Before deciding which flow instrument is right for your application it is vital you understand the difference between mass flow and volumetric flow. We will discuss both concepts and use cases for each measurement.
Volumetric flow rate, also called the actual flow rate, is a measure of the volume of fluid that flows through the instrument per unit time. Common units of measure include LPM (liters per minute) and CCM (cubic centimeters per minute).
In the gas mass flow industry, mass flow rates are an expression of volumetric flow rates corrected to standard conditions. Calculating mass flow requires a reference to standard temperature and pressure conditions, such as 25 °C and 14.696 PSIA or 0°C and 760 torr. Common units of measure include SLPM (standard liters per minute) and SCCM (standard cubic centimeters per minute).
Your application’s objectives will determine whether you should use volumetric flow or mass flow. Your first question should be if you want to measure or control a set volume or the number of molecules of process fluid.
When to use mass flow
The benefit of mass flow instruments is that they can precisely measure and control the flow of gas molecules into or out of a process. At any selected mass flow rate, the number of molecules flowing through the point of measurement is constant regardless of temperature or pressure conditions. Mass flow rates could also be considered molar flow rates.
Volumetric flow instruments are generally less expensive than mass flow devices and can be a great option if you need to measure or control a specific actual flow of gas without regard to the density of the process gas.
Industrial hygiene and environmental air monitoring are two applications that utilize volumetric flow. The objective in each is to quantify the number of particles within a specific volume of air under ambient conditions.
Should you like to know more about Mass & Volumetric Flow, please contact our Sales Team. We will be happy to find you the right instrument to fit your application requirements. You can also see the Mass Flow Meter ranges we have available on our website.
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