大连理工大学：《工程热力学》课程教学资源（PPT课件）1 基本概念 Basic Concepts of Thermodynamics

Basic Concepts of ThermodynamicsObjectiveDefinition of Thermodynamic System: Concepts of State and its properties: Pressure, Temperature and Specific Volume·Quasi-static or Quasi-equilibrium ProcessandReversibleProcessThermodynamic Cycle

Basic Concepts of Thermodynamics Objective • Definition of Thermodynamic System • Concepts of State and its properties • Pressure, Temperature and Specific Volume • Quasi-static or Quasi-equilibrium Process and Reversible Process • Thermodynamic Cycle

Thermodynamic SystemSystemA quantity of matter ora region in space bounded by anarbitrary surfacesfor studySURROUNDINGSSurroundingThe mass orregion outside the systemSYSTEMBoundaryThe surfacesseparate the system from itsBOUNDARYsurroundings.The boundary can be real or imaginary,fixed or variable-lt is critically important to define your system beforeattemptingtosolveathermodynamicproblem

Thermodynamic System System—A quantity of matter or a region in space bounded by an arbitrary surfaces for study. Surrounding—The mass or region outside the system. Boundary—The surfaces separate the system from its surroundings. The boundary can be real or imaginary, fixed or variable. –It is critically important to define your system before attempting to solve a thermodynamic problem

Thermodynamic SystemClosed systemNo mass can cross its boundary. Itconsistsof afixedamount ofmass(also known as control mass)Open systemAselected region inspace.Bothmassand energy can cross its boundary.(also known as control volume)ImaginaryboundaryReal boundaryNCmassCLOSEDSYSTEMMovingCVboundarym=constant(anozzle)CVYEenergyFixedboundary

Thermodynamic System Closed system—No mass can cross its boundary. It consists of a fixed amount of mass. (also known as control mass) Open system —A selected region in space. Both mass and energy can cross its boundary. (also known as control volume)

Thermodynamic System-Simple Thermodynamic SystemHeatSYSTEMSurroundingsOne Type WorkBOUNDARYAdiabatic System -No heat cross its boundaryIsolated SystemNether mass nor energy can cross itsboundary

Thermodynamic System –Simple Thermodynamic System Adiabatic System —No heat cross its boundary. Surroundings Heat One Type Work Isolated System— Nether mass nor energy can cross its boundary

Thermodynamic SystemSingle Composition SystemConsists of only one kindof substance.Multi-CompositionSystemConsists of tow or morekinds of substancesSinglePhaseSystemConsists ofonlyonephaseMulti-phases System Consists of tow or more phasesHomogeneous System The composition and propertyare identical all over the system

Thermodynamic System Single Composition System —Consists of only one kind of substance. Multi-Composition System —Consists of tow or more kinds of substances. Single Phase System —Consists of only one phase. Multi-phases System —Consists of tow or more phases. Homogeneous System —The composition and property are identical all over the system

Thermodynamic StateThermodynamic state of a system-the condition of the system as characterizedby the values of its properties.Property -any characteristic of a systemBasicProperty-can be directly measured· Derived Property-indirectly calculated from basic ones

Thermodynamic State Thermodynamic state of a system –the condition of the system as characterized by the values of its properties. Property –any characteristic of a system • Basic Property –can be directly measured • Derived Property –indirectly calculated from basic ones

PressureForceYPressureAreaCommon Use Units:1bf[= lpsiEnglishin?Nbar[= J10'Pa[- JPaSI2mtorr [ JmmHgOther

Pressure Force Pressure= Area [ ] 2 lbf psi in = [ ] 2 N Pa m = torr mmHg [= ] [ ] 5 bar 10 Pa = Common Use Units: English SI Other

PressureMeasurementatmosphericpressurevacuumfluidPatm△zI↓4systempressurePatmfluid△ZgasPsysPsys

Pressure Measurement

GageandAbsolutePressureScalesWe commonly use three different kinds pressure scales (notunits).Absolute is relative to full vacuum (absolute zero)Gage (Gauge) is relative to the ambient pressure.Used for pressure above the ambient pressureVacuum is relative to the ambient pressure.Usedforpressure belowtheambientpressurePg = Pa- PbP,= Pb- Pa

Gage and Absolute Pressure Scales We commonly use three different kinds pressure scales (not units). Absolute — is relative to full vacuum (absolute zero). Gage (Gauge) — is relative to the ambient pressure. Used for pressure above the ambient pressure. Vacuum — is relative to the ambient pressure. Used for pressure below the ambient pressure. g a b v b a p p p p p p = - = -

Gage and Absolute Pressure ScalesP. = 0.1MPa = 14.5psipoPbpvpaPbPbPaAbsoluteAbsolute川p.VacuumVacuum

Gage and Absolute Pressure Scales 0 a p = b p v p a p b p Absolute Vacuum b p a p g p Absolute Vacuum 0.1MPa 14.5psi a p = =