采用如图所示的管路系统测定离心泵的汽蚀余量。离心泵吸入径为84mm,压出径为52mm,泵吸入口装有真空表,输出管路装有板流量计,径为38mm。实验时,同时调节阀门A和B的开度,可使吸入管增大而流量保持不变,实测数据如下:吸入管真空度为73.3kPa,流量计U形管水银压差计读数为750mm,大气压强为101.325kPa,水温为20℃,此时离心泵恰好发生汽蚀。设流量计流系数C 0 =0.75,试求测定流量下该泵的有效汽蚀余量△h a 。
【简答题】阅读下面短文 , 在空白处填入一个适当的单词或括号内单词的正确形式。 Yesterday there was a very exciting debate at Xinhua Middle School about whether medical cloning should be allowed or not. 1 a lively discussion a vote was cast and ...
【单选题】SECTION B PASSAGES Directions: In this section, you will hear several passages. Listen to the passages carefully and then answer the questions that follow. 听力原文: In ancient times, many people believed...
A.
How the natural world was described in Greek mythology.
B.
What they observed directly.
C.
The writings of philosophers from other societies.