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 = - = -