Momentum balance derivation in equations

Fishinev

I'm a little confused, in my fluid mechanics course we've covered many equations and they are all derived using an x-direction fluid flow. If I was to use these in a system in which fluid flowed in the y-direction would I have to re-derive them? Or would it be more of a case of using a horizontal system in a vertical direction?

tiny-tim

Hi Fishinev! Welcome to PF!
Do you mean that the entire flow is horizontal, so that gravity doesn't have to be taken into account?

In that case, if you want to apply the equations to a vertical system, you'll need extra (ρgh) terms to deal with gravity.

Studiot

If this is a gas dynamics question you can usually ignore body forces such as gravity at chemical engineering scales.

If this is a liquids questions then a body force such as gravity may well come into play.

Remember in chemical engineering other body forces are often also in play.