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1、,Thermodynamics,Faculty of Mechanical Eng. Dr. QIN Kun (691566) 325#, Faculty building,Thermodynamics is the study of the conversion of energy into work and heat and its relation to macroscopic variables such as temperature, volume and pressure. The macroscopic approach to thermodynamics is called c
2、lassical thermodynamics. A more elaborate approach, based on the average behavior of large groups of individual particles, is called statistical thermodynamics.,Applications of thermodynamics,The laws of thermodynamics Zeroth law of thermodynamics, about thermal equilibrium; First law of thermodynam
3、ics, about the conservation of energy; Second law of thermodynamics, about direction of natural processes, entropy; Third law of thermodynamics, about the absolute zero of temperature.,Heat transfer is a study of the exchange of thermal energy through a body or between bodies which occurs when there
4、 is a temperature difference.,Heat Transfer & Thermodynamics,Thermodynamics deals with systems in equilibrium. It may be used to predict the amount of energy required to change a system from one equilibrium state to another.,Heat transfer supplements the first and second laws of thermodynamics by pr
5、oviding additional experimental rules which may be used to establish energy-transfer.,1,CHAPTER,Basic Concepts of Thermodynamics,INTRODUCTION,The study of thermodynamics is concerned with the ways energy is stored within a body and how energy transformations, which involve heat and work, may take pl
6、ace.One of the most fundamental laws of nature is the conservation of energy principle.,Systems,A thermodynamic system, or simply system, is defined as a quantity of matter or a region in space chosen for study. Surroundings are physical space outside the system boundary. The region outside the syst
7、em is called the surroundings. The real or imaginary surface that separates the system from its surroundings is called the boundary.,Closed, Open, and Isolated Systems,Systems may be considered to be closed or open, depending on whether a fixed mass or a fixed volume in space is chosen for study.,A
8、closed system consists of a fixed amount of mass and no mass may cross the system boundary. The closed system boundary may move.,An open system, or control volume, has mass as well as energy crossing the boundary, called a control surface. Examples of open systems are pumps, compressors, turbines, v
9、alves, and heat exchangers.,An isolated system is a general system of fixed mass where no heat or work may cross the boundaries. An isolated system is a closed system with no energy crossing the boundaries and is normally a collection of a main system and its surroundings that are exchanging mass an
10、d energy among themselves and no other system.,Isolated System Boundary,Mass,System,Surr 3,Mass,Work,Surr 1,Heat = 0 Work = 0 Mass = 0 Across Isolated Boundary,Heat,Surr 2,Surr 4,Properties of a SystemAny characteristic of a system in equilibrium is called a property. The property is independent of
11、the path used to arrive at the system condition. Some thermodynamic properties are pressure P, temperature T, volume V, and mass m.,Properties may be intensive or extensive. Extensive properties are those that vary directly with size-or extent-of the system. Some Extensive Properties a. mass b. volu
12、mec. total energy d. mass dependent property,Intensive properties are those that are independent of size.Some Intensive Properties a. temperature b. pressure c. age d. colore. any mass independent property,Extensive properties per unit mass are intensive properties. For example, the specific volume
13、v, defined as,and density , defined as,are intensive properties.,Units,State, Equilibrium, Process, and Properties Consider a system that is not undergoing any change. The properties can be measured or calculated throughout the entire system. This gives us a set of properties that completely describ
14、e the condition or state of the system. At a given state all of the properties are known; changing one property changes the state.,Equilibrium A system is said to be in thermodynamic equilibrium if it maintains thermal (uniform temperature), mechanical (uniform pressure), phase (the mass of two phas
15、es, e.g., ice and liquid water, in equilibrium) and chemical equilibrium.,Process Any change from one state to another is called a process. During a quasi-equilibrium or quasi-static process the system remains practically in equilibrium at all times. We study quasi-equilibrium processes because they
16、 are easy to analyze (equations of state apply) and work-producing devices deliver the most work when they operate on the quasi-equilibrium process.,The process on a P-V diagram as shown below.,Steady-Flow ProcessThe flow is often defined by the terms steady and uniform. The term uniform implies no
17、change with location over a specified region. The term steady implies that there are no changes with time. The fluid properties can change from point to point with in the control volume, but at any fixed point the properties remain the same during the entire process. Engineering flow devices that operate for long periods of time under the same conditions are classified as steady-flow devices.,
