Power needed for turbines and pumps

In summary, the conversation is about a friend's idea for creating more electric energy than the pump would use by drilling a well into the Earth and using multiple turbines at different heights. The formula for approximating electric power production at a hydroelectric plant is discussed, but ultimately the idea is dismissed as a Perpetual Motion Machine and not feasible according to basic physical laws. Several previous discussions on the topic have been locked on the forums.
  • #1
praondevou
2
0
I have a friend who insists in an idea and I want to prove to him that it cannot work because it would violate basic physical laws.

But somehow I don't find the right words.

He says if he drilled a well of 2km (or any other depth) into the Earth and at the bottom there was a pump that pumped water through a pipe back into to the head of the well he could create more electric energy than the pump would be using.

He would install a few, not just one, turbines into the well at different heights, where the sum of energy generated by all turbines is greater than the energy needed to pump all the water up.

Now according to this:

A simple formula for approximating electric power production at a hydroelectric plant is:
where P is Power in kilowatts, h is height in meters, r is flow rate in cubic meters per second, g is acceleration due to gravity of 9.8 m/s2, and k is a coefficient of efficiency ranging from 0 to 1.


the only parameter that is different for all turbines is the height. Unless the flow rate is changing.

This formula is similar for pumps. Leaving acceleration (fixed) and water density and losses aside the only parameters ar flow rate and height.

It looks like very easy to explain why it cannot work, yet...

Does anyone have a calculation example?
 
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  • #2
The formula quoted is for the energy available from an uninterrupted flow, assuming that each turbine is 100% efficient then at the outlet of each turbine the velocity flow will be zero and you have to plug inthe numbers for the drop to the next turbine.
 
  • #3
praondevou said:
I have a friend who insists in an idea and I want to prove to him that it cannot work because it would violate basic physical laws.

But somehow I don't find the right words.

He says if he drilled a well of 2km (or any other depth) into the Earth and at the bottom there was a pump that pumped water through a pipe back into to the head of the well he could create more electric energy than the pump would be using.

He would install a few, not just one, turbines into the well at different heights, where the sum of energy generated by all turbines is greater than the energy needed to pump all the water up.

Now according to this:

A simple formula for approximating electric power production at a hydroelectric plant is:
where P is Power in kilowatts, h is height in meters, r is flow rate in cubic meters per second, g is acceleration due to gravity of 9.8 m/s2, and k is a coefficient of efficiency ranging from 0 to 1.


the only parameter that is different for all turbines is the height. Unless the flow rate is changing.

This formula is similar for pumps. Leaving acceleration (fixed) and water density and losses aside the only parameters ar flow rate and height.

It looks like very easy to explain why it cannot work, yet...

Does anyone have a calculation example?

We do not waste people's time discussing Perpetual Motion Machines (PMMs) here at the PF. Here is a quote from the PF Rules link at the top of the page, giving some links to old locked PMM threads to help you understand why they do not work.

PF Rules said:
Perpetual motion and "free energy" discussions

Search PF and you will find many threads that have been closed in a number of forums. As for S&D, any claim of this nature would be reproducible and/or testable by the scientific community; hence there is no need for debate.
EDIT by berkeman -- here are some recent locked PMM threads:
https://www.physicsforums.com/showthread.php?t=522548
https://www.physicsforums.com/showthread.php?t=520290
https://www.physicsforums.com/showthread.php?t=7735
https://www.physicsforums.com/showthread.php?t=515402
https://www.physicsforums.com/showthread.php?t=403572
 

FAQ: Power needed for turbines and pumps

What is the relationship between power and speed for turbines and pumps?

The power needed for turbines and pumps depends on their speed. As the speed increases, the power needed also increases. This is because the faster the rotation, the more energy is required to maintain it.

What factors affect the power needed for turbines and pumps?

The power needed for turbines and pumps is affected by several factors including the size and type of the turbine or pump, the flow rate, and the pressure or head of the fluid being pumped.

How is the power needed for turbines and pumps calculated?

The power needed for turbines and pumps can be calculated using the following formula: P = Q x H x ρ x g, where P is power (in watts), Q is flow rate (in cubic meters per second), H is head or pressure (in meters), ρ is the density of the fluid (in kilograms per cubic meter), and g is the acceleration due to gravity (9.8 m/s²).

What is the difference between power needed for turbines and pumps?

The power needed for turbines and pumps differs in terms of their function. Turbines are used to convert the kinetic energy of a fluid into mechanical energy, while pumps are used to increase the pressure or head of a fluid. Therefore, the power needed for turbines is used to generate energy, while the power needed for pumps is used to transfer energy.

How can the power needed for turbines and pumps be reduced?

The power needed for turbines and pumps can be reduced by improving their efficiency. This can be achieved by using high-quality materials, maintaining proper lubrication and alignment, and reducing friction losses. Additionally, using variable speed drives can also help to reduce the power needed for turbines and pumps.

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