问题 问答题 简答题

尿素蒸发为什么采用膜式蒸发器?

答案

参考答案:

所谓膜式蒸发器,指液体并不充满管内而是沿管壁的一层液膜形式上升(称升膜式蒸发器),同时在管外加热蒸汽的作用下,在管内1/3高度处,大量蒸汽从液膜中蒸出,故管内中心为高速流动的气流,由于液膜极薄,流速极高,这样就使加热器有极高的传热系数,以致在极短的时间内就把尿液增浓到指标,这对减少缩二脲的生成是非常有利的,是保证尿素溶液迅速穿过结晶温度,而不致结晶。

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Lots people stress out(紧张) about talking in front of the class or getting laughed at if they make a mistake in front of an audience._71_ The “stress hormones” that your body produces at times like these can actually help you focus.

But when worry and stress about performing get to be too much, these hormones give people that “red alert(紧急状态)”---the one that causes you to feel cold or sweaty, or get butterflies in your stomach._72__

Be prepared. __73_ Rehearse(排练) as much as you can and practice in front of others at every opportunity. Most of all, think positively. Tell yourself “I’ll be OK” or “I can do this” even if you are not 100% sure of it.

Look after yourself. Before big performances, it’s easy to let taking care of yourself slip as you spend too much time on rehearsals and practice. __74__ Exercise can also can also help you feel good, and along with sleep and nutrition, is an excellent way of keeping those stress hormones from getting out of control.

Find out what the experts do. You can find books, DVD, and online information about how to give your best when you perform, depending on what type of performance you’re preparing for._75_ Or ask the cast of your school play or your drama or music teacher how they beat stage fright. And if your parents or grandparents ever performed, they may have their own secrets to share.

A Confidence helps beat stress hormones.

B The following tips can help you avoid that feeling.

C You’re less likely to freeze up if you’re well prepared.

D You can do this whether you’re performing alone or as part of a group.

E Check out stories about Olympic gymnasts or your favorite star to get their tips.

F Feeling nervous before a performance is part of body’s way of helping you do your best.

G You’ll look and feel your best if you get enough sleep and eat healthy meals before your performance.

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