Impurities from the boiler water surface can be removed thro

题目
单选题
Impurities from the boiler water surface can be removed through the ().
A

safety valve

B

blow down valve

C

scum valve

D

feed check valve

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相似问题和答案

第1题:

In a ______boiler the hot gases from the furnace pass through the tubes while the water is on the outside.

A.water-tube

B.fire-tube

C.exhaust gas

D.Composite


正确答案:B

第2题:

The separation of impurities and water from ______is essential for good combustion of diesel engines.

A.lube oil

B.fuel oil

C.turbine oil

D.grease


正确答案:B

第3题:

It can be learned from the passage that about four billion years ago ______.

A. the earth was in molten state

B. the earth surface temperature was above 100℃

C. the earth surface temperature was below 100℃

D. rain water could remain on the earth


正确答案:B

43.答案为B。根据第一段最后一句及第二段内容可知,雨水在地表温度降到水的沸点以下才能停在地表,由此可知大约在四十亿年前,地表温度应在沸点以上。

第4题:

单选题
A shallow dish positioned at the normal water level is connected to the()This enables the blowing down or removal of scum and impurities from the water surface.
A

main stern stop valve

B

auxiliary steam stop valve

C

scum valve

D

blow down valve


正确答案: B
解析: 暂无解析

第5题:

共用题干
第一篇

Water Resources on the Earth

The second most important constituent(构成成分)of the biosphere(生物圈)is liquid water. This can only exist in a very narrow range of temperatures,since water freezes at 0℃and boils a 100℃.Life as we know it would only be possible on the surface of a planet which had temperature: somewhere within this narrow range.
The earth's supply of water probably remains fairly constant in quantity.The total quantity of water is not known very accurately,but it is about enough to cover the surface of the globe to a depth of about two and three-quarter kilometers.Most of it is in the form of the salt water of the oceans一about 97 percent. The rest is fresh.But three-quarters of this is in the form of ice at the poles and or mountains and cannot be used by living systems until melted.Of the remaining fraction,which h somewhat less than one percent of the whole.There is 10—20 times as much stored underground water as there is actually on the surface.There is also a tiny,but extremely important fraction of the water supply which is present as water vapour in the atmosphere.
Water vapour in the atmosphere is the channel through which the whole water circulation(循环) of the biosphere has to pass.Water evaporated(蒸发)from the surface of the oceans,from lakes and rivers and from moist(潮湿的)earth is added to it. From it the water comes out again as rain or snow,falling on either the sea or the land. There is,as might be expected, a more intensive evaporation per unit area over the sea and oceans than over the land,but there is more rainfall over the land than over the oceans and the balance is restored by the run off from the land in the form of rivers.

Liquid water only exists________.
A: in the center of the earth
B:on the surface of our planet
C:in the coastal areas of the earth
D:in a very narrow range of temperatures

答案:D
解析:
文章第一段的第二句讲到液态水“only exist in a very narrow range of temperatures",虽然B(我们星球的表面)也有点道理,但是液态水对温度的要求很高,并非地球的所有表面都有液态水存在,所以答案D正确。
第二段第一句提到地球上水的供给“remains fairly constant in quantity",数量上是恒定的,它就没有增加也不会减少,只不过会以不同的形态出现,所以选择B(保持不变)。
问题是“地球上绝大部分淡水以什么形式出现?”第二段中间提到淡水时,说到“three-quarters of this is in the form of ice at the poles and on mountains",即3/4的淡水以冰的形式存在于两极和高山中,后面提到剩余部分的淡水存在于地下,但占比少于1%,所以选项A正确。
词义辫析题, fraction有“小部分”的意思,考虑到前面提到地球97%的水以海洋咸水的形式存在,剩下的3%则以冰的形式存在于两极和高山,余下的自然不多,所以选B。
第三段的最后一句说到“there is more rainfall over the land than over the oceans”,陆地的降雨比海洋要多,但没有提到河流和山脉的降雨比较,所以C正确。大气中的水蒸气是整个生物圈的水循环必经的途径。水从海洋的表面、湖泊、河流和潮湿的泥土中蒸发出来并补充到大气中。水以雨或雪的形式再次出现,降落在海洋或陆地上。可以预料到的是,海洋上空每单位面积的水蒸气比在陆地上空更为密集,但是,陆地比海洋有更多的降雨,水在陆地上以河流的形式流出以保持水资源的平衡。

第6题:

The boiler water alkalinity in a coil-type auxiliary boiler should be maintained at the pH recommended by the boiler manufacturer to______.

A.precipitate(使沉淀) silica (硅石)from solution

B.reduce corrosion in the heating coil

C.prevent clogging and erosion in the coil

D.maintain zero water hardness


正确答案:B

第7题:

The general circulation of the surface water in Mediterranean is ______.

A.counter-clockwise

B.clockwise

C.from east to west

D.from north to south


正确答案:A

第8题:

In a()boiler the hot gases from the furnace pass gases from the furnace pass water is on the outside.

A.water-tube

B.fire-tube

C.exhaust gas

D.composite


答案:B

第9题:

单选题
The concentration of total dissolved solids in the water of an auxiliary boiler can increase as a result of ().
A

seawater contamination

B

frequent surface blows

C

dissolved oxygen deaeration

D

frequent bottom blows


正确答案: B
解析: 暂无解析

第10题:

单选题
The water level of an exhaust gas boiler which is independent of the auxiliary boiler and just as the extra heating surface of it ()
A

will be modulated in proportion

B

will be modulated in proportion and integral

C

will be modulated in proportion and differential

D

will not be modulated at all


正确答案: C
解析: 暂无解析

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