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Physicists Explain How Heat Kills Machines and Electronics

2023-09-07 07:43:59
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The following essay is reprinted with permission from The Conversation, an online publication covering the latest research.

Not only people need to stay cool, especially in a summer of record-breaking heat waves. Many machines, including cellphones, data centers, cars and airplanes, become less efficient and degrade more quickly in extreme heat. Machines generate their own heat, too, which can make hot temperatures around them even hotter.

We are engineering researchers who study how machines manage heat and ways to effectively recover and reuse heat that is otherwise wasted. There are several ways extreme heat affects machines.

No machine is perfectly efficient – all machines face some internal friction during operation. This friction causes machines to dissipate some heat, so the hotter it is outside, the hotter the machine will be.

Cellphones and similar devices with lithium ion batteries stop working as well when operating in climates above 95 degrees Farenheit (35 degrees Celsius) – this is to avoid overheating and increased stress on the electronics.

Cooling designs that use innovative phase-changing fluids can help keep machines cool, but in most cases heat is still ultimately dissipated into the air. So, the hotter the air, the harder it is to keep a machine cool enough to function efficiently.

Plus, the closer together machines are, the more dissipated heat there will be in the surrounding area.

Deforming materials

Higher temperatures, either from the weather or the excess heat radiated from machinery, can cause materials in machinery to deform. To understand this, consider what temperature means at the molecular level.

At the molecular scale, temperature is a measure of how much molecules are vibrating. So the hotter it is, the more the molecules that make up everything from the air to the ground to materials in machinery vibrate.

As the temperature increases and the molecules vibrate more, the average space between them grows, causing most materials to expand as they heat up. Roads are one place to see this – hot concrete expands, gets constricted and eventually cracks. This phenomenon can happen to machinery, too, and thermal stresses are just the beginning of the problem.

Travel delays and safety risks

High temperatures can also change the way oils in your car’s engine behave, leading to potential engine failures. For example, if a heat wave makes it 30 degrees F (16.7 degrees C) hotter than normal, the viscosity – or thickness – of typical car engine oils can change by a factor of three.

Fluids like engine oils become thinner as they heat up, so if it gets too hot, the oil may not be thick enough to properly lubricate and protect engine parts from increased wear and tear.

Additionally, a hot day will cause the air inside your tires to expand and increases the tire pressure, which could increase wear and the risk of skidding.

Airplanes are also not designed to take off at extreme temperatures. As it gets hotter outside, air starts to expand and takes up more space than before, making it thinner or less dense. This reduction in air density decreases the amount of weight the plane can support during flight, which can cause significant travel delays or flight cancellations.

Battery degradation

In general, the electronics contained in devices like cellphones, personal computers and data centers consist of many kinds of materials that all respond differently to temperature changes. These materials are all located next to each other in tight spaces. So as the temperature increases, different kinds of materials deform differently, potentially leading to premature wear and failure.

Lithium ion batteries in cars and general electronics degrade faster at higher operating temperatures. This is because higher temperatures increase the rate of reactions within the battery, including corrosion reactions that deplete the lithium in the battery. This process wears down its storage capacity. Recent research shows that electric vehicles can lose about 20% of their range when exposed to sustained 90-degree Farenheit weather.

Data centers, which are buildings full of servers that store data, dissipate significant amounts of heat to keep their components cool. On very hot days, fans must work harder to ensure chips do not overheat. In some cases, powerful fans are not enough to cool the electronics.

To keep the centers cool, incoming dry air from the outside is often first sent through a moist pad. The water from the pad evaporates into the air and absorbs heat, which cools the air. This technique, called evaporative cooling, is usually an economical and effective way to keep chips at a reasonable operating temperature.

However, evaporative cooling can require a significant amount of water. This issue is problematic in regions where water is scarce. Water for cooling can add to the already intense resource footprint associated with data centers.

Struggling air conditioners

Air conditioners struggle to perform effectively as it gets hotter outside – just when they’re needed the most. On hot days, air conditioner compressors have to work harder to send the heat from homes outside, which in turn disproportionally increases electricity consumption and overall electricity demand.

For example, in Texas, every increase of 1.8 degrees F (1 degree C) creates a rise of about 4% in electricity demand.

Heat leads to a staggering 50% increase in electricity demand during the summer in hotter countries, posing serious threats of electricity shortages or blackouts, coupled with higher greenhouse gas emissions.

How to prevent heat damage

Heat waves and warming temperatures around the globe pose significant short- and long-term problems for people and machines alike. Fortunately, there are things you can do to minimize the damage.

First, ensure that your machines are kept in an air-conditioned, well-insulated space or out of direct sunlight.

Second, consider using high-energy devices like air conditioners or charging your electric vehicle during off-peak hours when fewer people are using electricity. This can help avoid local electricity shortages.

Reusing heat

Scientists and engineers are developing ways to use and recycle the vast amounts of heat dissipated from machines. One simple example is using the waste heat from data centers to heat water.

Waste heat could also drive other kinds of air-conditioning systems, such as absorption chillers, which can actually use heat as energy to support coolers through a series of chemical- and heat-transferring processes.

In either case, the energy needed to heat or cool something comes from heat that is otherwise wasted. In fact, waste heat from power plants could hypothetically support 27% of residential air-conditioning needs, which would reduce overall energy consumption and carbon emissions.

Extreme heat can affect every aspect of modern life, and heat waves aren’t going away in the coming years. However, there are opportunities to harness extreme heat and make it work for us.

This article was originally published on The Conversation. Read the original article.

参考译文
物理学家解释热量如何摧毁机器和电子设备
以下文章经授权转载自《The Conversation》,这是一家报道最新研究的在线出版物。不仅人类在打破纪录的热浪中需要保持凉爽,许多机器包括手机、数据中心、汽车和飞机在极端高温中效率也会下降,寿命也会缩短。机器在运行过程中也会产生自身的热量,这会使周围的温度更加炎热。我们是研究机器如何管理热量以及如何有效回收和再利用原本被浪费的热量的工程研究人员。极端高温对机器有几种影响。没有任何机器是完全高效的——所有机器在运行过程中都会遇到一定的内部摩擦。这种摩擦会导致机器散发一些热量,因此外界气温越高,机器本身的温度也会越高。当环境温度超过95华氏度(35摄氏度)时,手机和使用锂离子电池的类似设备的性能会下降,这是为了避免过热并减少对电子元件的损害。使用创新相变流体的冷却设计可以帮助机器保持凉爽,但大多数情况下,热量最终仍会散发到空气中。因此,空气越热,就越难以使机器保持足够的凉爽以高效运行。此外,机器摆放得越密集,周围区域散发的热量也会越多。材料变形 高温,无论是来自天气还是机器释放的多余热量,都可能导致机器材料的变形。为了理解这一点,我们可以从分子层面来看温度。在分子尺度上,温度是衡量分子振动程度的指标。因此,温度越高,构成从空气到地面再到机器材料的一切的分子振动得越剧烈。随着温度升高和分子振动加剧,它们之间的平均距离增大,使大多数材料在受热后膨胀。道路就是一个例子——炎热的混凝土会膨胀、受到限制,最终开裂。这种现象也可能出现在机器上,热应力只是问题的开始。出行延误与安全风险 高温还可能改变汽车发动机中机油的表现,从而导致潜在的发动机故障。例如,如果热浪使温度比正常高出30华氏度(16.7摄氏度),那么典型汽车机油的粘度——也就是其厚薄程度——可能会改变三倍。像机油这样的流体在受热后会变稀,因此如果温度太高,机油可能不够浓稠,无法充分润滑并保护发动机部件,防止磨损。此外,炎热的天气还会使轮胎内的空气膨胀,从而增加轮胎压力,这可能会加剧磨损并增加打滑的风险。飞机也不适合在极端温度下起飞。随着外界温度升高,空气开始膨胀,占据更多的空间,变得稀薄。空气密度的降低会减少飞机在飞行中所能承载的重量,这可能导致显著的出行延误或航班取消。电池退化 总体而言,手机、个人电脑和数据中心等设备中所含的电子元件由多种不同的材料组成,它们对温度变化的反应也各不相同。这些材料紧密地排列在有限的空间中。因此,当温度上升时,不同种类的材料可能会以不同的方式变形,从而可能导致早期磨损和故障。汽车和一般电子设备中的锂离子电池在较高的运行温度下会更快退化。这是因为高温会加快电池内部的反应速度,包括腐蚀反应,这些反应会耗尽电池中的锂。这一过程会削弱其存储容量。最近的研究表明,电动汽车在持续90华氏度(约32.2摄氏度)的天气中行驶时,其续航里程可能会减少大约20%。数据中心是一些装满服务器的建筑,用于存储数据,会散发大量热量以保持其组件的凉爽。在非常炎热的天气中,风扇必须更加努力地工作,以确保芯片不会过热。在某些情况下,强大的风扇也不足以冷却电子设备。为了保持数据中心的凉爽,通常会将室外的干燥空气首先通过湿润的垫子。垫子中的水蒸发到空气中,吸收热量,从而冷却空气。这种被称为蒸发冷却的技术,通常是一种经济且有效的保持芯片在合理运行温度的方法。然而,蒸发冷却可能需要大量水。在水资源稀缺的地区,这个问题尤为突出。冷却用水会增加数据中心本已沉重的资源消耗负担。挣扎的空调 随着外界温度升高,空调的性能会下降——而这正是它们最需要发挥效能的时候。在炎热的日子里,空调压缩机必须更加努力地工作,将房屋内的热量排出室外,这反过来会不成比例地增加电力消耗和整体电力需求。例如,在德克萨斯州,每上升1.8华氏度(1摄氏度),电力需求就会上升约4%。在炎热的国家,夏季的高温会导致电力需求激增50%,带来严重的电力短缺或停电风险,同时还会增加温室气体排放。如何防止热损伤 热浪和全球范围的升温趋势对人类和机器都会带来显著的短期和长期问题。幸运的是,有一些方法可以帮助你减少损害。首先,确保你的机器放置在有空调、良好隔热的空间中,或者避免阳光直射。其次,考虑在用电低峰时段使用高耗能设备,如空调或为电动汽车充电,这样可以减少电力需求高峰,避免局部电力短缺。热量的再利用 科学家和工程师们正在研究各种方法,以利用和回收来自机器的大量热量。一个简单的例子是利用数据中心的废热来加热水。废热还可以驱动其他类型的空调系统,例如吸收式制冷机,这种系统可以通过一系列化学反应和热交换过程,实际上利用热量作为能量来支持冷却设备。无论哪种情况,用于加热或冷却的能量都来自于原本被浪费的热量。事实上,理论上电厂排放的废热可以满足住宅空调需求的27%,这将减少整体能源消耗和碳排放。极端高温可能影响现代生活的各个方面,而热浪在未来几年不会消失。然而,我们也有机会利用极端高温,使其为我们服务。本文最初发表于《The Conversation》。阅读原文。
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