Archive for the ‘Global Warming’ Category

Running a Stirling Engine Using the Night Sky

November 28, 2018

I’m a failed inventor. I get strange ideas, try them out, and usually discover that I either got my physics wrong or built my prototype poorly, or that someone beat me to the punch thirty or three hundred years ago. I created what I thought was a great factoring algorithm for huge numbers and found out that Fermat developed it first. That’s the way it goes.

So here’s the latest invention. It’s not really an invention so much as an interesting application of an existing device.

Is it possible to make a heat engine that runs off the thermal differential between the night sky and the heat radiating from the ground? Stirling engines can run using fairly small temperature differences, such as the ambient air and the heat in the palm of your hand. You can get one of these hand-driven Stirling heat engines from ebay for under $50.  The real question isn’t so much whether you can make a device that runs off the heat sink of the night sky, but how much of a thermal delta you could provide to that engine.

How cold is the night sky? I’ve read that on a clear night, it can provide a radiative heat sink of -70˚C. Yeah, that’s negative 70 degrees centigrade. Pretty cold. Those with a background in heat transfer physics know that the other two forms of thermal transfer are conductive and convective, and with the right glass or plastic covered chamber, you can minimize those thermal paths so that your heat source/sink sees only the -70˚C of the night sky. This is why some telescopes have a problem with their optics freezing up. Really. It also explains why some windshields frost up even though it doesn’t reach freezing temperatures outside, and other related phenomena.

The other side of your Stirling heat engine could be getting its energy from the radiation from the ground, say, about 15˚C. Or if you heated up a tank of water during the day, maybe 40 or 50˚C. You could run your engine easily with a delta of 100 degrees, though as you thermal guys know, the engine would be a lot more efficient at higher temperatures during the day shift.

But, the hypothetical question is if you could run an engine off the night sky. My speculative answer is “yes”. What’s nifty about the ability to do this? Well, instead of dumping HEAT into the atmosphere to generate energy, which every power source on Earth currently does, you are actually dumping COLD (a.k.a, removing heat) into the atmosphere to run your engine. The net heat loss of your engine is NEGATIVE.

So yeah, we could cool down the Earth and generate energy at the same time. Crazy, huh? The biggest problem with the idea is that you could generate a lot more energy a lot more efficiently using a hot solar Stirling engine during the day at the same cost, while dumping more heat into the atmosphere.

And cost seems to drive everything except our self-preservation instinct.

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We Are The Meteor

July 20, 2013

Not that long ago I was reading an article by Robert Zubrin, called “Carbon Emissions are Good“, where he stated an oft-repeated mantra by those who think global warming, while real, is no big deal.

It generally goes like this; “Global Warming cycles have occurred in the past, life has dealt with it, and in some cases, done even better than now due to all the extra CO2 in the atmosphere.” Zubrin writes, “while it is entirely possible that the earth may be warming — as it has done so many times in the past — there is no rational basis whatsoever to support the contention that carbon-dioxide-driven global warming would be on the whole harmful to life and civilization. Quite the contrary: All available evidence supports the contention that human CO2 emissions offer great benefits to the earth’s community of life.”

Sorry, but this is a completely false statement, and apparently Zubrin neglected to read much of the “all available evidence” he mentions. It completely ignores one of the major components to the problem. As Brian Huntley puts it, “The rate of climate change forecast for the future is 10–100 times faster than the rate of deglacial warming.” His paper, “How Plants Respond to Climate Change: Migration Rates, Individualism and the Consequences for Plant Communities” in Annals of Botany talks about the critical issue; how fast plants and animals can migrate when an environment changes too much to support the plant life.

Herbivores can’t live without the plants they eat. Plants can’t migrate themselves except through a few very slow processes, including undigested seeds, wind distribution, sticky seeds, and water and mud flows. Given a thousand years of slow warming, the natural random distribution of seeds with these mechanisms might allow plant and animal species to spread to local environments that are more habitable. Given a hundred years, the slow random redistribution of seeds means that the old environment will die out before the new one has a chance to migrate or take hold; massive extinctions of the whole food chain will occur. Plants and animals have, indeed, evolved mechanisms to allow migration, but these depend on slow, natural rates of heating and cooling, rates that allow a slow peripheral migration, not the wholesale destruction of one habitat to be replaced by another more suitable 1000 miles away. There are barriers and thermal pinch-points that can prevent a species from migrating at all.

If you were in a room quickly filling with milk, and you had no exits, Dr. Zubrin would point out how healthful the milk is for you.

Rather than the slow process of deglaciation, a climate altering event more comparable to human global warming is a giant meteor strike, resulting in climate change that occurs in weeks and lasts for decades or longer. Sure, this is the other end of the scale, but we also know for a fact that such events are quite capable of wiping out 90% of the extant species. Species have no chance to recover from such an event, or migrate to more pleasant climes.

Unfortunately, we have become the meteor.