Oil pump velocity calculation

In summary: This is where it appears you are going wrong.In summary, the problem involves an oil suction pipe (pipe A) and a delivery pipe (pipe B) with a pump supplying a head of 11.3m. The pressure in pipe A is atmospheric and the pressure in pipe B is 850kPa. The vertical displacement is 0.8m, total head loss in the system is 0.44m, and the density of the oil is 850kg/m^3. The question asks for the velocity in pipe A, given that its diameter is twice the diameter of pipe B. The attempts at solving the problem involved using Bernoulli's extended equation and the continuity relationship, but there was a major mistake in the
  • #1
Gazza-85
2
0

Homework Statement



This problem is regarding an oil suction pipe, pipe A is the the suction pipe and pipe B is the delivery pipe. There is a pump in between which supplies a head of 11.3m. The pressure in pipe A is atmospheric and the pressure in pipe B is 850kPa. The vertical displacement is 0.8m, total head loss in the system is 0.44m and the density of the oil is 850kg/m3.

If the diameter of pipe A is twice the diameter of pipe B, calculate the velocity in pipe A.


Homework Equations



None given... I have tried using Bernoulli's extended equation

Pin/ρg + vin2/2g + zin = Pout/ρg + vout2/2g + zout + Hlosses - Hpump + Hturbine


The Attempt at a Solution



I initially tried to rearrange the the mass equation by subbing in piD^2 / 4 for area and rearranging to discover the relationship between the velocities in the two pipes with the diameter difference. It seems to be a dead end as my workings suggest the velocity for pipe A is half that of pipe B which doesn't make sense, considering the pressure increase is massive in pipe B. I expected the velocity to be higher in the pipe with lower pressure... Maybe my calculations are incorrect.

Another attempt included entering all of the data into bernoulli's extended equation and rearranging. I could only get as far as 'V_in - V_out = 1.62 (approx)' which is another dead end.

The final attempt consisted of suggesting that Pin/ρg + vin2/2g + zin = the sum of heads which, when rearranged, produced a figure of 14.77 m/s for V_in. Extended workings for this solution are written in my report but I am not convinced...

Thanks for reading, this is my first post so please let me know if I can improve anything. I could attach photos or word documents of my calculations if necessary/possible.

I hope someone can give me a push in the right direction, thanks again.
 
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  • #2
In your description of your calculations, I don't see any mention of the continuity relationship. Is this what you mean by the 'mass equation'?

A velocity of 14 m/s seems rather high for a liquid piping system.

Perhaps you should post the details of what you consider your 'best' calculation.
 
  • #3
Hi there, thanks for the prompt reply, attached is where I am so far.

Yep, continuity relationship and I meant quarter not half :/
 

Attachments

  • The diagram shows part of the lubrication system for an engine.docx
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  • #4
You've made a major mistake in your manipulation of the Bernoulli equation:

[itex]V_{A}^{2} - V_{B}^{2}[/itex] = Mess

but

[itex]\sqrt{V_{A}^{2} - V_{B}^{2}} ≠ V_{A} - V_{B}[/itex]
 
  • #5




Thank you for sharing your attempts at solving this problem. It seems like you have a good understanding of the equations involved, but your calculations may have some errors. Here are some suggestions for approaching this problem:

1. Start by writing down all the given data in a clear and organized manner. This will help you keep track of all the information and avoid confusion.

2. Use the equation for Bernoulli's principle in its simplest form: P1 + (1/2)ρv1^2 + ρgh1 = P2 + (1/2)ρv2^2 + ρgh2. This equation relates the pressure, velocity, and height at two points in a fluid flow.

3. In this problem, we are interested in the velocity in pipe A. So, let's label the two points in the equation as point 1 (at the entrance of pipe A) and point 2 (at the exit of pipe A). This will give us the equation: P1 + (1/2)ρv1^2 + ρgh1 = P2 + (1/2)ρv2^2 + ρgh2.

4. Now, we can plug in the given data for point 1: P1 = atmospheric pressure, v1 = unknown (we are trying to solve for this), h1 = 0 (since it is at the same height as point 2).

5. For point 2, we know that the pressure is 850kPa, the velocity is unknown (we are trying to solve for this), and the height is 0.8m higher than point 1.

6. We can also include the head loss in the system, which is given as 0.44m. This means that the total head at point 2 is 11.3m - 0.44m = 10.86m. So, we can rewrite the equation as: atmospheric pressure + (1/2)ρv1^2 + 0 = 850kPa + (1/2)ρv2^2 + ρg(0.8m) + 10.86m.

7. Now, we need to find a relationship between the velocities in pipes A and B. We can use the equation for the continuity of flow, which states that the flow rate (Q) at any point in a pipe is constant.
 

1. How is the oil pump velocity calculated?

The oil pump velocity is calculated by dividing the volumetric flow rate of the oil pump by the cross-sectional area of the pump's inlet or outlet.

2. Why is it important to calculate oil pump velocity?

Calculating oil pump velocity is important because it helps determine the efficiency and performance of the pump, as well as potential issues such as cavitation or excessive wear.

3. What units are typically used for oil pump velocity?

Oil pump velocity is typically measured in feet per second (ft/s) or meters per second (m/s), but can also be expressed in other units such as gallons per minute (gpm) or liters per minute (l/min).

4. How does viscosity affect oil pump velocity?

Viscosity, or the thickness of the oil, can affect oil pump velocity by creating resistance and reducing the flow rate. Higher viscosity oils will result in lower velocities, while lower viscosity oils will result in higher velocities.

5. Can oil pump velocity be changed?

Yes, oil pump velocity can be changed by adjusting the pump speed, changing the pump's design or size, or altering the oil viscosity. However, it is important to carefully consider the implications of changing the velocity on the pump's performance and efficiency.

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