# Converting Pressure to Energy

## Is a system for converting high pressures to energy possible?

• ### Unlikely for 75-250

• Total voters
12
caumaan
I'm not completely sure that this is the propor Engineering message board for this topic, but I am not an engineer so I have an excuse!

While I was watching something about sub-oceanic and sub-terranian colonies, I got an idea about a structure's exterior to use the force applied to it by the high pressure for two purposes;

1.To divert pressure from the structure.
2.To use this diverted pressure as an energy source for the colony.

I know that this is a radical idea, but I still don't know if it is possible in the near future (50 years or more). Tell me what you think.

one_raven
Do you have some idea of how the mechanism that would convert the pressure might work?

Artman
There is a direct relationship between steam pressure and temperature. You can actually tell what temperature the steam is if you know the pressure. There are tables to indicate how much sensible heat and how much latent heat (heat of vaporization) energy there is in each lb of steam at many different pressures.

Diverting the pressure is another story. Good idea, but how do you accomplish it?

Staff Emeritus
Gold Member
Humm... Suppose you have a sizable underwater structure. The distance from top to bottom would represent a significant pressure differential. If you were to run a duct from the bottom to the top there could/should be a current flowing through it. Insert a turbine and you could conceivably generate power. The amount of power would depend on the size of your structure.

Edit:
The more I think about this the more conviniced I become that it CANNOT work. It seems to imply that if you were to submerse a open ended pipe into water. Water would come gushing out the top end. This does not happen, so there is something missing.

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caumaan
No, I don't have a single idea as to how the strucutre itself would work, and the idea isn't to have some sort of pipe coming from the strucutre, but to have the exterior of a structure itself have this purpose.

Once again, I am not an engineer, but I believe that if one were to deterine how water would act on the structure, that would help the system along significantly.

Hmm, I never really thought of vertical pipes for this concept.

There are some things in this world that will never change.

Mentor
Pressure doesn't work the way you think it does, caumaan. You seem to be saying it is downward forces only. It is not. When you are underwater, you have the same pressure pushing at you from all directions - even from underneath you.

wimms
The only way to consume energy stored in pressure and let it do some work is to stop resisting its crushing force? Not very practical it seems.

Homework Helper
It might be feasible to use water pressure to pressurize gasses as an energy storage medium though.

With a valve arrangement, you could concievably just lower a tank into deep water and use it to pressureise the gas in the tank. Unfortunately the pressure gradient of water and necessary tank size would probably make this approach less than ideal.

A much more interesting technology is to use the temperature difference in the water at different depths to generate electricity. This is currently being done in Hawaii, and would be quite feasible for deep-water colonies.

Homework Helper

The principle is proven, and could plausibly be developed for sufficient power within the next 50 years.

Your colony could also use tidal or geothermal power.

young e.
No, it is not possible to convert even very high pressures into energy. In the sense that pressure is an amount of force per unit area while energy is the amount of doing work expressed in joules or calorie or btu .Take the following formula:

Energy= (force X distance)

Pressure= Force/ area

We can eliminate and create pressure but we can't eliminate and create energy. As the law of conservation of energy states that

"ENERGY CAN'T BE CREATED NOR DESTROYED IT JUST TRANSFORM FROM ONE FORM TO ANOTHER"

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Homework Helper
Originally posted by young e.
No, it is not possible to convert even very high pressures into energy. In the sense that pressure is an amount of force per unit area while energy is the amount of doing work per unit time.

For physicists, the amount of work per unit time is referred to as power.

Regarding your claim that energy cannot be converted to pressure - pressure is a form of potential energy, and there are many machines that use pressure differences to do work. These include all combustion motors and all pumps.

young e.
Originally posted by NateTG
For physicists, the amount of work per unit time is referred to as power.

Regarding your claim that energy cannot be converted to pressure - pressure is a form of potential energy, and there are many machines that use pressure differences to do work. These include all combustion motors and all pumps.

I think the right thing to say that statement is pressure is one of the media to create potential energy. Regarding your claim that pressure is one form of potential energy, all i can say is that the fact there is a presence of pressure, energy is there but not pressure is converted into energy. In fact the unit of pressure such as Pascal and Psi has no equivalent to Joules, Calorie or British Thermal Unit.

Homework Helper
Ah, I think there is a miscommunication here -- we're thinking of different meanings of convert.

Mentor
Originally posted by young e.
In fact the unit of pressure such as Pascal and Psi has no equivalent to Joules, Calorie or British Thermal Unit.
Pressure itself isn't energy, but the relationship is real. In a device like a compressor, using the pressure difference and volume you can easily find the energy. I think that was his point.

In any case, there are plenty of devices that convert pressure to energy and vice versa. There are even some newer ones such as piezzoelectric plastics that convert linear mechanical energy directly into electrical energy: when you stretch it, a voltage is induced. Very useful thing.

The way the question was originally posted (a dome at the bottom of the ocean) you have static pressure in an equilibrium situation. So there is no energy change to harness. The conversions we are talking about involve a CHANGE in pressure.

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pallidin
I agree with russ.
Pressure can easily be converted into useful energy. This has not been a problem for some time now.
To make it work, however, one must remember that the source of a pressure MUST propagate from a higher to a lower pressure environment in order to extract energy.(Think of hydroelectric dams, for instance)
In an underwater colony, one could easily designed a portion of the shell to perform a "controlled collapse" from water pressure, and thereby convert to useful energy. However, it is short-lived, and to return the system to a further potential state would require as much energy as was extracted. So, it would be a "one-shot" affair.

young e.
okay i understand now what you all mean, i have just misinterpreted the statement " conversion of pressure to energy". My point is rely purely on the law on conservation of energy that is energy is energy and can only be converted into another form of energy also. So guys I've got ur points. NateG was right that I hve misinterpreted him.

kishtik
We can use pressure differences of air to do work and generate electric. This bleeding-edge technology is called "windmill" among ordinary people.

Mentor
Originally posted by young e.
okay i understand now what you all mean, i have just misinterpreted the statement " conversion of pressure to energy". My point is rely purely on the law on conservation of energy that is energy is energy and can only be converted into another form of energy also. So guys I've got ur points. NateG was right that I hve misinterpreted him.
Your interpretation aside, your point is still quite valid and far too often ignored.

Gold Member
Originally posted by kishtik
We can use pressure differences of air to do work and generate electric. This bleeding-edge technology is called "windmill" among ordinary people.

This very real technology is technically solar since the winds involved originate from the heating of the sun. It works, it is used, and has been used for centuries. And if you want to get REALLY technical, it is nuclear energy. The sun is a nuclear furnace. We should exploit it as much as possible. No matter what we do here on earth, the sun will continue to shine. It's there for collecting.

///mon3y
pallidin said:
I agree with russ.
Pressure can easily be converted into useful energy. This has not been a problem for some time now.
To make it work, however, one must remember that the source of a pressure MUST propagate from a higher to a lower pressure environment in order to extract energy.(Think of hydroelectric dams, for instance)
In an underwater colony, one could easily designed a portion of the shell to perform a "controlled collapse" from water pressure, and thereby convert to useful energy. However, it is short-lived, and to return the system to a further potential state would require as much energy as was extracted. So, it would be a "one-shot" affair.
well put ^^

ValmirGP
Nor am I an engineer as the original poster, but what about some form of piezoelectricity?

Slightly altering the original topic, would it not be possible to incorporate such a mechanism in aircraft flight recorder boxes so that they continue to transmit a signal indefinitely when submerged, as in the case of AIR FRANCE flight 447, rather than stop transmitting when its batteries ran out?

Mentor
Welcome to PF, Valmir.

I'm not sure if you read the whole thread, but we discussed the issue of piezoelectricity. In short: a static pressure situation has no energy source to continuously harness. You need a mass flowing through a pressure difference (ie, water flowing through a hydro dam). For piezoelectricity, the peizo cell must be in constant motion (oscillating) in order to produce energy continuously. So your idea of a piezo cell for powering an aircraft black box wouldn't work: the piezo cell would produce a tiny amount of power while the box sinks, but once at the bottom, it isn't moving anymore and so isn't producing any power.

DR13
I do not think that this would be a practical idea but it works as a thought experiment.

Suppose that you have a long, closed cylinder placed underwater. This cylinder has a turbine placed in it. Now let us say that the cylinder is not very strong excxept for the area around the turbine and it is submerged *very* deep in the sea. The external pressure would cause the device to implode thus causing an air current which could turn the turbine and thus produce energy.

However, for this to produce any real power the structure would have to be unimaginably large. So I would say that this is impractical, but not impossible.

Anotoly1
It is possible for deep water applications. Simple design unit with min. two chambers can work as converter. Device called SPEC - Static Pressure to Energy Converter. When outside deep water pressure is applied it is creating internal kinetic flow between interconnected cylinder chambers and allowing piston movement. Piston is having input from deep water valves from both sides. When one of the valves opens and pressure wave delivered into chamber, to piston is supplied leverage 2:1 through lever connected to piston and allowing to create double pressure in opposite chamber and kinetic flow from this chamber into chamber with original pressure from outside. When piston reaches end pos. this valve closes and pressure is supplied from other side repeating the same function.
Energy output can be from lever oscillation or putting in kinetic flow between chambers through conversion device to rotary motion. Water pumping is very effective by having channel dia. connecting chambers with size of cylinder dia. If this explanation is not cleare, if you supply email address, I can give sketch. Power output huge, actual device is a different design and converts directly to high speed rotary motion of generator. Max. speed is limited by structural and pressure wave 1400m/s limitations.

Mentor
No, sorry, that would be perpetual motion.....and that appears to be all this thread is now, so it's locked.