The oceans contain an immense amount of heat energy. Why can a submarine not make use of it for propulsion?

Answer 1

because to make the most efficient use, or any use, of the heat energy, one must exploit a heat gradient. A sub is too small to span the hundreds, if not thousands of vertical feet to gain any benefit.

Answer 2

For energy to do work, like moving a submarine, you have to have a flow of energy. The fact that the ocean, or the earth, or the air has a temperature above absolute zero, then you could say, as in your question, that it "contains" energy, but to use it you have to establish an energy flow.

An easier to see example might be a rock sitting on the ground in front of your house. It has a lot of potential energy, because if is way above the center of the earth. If you suddenly had a shaft under it that went to the center of the earth, the rock would fall and you could generate energy with that fall by doing something like tying the rock to a rope wrapped many times around a generator rotor. The generator would turn and make electricity as the rock fell. But without the hole, the rock containing lots of potential energy, cannot do any work or power anything.

Same with ocean water. There are some possibilities of using temperature gradients, different temperatures from one part of the ocean to another, to allow heat to flow from the hotter to cooler and use that FLOW to do some work, but these have to be very large systems and the energy is very difficult to harness. Like any energy source, it is used up. After the heat has flowed awhile the two temperature come together and heat will not flow.

This was probably too long but perhaps it is helpful.

Answer 3

As other answers above note, you need a temperature difference to obtain work from thermal (heat) energy reservoirs. The reason is that entropy - the tendency to increase the disorder of any system - must always increase. Transfering heat from a high temperature reservoir into a low temperature reservoir increases entropy, allowing work to be done. If you were to extract energy from the ocean, you would have to dump it into a lower temperature reservoir to do work - otherwise it takes work to transfer the energy, and it winds up costing you energy instead! Air conditioners (heat pumps) are an example - it takes work - energy - to move heat from a lower temperature to a higher temperature.

However, there are projects underway to tap the ocean's energy. Ocean thermal gradients - temperature differences of 20 degrees Celsius or more - have the potential to generate reasonable amounts of useful energy (i.e., work). They take heat from warmer regions of the ocean and transfer it to colder regions, doing work and thereby generating electricity. They are very inefficient because the temperature difference is rather small, but there is so much energy available that it still makes sense.

See http://www.eere.energy.gov/consumer/renewable_energy/ocean/index.cfm/mytopic=50010, for example.

Answer 4

You really would need a heat differencial in order to make it do any useful work, and at the ambient temperature of the ocean, that wouldn't really be practical. Nuclear submarines do use seawater as coolant, and I believe they desalinize it for use as potable water, and as a thermodynamic medium for thier steam power cycle.

Edit - interesting idea using the change in temperature with depth to drive a power plant. May not be practicle, but interesting.

Answer 5

Anything's possible, but with current technology we do not have the capability to extract large amounts of heat that is spread out over a large area for the use of a tiny sub. It would require some sort of energy collection net spread out over a large surface area.

Answer 6

Simply because the technology needed to be able to harness that energy wouldn't fit inside the submarines.

Answer 7

yes, an immense amount of heat energy diffused evenly through out 75% of the earth.. which means theres not much heat energy at all in one point at one particular time.

Answer 8

HMMMMMMM neat idea. My bet is that the heat is dissipated so fast that no machine could harness it. I'm a scuba diver, and I can tell you that water in the ocean is not all that warm.......... so I'm not sure what you mean by immense heat energy in this case.

Answer 9

I think the refraction in the water and how as you go deeper theres less sun prolly affects it in some way.

Answer 10

look up "Carnot-cycle" on google

the sub is at the same temperature as the surrounding water ... no "delta-t" for energy extraction