问题 问答题 简答题

低负荷下运行对离心泵有何影响?

答案

参考答案:

每台泵都有一个设计的工况点,在设计工况运行时,泵的效率较高,零部件受力情况较好,调节方便,工作稳定。如离心泵在低负荷(60%负荷以下)运行,将带来以下问题:

(1)效率低,输送液体成本增加。

(2)由于在低负荷下运行,使离心泵圆周上各点受力不均等,造成径向力增加,加快了泵轴和机械密封之间的摩擦。

(3)离心泵出口压力增加,轴向力增加。

(4)离心泵易产生气蚀,在叶轮进口处易产生涡流脉动,造成泵振动。

(5)出口阀门要承受较高压差,阀门高速水力冲刷下易损坏。

阅读理解

阅读理解。

     The man of many secrets-Harry Houdini-was one of the greatest American entertainers in the theater this

century. He was a man famous for his escapes-from prison cells, from wooden boxes floating in rivers, from

locked tanks full of water. He appeared in theaters all over Europe and America. Crowds came to see the great

Houdini and his "magic" tricks.

     Of course, his secret was not magic or supernatural powers. It was simply strength. He had the ability to

move his toes as well as he moved his fingers. He could move his body into almost any position he wanted.

     Houdini started working in the entertainment world when he was 17, in 1891. He and his brother Theo

performed card tricks in clubs in New York. They called themselves the Houdini Brothers. When Harry

married in 1894, he and his wife Bess worked together as magician and assistant. Bur for a long time they

were not very successful. Then Harry performed his first prison escape in Chicago in 1898. Harry persuaded

a detective to let him try to escape from the prison, and he invited the local newspapermen to watch.

     It was the publicity (宣传) that came from this that started Harry Houdini's success. Harry had fingers

trained to escape from handcuffs and toes trained to escape ankle chains. But his biggest secret was how he

unlocked the prison doors. Every time he went into the prison cell, Bess gave him a kiss for good luck-and a

small skeleton key, which is a key that fits many locks, pass quickly from her mouth to his.

     Harry used these prison escapes to build his fame. He arranged to escape from the local prison of every

town he visited. In the afternoon, the people of the town would read about it in their local newspapers, and

in the evening every seat in the local theater would be full. What was the result? Worldwide fame and a name

remembered today.

1. According to the passage, Houdini's success in prison escapes depends on ______.

A. his special tricks and supernatural powers

B. his unusual ability and skeleton key

C. his magic tricks and inhuman powers

D. his wisdom and magic tricks

2. In the fourth paragraph, the underlined word "this" refers to ______.

A. his first prison escape

B. the year 1898

C. the publicity

D. Harry Houdini's success

3. It can be inferred from the passage that Houdini became famous ______.

A. in 1894

B. before he married

C. at the age of 17

D. when he was 24

4. Which of the following is the best title for the passage?

A. A skeleton key

B. A man of many secrets

C. Worldwide fame

D. Great escapes

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