What are the necessary fluid dynamics to make this work?

Question

The best way to ask this question is through visualization. Imagine a funnel with a hose sealed to the spout. Then imagine that you are at the beach holding the end of the hose above your head. The hose goes straight down from your hand into the sand at your feet to a depth of three feet underground, then turns out to the ocean and stays three feet underground all the way to where the ocean depth is thirty feet. There the hose comes up from the sandy bottom and opens into the funnel. How big would the funnel have to be to make salt water come spraying out of the end of the hose with enough force to drive an electric generating turbine?

Answer 1

This is an awfully vague question since you don't specify any hard numbers. I have no idea as to the force of the incoming waves, though you could time it by counting the seconds it takes waves to break on the beach and measuring the distance between the waves. This should give you speed.

Take the ratio of the funnel and the tube, and that should give you the amplification of the speed (the volume of water that enters through the funnel and leaves through the tube is constant over time since water is non-compressible) You can use bernolli's eqns to figure out the exit velocity and use that to figure out the KE which tells you how much energy you need to drive that turbine.

Answer 2

It is not a question of "how big". It's a question of "does it work?", and the answer is "no".

The weight of the column of water going up the vertical section of the hose will prevent the water from getting to the top of the hose, unless there is a pressure exerted on it from the under-sea end of the hose that is LARGER than the force caused by the weight of the column of water.

In a calm ocean, this will never happen. The water inside the hose will rise to the level that the rest of the sea is at, and it will stay there.

If you mean for the crest of a wave to crash into your funnel, temporarily driving the water in the hose up above sea level...well, there are FAR more efficient ways to extract energy from waves than this.

Answer 3

Regardless of the funnel size, water would not come out of the hose. Water will not travel from a lower energy state (30 feet below you) to a higher energy state (spraying out above you) without adding some form of energy.

The first law of thermodynamics states that energy can neither be created nor destroyed.

If your idea were possible, the water spraying out (after turning a generator) could drain back into the pool (the ocean) and continue the cycle producing an infinate amount of energy without adding any source of energy. Based of the first law of thermodynamics, we know that such a process is impossible.