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举例说明热胀冷缩原理在锅炉上的应用？

答案

参考答案：

1.锅炉的汽包，联箱，管子等都是承压的受热部件，由于材料受热后要膨胀，因此在制造.安装运行锅炉时必须考虑到热膨胀，如汽包一端固定，另一端用吊挂或活动滚柱来支承，或者两端都用吊挂或活动滚柱支承，上联箱支撑或悬吊在钢架上，下联箱则不能支撑；

2.空气预热器管箱，钢制烟道的热风道都没有波形补偿器，炉要留有膨胀缝.

3.锅炉升火过程中要注意，监视各部分膨胀指示值，检修的法兰，螺栓联接处要热紧螺丝.

4.水在4℃时比重最大，随着温度再降低，比重减小，体积增大，结冰时体积膨胀更大，会冻坏设备.

解答题

有大小两个水桶，一共装水20千克，两个水桶都倒出同样多的水后，小水桶还剩3千克，大水桶还剩9千克，原来大桶有多少千克？
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单项选择题

Aspirin is one of the safest and most effective drugs invented by man. The most popular medicine in the world today, it is an effective pain reliever. Its bad effects are relatively mild. It is also cheap.For millions of people suffering from arthritis, it is the only thing that works. Aspirin, in short, is truly the 20th-century wonder drug. It is also the second largest suicide drug and is the leading cause of poisoning among children. It has side effects that, although relatively mild, are largely unrecognized among users.Although aspirin was first sold by a German company in 1899, it has been around much longer than that. Hippocrates, in ancient Greece, understood the medical value of tree barks and leaves which today are known to contain a chemical found in aspirin. During the 19th century, there was a great deal of experimentation in Europe with this chemical, and it led to the introduction of aspirin. By 1915, aspirin tablets were available in the United States.A small quantity of aspirin relieves pain and inflammation. It also reduces fever by affecting some of the body’’s reactions. Aspirin is very irritating to the stomach lining. The best way is to chew the tablets before swallowing them with water, but few people can stand the bitter taste. Some people suggest crushing the tablets in milk or orange juice.

A good title for this passage would be:________

A．Why Do We Take Aspirin

B．How Do We Take Aspirin

C．Aspirin: The Unknown Side Effects.

D．Aspirin: The Most Popular Medicine.
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