# Fluid Mechanics problem: Oil pressure calculations in pipe flow

Homework Statement:
An oil with density 900 kg/m3 and viscosity 0.18 Ns/m2 flows through a circular pipe which inclines upwards
at 40° to the horizontal. The length of the pipe is 10 m and the diameter is 6 cm. The fluid pressure at the
lower end of the pipe is 350 kPa and the pressure at the upper end is 250 kPa. (i) Confirm that flow is upward
through the pipe
Relevant Equations:
Problem Statement: An oil with density 900 kg/m3 and viscosity 0.18 Ns/m2 flows through a circular pipe which inclines upwards
at 40° to the horizontal. The length of the pipe is 10 m and the diameter is 6 cm. The fluid pressure at the
lower end of the pipe is 350 kPa and the pressure at the upper end is 250 kPa. (i) Confirm that flow is upward
through the pipe
Relevant Equations: I think Steady flow equation

I have been trying really hard to start this question, but I don't know what equations are relevant or how to start. I would be very grateful if someone could kindly explain the problem to me in basic terms. This way I will hopefully be able to attempt the question and post my attempt here if I need further help.

Thank you.

Chestermiller
Mentor
If the fluid were not flowing, what would the pressure at the top end be if the pressure at the lower end were 350 kPa?

If the fluid were not flowing, what would the pressure at the top end be if the pressure at the lower end were 350 kPa?

The pressure would still be 250kPa at the top end because pressure decreases with altitude.

Chestermiller
Mentor
Oh yeah??? OK, let's see your calculation to prove it.

Oh yeah??? OK, let's see your calculation to prove it.

Am I correct in my understanding?

For the calculation, I will need to use the bernoulli's equation, is that right?

Chestermiller
Mentor
Am I correct in my understanding?

For the calculation, I will need to use the bernoulli's equation, is that right?

For the calculation without fluid flowing, the Bernoulli equation can be used.

For the calculation without fluid flowing, the Bernoulli equation can be used.

Thank you, can the sfee can be used instead?

Chestermiller
Mentor
Thank you, can the sfee can be used instead?
What is sfee?

What is sfee?
Ah sorry, I meant steady flow energy equation.

Chestermiller
Mentor
Ah sorry, I meant steady flow energy equation.
What does the steady flow energy equation reduce to if the flow is zero?

What does the steady flow energy equation reduce to if the flow is zero?
It reduces to zero?

Chestermiller
Mentor
It reduces to zero?
Let's stick with the Bernoulli equation (at least for now). So let's see your Bernoulli equation calculation.

Let's stick with the Bernoulli equation (at least for now). So let's see your Bernoulli equation calculation.
Sorry, I think misunderstood you. The steady flow energy equation should reduce to:

p1/pg + z1=p2/pg +z2+hf

I think this is correct for cases where the flow is zero.

Chestermiller
Mentor
Sorry, I think misunderstood you. The steady flow energy equation should reduce to:

p1/pg + z1=p2/pg +z2+hf

I think this is correct for cases where the flow is zero.
Well, hf is zero if there is no flow. Otherwise, OK.

Well, hf is zero if there is no flow. Otherwise, OK.

Okay great, I note that we have been given the viscosity in this problem, are we supposed to use it in this section?

Am I correct in thinking that the incline at 40 degrees is somehow related to z1 and z2?

Last edited:
Chestermiller
Mentor
Okay great, I note that we have been given the viscosity in this problem, are we supposed to use it in this section?9
if we are first doing the calculation for a case with no flow, why would we need the viscosity?
Am I correct in thinking that the incline at 40 degrees is somehow related to z1 and z2?
Correct.