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Chapter 2 Energy, Work and Heat Transfer

Chapter 2 Energy, Work and Heat Transfer. Launch of US Air Force early warning satellite- conversion of internal (chemical) energy into kinetic energy. (Courtesy USAF). Fixed reference frame at v ref = 0. z = distance from horizontal reference plane to center of mass. v. m.

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Chapter 2 Energy, Work and Heat Transfer

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  1. Chapter 2 Energy, Work and Heat Transfer Launch of US Air Force early warning satellite- conversion of internal (chemical) energy into kinetic energy. (Courtesy USAF)

  2. Fixed reference frame at vref = 0 z = distance from horizontal reference plane to center of mass v m 2.1 Energy Within a System Boundary • 2.1.1 Kinetic and Potential • Units: • SI: Joules (J) • USCS: feet-pound force (ft·lbf) Chapter 2: Energy, Work and Heat Transfer

  3. 2.1.2 Internal Energy • KE and PE: Macroscopic Properties • Internal Energy (U): Microscopic Property • SI Units: • Joules (J) • Like kinetic and potential energies • USCS Units: • British Thermal Unit (Btu) • Different than kinetic and potential energies (ft·lbf) Chapter 2: Energy, Work and Heat Transfer

  4. 2.2 Energy Transfer across a Boundary • 2.2.1 Energy Transfer by Work • F = Force • S = Path over which force acts No Work since dS = 0 Work = Area Under F-S diagram Chapter 2: Energy, Work and Heat Transfer

  5. 2.2.1 Boundary (PdV) Work: • Work to change the volume of a compressible substance. Chapter 2: Energy, Work and Heat Transfer

  6. P Boundary Work V1 V2 V 2.2.1 P-V (Indicator) Diagram Area under P-V diagram = Boundary Work Chapter 2: Energy, Work and Heat Transfer

  7. 2.2.1 Boundary (PdV) Work in Diesel Engine: PowerPoint frozen? Click here and try again Chapter 2: Energy, Work and Heat Transfer

  8. 2.2.2 Shaft Work • Most concerned with 3 types of work: • 1. Boundary (PdV) Work • 2. Shaft Work • 3. Electrical Work • To identifying presence of shaft work, draw system boundary around system. If any rotating shafts cross system boundary, shaft work is present. • Shaft work common for: • Pumps • Compressors • Blowers • Motors • Engines Chapter 2: Energy, Work and Heat Transfer

  9. 2.2.2 Shaft Work PowerPoint frozen? Click here and try again Chapter 2: Energy, Work and Heat Transfer

  10. 2.2.3 Power, The Rate of Doing Work • Speed determines how quickly we can travel a certain distance • Power determines how quickly we can do a certain amount of work. • Power = Rate of doing work. • Lightning has a lot of power. However, it occurs so rapidly (small t) that, relative to its power, it cannot do a lot of work. Chapter 2: Energy, Work and Heat Transfer

  11. 2.2.4 Heat Transfer • Heat Transfer: Energy crossing the system boundary because of a temperature difference between the system and the surroundings * NOTE: Rates are denoted by a dot on top of the variable. However, sometimes these dots are hard to see in PowerPoint. Chapter 2: Energy, Work and Heat Transfer

  12. 2.2.4 Heat Transfer in Steam Power Plant PowerPoint frozen? Click here and try again Chapter 2: Energy, Work and Heat Transfer

  13. 2.3 Energy Transfer by Mass Transport • Flow Work (Pv) • Enthalpy (h): h = u + Pv • Energy (due to mass) inside system boundary ECM,CV = u + ke + pe • Energy crossing system boundary with mass transfer (energy inherent to mass + flow work) EIN,OUT,MASS TRANSFER = u + ke + pe + Pv = h + ke + pe Chapter 2: Energy, Work and Heat Transfer

  14. 2.4 Energy: What is it? Energy is any quantity that changes the state of a closed system when crossing the system boundary An amount of energy equivalent to 100-megaton hydrogen bombs is released when a solar flare occurs Chapter 2: Energy, Work and Heat Transfer

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