# The mass flow rate calculation - Accuracy and Cost

"Why Mass Flow?"

A mass flow meter, also known as inertial flow meter and coriolis flow meter, is a device that measures how much liquid is flowing through a tube by calculating the amount of mass flow through the device in a set time frame. Therefore, mass flow rate is the movement of mass per time. Time being pound per second in US customary units. Its unit is calculated by dividing mass by time.

Mass flow rate can be calculated from the density of the liquid or gas, its velocity, and the cross sectional area of flow.

{\dot m} = {\rho \cdot V\cdot A}

Where:

{\dot m} = mass flow rate

ρ = density

V = velocity

A = flow area

The mass flow rate can also be calculated by multiplying the volume flow rate by the density.

{\dot m} = {\rho \cdot Q}

Where:

ρ = density

Q = volume flow rate

## Accuracy and Cost Effectiveness

Direct mass flow measurement is more accurate and cost effective than volumetric flow rate. Volumetric flow metering is proportional to mass flow rate only if the density of the fluids is constant. If the fluid contains bubbles, the volume flow rate is not an accurate measure.

In fluid dynamics, the volumetric flow rate is the volume of fluid passing through a given volume in a given time frame. Given an area (A) and a fluid flowing through it with uniform velocity (v) the flux is:

Q = A \cdot v \cdot \cos \theta.

If the velocity of the fluid through the area is non-planar, the rate of fluid flow can be calculated by means of a surface integral, but is not completely accurate. In a mass flow meter the fluid is contained in a smooth tube, with no moving parts that would need to be cleaned and maintained, and that would impede the flow.

## Repeatable Measurements

Mass flow meters provide immunity to process changes and supply very repeatable measurements. In Gases, density is highly variable. This makes volumetric gas flow very sensitive to changes in pressure and temperature.

## No Extra Equipment Needed

Direct mass flow meters do not need any pressure or temperature compensation equipment or flow computers.

## Mass Flow is the Basis for Many Industrial Processes

Over 80% of all industrial processes involving chemical reactions, combustion, respiration, and HVAC are based on mass flow, not volumetric flow. Volumetric flow rate is sometimes measured in "standard cubic centimeters per minute". The term "standard" indicates that the given flow rate assumes a standard temperature and pressure.

This article donated by Sierra Instruments, Inc. a manufacturer of mass flow meters, mass flow controllers, and partial flow sampling systems in the world in terms of quality, delivery, price, innovation, and customer support.