrangement shifting out of phase. The extent of this phase shift is directly proportional to the mass flow of the fluid in the tube. Sensors placed on the tube measure the amplitude, frequency, and phase shift of these oscillations. The mass flow of the fluid is then extrapolated from the sensor readings.

The second common type of mass flow meter, the thermal variant, uses the principle of heat transfer under controlled conditions to calculate flow rates. Gas or fluid is passed through a tube where it is exposed to a heat source. As the fluid molecules pass the heat source, they absorb thermal energy, thereby cooling the source. The larger the mass of fluid passing the heat source, the greater the cooling effect.

The rate at which the molecular energy transfer takes place is a known constant, and the extent of the cooling is a measurable variable. These two factors are used to calculate the number of molecules that have passed over the heat source in a given period. From this result, the exact mass flow is calculated. A detailed thermal profile of the fluid and its flow characteristics can also be learned from the thermal transfer results.

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