Static and stagnation properties

zaveri · 2013-05-11T21:35:36+00:00

What is the difference between static and stagnation properties involved in any thermodynamic cycle ? for example , what is meant by static pressure and stagnation pressure ?

Static and stagnation properties

zaveri

Member

Updated: Oct 26, 2024

Views: 2.2K

What is the difference between static and stagnation properties involved in any thermodynamic cycle ?

for example , what is meant by static pressure and stagnation pressure ?

0

Replies

Howdy guest!

Dear guest, you must be logged-in to participate on CrazyEngineers. We would love to have you as a member of our community. Consider creating an account or login.

Replies

kamal61435

Member • May 12, 2013

Static Pressure is the pressure exerted by the fluid in all directions at a certain point i.e stagnation point.

Stagnation Pressure is the static pressure at a stagnation point in a fluid flow i.e static pressure + dynamic pressure.To be more clear, Stagnation pressure is the pressure one would have after isentropically decelerating the fluid to a rest and properties at that point is stagnation properties.

In above fig, the total pressure indicates stagnation pressure.

They are measured using pitot tube.

Static properties are those that would be measured if one could travel with the fluid at its exact velocity.

Well, gathered from books and internet ,so if need more explanation tell me.

Are you sure? This action cannot be undone.
Cancel
Ammar Aziz

Member • May 12, 2013

Suppose that a fluid is moving with very high velocity. Due to this velocity it is obvious that it possesses some kinetic energy and may be some other type of energy as well. But if through some mechanism or arrangement this fluid is suddenly brought to rest then according to law of conservation of energy all the kinetic energy of the fluid is converted to other forms of fluid energy like fluid pressure etc. At this instant all the properties of the corresponding fluid is known as stagnation properties.

On the other hand if you have some fluid with no kinetic energy then the pressure exerted by the fluid on its surrounding due its molecular structure of that fluid is known as static pressure. so it is its inherent tendency.

Are you sure? This action cannot be undone.
Cancel
zaveri

Member • May 13, 2013

Thanks guys. i did manage to grab something from both your replies.

now consider this case:

air is being compressed in a reciprocating compressor and this in turn is being stored in the tank (the pressure vessel). now the pressure of the air in the tank is stagnation pressure, isn't it , since it was first imparted some pressure and velocity, and then brought to a complete rest in the tank ?

am i right guys ?

Are you sure? This action cannot be undone.
Cancel
Ammar Aziz

Member • May 13, 2013

you are saying that air is being compressed in a reciprocating compressor.
after passing through the compressor it enters a tank or pressure vessel.
actually the basic function of compressor is to compress, not to increase the velocity. on the other hand if you say that after passing through a nozzle, the air enters a tank and eventually tank's wall restricts the velocity of air to zero or near to zero, than the pressure of the air at this state is stagnation pressure. it only exists at the instant when air is stopped by the walls of container. because it may be possible that due to elastic collision between air molecules and wall, the air again gains some velocity.
you are also right in your scenerio. but keep in mind that this state only exists for an instant in your case.

Are you sure? This action cannot be undone.
Cancel
zaveri

Member • May 13, 2013

#-Link-Snipped-#

thanx

from what i have learnt, a reciprocating compressor delivers air at high pressure and low velocity, quite unlike the rotary compressor which delivers air at a lower pressure and higher velocity.

but then even in the case of the reciprocating machine, there does exist some velocity after all, since the compressed air has to move from the machine to the tank.

Are you sure? This action cannot be undone.
Cancel
Anand Tamariya

Member • May 13, 2013

zaveri
Thanks guys. i did manage to grab something from both your replies.

now consider this case:

air is being compressed in a reciprocating compressor and this in turn is being stored in the tank (the pressure vessel). now the pressure of the air in the tank is stagnation pressure, isn't it , since it was first imparted some pressure and velocity, and then brought to a complete rest in the tank ?

am i right guys ?
Stagnation pressure is defined only for incompressible fluid.

Are you sure? This action cannot be undone.
Cancel
zaveri

Member • May 13, 2013

Anand Tamariya
Stagnation pressure is defined only for incompressible fluid.
What do you mean by that ?

incompressible fluids are water, oil and other liquids.

Are you sure? This action cannot be undone.
Cancel
Anand Tamariya

Member • May 14, 2013

zaveri
What do you mean by that ?

incompressible fluids are water, oil and other liquids.
Meaning it doesn't apply to compressed air.

Are you sure? This action cannot be undone.
Cancel
zaveri

Member • May 14, 2013

#-Link-Snipped-#

you will deal with stagnation properties while dealing with centrifugal compressors and fans.

Are you sure? This action cannot be undone.
Cancel
Ammar Aziz

Member • May 14, 2013

to some extent it is true that to achieve the stagnation state, the corresponding fluid must be incompressible. because if something is compressible than it is possible to have more than one stagnation states for that. for example, at two different compressions although it have zero velocity but now internal energy plays role in defining the state of the gas .....

Are you sure? This action cannot be undone.
Cancel
Anand Tamariya

Member • May 14, 2013

zaveri
#-Link-Snipped-#

you will deal with stagnation properties while dealing with centrifugal compressors and fans.
A little more context would be helpful - if you can elaborate in detail.

Are you sure? This action cannot be undone.
Cancel
zaveri

Member • May 15, 2013

#-Link-Snipped-#

Well we have machines like centrifugal compressor and centrifugal fans.

these are used to increase the pressure of air.

the pressurised air from these machines also have stagnation properties.

and air as you know is a compressible fluid.

then how come you say that stagnation properties do not apply to compressible fluids.

Are you sure? This action cannot be undone.
Cancel