班級:环班姓名: 考试科目:工程热力学 2.(共10分)一空气晚管,其进口压力为20温度为5℃,要求流量为头背压五:附加题(共10分 You can answ er it in Chinese if you cann't put your idea correctly in 为06MPa,问应选择什么形状的喷管?求喷管出口截面空气的流速及出口截面积。若为渐Engi) 缩渐扩喷管,则还须求出喉部截面的尺寸和流速 1.(5 5)Please make a statement of the First Law of Thermodynamics and write out the energy 2. (5/)Explain why heat is always transferred from high temperature body to low temperature ones3 班级：建环 班 姓名： 考试科目：工程热力学 学号： 2．（共 10 分）一空气喷管，其进口压力为 2.0MPa, 温度为 350℃，要求流量为 5kg/s，背压 为 0.6MPa，问应选择什么形状的喷管？求喷管出口截面空气的流速及出口截面积。若为渐 缩渐扩喷管，则还须求出喉部截面的尺寸和流速。 五：附加题 （共 10 分,You can answer it in Chinese if you cann’t put your idea correctly in English.） 1．(5 分) Please make a statement of the First Law of Thermodynamics and write out the energy balance equation for closed system. 2. (5 分) Explain why heat is always transferred from high temperature body to low temperature ones naturally