西北大学《工程热力学》课件-Chapter1Basic Concepts.pptVIP

Chapter 1 Basic Concepts 1-1 Thermodynamic Systems 1-2 States and Basic Properties of Working Substances 1-3 Processes 1-4 Equilibrium States, Equations of State, Coordinate With Property1-5 Work and Heat1-6 Thermodynamic Cycles 西北大学《工程热力学》 System A fixed quantity of mass or region of space selected for the purpose of analysis. Surrounding All of the objects outside the system that have interactions with this system. Boundary The real or imaginary surface that separates the system from its surrounding. 1-1 Thermodynamic Systems mass exchangeForms of Interaction between system and its surroundings energy exchangeheatwork 1) Closed systemsIn closed systems, no mass leaves or enters the system boundaries. Fig. 1-1 closed system As seen in Figure 1-1, consider the fluid in the cylinder of a reciprocating engine during the expansion stroke. The system boundaries are the cylinder walls and the piston crown. Notice that the boundaries move as the piston moves. Fig. 1-1 closed systemBoundaryControll mass 2) Open systemIn open systems there is a mass transfer across the systems boundaries.Fig. 1-2 Open system As we see in Fig. 1-2, the steam flow through a steam turbine at any instant may be defined as an open system with fixed boundaries. Control volume Fig. 1-2 Open system Imaginary BoundaryReal boundary Simple compressible systemA system is called a simple compressible system in the absence of electrical, magnetic, gravitational, motion, and surface tension effects. Isolated System:If mass and energy is not allowed to cross the boundary, that system is called an isolated system.Adiabatic system: when no heat cross the boundary, the system is called an adiabatic system. 1-2 State and Basic PropertiesThermodynamic StateThe state of a system completely describes how the system exists. We call this situation a thermodynamic state. It is a description of the condition of a system.It has temperature, pressure, density, and other macroscopic properties. In solvi