Chapter 5 化工过程能量分析
Energy Analysis for Chemical Engineering Process
体系的分类：
封闭体系(closed system)：与环境没有物质交换。 体系 敞开体系(open system)：与环境有质量交换。 简单体系（simple system)：体系内部没有任何绝热 (adiabatic)、刚性(rigid)、不渗透(impermeable)的界 面(boundary)，而且不受外部和内部力场的作用。 复杂体系(composite system)：体系由两个或两个以 上的简单体系构成，如半渗透膜海水淡化体系；或 者体系处于外部或内部力场中，如磁场、电场等。 简单体系是最常见的一种体系。对于简单体系，体系的 能量等于其内能，即 E = U。
W s [( pV )m W ]
d ( mU ) dt
W s [(U 1 u2 gz )m Q ] [( pV )m ] 2
W s [(U pV 1 u2 gz )m Q ] 2
因为 H = U + pV，得到
d ( mU ) dt
2 W s [( H 1 u gz ) m ] Q 2
3rd Step: 分析热力学第一定律中的各个项 In this problem, the heat rate is zero because a power outage occurs and heat losses from the tank are negligible. The work rate is also zero since there is no mechanical equipment in the process. The mass in the tank and the mass flowrate are constant. Moreover, if the differences between inlet and outlet kinetic and potential energies can be neglected, the equation of 1st law is simplified as the following form: dU m m ( H H1 ) 0 dt where U and H refer to the internal energy and enthalpy of the water in the tank; H1 is the enthalpy of the cold water entering the tank.
