问题 问答题 简答题

直流锅炉各参数间的关系(即动态特性)有何特点?

答案

参考答案:

(1)功率的扰动。当汽轮机调汽门突然开大时,蒸汽流量迅速增加,由于燃料量不变,汽压降低,给水量将自动增加。由于饱和温度的降低,锅炉产生的附加蒸发量使汽压下降速度减慢,最终趋于稳定。同时蒸汽流量将逐渐减少,达到与给水流量相等的平衡状态。

(2)给水量的扰动。给水量突然增大时,蒸汽量相应增大。保持燃料量不变,直流炉的炉的加热、蒸发空间增大,过热段缩短,汽温下降。蒸汽流量增大到等于给水量时趋于稳定。

(3)燃料量的扰动。燃料量突然增大时,锅炉蒸发量经过一段时滞后先上升而后下降到等于给水量。汽压和汽温都降上升到一个新的水平。

完形填空

Stress for a teenager is as real a problem as stress for an adult. To deal with it, it’s important to understand the causes of stress in teenagers.

When parents change their jobs or if the family decides to move to a different place, the child has to change schools, find new friends, adapt to the new social circle and fit into new groups. It is always difficult for children to adapt to such changes, which can be a serious cause of stress in their life.

Academic difficulties, such as inability to understand a certain subject can cause stress. Not every child has the ability to understand every subject. Some kids need extra help besides school work to grasp a few concepts. Poor academic performance is often laughed at and is looked down upon by both teachers and peers. In such cases, it can make the child feel isolated, neglected and hurt. All of this, put together, can add to stress, which many times worsens grades.

Extra curricular activities (课外活动) such as playing a sport, or attending art classes can weigh heavily on your child’s mind. Juggling between school and extra curricular activities does seem like a burden when you have to excel at both. When the pressures from both the ends get unmanageable, teenagers tend to get tired and annoyed. Fatigue sets in, leading to stress related issues such as lack of concentration in school.

These are the common causes of stress in teenagers, which can be noticed through signs such as poor memory, anxiety, negative and pessimistic attitude. If the signs of teenage stress go unrecognized for a long time, it can make the child emotinally imbalanced.

小题1:Extra curricular activities may lead to additional pressure for teenagers when they have difficulty _________________________________________________________.

小题2:How can parents notice that their teenagers are under stress?

_________________________________________________________________.

小题3:____________________, ___________________, extra-curricular activities are the common causes of stress in teenagers.

小题4:According to your experience, what other causes of teenage stress do you know? (List two causes).

_________________________________________________________________.

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