5 replies to this topic

[janson_kaniaz]

I'm not sure this is basic enough, but on land, the pressure at point B in a pipe which is lower than point A is always higher due to the static head. If the same pipe is immersed underwater, does the same rule still apply? Do we need to take into account the static head outside of the pipe which is no longer atmospheric? 

[Bobby Strain]

What's your question?

 

Bobby

[fallah]

janson,

 

Fliuid inside the pipe is flowing or is at static position? If is flowing, it's a gravity flow? Is the fluid is liquid or gas?

[janson_kaniaz]

hi fallah, just curious. does it matter if the fluid is flowing or static? for the sake of argument let's assume the fluid is flowing. this is not a gravity flow. there is a pump upstream. fluid is mixed gas+liquid.

[fallah]

janson,

 

As long as the external pressure due to immersion in water don't affect the mechanical integrity of the pipe i.e. the pipe wall can isolate inside and outside of the pipe , the same rule still apply...

[shan]

Static head is a potential due to the gravity toward earth center.  It always exists everywhere unless you are talking about something that is not on the earth. 

You should not count for the static head differences outside your piping in your fluid flow calculations because it is outside the hydraulics systems you are considering. 

However, if your are calculating the piping wall stress in the deep water, you have to count for the outside liquid static changes from the water surface to the water bottom although you may ignore the static differences for the same calculations in the air because they will no more than 14.7 psi even if from the lowest valley to the highest mountain.