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ENTC 370: Announcements

ENTC 370: Announcements. Homework assignment No.8: Assigned Problems: 7.60, 7.66, 7.86, 7.88, 7.108, 7.112, 7.130, 7.147. Due Tuesday, Nov 18 th before 10:50 am For more information, go to: http://etidweb.tamu.edu/classes/entc370. ENTC 370: Announcements. Homework assignment No. 9:

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ENTC 370: Announcements

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  1. ENTC 370: Announcements • Homework assignment No.8: • Assigned Problems: • 7.60, 7.66, 7.86, 7.88, 7.108, 7.112, 7.130, 7.147. • Due Tuesday, Nov 18thbefore 10:50 am • For more information, go to: • http://etidweb.tamu.edu/classes/entc370

  2. ENTC 370: Announcements • Homework assignment No. 9: • Assigned Problems: 11.3, 11.10, 11.14, 11.47. • Due Friday, Nov 21stbefore 5:00 PM • For more information, go to: • http://etidweb.tamu.edu/classes/entc370 • Exam II • Tuesday, November 25th • Chapters: 6, 7 and parts of 11 • HWs: 6 – 9

  3. ENTC 370: ThermodynamicsAnnouncements • Last lab activity: • Design a scientific thermodynamic experiment • Propose your idea by Friday, November 21st • Send e-mail to Prof. Alvarado, jorge.alvarado@tamu.edu • One e-mail per group • What is required? Go to link: http://etidweb.tamu.edu/classes/entc370/ • Click on Link: Design Your Own Thermodynamic Experiment • Deadlines: • Electronic Report: Friday, Dec 5thbefore 5:00 pm • Oral Presentation: Monday, Tuesday or Wednesday, Dec 8th, 9th or 10th(by appointment) • Note: Reports should be sent electronically through turnitin.com • http://etidweb.tamu.edu/classes/entc370/Turnitin.htm • Grade: 20% of lab grade (15%) or 3% of final grade

  4. Example • Consider a steam power plant that operates between pressure limits of 10 MPa and 20 kPa. Steam enters the pump as saturated liquidand leaves the turbine as saturated vapor. Determine the ratio of the work delivered by the turbine to the work consumed by the pump (wT/wP). Assume the entire cycle to be reversible and heat losses in the pump and turbine to be negligible.

  5. Minimizing Compressor Work(Open System + Ideal Gas) • Three compression processes: • Isentropic (no cooling): Pvk = Constant • Polytropic (some cooling): Pvn = Constant • Isothermal (maximum cooling): Pv =Constant

  6. Minimizing Compressor Work

  7. Example • Air is compressed reversibly (in a steady flow compressor) from an initial state (100 kPa and 300 K) to 900 kPa. Determine the work input required if (a) the process is isentropic (assume k = 1.4) and (b) if the process is isothermal

  8. Isentropic Efficiencies • For Engines and Refrigerators, we used the CARNOT efficiency or COPfor the best engine/refrigerator we can conceive • For steady flow devices (turbines, compressors, pumps, nozzles) the best device we can get are the ones that closely match the isentropic process

  9. Turbine • Isentropic efficiency*: Energy loss due to irreversibilities *Isentropic = Adiabatic + Reversible

  10. Example • Steam flows into a turbine at 3 MPa and 400 °C, and leaves at 50 kPa and 100 °C. If the power output is 2 MW, determine the isentropic efficiency and the mass flow rate of steam.

  11. Compressors • Isentropic efficiency*: *Isentropic = Adiabatic + Reversible

  12. Example • Air is compressed adiabatically (in a steady flow compressor) from 100 kPa and 12 °C to 800 kPa at a steady rate of 0.2 kg/sec. If the isentropic efficiency is 80%, determine (a) the exit temperature of air and (b) the required power input.

  13. Entropy Balance

  14. Mechanism of Entropy Transfer

  15. Closed Systems

  16. Open Systems No heat transfer —› only Sgen

  17. Example • Steam at 7 MPa and 450 °C is throttled in a valve to a pressure of 3 MPa during a steady flow process. Determine the entropy generated per unit mass during the process.

  18. Chapter 11: RefrigerationRefrigerators and Heat Pumps

  19. Refrigeration Refrigerator http://www.rdisystems.com/minisite/service/refrigeration-animation

  20. Refrigeration and Air Conditioning

  21. Refrigeration Cycles http://brod.sfsb.hr/test/testhome/vtAnimations/animations/chapter09/refrigeration/index1.html

  22. Ideal Refrigeration Cycle • Compressor: Isentropic Compression • Condenser: Constant-Pressure Heat Rejection • Throttling Valve: Expansion • Evaporator: Constant-Pressure Heat Absorption

  23. Energy Analysis of Refrigeration System

  24. How to Find Refrigeration h’s • P1 & SV ( or g ) → h1=hg@P1 s1=sg@P1 • P2 & (s2 = s1) → h2 • P3 & SL ( or f ) → h3=hf@P3 • h4=h3

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