跟读练习: How does a Steam Turbine Work? - 通过视频学习英语口语
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Nuclear and coal -based thermal power plants together produce almost half of the world's power.
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Steam turbines lie at the heart of these power plants.
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They convert thermal energy in the steam to mechanical energy.
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This video will explain the inner workings of the steam turbines
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and why they are constructed in the manner they are in a step -by -step, logical manner.
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To understand its basic workings, let's first observe one of their blades.
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You can see that the blade of a steam turbine has an airfoil shape.
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When the high energy fluid passes over it, this airfoil shape will create a pressure difference.
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This will subsequently create lift force.
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The lift force will rotate the turbine.
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In short, the energy in the fluid transfers to the mechanical energy of the rotor.
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To further understand steam turbine operation, let's understand fluid energy in greater depth.
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A fluid has three forms of energy, due to its speed, pressure, and temperature.
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As the blades absorb energy from the fluid, all three forms of energy come down.
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The low -velocity jet is of no use to produce effective lift force.
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To increase velocity, the fluid is passed through a stator section.
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The stator set is stationary and attached to the turbine casing.
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You can see that flow area decreases along the stator and the speed thus increases.
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In short, the stator acts like a nozzle.
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As the speed of the jet increases in the stator, kinetic energy increases.
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As there is no net energy transfer in the fluid in stator section,
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the pressure and temperature of the jet should decrease to keep the total energy constant.
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Now, the next row of rotors is added.
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The stator also makes sure
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that the flow coming out of it will be at an optimum angle of attack to the next rotor set.
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After that, another nozzle set is added.
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Many such sets are used in a steam turbine.
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There is an important term while designing steam turbines, namely degree of reaction.
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This term is calculated by dividing pressure and temperature energy by the total energy change in the rotor.
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Pressure and temperature energy together is called enthalpy.
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The degree of reaction decides what type of steam turbine it is.
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As the pressure of the steam undergoes a drastic reduction during steam turbine operation, its volume increases proportionally.
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To accommodate such an expanded steam, we have to increase the flow area.
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Otherwise, the flow speed will become too high.
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This is the reason why the steam turbine blades are too long towards the outlet.
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You can see how long the last stage turbine blades are compared to the first stage blades.
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The tips of such long blades will have very high velocity compared to the root.
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A twist is given to it so that all blade cross sections will remain at an optimum angle of attack.
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This kind of large turbine uses two such symmetrical units.
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You can see how the steam is equally divided between these units.
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High -capacity power plants use different stages of steam turbines, such as high -pressure turbine,
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intermediate -pressure turbine, and low -pressure turbines.
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All these units are attached to a single rotating shaft.
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The shaft in turn is connected to a generator.
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The reason for such different stages is quite interesting.
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With greater steam temperature comes greater power plant efficiency.
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This is according to the second law of thermodynamics.
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But we cannot have temperature greater than 600 degrees Celsius, since the turbine blade material will not withstand temperature more than that.
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Temperature of the steam decreases as it flows along the rows of the blade.
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Consequently, a great way to increase power plant efficiency is to add more heat after the first stage.
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So after the first stage, the steam is bypassed to the boiler and more heat is added.
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This is known as reheating.
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This will increase the steam temperature again, leading to higher power plant efficiency and output.
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One challenging problem in power plant operation is to keep the speed of the steam turbine constant.
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This is important since frequency of the electricity produced is directly proportional to the generator speed.
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However, depending on the load or power demand, the steam turbine speed will vary.
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To keep the steam turbine speed constant, a steam flow governing mechanism is used.
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If the steam turbine rotates at a higher speed,
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the control valve will automatically reduce the steam flow rate to the turbine until the speed becomes normal.
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If the turbine rotates at a low speed, the inverse will be done.
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In this way, the balance of power demand and power supply will be perfectly synchronized.
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To learn more about degree of reaction and its implications, please check the next video.
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Please help us at patreon .com so
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that we can add one more member to the team and we will be able to release two educational videos per month.
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Thank you!
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本课的词汇与口语要点
这节口语课以视频“How does a Steam Turbine Work?”为素材。 视频中反复出现的词有：turbine, steam, energy, speed, blade。 这段视频共有 65 个句子、822 个单词可供跟读。 讲话部分时长为 5:42。 说话人语速平稳，每分钟约 144 个词，很适合跟读。 只有 80% 的单词属于英语最常用的 3,000 词，词汇难度较高。
视频中的重点词汇
视频中 15 个值得学习的单词，附发音和释义：
| 单词 | 发音 | 释义 |
|---|---|---|
| turbine 名词 | /ˈtɜː.baɪn/ | 渦輪機 /涡轮机, 輪機 /轮机 |
| blade 名词 | /bleɪd/ | 刃, 刀身 |
| fluid 名词 | /ˈflu.ɪd/ | 流體 /流体, 液體 /液体 |
| rotate 动词 | /ˈɹoʊ.teɪt/ | 旋转, 转动 |
| efficiency 名词 | /ɪˈfɪʃ.ən.si/ | 效率, 效能 |
| decrease 动词 | /dɪˈkɹiːs/ | 減少 /减少, 下降 |
| velocity 名词 | /vəˈlɑsəti/ | 速度 |
| compare 动词 | /kəmˈpɛɚ/ | 比, 比較 /比较 |
| angle 名词 | /ˈæŋ.ɡəl/ | 角, 角度 |
| divide 动词 | /dɪˈvaɪd/ | 分, 分裂 |
| generator 名词 | /ˈdʒɛnəɹeɪtə(ɹ)/ | 發電機 /发电机 |
| shaft 名词 | /ˈʃɑːft/ | 杆 |
| attach 动词 | /əˈtæt͡ʃ/ | 附上, 附 |
| output 名词 | /ˈaʊtpʊt/ | 輸出 /输出 |
| equally 副词 | /ˈiːkwəli/ | 一樣地 /一样地, 同樣地 /同样地 |
视频中出现的短语动词
| 单词 | 释义 |
|---|---|
| come down 动词 | 下來 /下来, 降 |
需要注意的发音
- “th” 音: thermal /ˈθɜːməl/, withstand /wɪðˈstænd/, enthalpy /ˈɛn.θəl.piː/, thermodynamics /ˌθɜː(ɹ)moʊdaɪˈnæmɪks/
- “sh” 和 “zh” 音: efficiency /ɪˈfɪʃ.ən.si/, shaft /ˈʃɑːft/, reduction /ɹɪˈdʌk.ʃən/, stationary /ˈsteɪʃəˌnɛɹi/, implication /ˌɪmpləˈkeɪʃən/
- 长单词——注意重音位置: efficiency /ɪˈfɪʃ.ən.si/, velocity /vəˈlɑsəti/, mechanical /məˈkænəkəl/, generator /ˈdʒɛnəɹeɪtə(ɹ)/, electricity /ɪˌlɛkˈtɹɪsɪti/
中文母语者容易读错的音：
- /v/ — 不要读成 /w/，上齿轻触下唇: velocity /vəˈlɑsəti/, divide /dɪˈvaɪd/, vary /ˈvɛəɹi/, valve /ˈvælv/, convert /kənˈvɝt/
- 词尾辅音 — 要读清楚，后面不要加元音: blade /bleɪd/, fluid /ˈflu.ɪd/, rotate /ˈɹoʊ.teɪt/, decrease /dɪˈkɹiːs/, divide /dɪˈvaɪd/
- /r/ 和 /l/ 的区别: electricity /ɪˌlɛkˈtɹɪsɪti/, proportionally /pɹəˈpɔɹʃənəli/, symmetrical /səˈmɛtrək(ə)l/
如何用这段视频练习
- 先完整听一遍视频，不要开口，记下不认识的单词。
- 用正常速度逐句跟读，每句重复到你的节奏与说话人一致为止。
- 录下自己的声音并与原声对比，特别注意 turbine, blade, fluid 这类单词。
什么是跟读法？
跟读法 (Shadowing) 是一种有科学依据的语言学习技巧，最初开发用于专业口译员的培训，并由多语言者Alexander Arguelles博士普及。这个方法简单而强大：您在听英语母语原声的同时立即大声重复——就像是一个延迟1-2秒紧跟说话者的影子。与被动听力或语法练习不同，跟读法强迫您的大脑和口腔肌肉同时处理并模仿真实的讲话模式。研究表明它能显着提高发音准确性，语调，节奏，连读，听力理解和口语流利度——使其成为雅思口语备考和真实英语交流最有效的方法之一。