大学英语听说教程

排放冷却是对流冷却的另一种。与再生冷却不同，用于排放冷却的冷却剂对推力室冷却吸热后不进入燃烧室参与燃烧，而是排放出去。直接排放冷却剂会降低推力室比冲，因此需要尽可能减少用于排放冷却的冷却剂流量，同时只在受热相对不严重的喷管出口段采用排放冷却。还有一种是辐射冷却，其热流由燃烧产物传给推力室，再由推力室室壁想周围空间辐射散热。辐射冷却的特点是简单、结构质量小。主要应用于大喷管的延伸段和采用耐高温材料的小推力发动机推力室。在组织推力室内冷却时，是通过在推力室内壁表面建立温度相对较低的液体或气体保护层，以减少传给推力室室壁的热流，降低壁面温度，实现冷却。内冷却主要分为头部组织的内冷却（屏蔽冷却）、膜冷却和发汗冷却三种方法。推力室采用内冷却措施后，由于需要降低保护层的温度，所以燃烧室壁面附近的混合比不同于中心区域的最佳混合比（多数情况下采用富燃料的近壁层），造成混合比沿燃烧室横截面分布不均匀，使燃烧效率有一定程度的降低。膜冷却与屏蔽冷却类似，是通过在内壁面附近建立均匀、稳定的冷却液膜或气膜保护层，对推力室内壁进行冷却，只是用于建立保护层的冷却剂不是喷注器喷入的，而是通过专门的冷却带供入。冷却带一般布置在燃烧室或喷管收敛段的一个横截面上。沿燃烧室长度方向上可以有若干条冷却带。为提高膜的稳定性，冷却剂常常经各冷却带上的缝隙或小孔流入采用发汗冷却时，推力室内壁或部分内壁由多孔材料制成，其孔径为数十微米。多孔材料通常用金属粉末烧结而成，或用金属网压制而成。此情况下，尽可能使材料中的微孔分布均匀，是单位面积上的孔数增多。液体冷却剂渗入内壁，建立起保护膜，使传给壁的热流密度下降。当用于发汗冷却的液体冷却剂流量高于某一临界值，在推力室内壁附近形成的是液膜。当冷却剂流量低于临界值流量时，内壁温度会高于当前压力下的冷却剂沸点，部分或全部冷却剂蒸发，形成气膜。除了以上热防护外，还有其他热防护方法如：烧蚀冷却、隔热冷却、热熔式冷却以及室壁的复合防护等。3 高焓气体发生器热防护方案综合上述方法结合实际情况，便得到高焓气体发生器的热防护方法。高焓气体发生器的燃烧室与液体火箭发动机的不同，省去前面的推力室部分，使得其结构更简单而有效。那么，所涉及到的热防护即为对燃烧室室壁的热防护部分。由于燃料进入燃烧室内迅速分解并放出大量

全新版第二版听说B3U7-A Part I Listening Comprehension ( 28 minutes )1. A) For a wedding. B) For a farewell party. C) For a business banquet. D) For a birthday party. Script: Woman: Great. I have the banquet room reserved for a luncheon for Nika Corporation on the 2nd of December. May I have your name and contact information? Man: Sure. I'm Jeff McQuillan and my number is , extension 42. Question: What does the man book the room for? 正确答案： C 2. A) 15 dollars' corkage fee a bottle and no charge for the cake brought. B) Free of charge. C) 50 dollars of corkage fee. D) Not mentioned. Script: Man: That's great. I'd like to go ahead and reserve the room, then, for Friday, December 2, at around noon. This is a retirement party and we would like to bring a cake for the guest of honor and some bottles of champagne. Will that be acceptable? Woman: The cake is no problem at all, but we do charge a corkage fee of $15 a bottle for any alcohol not purchased from the restaurant. Question: How much does the man need to pay for the cake and champagne? 正确答案： A 3. A) Review her cover letter at home. B) Go to the employment fair with her revised cover letter. C) Go to see the advertisement. D) Help the man to review his cover letter. Script: Man: Did you see the advertisement for the Employment Fair? Woman: Sure did. I'm just revising my cover letter now. Question: What will the woman probably do next? 正确答案： B 4. A) Grilled cheese. B) Peanut butter and jelly. C) Burger king. D) Either a grilled cheese or peanut butter and jelly. Script: Woman: All places are closed now, come to my place and I will make you a good sandwich. You'll have a choice of grilled cheese or peanut butter and jelly. What do you say? Man: I guess beggars can't be choosers. Question: What does the man want for his sandwich? 正确答案： D 5. A) Something is wrong with the deposits. B) His withdrawals from last month were missing. C) His bank charges a fee for his checking account. D) His bank statements are not complete. Script: Woman: Let me take a look at your bank statement. Okay, here are your deposits and withdrawals from last month. Did you know that your bank charges you a fee just to have a checking account? Man: It does? I didn't know that. Question: What does the woman say about the man's bank statement? 正确答案： C 6. A) 14 years. B) 40 years. C) 20 years. D) 30 years. Script: How long have the man's parents run a store? 正确答案： B 7. A) He will have to consider the duration of the business. B) He will think carefully about the taxation. C) He needs to consider the profits distribution. D) He will have to consider the complicatedness of the business. Script: What need the man consider if there are two partners in the business? 正确答案： A 8. A) The man should learn about the business from his parents. B) The man should give up the idea of starting a business. C) The man should be careful about his partners. D) The man should find a lawyer and consider some legal issues. Script: What is the woman's advice? 正确答案： D to wait for a chance to sit back and watch you work! 9. A) Saturday. B) Monday. C) Sunday. D) Tuesday. Script: What day is it today? 正确答案： B 10. A) He hopes to be the co-worker with the woman. B) He wants to go home and have a rest. C) He hopes to do some planning for next weekend. D) He wants to sit back and asks the woman to take most the work. Script: What does the man want to do? 正确答案： D 11. A) He had too much work to finish. B) He had to go on a business trip. C) He went partying too much. D) He drank too much. Script: Why did the man have a rough weekend? 正确答案： C12. A) Conference. B) Flight. C) Traveling. D) Preparation. Script: According to the speaker, what is the worst part of going on a business trip? 正确答案： D 13. A) Next morning. B) This month. C) Next week. D) This week. Script: When will the speaker go for the conference? 正确答案： D 14. A) His badge. B) His computer. C) His notepad. D) His CD. Script: Which item is not included in the briefcase? 正确答案： D Passage Two 15. A) 5 years. B) A decade. C) A fortnight. D) A century. Script: How long may the trends talked about influence the audience's industry in the future? 正确答案： B 16. A) How to change to an environment related company. B) How to grow green. C) How going green will influence the company's future. D) How to save the world. Script: What is the biggest concern at present? 正确答案： C 17. A) The trend in the next 10 years. B) The growth of green products in the past 10 years. C) The increase of environmental unfriendly products in the past 4 years. D) The growth of green products in the past 5 years. Script: What does the chart show? 正确答案： D 18. A) She works in a large company. B) She runs a small sized company. C) She provides consulting services. D) She runs a medium sized company. Script: What does the woman start up as her own business? 正确答案： C 19. A) She was not sure about the size of the company. B) She was not certain whether she could raise the fund. C) She was not sure about her office. D) She was not certain about he services. Script: What was the woman entrepreneur not sure about at first? 正确答案： B 20. A) Her apartment. B) Her original office. C) Her living room. D) Her garage. Script: What was made into an office? 正确答案： DMany students just graduating from high school or college face the same problem. Often job openings (21)_________________ experience. How can you gain experience without first getting a job? One way to handle this (22)_________________ is for students to work in internships. Internships are jobs that don't pay any money, but that people can do to get experience. It is quite common, for example, for a college student to work in an internship while going to school or in the summertime between school years. Internships provide (23)_________________ for both students and employers. Students get experience, make contacts, and get their foot in the door if the company or (24)_________________ is looking for future employees. Similarly, a company gets (25)_________________ labor and can see how well a person works before hiring that person for a full-time job. Until recently, most interns have been students. With the (26)_________________ , however, more and more people who have worked in their jobs for 10, 15, 20 years professionals who have been (27)_________________ are taking internships for some good reasons. First, internships allow professionals to gain experience in close fields, giving them a wider range of (28)_________________ and skills. Second, internships allow professionals to avoid gaps in their resumes. Traditionally, employers don't like gaps in resumes because the gaps may mean that a person has had difficulty finding a job, had (29)_________________ problems, or, with a lot of gaps, had difficulty keeping a job. Employers may also see long gaps between jobs as a sign of worsening skills. Employers may be more (30)_________________ of gaps these days, but as is true for college students, working in an internship also allows these professionals to show a company their skills, which may put them at the front of the line when any new jobs become available. Script: Many students just graduating from high school or college face the same problem. Often job openings require experience. How can you gain experience without first getting a job? One way to handle this situation is for students to work in internships. Internships are jobs that don't pay any money, but that people can do to get experience. It is quite common, for example, for a college student to work in an internship while going to school or in the summertime between school years. Internships provide benefits for both students and employers. Students get experience, make contacts, and get their foot in the door if the company or organization is looking for future employees. Similarly, a company gets unpaid labor and can see how well a person works before hiring that person for a full-time job. Until recently, most interns have been students. With the weak economy, however, more and more people who have worked in their jobs for 10, 15, 20 years professionals who have been laid off are taking internships for some good reasons. First, internships allow professionals to gain experience in close fields, giving them a wider range of knowledge and skills. Second, internships allow professionals to avoid gaps in their resumes. Traditionally, employers don't like gaps in resumes because the gaps may mean that a person has had difficulty finding a job, had personal problems, or, with a lot of gaps, had difficulty keeping a job. Employers may also see long gaps between jobs as a sign of worsening skills. Employers may be more forgiving of gaps these days, but as is true for college students, working in an internship also allows these professionals to show a company their skills, which may put them at the front of the line when any new jobs become available. 正确答案： require 正确答案： situation 正确答案： benefits 正确答案： organization 正确答案： unpaid 正确答案： weak economy 正确答案： laid off 正确答案： knowledge 正确答案： personal 正确答案： forgiving

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大学英语听说教程1课件_U5|大学英语听说教程1_Unit 5.pptx|zone.mp3|VL.mp3|vault.mp3|van.mp3|Uzbek.mp3|U5_ViewTheWorld.mp3|U5_Passage_2.mp3|U5_Passage_1.mp3|U5_NewsReport_3.mp3|U5_NewsReport_2.mp3|U5_NewsReport_1.mp3|U5_Further_Passage.mp3|U5_Further_NewsReport.mp3

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