【简答题】听下面一段独白, 回答第1-3题。 1. What had the speaker done before he wrote the letter? A. He had played tennis. B. He had taken some exams. C. He had fed cats. 2. What can we learn about the weather then? A. Hot....
【单选题】空气流经渐缩喷管作定熵流动。已知进口截面上空气参数为 p 1 =0.6MPa , t 1 =700°C , c f1 =312m/s ,出口截面积 A 2 = 30 cm 2 。试确定喷管所能达到的最大质量流量时对背压的要求。设空气 R g = 0.287kJ/(kg·K) ,比热容 c p = 1.005 kJ/(kg·K) ,临界压力比 ν cr =0.528 。