Volumetric flow rate and Mass flow rate
Volumetric flow and mass flow,two important terms related to industrial flow measurement .
Volumetric flow rate
It is the rate of volume of a fluid that passes through a stream per unit time.It is expressed in m³/Hr ,cm³/Hr, m³/s etc.In this type of flow measurement only the volume of fluid is considered and not the mass or density of the flowing fluid .
Volumetric flow rate Q =V . A
V=velocity
A = Area of cross section of the flow path .
Mass flow rate
It is the rate of mass of a fluid that passes through a stream per unit time.It is expressed in kg/s,kg/hr, tonnes/Hr .It considers the volume and density of the flowing fluid . That is this flow rate corresponds to the rate of Passage of mass .
Mass flow rate = Volumetric flow rate × Density
Q(m ) =Q(v) ×density of the liquid .
Volumetric flow measurement and mass flow measurement
volumetric flow measuring instruments senses only the velociy of fluid passage .The sensor output is propotional to the velocity of fluid hence it is proportional to the volumetric flow as
Q(v ) = V.A
.And it doesn’t calculate the mass flow directly .In other words it doesn’t respond to the density changes .Mass flow can be measured by this type of flowmeters provided density of the fluid is invariant .Mass flow can be calculated as,
Mass flow = volumetric flow × Density
Examples for volumetric flow measuring instruments
Magnetic flowmeter,positive displacement flowmeter
Mass flow Instruments measure flow rate in terms of mass .Or it senses the rate of flow of the mass directly. The. sensor output is directly proportional to the mass of the flowing fluid .
Ex:coriolis flowmeter
Why we need mass flow measurement???
Suppose we have to monitor a process,or control a process which includes fluids with its density depends on pressure and temperature .And also the process is more mass dependent than volume . So we need mass flow measurement in such situations .For example in process applications which includes gases which shows density variations with temperature and pressure .In process involving gases these temperature and pressure variations is common . So inorder to control such process which are more mass dependent,it is better to employ mass flow meter there .
Also in custody transfer applications mass flowmeter is more compatible than volumetric type flow meter .
