Mechanical Engineering - Hydraulics and Fluid Mechanics - Discussion


The pressure of the liquid flowing through the divergent portion of a venturimeter

[A]. remains constant
[B]. increases
[C]. decreases
[D]. depends upon mass of liquid

Answer: Option C


No answer description available for this question.

Prasad said: (Jan 18, 2014)  
Part of the kinetic energy at the throat will convert back to pressure energy, and so pressure should increase in the divergent (or Enlarging) portion.

Waseem Iqbal said: (Apr 22, 2014)  
Yes @Prasad according to Bernoulli equation.

Summation of total energy of fluid at a point remains same.

So potential energy terms cancel out.

And according to continuity equation we know velocity will decrease with increase in area in diverging portion so as the kinetic energy increase and according to bernoulli eq pressure must decrease otherwise law of conservation of energy will be violent.

Rahul said: (Nov 9, 2014)  

If the velocity of flow decreases then kinetic energy should also decrease and hence pressure will increase according to Bernoulli equation.

Ravi said: (May 21, 2015)  
In order to maintain the total energy to be constant according to Bernoulli pressure should increase.

Kaushal Kishore said: (Aug 8, 2015)  
From continuity equation: Area in divergent section increases correspond to the decrease in velocity.

And by Bernoulli's theorem, if kinematic head decreases correspond to the increase in pressure head.

Balasaheb said: (Aug 26, 2015)  
Pressure should be always increases in divergent section.

Shubham Gondane said: (Feb 11, 2016)  
According to Bernoulli's theorem pressure must increases at divergent section.

Soumya said: (May 3, 2016)  
Pressure should increase through the divergent portion.

Knowledge said: (Jun 30, 2016)  
Pressure must increases at divergent section.

Akki said: (Aug 31, 2016)  
In divergent, pressure should be increased.

Vaishali said: (Sep 20, 2016)  
By continuity equation, the area is inversely proportional to velocity so with the increase in area in the diverging section velocity decreases and therefore by Bernoulli's equation we can conclude that the pressure must increase in this region.

Sagar Ladkat said: (Nov 14, 2016)  
Pressure must increase in the divergent portion of venturimeter as the velocity of flow decrease.

Sagar Dudhal said: (Dec 23, 2016)  
Yes, as area increases velocity decreases and pressure should increase.

Sidhant Singh said: (Feb 23, 2017)  
Why should decrease?

We know that area increase velocity decrease and pressure increase.

Abin said: (Feb 28, 2017)  
Pressure = force / area.

Arun said: (Mar 23, 2017)  
Through convergent section : kinetic energy will increase and presser energy will decrease.

Through Divergent section : kinetic energy will decrease and pressure energy will increase.

Pushpendra said: (Jun 21, 2017)  
Yes, the answer should be B according to Bernoulli's equation.

Akshay Patil said: (Jul 14, 2017)  
The Correct answer is C decrease because P=F/A so as area increase pressure decrease.

Atul Awchar said: (Aug 5, 2017)  
The velocity reaches its maximum value and pressure reaches its minimum value at the throat. Subsequently, a decrease in the velocity and an increase in the pressure takes place in course of flow through the divergent part.

Himanshu Garg said: (Sep 15, 2017)  
What's the right answer?

Vipul Kumar said: (Oct 17, 2017)  
Actually, in case of compressible fluid combining the BERNOULLI equation and CONTINUITY equation we get the resulting equation dA/A=-dV/V (1-Ma*2). In the divergent section of the venturi meter, the fluid velocity reaches beyond sonic velocity and attains a supersonic velocity and in such case with the increase in area pressure decreases and velocity increases. Since we generally consider liquid to be incompressible so we do not take into account this Ma factor in liquid flow but in case we consider liquid to be compressible we had to understand this peculiar behavior. SO THE GIVEN ANSWER C IS CORRECT.

Brajesh Singh Yadav said: (Jan 20, 2018)  
Answer should be B.

Mayur Dale said: (May 5, 2018)  
Option B is CORRECT.

The velocity reaches its maximum value and pressure reaches its minimum value at the throat. Subsequently, a decrease in the velocity and an increase in the pressure takes place in course of flow through the divergent part. This typical variation of fluid velocity and pressure by allowing it to flow through such a constricted convergent-divergent passage was first demonstrated by an Italian scientist Giovanni Battista Venturi in 1797.

V@Dil said: (Oct 24, 2018)  
Venturimeter is an instrument used to measure the discharge of liquid flowing in a pipe. It consists of three parts, i.e the converging cone, the throat and the diverging cone. The length of the divergent cone is made about three to four times convergent cone in order to avoid the tendency of breaking away the stream of liquid and to minimise frictional losses. It may be noted that

(a) The velocity of liquid at the throat is higher than that of the inlet.
(b) The pressure of the liquid at the throat is lower than that of the inlet.
(c) The velocity and pressure of the liquid flowing through the divergent portion decrease.

The discharge through a Venturimeter is given by;

Q = Cda1a2 √2gh/(a1^2 - a2^2).
Cd = Coefficient of discharge,
a1 = Area at inlet,
a2 = Area at the throat, and
h = Venturi-head.

Umesh said: (May 26, 2019)  
In divergent portion, velocity is supersonic so velocity is increase as increase in area of nozzle.

As per Bernoulli's equation, velocity increase will decrease pressure.

Atul Kumar said: (Jul 12, 2019)  
Option B is absolutely correct.

Av = constant implies as area increases velocity decreases.

From applications of Bernoulli equation we know, pressure α 1/velocity (pressure is inversely proportional to velocity, as velocity decreases pressure increases. As simple as that don't complicate it guys.

Salahuddin said: (Aug 11, 2019)  
Why draft tube is used in turbine?

To convert part of kinetic energy into pressure head, right?

In the same way. In the divergent part, pressure increases.

Raghu said: (Sep 8, 2019)  
The answer should be B. If it decreases it doesn't obey the Bernoulli's equation which is on principle of conservation of energy.

Nilesg Harhila said: (Dec 2, 2019)  
The answer is B.

Divergent portion velocity decrese and pressure increase exit.
Divergent portion inlet velocity increase and pressure decrease.

Vinzenz said: (Dec 13, 2019)  
The answer is definitely A!

Sandeep Chaure said: (Jul 11, 2020)  
As we know the pressure is calculated by formula gamma *h, hence h will become less than in convergent portion so the answer is "decreases".

Pappu Kumar said: (Aug 14, 2020)  
Pressure will be increase to divergent portion.

Vinay Bel said: (Oct 21, 2020)  
It should be Increases.

Sachin said: (Apr 10, 2021)  
Pressure increases in divergent section that's why length of divergent section is increased so that pressure increases gradually else flow would not happen from low pressure region in throat to high pressure region.

Er. P. C. Meena said: (Jun 5, 2021)  
According to Bernoulli equation in divergent portion Area increases, than Kinetic energy decreases, thus pressure energy also increases.

So, exactly Pressure energy increases.

Aneesh said: (Jun 14, 2021)  
According to NPTEL, pressure increases as velocity reduces in the Divergent section So, the answer should be Option B.

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