问题 问答题 简答题

为什么液氮过冷器中能用气氮来冷却液氮?

答案

参考答案:

1.因为对同一种物质来说,相变温度(饱和温度)与压力有关。压力越低,对应的饱和温度也越低。

2.在上塔顶部,处于气氮和液氮共存的饱和状态,二者具有相同的饱和温度。

3.氮气出上塔的绝对压力在0.13MPa左右,对应的饱和温度为-193℃,出塔的氮饱和蒸气的温度也为该温度。

4.而下塔顶部的绝对压力为0.55MPa左右,对应的氮饱和温度为-177℃左右。抽出的饱和液氮也为该温度。

5.该液氮的温度要比上塔气氮的温度高16℃左右,因此,两股流体在流经液氮过冷器时,经过热交换,液氮放出热而被冷却成过冷液体,气氮因吸热而成为过热蒸气。

阅读理解

Tom and Fred are talking about the year 2020."What will our world be like in the year 2020?""I don’t know."says Fred."What do you think?""Well, no one knows, but It’s interesting to guess.""In the year 2020 everyone will carry a pocket computer. The computer will give people the answers to all their problems. We shall all have telephones in our pockets, too, and we’ll be able to talk to our friends all over the world. Perhaps we’ll be able to see them at the same time.""A lot of people will live and work under the sea. Perhaps there will be big towns, factories and farms under the sea, too.""Machines will do most of the work, and so people will have more holidays, perhaps they’ll work only two or three days a week. They’ll be able to fly to the moon by spaceship and spend their holidays there.""I’m looking forward(期待) to the year 2020. I hope to go to the moon!""And I hope I’ll be able to live under the sea."says Fred."Won’t that be very interesting? Just like a fish!"

小题1:根据Tom and Fred are talking about the year 2020.及下文描述,可知他们谈论的是将来的生活,故选D

小题2:根据"Machines will do most of the work,可知选A

小题3:根据""I’m looking forward(期待) to the year 2020. I hope to go to the moon!"描述,可知选C

小题4:根据"And I hope I’ll be able to live under the sea."says Fred."Won’t that be very interesting? Just like a fish!"可知选B

小题5:D

小题6:Tom and Fred talked about          .

A.their school life

B.some interesting news

C.their life in the past

D.their life in the future小题7:Machines will          .

A.do most of the work instead of people

B.do some of the work instead of people

C.do as much work as people

D.do as 1ittle work as people小题8:From their talk, we know that          .

A.only Fred hopes to fly to the moon

B.both of them hope to fly to the moon

C.one of them hopes to fly to the moon

D.neither of them hopes to fly to the moon小题9:Fred said          .

A.he liked fish very much

B.he would like to live under the sea like a fish

C.he would go fishing under the sea

D.he would spend a few days on the moon小题10:Which of the following statements is Not mentioned?

A.People will be able to fly to the moon in a spaceship.

B.People will have more holidays.

C.Many people will live and work under the sea.

D.All the factories and farms will be built under the sea.

单项选择题