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ENTC 370: Announcements

ENTC 370: Announcements. Homework assignments No.3: Assigned Problems: 3.17, 3.26, 3.29, 3.30, 3.34, 3.44, 3.61, 3.75, 3.78, 3.81. Due Tuesday, September 30 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.3: • Assigned Problems: • 3.17, 3.26, 3.29, 3.30, 3.34, 3.44, 3.61, 3.75, 3.78, 3.81. • Due Tuesday, September 30th 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. Saturated Liquid-Vapor Mixture (MX) During vaporization: part liquid-part vapor Quality of Steam: x = 0.0 (saturated liquid) 0.0 < x < 1.0 (mixture) x = 1.0 (saturated vapor)

  4. Example • An 80 L vessel contains 4 kg of R 134-a at a pressure of 160 kPa. Determine the temperature, quality (x), enthalpy and volume occupied by vapor phase.

  5. Superheated Vapor • Single phase: Pressure and Temperature are no longer dependent properties SHV SHV

  6. Superheated Vapor • Superheated vapor (SHV) is characterized by the following conditions: P < Psat at a given T T > Tsat at a given P v > vg at a given T or P u > ug at a given T or P h > hg at a given T or P

  7. Table A-6

  8. Example • Determine the internal energy of water at 20 psia and 400° F (Hint: Use table A-6E) • Determine the temperature of water at a state of P = 0.5 MPa and h = 2890 kJ/kg

  9. Compressed Liquid (CL) • Compressed liquid is characterized by the following conditions: • P > Psat at a given T • T < Tsat at a given P • v < vf at a given T or P • u < uf at a given T or P • h < hf at a given T or P

  10. Compressed Liquid (CL) • Variation of properties with pressure is very mild (Table A-7) • Approximation: Compressed Liquids ≈ Saturated Liquids Good approximation for specific volume (v) and internal energy (u). For enthalpy (h): h ≈ hf@T + vf@T(P – Psat@T)

  11. Example • Compressed liquid water at 80° C and 5 MPa. Determine the internal energy using compressed liquid table, and saturated liquid data. What is the error involved by using saturated liquid data? Hint: Table A-7 and A-4. Facts and Assumptions:

  12. Fluids: Liquids vs. Gases A liquid will take the shape of its container but exhibits a free surface. A gas will fill its container completely and does not exhibit a free surface.

  13. What is gas?

  14. Ideal-Gas Equation of State • For ideal gases: • Molar Mass • Mass of 1 kilomol • Mass • m = M*N, where M, N and m are molar mass, mole number, m of gas, respectively • Temperature • In Kelvin (K): T(K) = T(°C) +273.15 For fixed mass → Values of R for different gases can be found in appendices A-1 and A-2

  15. Water and R134a at normal pressures (i.e. atmospheric pressure) do not behave as ideal gas at normal pressures

  16. Example • Determine the mass of air in a room whose dimensions are 4m x 5m x 6m at 100kPa and 25° C. Facts and Assumptions:

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

  18. 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)

  19. Moving Boundary Work(Piston-cylinder device)

  20. 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

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

  22. 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 gas k = 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.

  23. Polytropic Process

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

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