Flow rate or rate of flow is the quantity of fluid passing through any section(pipe line or open channel) per unit time.
It can be expressed in terms of
Volume Flow rate
It is the volume of any fluid passing through any section per unit time.
It is denoted by Q. It is equal to the magnitude of the mean velocity multiplied by the flow area at right angles to the direction of mean velocity.
where A is the flow area at right angles to the direction of mean velocity and v is the mean velocity.
The units of volume flow rate are
- m3/sec in SI system which is also known as Cumec.
- Another unit is ft3/sec which is also known as Cusec.
Weight flow rate
It is defined as the weight of any Fluid passing through any section per unit time.
It is denoted by G.
where W is the weight of fluid . Its unit is N/sec or kN/sec.
We know that
Specific weight = Weight/ unit volume
From this we conclude
So the above equation will be
G=(Spec. weight* unit volume)/Time
As we know
Volume/time =volume flow rate
so the equation becomes.
From this we conclude that weight flow rate may be computed by multiplying the volume flow rate and specific weight of fluid.
Mass flow rate
It is defined as the mass of fluid passing through and section in a unit time.
It is denoted by Mf.
Its unit will be kg/sec or g/sec.
We know that
density=mass /unit volume.
From this we can see
Now substitute the value of mass in Mf =M/t.
Mf =(density *volume)/time
Again we see
Mf =density * volume flow rate
From this we conclude that mass flow rate is the product of volume flow rate and density of that fluid.