Boiling Water In Space

[Alpha_Geek]

Most solar panels boast an efficiency rating of... Are you ready?

20%!

Experts (not you) state that the most advanced designs get close to 40% efficiency.

So whatever math you might try, multiply the size of your incredibly massive solar array in this latest cocktail napkin fantasy by 2.2 or so in order to get what you think you'll get.

[I Am Legend]

Trekker4747 wrote:

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So, now the entire premise of your idea has changed from wanting to solve the energy crisis on earth

I never said that was the premise and I mention space based colonys in my original post, do I need to quote it?.
It was never all about getting power to Earth, there were multiple options on the table.

[Jadzia]

Alpha_Geek wrote:

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Most solar panels boast an efficiency rating of... Are you ready?

20%!

Experts (not you) state that the most advanced designs get close to 40% efficiency.

So whatever math you might try, multiply the size of your incredibly massive solar array in this latest cocktail napkin fantasy by 2.2 or so in order to get what you think you'll get.

This is irrelevant, since the idea doesn't propose use of photovoltaic cells.

In fact, I see this idea is more about the design of an engine, not so much the applications of it, which is more speculative.

I Am Legend has a perfectly good idea here for an orbital heat engine driven by solar power. He doesn't need to provide us blueprints for a complete energy delivery system.

[Alpha_Geek]

...and this would be MORE efficient than photrovotaics?

[Jadzia]

Efficiency depends on many factors, including the working temperatures, which itself would depend upon orbital altitude. Some designs can have 1% efficiency, some designs can have well over 50% efficiency.

[sojourner]

For once, Tacky has science on his side. Solar furnaces are nothing new, he is just proposing using them in space. Maybe everyone should do a little research before just jumping on the bashwagon.

http://en.wikipedia.org/wiki/Solar_power_tower

[Scout101]

You don't see any problem with instantly translating a ground-based solution for use in deep space? Nor the MASSIVE losses in energy by trying to transmitting anything of use all the way to a final destination? A little different than being able to plug in directly to the generator, or having to deal with temps a little warmer than absolute zero...

not saying there's NOTHING of value here, but doesn't seem like much of an idea without working out some sort of practical application. Or, like most of these threads, a reason to go with this massively complicated solution when cheaper and easier ideas would work just as well, with much less risk.

[sojourner]

Yes, I do see problems with instantly translating a ground based solution for use in deep space.
Did anyone ever suggest instantly translating it to deep space? No. It would obviously need to be adapted for that use, as is every other technology used in deep space.

The concept is sound. Only a moron would suggest using the exact same design in space.

He did concede that transmission back to Earth might be problematic and raised another application - as a power source for space colonies.

There is nothing fundamentally wrong with this idea. Quit trying to sink it just because Tacky brought it up.

[Trekker4747]

The idea is "sound" but loses some of that soundness when we talk about using laser beams to transmit power -which granted isn't all that out of wack- or the application of using it power space colonies (when by that time better and power-producing options would be available.)

But to some marginal credit, this idea is one of his that makes the "most sense."

However, it's tarnished greatly by many of his other ideas in the past.

[Chaos Descending]

I Am Legend wrote:

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In space there's no Earth gravity affecting the turbines meaning they will move even quicker and more effectively than in a gravity environment, obviously therefore producing far more power output.

This is kind of nonsense.

Gravity does not affect the operation of a rotary turbine one way or another.

[sojourner]

^true. it points to a lack of understanding of the forces involved. The real benefit of the generator being in space is the lack of atmosphere (including inclement weather)diluting the sunlight. Also, the possibility of having it in a location where it is never blocked from the sun.

[I Am Legend]

Chaos Descending wrote:

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This is kind of nonsense.

Gravity does not affect the operation of a rotary turbine one way or another.

In space you would not need to use as much force to turn/push the turbine.

Scout101 wrote:

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Or, like most of these threads, a reason to go with this massively complicated solution when cheaper and easier ideas would work just as well, with much less risk.

But there's nothing complicated about it. Water near the sun boils, creating steam, turning turbines to generate power and the power is then used to power a space colony. It's renewable and produces more power than any alternative method.

[Trekker4747]

I Am Legend wrote:

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In space you would not need to use as much force to turn/push the turbine.

But there's nothing complicated about it. Water near the sun boils, creating steam, turning turbines to generate power and the power is then used to power a space colony. It's renewable and produces more power than any alternative method.

Stop thinking of the sun as a ball of fire -it isn't, by the way.

"Water near the sun boils" is wrong. I mean it does boil, but it doesn't need to be there to boil.

Water in space boils because there's no atmospheric pressure. Ever heard of high-altitude cooking instructions? The boiling point of water at sea level is 212*F, on top of Mt. Everest -29,000 FT above sea level- is 156*F because there's less air pressure. In space, water boils almost instantly.

[Jadzia]

Trekker4747 wrote:

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Stop thinking of the sun as a ball of fire -it isn't, by the way.

"Water near the sun boils" is wrong. I mean it does boil, but it doesn't need to be there to boil.

Water in space boils because there's no atmospheric pressure...

You're missing the point, Trekker. The design (as I understand it) is proposing a sealed system, where the water will always be at a significant pressure because it cannot expand out of the manifold. The water isn't exposed to vacuum. The role of the sun in this system is just a ball of fire providing thermal energy.

[Scout101]

is a heating system of some sort needed for the 'dark' side of the aparatus? Getting liquid and then steam water on the sun side seems alright, but I'd be concerned about the steam or water flashing back to ice rather than circulating around the device. Just too extreme of a cold temp on the back side of the device, without additional heating, i'd think. May also cause some extreme fatigue in the parts of the machine, with such temp changes...

[Jadzia]

Scout101 wrote:

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is a heating system of some sort needed for the 'dark' side of the aparatus? Getting liquid and then steam water on the sun side seems alright, but I'd be concerned about the steam or water flashing back to ice rather than circulating around the device. Just too extreme of a cold temp on the back side of the device, without additional heating, i'd think. May also cause some extreme fatigue in the parts of the machine, with such temp changes...

I wouldn't expect the individual bits of piping to fatigue, since they'll be at relatively constant temperatures. The back side isn't extreme cold. Heat will radiate, at a gradual rate in proportion with stefan's law. It's not like having liquid nitrogen poured over it.

In many ways it would be a self regulating system. If water in the fringes of the cooling plate did freeze, then less heat will be radiated, resulting in a temperature build up. So the water coming through the turbines will be hotter and better able to defrost it. Normal operation is a stable equilibrium.

[sojourner]

I Am Legend wrote:

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In space you would not need to use as much force to turn/push the turbine.

This is incorrect. It takes as much force to move a mass in space as it does on Earth. Now, if you were lifting the turbine against Earth's gravity (say, trying to get it into space) you would require more net force.

Rotating your turbine requires the same amount of power whether in space or on Earth.

In many ways it would be a self regulating system. If water in the fringes of the cooling plate did freeze, then less heat will be radiated, resulting in a temperature build up. So the water coming through the turbines will be hotter and better able to defrost it. Normal operation is a stable equilibrium.

You could also design the system as a (I think this is the correct term) reverse flow system. Basically you would entwine the hot pipes going out to the cooler with the cold pipes coming back. Heat would transfer between the 2 sides of the pipe system. Thus at the same time you are keeping the cold water from freezing, you are starting the cooling process on the hot water.

[newtype_alpha]

As has been pointed out, the thing doesn't need to be near the sun for the water to boil. It depends entirely on the pressure of the water; lower pressure means lower boiling point, but the steam is also cooler so you get less energy.

If you want hotter water, it's more efficient to just stack a bunch of mirrors angled in a way to collect sunlight and use it as a heat source. This is why old sci-fi artists used to put mercury boiler tubes on all their space station designs until someone pointed out that solar panels are actually MORE efficient in this application than turbines.

So, in the end, no matter how close you are to the sun, you'll usually get more energy from solar panels than from steam turbines.

[Jadzia]

This is incorrect. It takes as much force to move a mass in space as it does on Earth.

Maybe he's thinking of friction in the bearings? In a weightless environment, the bearings wouldn't be under much stress at all

[sojourner]

At the tolerances power turbines are built to, no, bearing friction would not be a big issue.

Hate to say it, but I doubt that was what he meant anyway.