『新东方在线托福听力』为托福考生准备了ETS托福TPO/Official 61 Lec2听力练习：What two properties of supercritical fluids does the professor mention? (Click on 2 answers)原文题目答案解析，TPO/Official 61 Lec2听力原文范文音频翻译。

托福TPO/Official 61 Lec2听力原文What two properties of supercritical fluids does the professor mention? (Click on 2 answers)【新东方在线】

旁白：听一段食品科学与技术课程中的讲座节选。

Narrator: Listen to part of a lecture in a food science and technology class.

教授：咖啡是全球最受欢迎的饮料之一。这大概不会让你感到惊讶。

Professor: One of the most popular beverages worldwide is coffee.You're probably not surprised to hear that.

在美国，超过半数的成年人每天至少喝一杯咖啡。

Here in the United States, for example, more than half of the adult population drinks at least one cup of coffee every day.

出于各种原因，一些喝咖啡的人会选择部分或全部时间饮用脱因咖啡。

For various reasons, some of those who drink coffee choose to drink decaffeinated coffee either some of the time or all of the time.

因此，咖啡行业不得不面对这种对脱因咖啡的需求。

So the coffee industry had to face this sort of need or demand for decaffeinated coffee.

真正的问题在于，在去除咖啡因的同时，不能改变咖啡的味道，也不能增加饮用咖啡的健康风险。

It was actually taking the caffeine out without changing the flavor of the coffee or without increasing the health risk to drinking the coffee.

尽管咖啡脱因的历史大概只有一百年左右，

And,although coffee has been decaffeinated for probably just about a century.

目前有一种相对较新且现今较为常用的方法用于咖啡脱咖啡因。

At this point, there's one relatively new method that's fairly commonly used these days to decaffeinate coffee.

这种方法叫做超临界流体萃取。

And that's supercritical fluid extraction.

超临界流体，是个大词，已经在黑板上写下了。

Supercritical fluid, big word, it's on the board.

如果我们不了解这个概念，就无法理解从咖啡中提取咖啡因的过程。

We can't understand the process of extracting the caffeine from the coffee if we don't get this concept down.

为了做到这一点，让我们看一下相图。这应该是一个复习内容。

In order to do that, let's take a look at the phase diagram.This should be a review.

相图显示了物质在不同压力和温度条件下存在的三种状态：固态、液态和气态。

So, the phase diagram, it shows the conditions of pressure and temperature at which a substance exists in one of three phases, a solid, a liquid, and a gas.

我们有垂直轴上的压力和水平轴上的温度。

So we've got pressure on the vertical axis, temperature on the horizontal.

正如你们所知，如果开始改变温度或压力，物质会改变其相态。

And, as you know, a substance will change its phase if you start changing temperature or pressure.

例如，如果我们选择一种任意的压力值，在这里。

For example, if we choose sort of an arbitrary pressure right about here.

保持压力不变并增加温度，我们从固态开始。

And keep the pressure constant and increase the temperature, we start as a solid.

但是正如你看到的，沿着向右的线。

But as you can see, just follow the line going to the right.

随着温度的升高，固态变为液态，然后变为气态。

As we increase the temperature, the solid changes to a liquid, and then changes to a gas.

我们当然知道冰会发生这种情况。如果保持压力不变，它会从固态变成液态再到气态。

We certainly know that happens with ice.It goes from a solid to a liquid and to a gas if we keep the pressure constant.

现在我们反过来，保持温度不变。

Now let's do it the other way and keep the temperature constant.

我们选取几个任意的温度值并增加压力。

Let's pick a couple of arbitrary temperatures and increase the pressure.

我们从气态开始，并从X轴向上走。

We start as a gas, and we go up from the x axis.

我们会看到，气态会根据我们保持不变的温度，变成固态或液态。

And we see that gas will change either to a solid or to a liquid, depending on what temperature we're keeping constant.

然而，存在这样一个温度点，如果超过了这个温度点，无论我们增加多少压力，气体都不会变成液态或固态。

There is, however, a temperature at which, if we exceed that temperature, regardless of how much we increase the pressure, this gas will not change into a liquid or a solid.

我们称这个为临界温度点TC，因此不会发生完全的相变。

Let's call this critical temperature point, TC, so there won't be a full phase change.

但它的性质会发生变化，它不再像气体那样行为。

There will be a change in its properties, however, it won't behave like a gas anymore.

它具有介于液体和气体之间的性质，我们称之为超临界流体。

It will have the properties intermediate between a liquid and a gas, and we refer to it as a supercritical fluid at that point.

它位于右上角这里，意味着它仅存在于高压和高温下。

It's in the upper-right hand corner here.So that means it only exists at high pressure and high temperature.

注意听，超临界流体扩散起来像气体，但密度却像液体。

Listen carefully, a supercritical fluid diffuses like a gas and yet it's dense like a liquid.

其重要性在于，超临界流体可以渗透固体物质，就像气体一样。

The significance of this is that a supercritical fluid can go through, can permeate a solid substance.

For example, a coffee bean, because it diffuses like a gas.

同时，由于它的密度，它也可以溶解其他物质，如咖啡因，类似于液体的作用。

And it can also dissolve other substances like caffeine, much like a liquid can because of its density.

通过改变压力和温度，可以微调这些特定性质的值或进行调整。

These particular properties, or the values of these properties, can be fine-tuned, or adjusted by changing the pressure and the temperature.

在脱咖啡因过程中的应用是这样的：如果我们把咖啡豆放在一个能承受极高压力的罐子里。

Now, the way this is used in decaffeinating coffee is if we take the coffee beans and put them in a tank that can withstand extremely high pressures.

然后使用超临界二氧化碳通过罐子，使其流经咖啡豆。

And then we take supercritical carbon dioxide and pass it through the tank so it's passing over the coffee beans.

实际上，它会渗透进咖啡豆里。

如果我们将压力和温度调节得恰到好处，咖啡因会选择性地溶解到超临界二氧化碳中。

And,if we have the pressure and temperature just right, the caffeine will selectively dissolve into the supercritical carbon dioxide.

然后，超临界二氧化碳和溶解的咖啡因会一起从第一个容器中流出，进入第二个容器，留下脱因的咖啡豆。

Together, the supercritical carbon dioxide and dissolved caffeine will pass out of that tank and into a second tank, leaving decaffeinated coffee beans behind.

然后我们在第二个罐子上有一个减压阀。

Then we have a pressure relief valve on that second tank.

压力降低，超临界二氧化碳又变成了气体，从而释放出结晶状的咖啡因。

The pressure decreases, and the supercritical carbon dioxide changes back into a gas,which then releases the caffeine in a crystallized form.

How does the professor organize the review of the phase diagram?

Under what conditions do supercritical fluids form?

What two properties of supercritical fluids does the professor mention? (Click on 2 answers)

The professor describes a process of caffeine extraction from coffee beans using carbon dioxide (CO2). Put the steps of the process in the correct order.(Click on a sentence. Then drag it to the space where it belongs. The first one is done for you. Supercritical CO2 is led into a high-pressure chamber.

What does the professor imply when he says this:

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