B Dynamic pressure in pressure units

[T C]

TL;DR Summary

I want to know how to convert dynamic pressure of a flowing fluid into pressure units by which static pressure is being measured.

We all know that a flowing fluid acquires dynamic pressure as a result of this velocity. But the pressure has been known to be the kinetic energy of unit volume of flow i.e. 0.5 times density multiplied by the square of the velocity. I just want to know how to convert that into units that are being used to measure static pressure.

 

[Frabjous]

Summary:: I want to know how to convert dynamic pressure of a flowing fluid into pressure units by which static pressure is being measured.

We all know that a flowing fluid acquires dynamic pressure as a result of this velocity. But the pressure has been known to be the kinetic energy of unit volume of flow i.e. 0.5 times density multiplied by the square of the velocity. I just want to know how to convert that into units that are being used to measure static pressure.

The units are identical. Find out what system your pressure unit is in and then look up what are the units for velocity and density in that system.

 

[T C]

Static pressure is measured in BarA, BarG. PsiA, PsiG etc. But, the way dynamic pressure is defined, the possible result will come in units of energy. Kindly tell me how to convert that into units of pressure. Suppose in case of a fluid, the dynamic pressure is 8 ergs. I want to know how to convert that into psi, bar etc. if we know the density and other details of the fluid.

 

[Frabjous]

ergs are in the cgs system.
dynamic pressure has units of ergs/cm³ which equal 1 barye
1 bar = 1,000,000 barye

 

[cjl]

No, you appear to have done your unit analysis incorrectly here. Dynamic pressure shouldn't come out in units of energy, it should come out in units of energy per volume, and with a bit of unit rearrangement, you should be able to find that energy per volume and pressure both are actually dimensionally the same.

 

[Baluncore]

But, the way dynamic pressure is defined, the possible result will come in units of energy.

Dynamic pressure is defined as ½⋅density⋅velocity²
Pressure is defined as kg⋅m⁻¹⋅s⁻²
( kg⋅m⁻³ )⋅(m²⋅s^-2) = kg⋅m⁻¹⋅s⁻²

 

[T C]

No, you appear to have done your unit analysis incorrectly here. Dynamic pressure shouldn't come out in units of energy, it should come out in units of energy per volume, and with a bit of unit rearrangement, you should be able to find that energy per volume and pressure both are actually dimensionally the same.

I have clearly said that the energy given is for unit volume.

 

[T C]

Dynamic pressure is defined as ½⋅density⋅velocity2
Pressure is defined as kg⋅m−1⋅s−2
( kg⋅m−3 )⋅(m2⋅s-2) = kg⋅m−1⋅s−2

Kindly give me a clear example. As for example, if it's 8 ers/cubic cc, how to convert it into pressure unit.

 

[Baluncore]

I suggest you use the SI units only. That way you will not get confused.

 

[jack action]

But the pressure has been known to be the kinetic energy of unit volume [J/m³] of flow i.e. 0.5 times density multiplied by the square of the velocity [(kg/m³)(m/s)²]. I just want to know how to convert that into units that are being used to measure static pressure [Pa].

It is just a matter of unit conversion:

1 (kg/m³)(m/s)² = 1 J/m³ = 1 Pa

 

[russ_watters]

Kindly give me a clear example. As for example, if it's 8 ers/cubic cc, how to convert it into pressure unit.

Write out the base units for us. What are the units that make up an erg? You really ought to be able to do this yourself.

…though the fact that you can’t fits with the oddity of the question, which probably points to additional misunderstandings. Meaning, you are never going to get velocity pressure in random/bizarre units, so this problem you are struggling with isn’t really even a thing anyway. The real problem here is likely that you don’t understand Bernoulli’s Principal/equation and you didn’t accept the correct answer you got in post #2.

 

[Lnewqban]

Both types of pressures can also be measured in terms of height of the column of a fluid when using a pressure gauge, which is a type of manometer using a U-shaped glass tube filled with mercury or colored water.

You can also compare the concept of total pressure, which is the addition of both types of pressures, to the concept of total energy, which if the addition of kinetic and potential energy.

Copied from
https://en.m.wikipedia.org/wiki/Pressure#Units

"Since a system under pressure has the potential to perform work on its surroundings, pressure is a measure of potential energy stored per unit volume. It is therefore related to energy density and may be expressed in units such as joules per cubic metre (J/m3, which is equal to Pa)."

 

[T C]

The real problem here is likely that you don’t understand Bernoulli’s Principal/equation and you didn’t accept the correct answer you got in post #2.

This has noting to do with Bernoulli's principle.

 

[Motore]

If you just want this

Kindly give me a clear example. As for example, if it's 8 ers/cubic cc, how to convert it into pressure unit.

then google is your friend.

You spare yourself and us the time of opening a thread, asking a question, waiting for an answer and debating the answers.

 

[russ_watters]

This has noting to do with Bernoulli's principle.

It’s pretty much entirely Bernoulli’s Principle and unit conversion. The static and dynamic pressure terms are sitting right next to each other in the equation.

 

[boneh3ad]

This has noting to do with Bernoulli's principle.

This is literally the heart of Bernoulli's equation.

 

[T C]

What I want to know is how to express dynamic pressure into pressure units.

 

[Baluncore]

What I want to know is how to express dynamic pressure into pressure units.

Use SI units.
Velocity; v, in metre/sec; Density; d, in kg/metre³; Pressure P, in Pa = pascal.
The dynamic pressure will be; P = ½·d·v² pascal.

Simply put, conservation of energy in a gas flow requires that the sum of kinetic energy and potential energy be constant. That is the heart of Bernoulli's principle. The kinetic energy term is a function of gas velocity, the potential energy term is a function of pressure.

 

[russ_watters]

What I want to know is how to express dynamic pressure into pressure units.

Pressure units are pressure units; Pascals, psi, whatever - dynamic pressure (as the name says) comes in pressure units. But you've already been told this. This issue is something any minimally competent junior high student should be able to grasp. So you need to start putting more effort into this or we'll need to lock the thread.

 

[T C]

@Baluncore, Jack Action clearly defined what I want to know and now I can transfer calculated value of dynamic pressure into pressure units. My only motto for starting this thread is to find it out and Jack Action now clarified it.
Russ is now in a hurry and can now lock this thread.

 

[russ_watters]

Thread closed.