Flow Rate | Volume flow rate | Weight flow rate | Mass flow rate

Thursday, March 10, 2011 16:39
Posted in category Fluid Mechanics 1
Views: 10,326 views


Flow Rate

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

  1. Volume
  2. Weight
  3. Mass

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.

Q=A.v

where A is the flow area at right angles to the direction of mean velocity and v is the mean velocity.

Units

The units of volume flow rate are

  1. m3/sec in SI system which is also known as Cumec.
  2. 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.

G=W/t

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

W=Spec.weight*unit volume.

So the above equation will be

G=(Spec. weight* unit volume)/Time

As we know

Volume/time =volume flow rate

so the equation becomes.

G=spec. weight*Q

Conclusion

 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.

Mf =M/t

Its unit will be kg/sec or g/sec.

We know that

density=mass /unit volume.

From this we can see

mass=density*volume.

Now substitute the value of mass in Mf =M/t.

We get

Mf =(density *volume)/time

Again we see

Volume/time =Q

So

Mf =density * volume flow rate

Conclusion

From this we conclude that mass flow rate is the product of volume flow rate and density of that fluid.

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