Hydraulics problem - calculate pressure at different points

jet1985

1. The problem statement, all variables and given/known data

Hey, stuck on this question in my hydraulics course:

Question involves lubricating oil pumped around a large piece of machinery.
Density of oil = 810 km/m3.
Viscosity = 0.01 kg/m.s throughout the system.
Flow rate is 0.140 Litres/sec
Pipe diameter = 3mm

Pressure at point A = 1.55 kPa.
Point A is 5m above the ground.

Point B is 36.5m above the ground. Question requires pressure to be found at this point ignoring minor losses and friction.



2. Relevant equations

Bernoulli

3. The attempt at a solution

I attempted to solve this problem using Bernoulli equation: (p_A/Pg)+(V_A²/2g) + Z_A = (p_B/Pg)+(V_B²/2g)+Z_B, However the result I get is negative and looks all wrong.

We were given very limited information but I assume we have enough info to answer the question. I don't see how the pressure at point A could possibly be only 1.55 kPa, given the oil is being lifted 31.5m high and 1.55 kPa is many times less pressure than even a car tyre.

The flow rate also seems unrealistically high, and the pipe diameter seems unrealistically narrow.

The question only specifies "pressure = 1.55 kPa". Is it possible they meant dynamic pressure?
1. The problem statement, all variables and given/known data



2. Relevant equations



3. The attempt at a solution

LawrenceC

Something seems wrong with the numbers given in the problem. They seem unrealistic to me as well. Besides pressure issues as you say, the velocity is almost 20 m/sec. That would cause a lot of heating of the oil and large pressure drops.

jet1985

For the purposes of answering the question, that would not matter as we have been told to ignore minor losses and friction losses. However I cannot get my head around the pressure drop.

Also, I have asked to lecturers for clarification on the question, but they have been very lazy about getting back to me... I thought perhaps they meant MPa instead of kPa.