Is Flow Rate Constant: Why, How and Problems


In the article we will investigate the topic of “Is flow rate constant “with a focus of how it is worked in the piping system. In below we also discussing the related facts with the Is flow rate constant.”

Yes,flow rate is constant only under some fixed standard condition. In an open system the liquid substance or gas moving in a motion of the system from one place to another place by applied net force parallel axis to the pipe or the channel at standard temperature and pressure.

In an open system through a medium in a certain time period at some standard condition the liquid substances go through in a motion by unbalanced force, this is called the flow rate.

is flow rate constant
Flow rate
Image Credit – Wikimedia Commons

The flow rate can be classified in two categories. They are given below,

Mass flow rate

Volumetric flow rate

Mass flow rate:

From the law of conversion of mass we get a clear concept about the mass flow rate. The conversion of mass flow rates states that, the amount of the mass of a particular object cannot not be created or destroyed. The mass of a body is measured by lever balance.

Mass flow rate can be defined as the, an object which is containing mass is constant at standard temperature and pressure when force is applied to the pipe or the channel externally.

The formula for the mass flow rate is,

Mass flow rate = (Density of the liquid substance)* (Velocity of the liquid substance)* (Cross sectional area of the system)

Mathematically it can be expressed as,

ṁ= ρVA

Where,

ρ = Density of the liquid substance

V = Velocity of the liquid substance

A = Cross sectional area

When we go through  the above equation the mass flow rate can be easily recognize that, the mass flow rate depend on the density and velocity of the liquid substance, area and it is has direct relation with these three parameters at fixed temperature and pressure.

The unit of the mass flow rate is kilogram per second (kg/s).

Read more about Mass Flow Rate:Is Important relations and FAQs

Volumetric flow rate
Mass flow rate
Image Credit – Wikipedia

Volumetric flow rate:

With the help of the volumetric flow rate we could understand how much volume is inside of the pipe in the piping system.

The volumetric flow rate can be defined as the for an object the inside volume is moving in a particular space from one area to another by the external applied force.

The formula for the volumetric flow rate is,

Volumetric flow rate = flow velocity of the liquid substance * cross section area of the open system

Mathematically volumetric flow rate can be written as,

Q = vA

Where,

Q = Volumetric flow rate of the liquid substance

V = Velocity of the liquid substance

A = Cross sectional area of the open system

When we go through the above equation we easily can recognize the relation for the volumetric flow rate is, the velocity and the cross section area are directly proportional to each other. The unit of the volumetric flow rate is cubic meter per second.

Volumetric flow rate
Image credit – Wikipedia

Read more about Volumetric flow meter:It’s All Important Concept

Why is flow rate constant?

If we go through of the equation of continuity the flow rate of a pipe or a channel is equal to the each and every point of the piping system. In other word we can say the rate of inflow and outflow of the pipe or channel is equal.

The flow rate is constant only for the incompressible fluids.The flow rate can be regulated by the output pressure of the pump.

The pump is a device by which the fluid is pumped in the piping system. The output pressure control by the pump with which the back pressure regulator is attached.

How is flow rate constant?

The flow rate is a very important factor of an industrial area. By the help of this parameter we could easily understand the inside condition of a pipe or a channel. This parameter reduces the cost of the process and also helps to maintain the whole system.

The flow rate constant when the density of the fluid is unchanged.In the piping system the liquid substance flow through the parallel axis of the pipe or channel at the certain crosses sectional area, in this time laminar flow can be observed.

Is volumetric flow rate constant?

The volumetric flow rate used in the engineering field in the piping system. The main purpose of the volumetric flow rate is to measure the quantity of volume, in the pipe or channel for the liquid substance. The mass flow rate used to measure the molecules in the flowing fluid.

The volumetric rate for a gas or a fluid is remains constant only when the value of volumetric flow rate is measure under unchanged conditions which is mainly imaginary.

The volumetric flow rate only unchanged in the constant pressure and temperature for the ideal gases and ideal liquid.

How is volumetric flow rate constant?

Volumetric flow rate can be defined as the, in a 3 – dimensional cross sectional area the present gas or liquid substance is moving at a fixed temperature and pressure in a given time period.

When the liquid substance flow through a pipe or a channel in the piping system the volume of the liquid substance is close to incompressible at fixed time.

The dimension of the volumetric flow rate is,L3T-1.

Problems on are flow rate constant and how are flow rate constant

Problem: In a water tank the water is pumped in the top of roof. The water tank is situated in the 7th floor of the house. The water is flow by the pipeline. The water is travelled by the pipes of the pipeline is 10 ft/sec.The width of the pipe is 36 inch. Now calculate the amount of flow rate of the water in the pipe.

Solution:

Given data are, v = 10 ft/sec

We know the formula of the area of the pipe is,

A = π x r2 = = 0.785 x D x D = 0.785 x 3 x 3 = 7.06 ft2

Now the volumetric flow rate formula is,

Q = Velocity of the water * Cross sectional area of the pipe

Q = 70.6 ft3/sec = (70.6ft3 x 60sec x 7.48gal)/(sec x 1min x 1ft3) = 31,685 gpm

The flow rate of the water pipe is,31,685 gpm.

Problem: In a XYZ named industry has four oil tanks. All the oil tanks are   attached with the oil supplier tank. The oil has the density is 489 kg per cubic meters and velocity is 10.9 meter per second. The oil tank’s pipe diameter is about 6 cm. Determine the value of volumetric flow rate.

Solution:

Given data are, d = 6 cm, v = 10.9 m/s

Radius = r = d/2 = 6/2 = 3 cm

A = π x r2 =π x 32 = 28.26 cm2 x 1m2/100 cm2 = 0.2826 m2

Q = A x v = 0.2826 x 10.9 = 3.080 cubic meter per second.

So, the volumetric flow rate of the pipe is,3.08 cubic per meter.

Frequent Asked Questions:

Question: Explain the equation of the continuity.

Solution: When the liquid substance flow through a pipe the tendency of the liquid is to maintain the volume. In this condition the liquid is incompressible.

An incompressible liquid substance which is flow in a certain amount of cross sectional area through a channel or a pipe at a fixed time period then quantity of the liquid substance which is passes in the piping system is same and each section of the pipe or the channel. This is the Equation of continuity.

Mathematically it can be expressed as,

Q1 = Q2 = Q3 =Q4 =…………….

a1v1 = a2v2 = a3v3 = a4v4 = …………..

Problem: In a house a water tank is situated in the roof of the house. The water is supply in the whole house through the pipe lines which are attached with the water tank. The water flows through the pipe 0.9 meters per second. Now from where the flow is emitted that is the one third of the sourcing pipe. Determine the amount of speed at which the water is flow through the pipeline.

Solution: Given data, v1 = 0.90 meters per second

We know the equation of continuity is,

A1v1 = A2v2

A2 = 1/3A1

A2 = 1/3A1v2

v2 = 3 x v1= 3 x 0.90 meter/second = 2.7 meter per second

The amount of speed at which the water is flow through the pipe is, 2.7 meter per second.

Question: What is the alternative formula of the volumetric flow rate?

Solution: The another way to write the volumetric flow rate is,

Volumetric flow rate =Q = V/t ……eqn(1)

In a pipe from where the fluid is flowing there volumetric flow can be written as,

V = Ad …..eqn(2)

Where, V = Volume of the liquid in the pipe

A = Cross sectional area of the flowing fluid in the pipe

d = Width of the pipe

Now we could write volumetric rate for the cylindrical pipe is,

Q = V/t = Ad/t

The term d/t is written for express the fluid is flowing in a fixed time in fixed diameter of the pipe.

Comparing the eqn (1) and eqn (2) we get,

Q = Av [v = d/t]

Where, A = Cross sectional area of the pipe in the piping system.

We also know that, the formula for the area,

A = π x r2

So in the above equation we get three parameters.

1. If area and density if given then we easily can calculated the value of velocity.

2. In another way if density and velocity given then we also can calculated the value of area.

3. And finally velocity and area is given then the value of density of the liquid we can calculate.

Question: What is the incompressible fluid?

Solution: In all liquid substance the incompressible flow is visible.

Incompressible flow: When a liquid substance is flow in a certain amount of a cross sectional area at a given time period at fixed temperature and pressure, if that time the velocity and the density of the flied substance s remain unchanged is called incompressible flow.

What is incompressible liquid?

Solution: Water flow in a pipe or a channel in the piping system the incompressible liquid is present.

Incompressible liquid: When the fluid is moving in the piping system through a pipe or a channel at a given area in fixed time period, that time if the density and the velocity is remain unchanged is called the liquid as incompressible liquid.

Indrani Banerjee

Hi..I am Indrani Banerjee. I completed my bachelor's degree in mechanical engineering. I am an enthusiastic person and I am a person who is positive about every aspect of life. I like to read Books and listen to music. Let's connect through LinkedIn-https://www.linkedin.com/in/indrani-banerjee-2487b4214

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