2013-2-27 Learning Outcomes(1) Demonstrate understanding of key concepts including phase and pure substance,state principle for simple compressible systems,p-- T surface,saturation temperature and saturation pressure.two-phase liquid-vapor mixture,quality,enthalpy,and specific heats Apply the closed system energy balance with property data. 3-3 Learning Outcomes(2) Sketch T-v,p-v,and phase diagrams,and locate states on these diagrams Retrieve property data from Tables A-1 through A-23. Apply the ideal gas model for thermodynamic analysis,including determining when use of the model is warranted. 3-4 2
2013-2-27 2 Learning Outcomes(1) ►Demonstrate understanding of key concepts . . . including phase and pure substance, state principle for simple compressible systems, p-vT surface, saturation temperature and saturation pressure, two-phase liquid-vapor mixture, quality, enthalpy, and specific heats. ►Apply the closed system energy balance with property data. 3-3 Learning Outcomes(2) ►Sketch T-v, p-v, and phase diagrams, and locate states on these diagrams. ►Retrieve property data from Tables A-1 through A-23. ►Apply the ideal gas model for thermodynamic analysis, including determining when use of the model is warranted. 3-4
2013-2-27 Phase A quantity of matter that is homogeneous throughout in both chemical composition and physical structure. Homogeneity in physical structure means that the matter is all solid,or all liquid,or al vapor (gas). Examples: The air we breathe is a gas phase consisting of a mixture of different gases. Drinking water with ice cubes contains two phases of water:liquid and solid. Vinegar and olive oil salad dressing contains two different liquid phases. 3-5 Pure Substance A substance that is uniform and invariable in chemical composition. A pure substance can exist in more than one phase,but its chemical composition must be the same in each phase. Examples: Drinking water with ice cubes can be regarded as a pure substance because each phase has the same composition. A fuel-air mixture in the cylinder of an automobile engine can be regarded as a pure substance until ignition occurs 3-6 3
2013-2-27 3 Phase ►A quantity of matter that is homogeneous throughout in both chemical composition and physical structure. ►Homogeneity in physical structure means that the matter is all solid, or all liquid, or all vapor (gas). ►Examples: ►The air we breathe is a gas phase consisting of a mixture of different gases. ►Drinking water with ice cubes contains two phases of water: liquid and solid. ►Vinegar and olive oil salad dressing contains two different liquid phases. 3-5 ►Examples: ►Drinking water with ice cubes can be regarded as a pure substance because each phase has the same composition. ►A fuel-air mixture in the cylinder of an automobile engine can be regarded as a pure substance until ignition occurs Æ Pure Substance 3-6 ►A substance that is uniform and invariable in chemical composition. ►A pure substance can exist in more than one phase, but its chemical composition must be the same in each phase
2013-2-27 Phase Pure Substance 3-1 State Principle for Simple Compressible Systems ar imple co The intensive state of a simple compressible system at equilibrium is described by its intensive properties,including temperature,pressure, specific volume,density,specific internal energy, and specific enthalpy. Properties such as velocity and elevation are excluded because their values depend on arbitrary datum choices.such as zero values at the surface of the earth.For the state principle,these properties are not relevant. 3-8 4
2013-2-27 4 Phase & Pure Substance 3-7 State Principle for Simple Compressible Systems ►Systems of commonly encountered pure substances are called simple compressible systems. These substances include those in appendix tables A-2 through A-18, A-22, and A-23. ►The intensive state of a simple compressible system at equilibrium is described by its intensive properties, including temperature, pressure, specific volume, density, specific internal energy, and specific enthalpy. ►Properties such as velocity and elevation are excluded because their values depend on arbitrary datum choices, such as zero values at the surface of the earth. For the state principle, these properties are not relevant. 3-8
2013-2-27 State Principle for Simple Compressible Systems Not all of the relevant intensive properties are independent. Some are related by definitions-for example,density is 1/and specific enthalpy is u+pv. Others are related through expressions developed from experimental data. Some intensive properties may be independent in a single phase,but become dependent when there is more than one phase present. 3-9 State Principle for Simple Compressible Systems For a simple compressible system,values for any two independent intensive properties determine the values of al/other intensive properties.This is the state principle for simple compressible systems. Among alternative sets of two independent intensive properties,(T,and (p,are frequently convenient.We soon show that temperature and pressure are not always an independent set(within the two-phase regions p and T are not independent). 3-10 5
2013-2-27 5 State Principle for Simple Compressible Systems ►Not all of the relevant intensive properties are independent. ►Some are related by definitions – for example, density is 1/v and specific enthalpy is u + pv. ►Others are related through expressions developed from experimental data. ►Some intensive properties may be independent in a single phase, but become dependent when there is more than one phase present. 3-9 State Principle for Simple Compressible Systems ►For a simple compressible system, values for any two independent intensive properties determine the values of all other intensive properties. This is the state principle for simple compressible systems. ►Among alternative sets of two independent intensive properties, (T, v) and (p, v) are frequently convenient. We soon show that temperature and pressure are not always an independent set (within the two-phase regions p and T are not independent). 3-10
2013-2-27 STATE AND EQUILIBRIUM ynmic ea with Fauilibrium A state of balance In an equilibrium state there are no m2kg T1=209 =15 w. The Mechanical eauilibrium:If there is n at any point ofh 20C 23℃ 32 32℃ d when the 30 32 involves two ph is c level and stays there Acosed system reacn mica (a)Before (b)After change with tim thermal equilibrium. 3.11 The State Postulate The number of properties required to fix the state of a system is given by the state postulate: The state of a simple compressible system is Nitrogen T=25C properties. V=0.9 m/kg Simple compressibles syste a system involves no electrical. State of nitrogen is magnetic,gravitational,motion. and surface tension effects.(the fixed by two independent, only energy transfer by work is by volume change). intensive properties 3.12 6
2013-2-27 6 A closed system reaching thermal equilibrium. 3-11 STATE AND EQUILIBRIUM Thermodynamics deals with equilibrium states. Equilibrium: A state of balance. In an equilibrium state there are no unbalanced potentials (or driving forces) within the system. Thermal equilibrium: If the temperature is the same throughout the entire system. Mechanical equilibrium: If there is no change in pressure at any point of the system with time. Phase equilibrium: If a system involves two phases and when the mass of each phase reaches an equilibrium level and stays there. Chemical equilibrium: If the chemical composition of a system does not change with time, that is, no chemical reactions occur. A system at two different states. The State Postulate The number of properties required to fix the state of a system is given by the state postulate: The state of a simple compressible system is completely specified by two independent, intensive properties. Simple compressible system: If a system involves no electrical, magnetic, gravitational, motion, and surface tension effects.(the only energy transfer by work is by volume change). 3-12 State of nitrogen is fixed by two independent, intensive properties