9.2 热传输

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  热热传输

  

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  Can you see energy moving?
  ::你能看见能量在移动吗?

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  It's hard to see moving. But is the reason that air moves, and it is sometimes possible to see that. In this ph oto, differences in are causing air to move—in fantastic ways!
  ::很难看到空气在移动。但这是空气运动的原因,有时也有可能看到这一点。在这张照片中,空气移动的差异正在引起空气的移动——以惊人的方式!

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  Conduction
  ::指挥

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  occurs when a difference exists, causing the molecules of an object to transmit energy throughout the object. We usually associate conduction with solids. The atomic structure of a solid is more rigid than a liquid or gas, and thus better able to communicate atomic vibrations caused by heating. Conduction is the transfer of from one molecule to another by molecular collision. Conduction occurs, for example, when a metal spoon is put into a hot cup of tea and the handle of the spoon gets hot.
  ::当存在差异时发生,导致物体的分子在整个物体中传输能量。 我们通常将导电与固体联系起来。 固体的原子结构比液体或气体更硬, 因而更能够交流取暖引起的原子振动。 导电是指通过分子碰撞从一个分子向另一个分子转移。 例如, 当金属勺放入热茶杯和勺子的把手热时, 导电就会发生。

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  We mentioned above that some of the food energy we consume is used to maintain a constant body temperature. What happens on a hot day when our body temperature is the same as the outside temperature? No energy will be transferred, since the temperatures are equal and therefore we’ll feel uncomfortably warm since we won’t be able to shed our . In contrast, when it is very cold, the temperature difference between our body and the outside temperature can be considerable and thus energy is transferred (rather quickly, if we’re not dressed warmly) from our body to the outside environment. We interpret this rapid transfer of energy as feeling cold .
  ::我们在上面提到,我们所消费的一些食物能量被用于保持恒定的体温。 当我们的身体温度与外部温度相同时,在炎热的一天会发生什么情况? 任何能量都不会被转移,因为温度相等,因此我们将感到不适热,因为我们无法解脱。 相反,当温度非常寒冷时,我们的身体和外部温度之间的温度差异可能相当大,因此能量(如果我们不热身,那么温度就会很快地转移)从我们的身体转移到外部环境。 我们将这种能量的迅速转移解释为感到寒冷。

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  On a cold day, an object made of metal typically feels colder to the touch than wood, because energy leaves your hand more quickly when touching metal than wood. We say that metal has a higher conduction rate than wood. For example, for the same temperature difference, the conduction rate of copper is over 3,000 times greater than that of wood. Energy will flow from your hand 3,000 times more quickly if you hold a piece of copper, compared to holding a piece of wood of the same temperature. This means, of course, that you don’t want to grab the handle of a copper (or any metal) pot when it’s being heated on your stove. Heat conduction assures that the energy from the flame under the pot is conducted to the handle of the pot and to your hand should you touch it. Ouch!
  ::在寒冷的一天,用金属制成的物体一般比用木材冷,因为触碰金属时,能量会比用木材更快地离开你的手。我们说金属的导流率比木材高。例如,同样的温度差异,铜的导流率是木材的3000倍以上。 与持有同一温度的一块木头相比,如果持有一块铜,那么从你的手中流出的能量会更快3000倍。这当然意味着在炉灶加热时,你不想抓住铜(或任何金属)锅的把手柄。热导能保证锅下火焰的能量会用在锅柄上,如果触碰它,就会用手得到3000倍的能量。 哎哟!

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  The relationship between the rate of heat flow (heat conduction) between two objects and the difference in their temperature can be modeled using the following equation.
  ::两个天体之间的热流速(热导)与温度差异之间的关系,可以用以下方程进行模型分析。

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  $$\begin{array}{r}\frac{\mathrm{\Delta }Q}{\mathrm{\Delta }t}=\frac{kA\mathrm{\Delta }T}{d}\end{array}$$

  
  ::{\fn华文楷体\fs16\1cHE0E0E0}塔德

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  Where $\begin{array}{r}\frac{\mathrm{\Delta }Q}{\mathrm{\Delta }t}\end{array}$   is the change in heat over the change in time,  $\begin{array}{r}k\end{array}$   is the thermal conductivity constant for the material, $\begin{array}{r}A\end{array}$   is the surface area of the conducting material and $\begin{array}{r}d\end{array}$   is the between the two temperatures used to determine $\begin{array}{r}\mathrm{\Delta }T\end{array}$  , $\begin{array}{r}{T}_2-T_1=\mathrm{\Delta }T\end{array}$ .
  ::K是材料的热传导常数,A是助导材料的表面区域,d是用于确定T,T2-T1T的两种温度之间的温度。

   

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  The Direction of Heat Flow
  ::热热流方向

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  There is a misconception regarding heat flow that we should dispel at this point. Under normally occurring conditions, heat flows only from a hot environment to a cold environment, never in reverse. An open door on a very cold day does not let the cold in. It permits the heat to flow more readily to the outside.
  ::在通常情况下,热量只能从热环境流向冷环境,从不倒流。 寒冷的一天开着的门不能让寒冷进入。 它允许热量更容易地流向外部。

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  On a cold day, even in a warm room, if you put your hand on a window pane inside your home, it will feel cold. The room temperature may be comfortable, but heat is flowing from the inside of the room to the outside through the glass pane. The air close to the glass pane inside the room has a lower temperature than the average temperature of the room because of its proximity to the outside. Conversely, the layer of air on the outside of the window pane has a higher temperature than the air farther from the window. On windy days, this effect is considerably lessened.
  ::寒冷的一天,即使在温暖的房间里,如果你把你的手放在家中的窗帘上,它就会感到寒冷。房间温度可能比较舒适,但热量却从室内内部通过玻璃玻璃窗向外流动。室内靠近玻璃窗的空气温度比室内平均温度低,因为离外面很近。相反,窗帘外的空气层温度比离窗户更远的空气层高。在风中,这种效应大大减弱。

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  Example 1
  ::例1

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  The temperature very near a glass window pane on the inside of a house is measured as $\begin{array}{r}{13}^{\circ }\text{C}\end{array}$ and the temperature on the outside near the window is measured as $\begin{array}{r}{10}^{\circ }\text{C}\end{array}$ . The window has dimensions 1.25 m by 0.90 m.The thickness $\begin{array}{r}d\end{array}$   of the window is 4 mm, and its thermal conductivity $\begin{array}{r}k\end{array}$ is $\begin{array}{r}0.80\frac{\text{J}}{\text{s}\cdot \text{m}{\cdot }^{\circ }\text{C}}\end{array}$ . Find the rate at which energy is transferred from the inside of the room to the outside environment.
  ::房内玻璃窗玻璃窗玻璃箱附近的温度测量为13°C,窗外的温度测量为10°C。 窗外的温度测量为10°C。 窗外的尺寸为1.25米x0.90米。 窗外的厚度为4毫米,其热导电率K为0.80 JsmC。 找到能量从房内转移到外部环境的速度。

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  Answer:
  ::答复:

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  Remembering that the area $\begin{array}{r}A=(1.25\text{m})(0.90\text{m})\end{array}$ , and substituting the  known values  into the equation $\begin{array}{r}\frac{\mathrm{\Delta }Q}{\mathrm{\Delta }t}=\frac{kA\mathrm{\Delta }T}{d}\end{array}$ we have:
  ::记住A=( 1. 25m)( 0. 90m) 区域, 并将已知值替换为 {t= kA}Td 等式, 我们有 :

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  $$\begin{array}{r}\frac{\mathrm{\Delta }Q}{\mathrm{\Delta }t}=\frac{(0.80\frac{J}{s\cdot m{\cdot }^{\circ }C})(1.25m)(0.90m)({13}^{\circ }C-{10}^{\circ }C)}{0.004m}=675\frac{J}{s}\end{array}$$

  
  ::T=(0.80JsmC)(1.25米)(0.90米)(13°C-10°C)0.004米=675日元)

   

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  This amount of energy transfer is equivalent to seven-and-one-half incandescent 60-W light bulbs. And this is through only one window! Installing energy-efficient windows in your home saves a good amount of money and helps the environment since most people still use fossil fuels to heat their homes.
  ::这种能量转移量相当于7个半白种60W灯泡。 这只能通过一个窗口! 在你家安装节能窗口可以节省大量资金,并有助于环境,因为大多数人仍然使用化石燃料为家取暖。

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  Convection
  ::对等对等

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  typically arises from the movement of gases or liquids over large distances. Convection takes place throughout the Earth’s atmosphere all the time. Heated air is less dense than cooler air, so it rises. As the air rises, it cools down and becomes denser. The air then falls back to the ground where it is heated again, and the process repeats. A convection cell, which is a circulating pattern of moving energy, is created. The  Figure shows how the convection cell reverses direction from day to night due to the ground giving off the heat in the evening that it absorbed during daylight hours.
  ::通常是气体或液体的远距离移动产生的。对流器在整个地球大气层中一直发生。加热空气比较冷的空气密度小,因此它会上升。随着空气的上升,空气会降温,变得较稠密。空气会回落到又变暖的地面,过程会重复。建立一个对流细胞,它是一种流动能量的循环模式。图显示对流细胞如何在白天和晚上向反方向移动,因为地面在白天吸收热量。

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  Imagine the air that is heated by the asphalt and the concrete within a city rising, cooling, falling back, and being reheated by the asphalt and concrete, over and over again.
  ::想象一下在一座城市里 由沥青和混凝土加热的空气 上升,冷却,后退, 并被沥青和混凝土再热, 一遍又一遍。

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  Many atmospheric conditions are the result of convection.
  ::许多大气条件都是对流的结果。

  

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  Convection cell reverses direction at night.
  ::对流细胞在晚上向反方向移动

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  In hot climates, convection is used to cool homes. Ducts within the house provide pathways for the warm air to circulate. As the sun goes down and the temperature drops outside, the warmer air in the house flows through the ventilation ducts and to the cooler environment outside.
  ::在炎热的气候中,对流习惯于冷却房屋。室内的污点为温暖空气的循环提供了途径。 随着太阳下山和气温下降,室内的暖气通过通风管道流到外面的冷却环境。

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  Convection is not restricted to earthly phenomena. The interior region of the sun is in a constant state of convection, which is seen in photographs showing what astronomers call “granulation.” The granulation represents an innumerable amount of convection cells "boiling” to the sun’s surface. See Figure for a diagram of the sun’s interior and a photograph of the convection cells (granulation).
  ::对流并不限于地球现象。 太阳的内部区域处于恒定的对流状态,在显示天文学家称之为“调节”的图片中可以看到这一点。 颗粒代表了无数的对流细胞“粘合”太阳表面。 太阳的内部图和对流细胞的照片(对流)见图表。

  

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  See Convection zone above
  ::见上文对流区

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  Radiation
  ::辐射辐射辐射

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  Both conduction and convection rely upon moving matter. Radiation does not. Radiation is energy transferred by (or photons). We will say more about radiation when we discuss the electromagnetic spectrum .
  ::电导和对流都依赖于移动物质。 辐射不是。 辐射是( 光子或光子) 传输的能量。 当我们讨论电磁频谱时, 我们将更多地谈论辐射。

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  Energy transferred by radiation from the sun travels millions of kilometers through the vacuum of space before reaching the Earth. Some of this energy is visible radiation (sunlight, for example), while other energy is invisible. Heat radiation is an example of invisible radiation. It belongs to a part of the electromagnetic spectrum below the threshold of human sight. Just as there are sounds we cannot hear, there is light we cannot see.
  ::太阳辐射转移的能量在到达地球之前通过空间真空穿越数百万公里。有些能量是可见辐射(例如太阳光),而其他能量是隐形的。热辐射是隐形辐射的一个例子。它属于人类视线下方的电磁波谱的一部分。正如我们听不到的声音一样,我们看不到光。

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  When you sit next to a campfire or a fireplace and feel all warm and cozy, thank radiation! If the only heating we could experience was through convection, we would not be warmed. We would benefit very little from a convection cell up a chimney or directly above a campfire. It is the flow of radiation from the fire that warms us.
  ::当你坐在一个营火或壁炉旁边,感受温暖和舒适的时候,谢谢辐射!如果我们唯一能经历的热量是通过对流的,我们就不会暖和了。我们从烟囱上的对流牢房或直接在营火上方的对流牢房受益甚少,而温暖我们的是火的辐射流动。

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  Example 2 :
  ::实例2:

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  What form of energy transfer is the most likely cause of sunburn?
  ::哪种形式的能源转移最有可能造成日晒?

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  a. conduction
  ::a. 指挥

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  b. convection
  ::b. 对流

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  c. radiation
  ::c. 辐射

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  Answer : The answer is C. If it’s a hot day and you touch any metal on a car, you might suffer a burn. This happens through conduction. If you feel a warm breeze, this is through convection. But sunburn is caused by ultraviolet radiation from the sun. As with infrared radiation, ultraviolet radiation is also invisible. It is, however, just above the threshold of human vision. And just as some animals can hear higher frequency sounds than we can (dogs, for example), other animals can see higher frequencies of light than we can (bees can see ultraviolet light).
  ::答案是:答案是C。如果天气热,而且你触碰汽车上的任何金属,你可能会受到烧伤。这是通过导火线发生的。如果你感到温暖的微风,这是通过对流造成的。但太阳灼伤是由太阳的紫外线辐射造成的。与红外线辐射一样,紫外线辐射也是隐形的。不过,紫外线辐射仅仅高于人类视线的门槛。正如一些动物能够听到比我们能听到的更高频率的声音(例如狗)一样,其他动物也能看到比我们能看见的更高的光频率(蜜蜂可以看到紫外线光)。

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  Further Reading
  ::继续阅读

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  Summary
  ::摘要

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  • Conduction is the transfer of thermal energy between particles of matter that are touching. Thermal energy is always transferred from particles of warmer matter to particles of cooler matter.
    ::热能从温暖物质的粒子转移到冷却物质的粒子。
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  • When particles of warmer matter collide with particles of cooler matter, they transfer some of their thermal energy to the cooler particles.
    ::当温暖物质的粒子与冷却物质的粒子相撞时,它们将一些热能转移到冷却的粒子上。
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  • Convection is the transfer of thermal energy by particles moving through a fluid. Thermal energy is always transferred from an area with a higher   to an area with a lower temperature.
    ::对流是指通过流体流动的微粒转移热能,热能总是从较高区域转移到低温区域。
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  • Convection currents move thermal energy through many fluids, including molten rock inside Earth, water in the oceans, and air in the atmosphere.
    ::对流流通过许多流体移动热能,包括地球上熔岩、海洋中的水和大气中的空气。
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  • Thermal radiation is the transfer of thermal energy by waves that can travel through air or even through empty space. This is how thermal energy from a fire is transferred to your hands and how thermal energy from the   is transferred to Earth.
    ::热辐射是热能通过能够通过空气或空空空间穿行的波浪转移的热能,这就是如何将火灾产生的热能转移到你的手上,如何将热能从热能转移到地球。
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  • Everything radiates thermal energy, even objects that aren’t very warm.
    ::所有东西都会辐射热能, 甚至是不热的物体。

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  Review
  ::回顾

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  1. What is conduction? convection? radiation?
     ::什么是导体?对流?辐射?
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  2. Describe an original example of conduction.
     ::描述最初的行为举例。
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  3. Describe how convection occurs and why convection currents form.
     ::描述对流是如何发生的,为什么对流流流形成。
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  4. If you sit close to a campfire, the fire warms you. Describe how thermal energy is transferred from the fire to you.
     ::如果你坐在靠近营火的地方,火会温暖你。描述热能是如何从火中转移到你身上的。