ChemE 260 Isobaric and Isochoric Processes, Thermodynamic Cycles April 12, 2005 Dr. William Baratuci Senior Lecturer Chemical Engineering Department University of Washington TCD 4: E & F CB 4: Supplements (2)

Isobaric Processes P = constant 1 st Law –closed system, integral form –Assume:  E pot = 0 and  E kin = 0 IF boundary work is the only form of work: Definition of boundary work: 1 st Law becomes: Baratuci ChemE 260 April 12, 2005

V = constant 1 st Law –closed system, integral form –Assume:  E pot = 0 and  E kin = 0 IF boundary work is the only form of work: Definition of boundary work: 1 st Law becomes: Isochoric Processes Baratuci ChemE 260 April 12, 2005

Cycle Types and Characterization Three types of cycles –Power Cycles or Heat Engines –Refrigeration Cycles –Heat Pump Cycles How to Categorize Systems that Undergo Cycles –Open vs. Closed Cycles Closed Cycles: use a working fluid that never leaves the system Open Cycles:take in fresh fluid and reject the used fluid when the cycle is complete. Usually the fluid is air. –Gas vs. Vapor Cycles Vapor Cycles:take advantage of a phase change in the fluid Gas Cycles:the fluid always remains in the gas phase. The fluid is usually air or an air-fuel mixture (as in an internal combustion engine). Baratuci ChemE 260 April 12, 2005

Power Cycles 1 st Law: Tie-fighter Diagrams –No sign convention ! All quantities are positive. –1 st Law : Thermal Efficiency: Hot Cold HE QHQH QCQC W HE Baratuci ChemE 260 April 12, 2005

Refrigeration Cycles 1 st Law: Tie-fighter Diagram –No sign convention ! All quantities are positive. –1 st Law : Coefficient of Performance: Hot Cold Ref QHQH QCQC W ref Baratuci ChemE 260 April 12, 2005

Heat Pump Cycles 1 st Law: Tie-fighter Diagram –No sign convention ! All quantities are positive. –1 st Law : Coefficient of Performance: Hot Cold HP QHQH QCQC W HP Baratuci ChemE 260 April 12, 2005

Next Class … Problem Session After that… –Chapter 5 – 1 st Law of Thermodynamics for Open Systems After that… –Review for Test #1 After that… –Test #1 Baratuci ChemE 260 April 12, 2005