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coppice:
--- Quote from: CatalinaWOW on June 07, 2023, 05:15:43 pm ---I was surprised to see the comment that stainless steel wasn't that expensive, so did some searches and found that the relative prices of materials has changed a lot since I last bought any a couple of decades ago.
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It depends a lot on where you are. In the UK stainless steel is treated like a precious metal. In East Asia a huge amount of stuff is made from stainless steel, and its not that expensive to have really thick stainless steel.
Zero999:
--- Quote from: james_s on June 07, 2023, 08:03:12 pm ---Global warming has raised the average temperature of the planet only 0.8C per decade since 1981 according to what I've found. That's enough to cause problems but not likely going to be very perceptible to humans or affect the amount of time you'd want to open the windows. Where I live has weather similar to that in the UK and it does seem like our summers are a bit hotter than when I was a kid, but it's always gotten pretty hot for at least a few weeks.
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You've put the decimal point in the wrong place. Global temperatures have risen by 0.08°C per decade.
https://www.climate.gov/news-features/understanding-climate/climate-change-global-temperature
Some regions have warmed more than others and there are a few places which have actually cooled, due to changes in atmospheric circulation. Care needs to be taken with temperature and precipitation measurements, since human activity can affect the local microclimate. For example, a weather station which was previously in a rural area, which has recently become urbanised, will show an increase in temperature. The Met Office actually subtract 0.2°C from the modern Central England average to account for this.
--- Quote from: MK14 on June 07, 2023, 11:32:46 pm ---Pity we can't just invent something, which can turn heat (temperature) as opposed to temperature differences, into electricity.
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Of course not. It would violate the second law of thermodynamics. There's no way to do work without a temperature differential. It would be like using ambient air pressure to spontaneously make a vacuum. Daily/seasonal changes in temperature and air pressure can be used to generate electricity, but only a tiny amount, as the differential is tiny.
IanB:
--- Quote from: Zero999 on June 08, 2023, 09:26:12 pm ---Of course not. It would violate the second law of thermodynamics. There's no way to do work without a temperature differential. It would be like using ambient air pressure to spontaneously make a vacuum. Daily/seasonal changes in temperature and air pressure can be used to generate electricity, but only a tiny amount, as the differential is tiny.
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In principle, if you could use outer space as your heat sink, where the temperature is about 4 K, then you could have quite a nice temperature differential of 300 K or so. Not huge, but plenty good enough for heat pumps. Unfortunately, it would require some kind of very efficient radiator with access to clear skies at night. It's a shame there is unlikely to be a way to engineer such a thing.
Zero999:
--- Quote from: IanB on June 08, 2023, 09:57:04 pm ---
--- Quote from: Zero999 on June 08, 2023, 09:26:12 pm ---Of course not. It would violate the second law of thermodynamics. There's no way to do work without a temperature differential. It would be like using ambient air pressure to spontaneously make a vacuum. Daily/seasonal changes in temperature and air pressure can be used to generate electricity, but only a tiny amount, as the differential is tiny.
--- End quote ---
In principle, if you could use outer space as your heat sink, where the temperature is about 4 K, then you could have quite a nice temperature differential of 300 K or so. Not huge, but plenty good enough for heat pumps. Unfortunately, it would require some kind of very efficient radiator with access to clear skies at night. It's a shame there is unlikely to be a way to engineer such a thing.
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4 K to 300 K is a huge temperature differential. You've forgotten that the lower the overall temperature of the system, the higher the maximum theoretical efficiency of the heat engine.
Carnot's theorem.
ηMAX = 1 - TC/TH
TC = 4 K
TH = 300 K
ηMAX = 1 - 4/300 = 98 2/3%
It's obviously impractical to get anywhere near this. The atmosphere returns a huge amount of radiation back to the earth, which is obviously a good thing.
MK14:
--- Quote from: Zero999 on June 08, 2023, 10:18:33 pm ---4 K to 300 K is a huge temperature differential. You've forgotten that the lower the overall temperature of the system, the higher the maximum theoretical efficiency of the heat engine.
Carnot's theorem.
ηi = 1 - TC/TH
TC = 4 K
TH = 300 K
ηi = 1 - 4/300 = 98 2/3%
It's obviously impractical to get anywhere near this. The atmosphere returns a huge amount of radiation back to the earth, which is obviously a good thing.
--- End quote ---
I wondered if a super-conductor, threaded through a massive space elevator, between the planet surface (Earth) and out-space, could conduct enough heat, to make a powerful energy source. While making my earlier posts in this thread, about using temperature as an energy source.
But unfortunately, the reality seems to be that super-conductors, make very poor thermal conductors. So I had to throw that idea out of the window. Which worked, because there was no insect screen in the UK, for it to bounce off (this sentence is a joke).
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