Well, I finally can think of a real experiment worth doing in microgravity.

[NNadir]

I am generally not a supporter of human spaceflight, and I find most arguments for doing it specious.

Granted there have been a few very important tasks accomplished by astronauts - the repair of the Hubble comes to mind - but mostly I regard the whole business as theatrics.

However, today I was considering some issues on thermal heat flows in classes of molten salts and issues associated with Prandtl numbers blah, blah, blah, blah, and it occurred to me that it would be very interesting to obtain data about thermal diffusion in the absence of gravity.

I don't know whether this concern would be worth a few tens of billions of dollars or whether a robot couldn't do the same experiment in space as a human, but anyway, it's an interesting thought.

I suppose it would be useful, in a lazy sort of way, to have an astronaut flying around with a shit load of salt to investigate these sorts of phenomenon.

[knowbody0]

1. you have a beautiful mind

[NNadir]

3. Thanks. That's nice of you to say.

[joshcryer]

2. I won't dispute that it's mostly theatrics, but check this out:

http://www.space-multimedia.nl.eu.org/index.php?option=com_content&task=view&id=3716&Itemid=1

It'll make you smile at least. Or at least, it did me! Ah, to dream.

[geckosfeet]

4. Save some time and $$$. Measure thermal diffusion parallel to gravity

in both directions and see if there is a measurable difference.

I expect that the effects all kinds of fields on all kinds of diffusion rates have been well studied.

But I could be wrong.
:evilgrin:

[NNadir]

6. You could be wrong.

There is surprisingly little published about certain kinds of systems.

The matter is rendered even more complex by phase behavior.

There is an entire journal called Computer Coupling of Phase Diagrams and Thermochemistry (also known as CALPHAD) wherein one can read all about quasipertitetic saddle points and blah, blah, blah, blah, but I assure you the heat transfer in these systems is non-trivial, if only because of these effects.

For my purposes a completely empirical approach is probably OK, but I have to be able to frame the issue.

[geckosfeet]

9. I am suprised - sort of. The technical problems in acquiring data in

the systems you speak of is a problem. Measurement equipment simply cannot survive extreme environments. Measuring thermal diffusion rates in any system - even the most stable - is a tricky proposition. I would expect that when there are phase changes taking place that physical properties are changing almost constantly.

[NNadir]

11. The systems I am considering are even more tricky, fun but tricky.

Their composition is constantly changing because they're in a neutron flux, and because some of the components have appreciable vapor pressures. Small amounts of gases are generated as well internally.

I am mostly concerned with crystalization issues.

After a night of looking into the matter, it turns out that the most well characterized melts for thermal flows involve the semiconductor industry, because of the importance of obtaining extremely pure crystals as in Czochralski processes. This stuff is sort of weeny, since they are working with very pure melts.

There is, however, a lot of literature on phase behavior in very complex mixtures of salts, in the journal I referenced earlier, but not much on heat transfer properties. It's a nice exercise in showing my boys the utility of multidimensional graphics.

[RaleighNCDUer]

5. There is only one good reason for man to go to space -

we MUST become a two-planet species. We will not survive as a species otherwise.

Explore and colonize. It is our only hope.

[NNadir]

7. If we can't manage one planet, it's unlikely we'll do much better with two.

[joshcryer]

12. The planet is destined to die, I think is the point of the above poster.

Not necessarily that we're fucking up this planet (we use less energy than algae, less resources than low trophic plants, it's not our population levels or civiization, it's our pollution culture).

[qazplm]

18. we could manage it perfectly

and it will be all for naught when the inevitable species killer meteor or comet heads our way.

And it is inevitable and we can't guarantee that we will have the tech then to move it out of our path, or if it is a comet that we will see it in time even if we have the tech.

Mars has no life or if it does, its darn minimal, and somehow I think the native bacteria might like a warmer, wetter clime that terraforming can provide.

[geckosfeet]

10. We'll crap up the second planet too. We need to learn to care for the planet we have.

[Posteritatis]

13. 'Cause seven billion people can't walk and chew gum at the same time. (nt)

[Ready4Change]

14. Well then...

When an asteroid clobbers one of our crapped up planets, we, as a species, might find it handy to have a spare around.

[Festivito]

8. Guess it depends on what one considers specious.

If one holds that people are not inherently good for example, then setting them on a pie-in-the-sky project would not produce good such as plastics.

If God will destroy earth, maybe we should all go with it. No need to propagate and move along. If nature destroys earth and we are just nature, perhaps we should go with our nature.

But, aside from these I'd probably find the other reasons to not go into space specious.

[Ready4Change]

15. What sort of energies are needed to obtain molten salts?

I know they are used in nuclear reactors. However, there are many groups who get nervous whenever such things are to be launched into orbit. For the sake of easy political hurdles in arranging such an experiment, are there other methods would could be used to achieve a molten state in the salts?

[NNadir]

16. It depends on the salt.

You could make them in your back yard with a crucible and a blow torch using sodium chloride.

Other salts melt at much lower temperatures. There are in fact, an important class of salts that are molten at room temperature, and generally they are organic molecules.

They need not be radioactive.

Radioactive materials are regularly launched into space, and the representations of people who get paranoid about them aside, they have been relatively reliable and harmless.

Examples of radioactive spacecraft that were launched in spite of ignorance include both Pioneer craft, both Voyager craft, Galileo, and Cassini Hyugens.

If we did nothing to confront ignorance, we would still be living in the agraian middle ages.

[TZ]

17. Medical advances are useless then?

A hell of a lot of biology has been learned through microgravity experiments. Seems to get overlooked ALOT.
But I guess a robot can replace actually biological activity right?:crazy:

[Indenturedebtor]

19. Already done - here's a link

Not with salts as far as I know, but there have been quite a few experiments on many aspects of thermodynamics in microgravity, and more are planned.

http://www.springerlink.com/content/pt275q4165n0k563/

There have been a lot of great strides in understanding crystal formations, viruses, plants... biology in general. New super efficient fiberoptic cables have also been developed. Use teh google. There is a lot of good science taking place on the ISS, and a lot more to come that really does require humans at this point.

Further if we're ever going to learn to get off this rock we need to learn how to sustain people in space as well as possible. Visiting planets is another story...

[NNadir]

20. I have accessed the paper, which oddly enough, I had in my files.

I wasn't aware of that until I looked after you were so kind to offer the reference.

In fact, it would not surprise me that the origins of this thread - while I was not concious of as such - derive from this paper.

The experiment is somewhat interesting, but it's not the one I was looking to do, since the liquids in question are low viscosity liquids, to wit, from the body of the paper: "ethanol, methanol, toluene, acetone, and pure water as a standard liquid..."

Convection is well known in this materials of course, and I was interested in a particular class of ionic liquids, molten salts.

I note however that this experiment did not involve human astronauts. It was performed in a Japanese free falling microgravity chamber.

From the paper:

These measurements are carried out automatically
using a sequential program and GP-IB controlled by a personal computer. The measuring system was installed into a capsule of JAMIC (Japan Microgravity Center) and experienced measurements under microgravity conditions during about 10 s of its free fall in the drop shaft.

In other words, the experiment doesn't justify a manned space program at all. It could have been conducted by buying a ticket on the "Tower of Terror" ride at MGM studios in Orlando Florida, and brinking some apparatus and a PC along for the ride.

Thanx.