问题 问答题 简答题

石油化工企业常用的伴热介质有哪几种?其适用范围如何?

答案

参考答案:

石油化工企业常用的伴热介质有四种:

(1)热水:选用于在操作温度不高或不能采用高温伴热的介质的条件下,作为伴热的热源;

(2)蒸汽:一般用于管内介质的操作温度小于150℃的伴热;

(3)热载体:一般用于是管内介质的操作温度大于150℃的夹套伴热系统。常用的热载体的重柴油或馏程大于300℃馏分油,联苯-联苯醚或加氢联三苯等;

(4)电热:电伴热不但适用于蒸汽伴热的各种情况,而且适用于热敏性介质管道,能有效地进行温度控制,防止温度过热;适用于分散或远离供汽点的管道或设备、以及无规则外型的设备(如泵)的伴热。

单项选择题 A1/A2型题
阅读理解

阅读理解。

   Are morning people born or made? In my case it was definitely made. In my early 20s, I rarely went to

bed before midnight, and I would almost always get up late the next morning.

   But after a while I couldn't ignore the high relationship between success and rising early. On those rare

occasions where I did get up early, I noticed that my productivity(效率)was almost always higher. So I set out to become a habitual early riser. But whenever my alarm went off, my first thought was always to stop

that noise and go back to sleep. Eventually some sleep research showed me that I was using the wrong strategy.

   The most common wrong strategy is this: You assume that if you're going to get up earlier, you'd better

go to bed earlier. It sounds very reasonable, but will usually fail.

   There are two main schools (流派) of thought on sleep patterns. One is that you should go to bed and

get up at the same time every day. The second school says you should go to bed when you're tired and get up when you naturally wake up. However, I have found both of them are wrong if you care about productivity. If you sleep at set hours, you'll sometimes go to bed when you aren't sleepy enough. You're wasting

time lying in bed awake and not being asleep.

   If your sleep is based on what your body tells you, you'll probably be sleeping more thanyou need. Also, your mornings may be less predictable if you're getting up at different times.

   The solution for me has been to combine both methods. I go to bed when I'm sleepy and get up with an alarm clock at a fixed time. So I always get up at the same time (in my case 5 am), but I go to bed at different times every night - sometimes at 9:30pm, and other times at midnight. Most of the time I go to bed between 10-11 pm.

   However, going to bed only when I'm sleepy, and getting up at a fixed time every morning is my way. If you want to become an early riser, you can try your own.

1. According to the passage, the underlined phrase refers to ________.

A. people who stay up until the next morning.    

B. people who get up early in the morning.

C. people who feel sleepy in the morning.   

D. people whose productivity is the highest in the morning.

2. Why did the author want to become a habitual early riser? 

A. Because he/she wanted to form the habit of going to bed early and getting up early.

B. Because he/she had found that his / her productivity was higher when he/she got up early.

C. Because he/she wanted to see which of the two main schools of thought on sleep patterns was right.

D. Because he/she was told the high relationship between success and rising early.

3. The author experienced all the following EXCEPT ________.  

A. going to bed after midnight          

B. getting up early occasionally

C. pressing off the alarm to go on sleeping      

D. asking scholars for advice on sleeping habits

4. The passage is mainly about ________. 

A. how to become an early riser        

B. how to have good sleep

C. wrong strategies for getting up early    

D. main schools of thought on sleep patterns