Confused on static vs. dynamic pressure

[chemeng12345]

Hello everyone,

I am a new chemical engineering grad and trying to work my way through some of my first line sizing calculations.

I was hoping someone could clarify for me the difference between dynamic and static pressure, and how the two are calculated.

Also, how is the static pressure of a gas calculated? For instance, if natural gas is being drawn from a pipeline at 4400 kPa, 0 deg C, 4000 kg/hr from ground level, how do I calculate the static pressure for that?

 

[SeanB]

To understand the difference in the two refer to Bernoulli's equation - Total pressure is equal to static pressure + dynamic pressure. The dynamic portion is due to a velocity change in your pipe - or "velocity head".

 

[shahyar]

Static Pressure: 4400 KPag
Dynamic Pressure: Rho.V^2/2 (Calculate the velocity of gas by 4000 kg/hr/3600/(Rho.A), which A is cross section area of thr\e pipe).

Hope this help

 

[Artisi]

I can give you a clue - static means it does not move or change whereas dynamic means something is/has changed or processing.

 

[hacksaw]

Unless you are dealing with mach>0.1(in gas) or so static pressure it the pressure you'd measure without impingement effects.

the effect of elevation change is minimal for most gases,but not for liquids and total head is important.

Get a copy of Perry's C.E. HB they have a great section on this.

 

[GL431]

The concept of dynamic pressure is nicely illustrated by the working principle of pitot tubes (air plane air speed) and anubars.

The pitot tube is bent into the direction from which the fluid is flowing (or into which the air plane is flying). It measures the dynamic pressure plus the static pressure at the altitude at which the plane is flying. The alti-meter measures the static pressure at a point which is not affected by the speed of the plane. The difference between the two readings is the dynamic pressure and the air speed of the plane can be calculated from this.

With anubars, through the holes facing the flow, the dynamic plus static pressure can be measured. Through the holes on the opposite side, the static pressure is measured. The difference is the dynamic pressure and the flow can be calculated once again from this difference.