问题 单项选择题

验算由分汽缸送出的供汽压力P0能否使凝结水回到闭式水箱中(见下图),求最小供汽压力P0的正确值为下列哪一项()。

已知:1.蒸汽管道长度L=500m,平均比摩阻ΔPm=200Pa/m,局部阻力按总阻力的20%计。

2.凝结水管道总阻力为0.01MPa。

3.疏水器背压P2=0.5P1

4.闭式水箱内压力P4=0.02MPa。

A.0.49~0.5MPa

B.0.45~0.47MPa

C.0.37~0.4MPa

D.3.4~3.5MPa

答案

参考答案:C

解析:

根据《二版教材》:P2=P3+P4+Pz,因为P1=2P2,所以,p0=500×200×(1+20%)/106+2×(0.01+10×1000×9.8/106+0.02)=0.376MPa。

单项选择题
完形填空

第二节(共5小题;每小题2.5分,满分12.5分)

根据短文内容,从短文后的选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。

People know the dangers of fires. It’s good for a family to learn how to prepare for a fire. Here are some suggestions.

Put a smoke alarm in the house. The alarm makes a loud sound.   71    

Make escape plans. They should know all the ways out of the house. If there is a fire, everyone follows the plan to get out.   72  

Practise for a fire. They do fire practice because they teach children about fire safety.Everyone in the family should know the following fire rules:

Don't open a hot door! The fire can grow more quickly if you open the door. 73   Smoke can be more dangerous than fire. The best air is near the floor because smoke rises.

What will you do if your hair or clothes start to burn? First, don’t run! The fire burns faster because of more air. Drop! Fall to the floor. Then roll!    74    Put a blanket around you to keep air away from the fire that may still be on you.

There are many possible causes for fires.    75    If there is a fire, don’t forget to call 119 for help.

A.Turning over and over will make the fire go out.

B.Smoke from a fire causes the alarm to go off.

C.The cleanest air is found at the top.

D.Stay close to the floor!E. A wise family is ready all the time.

F. Make sure all the windows can be opened easily.

G. Do not go back to the house for any reason.