Re: Solar breakthrough - when?

From: Fred B. McGalliard (frederick.b.mcgalliard_at_boeing.com)
Date: 08/19/04 

Date: Thu, 19 Aug 2004 22:21:21 GMT

"Don Lancaster" <don@tinaja.com> wrote in message
news:4125024B.D2CDE4F8@tinaja.com...
...
> The fundamental problem with low delta T is the drops BETWEEN ambient and
the actual system.
> At, say two percent efficiency (highly unlikely), these will have FIFTY
> times the thermal drop across them.
>
> Also, of course, the size goes up hyperbolically with decreasing
efficiency.
>
> Low detla-T heat engines are fundamentally and profoundly futile.

I think you should have used parabolically rather than hyperbolically.
Sounds a bit odd.

The killer here is that you need both a large turbine and a very large heat
exchanger (two actually). Very large heat exchangers sitting in salt water
tend to become reefs. I would not give up so easily though. In a manner of
speaking, wind power is a large scale low temperature difference motor. Of
course no one would consider building a desert and mountain range if one
were not sitting there mostly unused, but there may be some ways to take
advantage of the OTEC small temperature differences as well. I would
consider a bay sized fresh water covered heavy saline heat collector, and
perhaps a more cunning way to bring the cold and hot side together without
having to pump water so far. You need to go to very large pipes, or
unconstrained flows using natural convection, eh. Might be able to pump
fresh water down, let it cool and then rise to where we need it. With a flow
as large as the Mississippi, perhaps we could do it without any walls at
all. Perhaps a heat pump to turn fresh water to ice, let the ice just float
up to where we need it. An Ice water version of a heat pump, or perhaps a
cold pump in this case. So we have a 30 ft diameter insulated tube perhaps a
mile long? Of course it will help to have the hot water start out closer to
100C than to 30C, and this should make the collector less prone to fouling.
I think this is not going to be solved with 1940s vintage engineering.

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