Talk-Polywell.org

While not as impressive as a Bussard thruster, a novel use of nuclear batteries.

http://www.wired.com/wiredscience/2012/ ... ploration/

It is not really a nuclear battery (RTG) but a real small reactor. It is pretty cool and scalable.

I like the idea of using sterlings in orbit as well. I remember seeing some other stuff on it a while back. All you need is a heat source and heat sink. Closed loop fluid cycle, useful.

I wonder whether some of the dumped heat couldn't be harvested by conventional thermoelectric generators in a sort of hybrid design, saving weight in the heat sinks as well.

I wonder whether some of the dumped heat couldn't be harvested by conventional thermoelectric generators in a sort of hybrid design, saving weight in the heat sinks as well.

Thermoelectrics also need a heat differencial, just like the Stirlings do. I am not sure you would save much weight with them. There is some tech for conversion of radiation into electricity though that does not seem to rely on a heat differencial (but rather works like photovoltaics for radiation). You dont hear much about that, but it does sound cool.

Sterling Engines have moving parts, how reliable is this going to be?

daveklingler wrote:I wonder whether some of the dumped heat couldn't be harvested by conventional thermoelectric generators in a sort of hybrid design, saving weight in the heat sinks as well.

With the same weight of added radiator, the dump temperature could enough lower to allow a Stirling to generate more added power than the TE device. It is all a matter of economics.

spirc wrote:Sterling Engines have moving parts, how reliable is this going to be?

Last time I looked, the Stirling engine proposed for NASA had, aside from the working gas, one moving part that never touches the rest of the system. It should last for as long as there is a working gas which also creates the bearing tween the two surfaces.

That, to me, is the real issue. The gasses that won't freeze out can work their way thru most metals, especially red hot ones, over time. Just how long will there be a working gas?

Skipjack wrote:

I wonder whether some of the dumped heat couldn't be harvested by conventional thermoelectric generators in a sort of hybrid design, saving weight in the heat sinks as well.

Thermoelectrics also need a heat differencial, just like the Stirlings do. I am not sure you would save much weight with them. There is some tech for conversion of radiation into electricity though that does not seem to rely on a heat differencial (but rather works like photovoltaics for radiation). You dont hear much about that, but it does sound cool.

In these cases, don't the cells have to be much colder than the radiant source? Otherwise, don't the internal signals swamp the received; i.e., the holes can't make it thru the cell.

In these cases, don't the cells have to be much colder than the radiant source? Otherwise, don't the internal signals swamp the received; i.e., the holes can't make it thru the cell.

I honestly dont know. The information on this is very sparse. There are actually two concepts which seem to be somewhat different. I cant even find anything about the actual efficiency (other than that they are more efficient than thermoelectrics, which does not really mean much). I keep mentioning these every now and then in the hope that someone who knows more about them will feel compelled to comment

Skipjack wrote:

In these cases, don't the cells have to be much colder than the radiant source? Otherwise, don't the internal signals swamp the received; i.e., the holes can't make it thru the cell.

I honestly dont know. The information on this is very sparse. There are actually two concepts which seem to be somewhat different. I cant even find anything about the actual efficiency (other than that they are more efficient than thermoelectrics, which does not really mean much). I keep mentioning these every now and then in the hope that someone who knows more about them will feel compelled to comment

Silicon's band gap is in the infrared region. One proposal to improve the efficiency of silicon cells is to redirect the incoming solar energy via a black body to a temperature that will better match it's color. Might that be what you mean?

Here is a (rather vague) description of one of them:
http://www.newscientist.com/article/dn1 ... icity.html

This here is a description of the other method that I am aware of, but I the first one sounded more promising:
http://prelas.nuclear.missouri.edu/Publ ... 03RECS.pdf

I BELIEVE THAT THERMOPHOTOVOLTAICS ARE WHAT YOU WANT. THE IDEA IS TO COAT A HEAT SOURCE WITH A SELECTIVE SURFACE THAT ONLY RADIATES ENERGY AT ONE SPECIFIC WAVELENGTH. THEN YOU SURROUND THE HEAT SOURCE WITH PHOTOVOLTAICS WHOSE MAXIMUM CONVERSION EFFICIENCY IS AT THAT WAVELENGTH. THE LAST TIME I CHECKED NEWS ON THIS TECHNOLOGY THEY HAD ACHIEVED A TOTAL SYSTEM EFFICIENCY OF THIRTY PERCENT. AT PRESENT THIS IS NO BETTER THAN A DIESEL-ELECTRIC GENERATOR BUT THERE IS A LOT OF THEORETICAL ROOM FOR IMPROVEMENT. EVEN NOW, A POWER SOURCE AT THIS LEVEL OF EFFICIENCY WITH NO MOVING PARTS TO WEAR OUT HAS A LOT TO RECOMMEND IT.

SHOUT, SHOUT, LET IT ALL OUT. THESE ARE THE THINGS I CAN DO WITHOUT.
COME ON, I'M TALKING TO YOU, COME ON. . .