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ENTC 370: Announcements

ENTC 370: Announcements. Homework assignments No.4: Assigned Problems: 4.13, 4.23, 4.32, 4.37, 4.44, 4.46, 4.52, 4.81 4.85. Due Thursday , October 9 th before 10:50 am For more information, go to: http://etidweb.tamu.edu/classes/entc370. ENTC 370: Announcements. Exam I:

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ENTC 370: Announcements

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  1. ENTC 370: Announcements • Homework assignments No.4: • Assigned Problems: • 4.13, 4.23, 4.32, 4.37, 4.44, 4.46, 4.52, 4.81 4.85. • Due Thursday, October 9th before 10:50 am • For more information, go to: • http://etidweb.tamu.edu/classes/entc370

  2. ENTC 370: Announcements • Exam I: • Tuesday (Oct 21st) or Thursday (Oct 23rd ) • Chapters 1 – 5 • Homeworks1 – 5 • Closed book/closed notes • Students will be allowed to bring own equation sheet • Double-sided is ok • Size: 8½ x 11

  3. Determine Properties Using Tables Legend: CL = Compressed Liquid SL = Saturated Liquid MX = Mixture SV = Saturated Vapor SHV = Super Heated Vapor

  4. Chapter 4: Energy Analysis of Closed Systems • Moving boundary work • 1st Law of Thermodynamics in closed systems • Specific Heat • Internal Energy, Enthalpy and Specific Heat of Ideal Gases and Solids • Examples of closed systems: • Piston-cylinder device (internal combustion engine) • Rigid container (pressurized vessel)

  5. Moving Boundary Work(Piston-cylinder device)

  6. P 1 2 V P-V diagram for V = constant Some Typical Processes Constant volume If the volume is held constant, dV= 0, and the boundary work equation becomes

  7. P 1 2 V P-V DIAGRAM for P = CONSTANT Constant pressure If the pressure is held constant, the boundary work equation becomes

  8. The polytropic process The polytropic process is one in which the pressure-volume relation is given as: The exponent n may have any value from minus infinity to plus infinity depending on the process. Some of the more common values are given below. Process Exponent n Constant pressure 0 Constant volume  Isothermal & ideal gas 1 Adiabatic & ideal gask = CP/CV Here, k is the ratio of the specific heat at constant pressure CP to specific heat at constant volume CV. The specific heats will be discussed later.

  9. Polytropic Process

  10. Polytropic Process For an ideal gas under going a polytropic process, the boundary work is Isothermal case →

  11. Example of Boundary Work • A rigid tank contains air at 500 kPa and 150 °C. Heat is transfer from the tank to the surroundings, and the pressure and temperature drop to 400 kPa and 65 °C, respectively. Determine the boundary work done.

  12. Example of Boundary Work • A frictionless piston-cylinder device contains 10 lbm of steam at 60 psia and 320 °F. Heat is added to the system until the temperature reaches 400 °F. Determine the work done by the steam.

  13. Example of Boundary Work • A piston-cylinder device contains 0.4 m3 of air initially at 100 kPa and 80 °C. The air is now compressed to 0.1 m3 in a way that the temperature remains constant. Determine the work done during the process.

  14. 1st Law of Thermodynamics for Closed Systems Textbook →

  15. Energy Balance for Closed Systems (kJ) In Rate Form: (kW) Per unit mass:

  16. Closed System Undergoing Cycle For closed system undergoing a cycle:

  17. Example Example: An unconstrained piston-cylinder device contains 25 g of saturated water vapor that is maintained at a constant pressure of 300 kPa. A resistance heater within the cylinder is turned on, and current passes (0.2 A) for 5 min from a 120-V source. Heat loss is 3.7 kJ. Show that (a) boundary work and internal energy can be combined into one term, DH. (b) Determine the final temperature of the Steam. (H = U + PV)

  18. Example • A rigid tank is divided into equal parts. One side of the tank contains 5 kg of water at 200 kPa and 25 °C. The other side is empty. The partition that divides the tank is removed and water expands into the entire two parts. Heat transfer is allowed so the entire tank can reach a temperature of 25 °C. (a) Determine the volume of the tank, (b) final pressure, and (c) amount of heat transfer. http://brod.sfsb.hr/test/testhome/vtAnimations/animations/chapter05/closed/processes/nonuniformmixing/index.html

  19. Example Observation: No work crosses the system boundary during the expansion process, only heat

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