First, a bit of background: MHD is an abbreviation for magneto-hydro-dynamic.
An MHD generator works by first taking a high pressure fluid, making it conductive if it isn't already so, then passing the fluid between a pair of magnets.
Due to the shape of the piping and the shape of the magnetic field, some of the fluid's kinetic energy is converted to electrical energy.
People have built pumps that use the MHD principle for all sorts of liquids, including hot molten metals and cold seawater... there's even been an MHD propelled boat.
People have also build MHD generators using all sorts of fluids, including flames from fossil fuel combustion, molten salts, and molten metals.
No one has physically constructed an MHD generator using moving seawater, but simulations have been done.
This idea takes an MHD generator, and feeds it with the hot water from an undersea hydrothermal vent.
The liquid from these vents is acidic, approximately the PH of vinegar, which undoubtedly sours the vast majority of other half-baked ideas for making use of deep sea hydrothermal vent energy.
But since MHD doesn't require that there be any moving parts in contact with the fluid, it should still work in spite of the caustic hot water.
As with any hydro-power generator, the greater the pressure differential between the inlet and the outlet, the greater the power produced.
To maximize power, the exhaust stream of the generator would leave through a pressure resistant, thermally insulated, manmade chimney, a few hundred feet tall. This chimney would prevent the hot wastewater from mixing with ambient seawater until it exited at the top.
Since the density of the wastewater would be less than that of the surrounding water (due to it's temperature), this would result in relatively low pressure in the MHD generator's exhaust, compared to it's input.-- goldbb, Feb 14 2013 MHD for the high seas http://www.sara.com/RAE/ocean_wave.htmlMHD for converting salty water into elctricity. [travbm, Oct 30 2015] One of us took a crack at this one a while back using some crackpot variation on geothermal generation. I like the MHD angle much better, and will enjoy watching it torn apart by the engineering section. Here's a bun to munch on while we wait.-- Alterother, Feb 14 2013 If the water's acidic then it can't be caustic. I think you meant corrosive?-- UnaBubba, Feb 14 2013 While "caustic" is most commonly used in "caustic soda" or "caustic lye", it is not necessarily indicative of an aggressive base; it can, indeed, be acidic. Root is from "burning", as in "holocaust", "hypocaust"... [goldbb]'s usage, while unusual, is correct.-- lurch, Feb 14 2013 I shall refrain from snide and insulting remarks.-- UnaBubba, Feb 14 2013 Why?-- Alterother, Feb 14 2013 (it's a campaign promise, shortly to be forgotten)-- lurch, Feb 14 2013 The water flow from the vent travels along the path of least resistance; when you add the generator, that will be quite a bit of resistance to the flow, and the water will want to go elsewhere. Since the "chimneys" built by the venting water's precipitates are not extremely structurally sound, preparing the base to get the water into the generator will be a quite a major part of the project. I think it will be a pretty tough construction environment.
[+] overall-- lurch, Feb 14 2013 Because they would be caustic remarks.-- UnaBubba, Feb 14 2013 I hate to burst your bubble but someone already developed this idea. SARA has developed a cost-effective solution to energy extraction from ocean waves that is based on the company’s patented magnetohydrodynamics (MHD) generator (US Patents 7,166,927 & 5,136,173). The application of this technology promises to cut the costs of wave energy conversion (WEC) systems by a factor of three. With low capital and operating costs the SARA MWEC system has the potential to finally capitalize on this abundant and renewable energy resource.
SARA has designed, built and tested a 100 kW MHD generator that is a laboratory demonstration of a MWEC design and is also developing a deep-ocean-moored concept that is based on the MHD generator. This combination will lead to the development of cost-effective, rapidly deployable systems not only for coastal communities, but also for deep ocean applications for the Navy and the offshore oil industry. Although putting this over an under water volcano or hydrothermal vents may be new to the idea.-- travbm, Oct 27 2015 Well, based on [goldbb]'s own post the idea was already preheated.
" No one has physically constructed an MHD generator using moving seawater, but simulations have been done."
Welcome to the Halfbakery, [travbm]. Careful you don't sprain something posting so hard on the first day here - it's a good idea to work into it gradually.
Your post about SARA reads as though you are a stockholder.-- normzone, Oct 27 2015 what normone said, adding to point out that the link this time is to the point.-- pashute, Nov 01 2015 random, halfbakery