问题 问答题 简答题

朗肯循环的热效率如何计算?影响其热效率的主要因素是什么?

答案

参考答案:

朗肯循环的热效率计算公式为

η=(H1—H2)/(H1—H2′)

式中H1——过热蒸汽焓;

H2——汽轮机排汽焓;

H2′——凝结水焓。

从朗肯循环的效率公式看,其热效率取决于过热蒸汽焓、汽轮机排汽焓和凝结水焓。而过热蒸汽焓取决于过热蒸汽压力和温度,排汽焓和凝结水焓取决于排汽压力。所以,在其他条件不变的情况下提高蒸汽初参数(压力、温度),热效率将提高。在初参数不变的情况下,降低蒸汽终参数(排汽压力),可提高循环热效率;反之,热效率将下降。

阅读理解

On Thursday afternoon Mrs. Clarke, dressed for going out, took her handbag with her money and her key in it, pulled the door behind her to lock it and went to the Over 60s Club. She always went there on Thursdays. It was a nice outing for an old woman who lived alone.

At six o’clock she came home, let herself in and at once smelt cigarette smoke. Cigarette smoke in her house? How? Had someone got in? She checked the back door and the windows. All were locked or fastened, as usual. There was no sign of forced entry.

Over a cup of tea she wondered whether someone might have a key that fitted her front door—“a master key ”perhaps. So she stayed at home the following Thursday. Nothing happened. Was anyone watching her movements? On the Thursday after that she went out at her usual time, dressed as usual, but she didn’t go to the club. Instead she took a short cut home again, letting herself in through her garden and the back door. She settled down to wait.

It was just after four o’clock when the front door bell rang. Mrs. Clarke was making a cup of tea at the time. The bell rang again, and then she heard her letter box being pushed open. With the kettle of boiling water in her hand, she moved quietly toward the front door. A long piece of wire appeared through the letter box, and then a hand. The wire turned and caught around the knob on the door lock. Mrs. Clarke raised the kettle and poured the water over the hand. There was a shout outside, and the skin seemed to drop off the fingers like a glove. The wire fell to the floor, the hand was pulled back, and Mrs. Clarke heard the sound of running feet.

小题1:Mrs. Clarke looked forward to Thursday because__________.

A.she worked at a club on the day

B.she lived alone

C.she visited a club on Thursdays

D.a special visitor came on Thursday Clarke小题2: If someone had made a forced entry,________.

A.Mrs. Clarke would have found a broken door or window

B.he or she was still in the house

C.things would have been thrown about

D.he or she would have needed a master key小题3:According to the passage, which of the following is right?

A.She is about more than 50 years old.

B.The next day after she found something unusual in her house, she stayed at home.

C.The man who tried to enter her house wore a pair of gloves.

D.Mrs. Clarke was in an attempt to trick the thief when she noticed something unusual.小题4:The wire fell to the floor________.

A.because Mrs. Clarke refused to open the door

B.when the man’s glove dropped off

C.because it was too hot to hold

D.because the man just wanted to get away

多项选择题