如何把外太空的低温转换成可再生资源

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照着视频纯手打的，应该不能投原创，所以投了转载，但是打这么多字也不容易 😂

Every summer when I was growing up, I would fly from my home in Canada to visit my grandparents, who lived in Mumbai, India. Now, Canadian summer are pretty mild at best, about 22 degrees Celsius(摄氏度) or 72 degrees Fahrenheit(华氏度), is a typical summer’s day, and not too hot. Mumbai, on the other hand, is a hot and humid place, well into the 30s Celsius or 90s Fahrenheit. As soon as I’d reach it, I’d ask, how could anyone live, work or sleep in such weather? To make things worse, my grandparents didn’t have an air conditioner(空调). And I tried my very, very best, I was never able to persuade(劝说) them to get one. But this is changing, and fast.

Cooling systems today collectively(adv.共同地，全体地) account for 17 percent of the electricity we use worldwide. This include everything from air conditioners I so desperately wanted during my summer vacations, to the refrigerations systems that keep our food safe and cold for us in our supermaket, to the industrial scale systems that keep our data centers operational. Collectively, these systems account for eight percent of global greenhouse gas emissions(来源).

But what keeps me up at night(让我晚上睡不着的事情是) is that our energy use for cooling might grow sixfold(六倍) by the year of 2050, primarily driven by increasing usage in Asian and African countries. I’ve seen this firsthand(adj.直接的，直接采购的，直接的来的/adv:直接地). Nearly every apartment in and around my grandmother’s place now has an air conditioner. And that is, emphatically(adv.明显地，强调地，断然地), a good thing for the health, well-being and productivity of people living in warmer climates. However, one of the most alarming things about climate change is that the warmer our planet gets, the more we are going to need cooling systems. Systems that are themselves large emitters(emiit 发射；emmitter发射源) of greenhouse gas emissions. This then has the potential to cause a feedback loop(反馈循环，恶性循环), where cooling systems alone could become one of our biggest sources of greenhouse gases later this century. In the worst case, we might need more than 10 trillion(万亿) kilowatt-hours(千瓦时) of electricity every year just for cooling, by the year 2100. That’s half our electricity supply today. Just for cooling.

But this also point us to an amazing opportunity. A 10 or 20 percent improvment in the efficiency of every cooling system, could actually have an enormous(巨大的) impact(影响) on our greenhouse gas emissions both today and later this century. And it could help us avert(避免) that worst-case feedback loop. I’m a scientist who think a lot about light and heat. In paticular, how new materials allow us to alter(改变) the flow of these basic elements of nature in ways we might have once thought impossible. So, while I always understood the value of cooling during my summer vacations, I actually wound up(原型：wind up 收场，清场，扫尾，结束) working on this problem because of an intellectual(adj.智力的，脑力的) puzzle that I came across about six years ago.

How were ancient peoples able to make ice in desert climates?

This is a picture of an ice house, also called a Yakhchal, located in the southwest of Iran. There are ruins of dozens of such structures throughout Iran, with evidence of similar such buildings throughout the rest of the Middle East and all the way to China. The people who operated this ice house many centuries ago, would pour the water in the pool you see in the left, int the early evening hours, as the sun set(太阳下山的时候). And then something amazing happen, even though the air temperature might be above freezing, say five degrees Celsius or 41 Fahrenheit, the water would freeze. The ice generated would then be collected in the early morning hours, and stored for use int the building you see on the right, all the way through the summer months.

You’ve actually likely seen something very similar at play(正在展示的，正在上映，这里指的是ppt上正在放的下霜的图片),


if you’ve ever noticed frost form on the ground on a clear night, even when the air temparature is well above freezing. But wait. How did the water freeze if the air tempreature is above freezing? Evaporation(蒸发) could have played an effect, but that’s not enough to actually cause the water to become ice. Something else must have cooled it down. Think about a pie cooling on a window sill(窗台；基石；门槛；海底脊山). For it to be cool down, its heat needs to flow somewhere cooler. Namely, the air that surrounds it. As implausible(adj.难以置信的) as it may sound, for that a pool of water, its heat actually flowing to the cold of space, How is this possible? Well, that pool of water, like most natural materials, sends out its heat as light. This is a concept known as thermal radiation(热辐射). In fact, we’re all sending out our heat as infrared(红外线) light right now, to each other and our surroundings. we can actually visualize this with thermal cameras(热感摄像机) and images they produce, like the ones I’m showing you right now. So that pool of water is sending out its heat upward to the atmosphere. The atmosphere and the molecules(n.[化学]分子，微粒;[化学]摩尔(molecule的复数)) in it absorb some of that heat and send it back. That’s actually greenhouse effect that’s responsible for climate change. But here is the critical(adj.鉴定的；批评的；爱挑剔的；危险的；决定性的) thing to understand. Our atmosphere doesn’t absorb all of the heat. If it did, we’d on a much warmer planet. At certain wavelength(波长), in particular between 8 and 13 microns(n.微米，micron的复数), our atmosphere has what’s shown as a transmission

window. This window allows some of the heat that goes up as infrared light to effectively escape, carrying away that pool’s heat. And it can escape to a place that is much, much colder. The cold(这里指的是大气上层的低温层) of this upper atmosphere and all the way out to outer spce, which can be as cold as minus 270 degrees Celsius, or minus 454 Fahrenheit. So that pool of water is able to send out more heat to the sky than the sky sens back to it. And because of that, the pool will cool down below its surroundings’ temparature. This is an effect known as night-sky cooling or radiate cooling. And it’s always been understood by climates scientists and meteorologists(气象学家；气象学：meteorology, the sicentific study of the processes that cause paticular weather coditions) as a very important natural phenomenon. When I came across all of this, it was towards the end of my PhD at Stanford. And I was amazed by its apparent simplicity as a cooling method, yet really puzzled. Why aren’t we making use of this?

Now scientists and engineers had investigated this idea in previous decades. But there turn out to be at least one big problem. It was called night-sky cooling for a reason. Why? Well, it’s a little thing called the sun.


So for the surface that’s doing the cooling, it needs to be able to face the sky. And during the middle of the day, when we might want something cold the most, unfortunately, that means you’re going to look up to the sun. And the sun heats most materials up enough to completely counteract(vt.抵消;中和) this cooling effect. My colleagues and I spend a lot our time think aoubt how we can structure materials at very small length scales(长度刻度) such that they can do new and useful things with light, length scales smaller than the wavelength of light itself. Using insight(n.洞察力;眼见;见识) from this field, known as nanophotonics(n.纳米光子学) or metamaterials(超导材料) research, we realized that might be a way to make this possible during the day from the first time. To do this, I designed a multilayer optical materical shown here in the microscope imag.


It’s more than 40 times thinner than a typical human hair. And it’s able to do two things simultaneously(同时地). First, it sends its heat out precisely(恰好地) where our atmosphere lets that heat out the best. We targeted the window to the space. The second thing it does is it avoids getting heated up by the sun. It’s a very good mirror to sunlight. The first time I tested this was on a rooftop in Stanford and I’m showing you right here.


I left the device out for a little while, and I walked up to it after a few minutes, and within seconds, I knew it was working. How? I touched it and it felt cold.

Just to emphasize(强调) how weird and counterintuitive(/ˌkoun(t)ərinˈt(y)o͞oədiv/ adj.违反直觉的) it is, this material and others like it will get colder when we take them out of shade, even though the sun is shining on it. I am showing you data here from our very first experiment, where that material stayed more than 5 degrees Celsius, or 9 degrees Fahrenheit, colder than the air temperature, even though the sun was shining directly on it.

The manufacturing method we used to actually make this material already exists at large volume(体积) scales(大量地). So I was really excited because not only do we make somthing cool, but we might actually have the opportunity to do something real make it useful. That brings me to the next big question. How do you actually save energy with this idea?

Well, we belive the most direct way to save energy with this technology is as an efficiency boost for today’s air-conditioning and refrigeration systems. To do this, we’ve built fluid cooling panels.

These panels have a similar shape to solar water heaters, except they do the opposite–they cool the water, passively(被动地) using our spacialized material. These panels can then be integrated(integrate v.使……整合，成为整体) with a component almost every cooling system has, called a condenser(冷凝器), to improve the system’s underlying(adj.潜在的；根本的；在下面的；优先的) efficiency. Our start-up, SkyCool Systems, has recently completed a field trial in Davis, Califonia, shown right here. In that demonstration, we show that we can actually improve the efficiency of that cooling system as much as 12 percent in the field. Over the next year or two, I’m super excited to see this go to its first commercial-scale pilots in both the air conditioning and refrigeration space. In the future, we might be able to integrate these kinds of panels with higher efficiency building cooling systems to reduce their energy usage by two-thirds. And eventually, we might actually be able to build a cooling system that requires no electricity input at all. As a first step towards that, my colleagues at Stanford and I have shown that you counld actually maintain something more than 42 degrees Celsius below the air temparature with better engineering.

So just image that something that is below freezing on a hot summer’s day. So, while I’m very excited about all we can do for cooling, But I think there’s a lot yet to be done, as a scientist, I’m also drawn to be a more profound opportunity that I believe this work highlights. We can use the cold darkness of space to improve the efficiency of every energy-related process here on earth. One such process I’d like to highlight are solar cell, they heat up under the sun and become less efficient the hotter they are. In 2015, we showed that with deliberate kinds of microstructures on top of solar cells, we could take better advantage of this cooling effect to maintain a solar cell passively at a lower temperature. This allow the cell to operate more efficiently. We’re probing these kinds of opportunities futher. We are asking whether we can use the cold of space to help us with water conservation. Or perhaps with off-grid scenarios. Perhaps we could event directly generate power with this cold. There’s a large temperature difference between us here on earth and cold of space. That difference, at least conceptually, could be use to drive something called a heat engine to generate electricity. Could we then make a nighttime power-generation device that generates useful amounts of electricity when solar cells don’t work? Could we generate light from darkness? Central in this ability is being able to manage the thermal radiation that’s all around us. We are constantly bathed in infrared light, if we could bend it to our will, we could profoundly change the flows of heat and energy that permeate around us every single day. This ability, coupled with the cold darkness of space, points us to a future where we, as a civilization, might be able to more intelligently manage our thermal energy footprint, at the very large scales. As we confront climate change, I believe having this ability in our toolkit will prove to be essential. So, the next time you’re walking around outside, yes, do marvel at how the sun is essential to life and erath itself, but don’t forget that the rest of the sky has something to offer us as well. Thank you.