ENTC 370: Announcements

1. ENTC 370: Announcements • Homework assignments No.1: • Assigned Problems: • 1.8, 1.22, 1.23, 1.27, 1.28, 1.37, 1.39, 1.48, 1.49, 1.58. • Due next Tuesday, September 16thbefore 10:50 am • For more information, go to: • http://etidweb.tamu.edu/classes/entc370 • Yes, we have labs this week • We will meet at Thompson 008 (DXP Pump Lab)

2. Manufacturing & Mechanical Engineering Technology Program New and Transfer Student Orientation Meeting You are cordially invited to participate in the MMET New and Transfer Student Orientation Meeting. The purpose of this event is to introduce you to the MMET program faculty and staff as well as to share with you our vision, mission, and expectations during your undergraduate career. DATE: Monday, September 15th, 2014 TIME: 6:00 p.m. to 7:00 p.m. PLACE: Thompson 112D Pizza and refreshments will be served. Include any dietary restrictions you might have in your RSVP. Please respond before 5:00 PM on Thursday, Sep 11th to Linda (ljchandler@tamu.edu)

3. Key Concepts • Pressure: • Amount of Force exerted on a unit area • P = Force/Area • Pressure acts uniformly in all directions and perpendicular to the boundaries in the container • Example: Piston Force Area= p/4*D2 P Pressure=Force/Area Unit: Psi or Pa (SI)

4. Units of Pressure • 1 bar = 105 Pa = 0.1 MPa = 100 kPa • 1 atm = 101,325 Pa = 101.325 kPa • 1 atm = 1.01325 bars • 1 mm Hg = 0.13333 kPa • 1 atm = 14.696 psi

5. Example Determine the pressure in kPa inside a piston-cylinder device, if the weight of the piston is 50 kg. Atmospheric pressure is 900 mbars. Dpiston = 0.1 m

6. Pressure Measurement Devices Pressure Transducer http://www.omega.com/

7. Problem-Solving Technique • Problem Statement • Write down what you know and need to find • Schematic • Draw a simple sketch of the physical system involved • Assumptions and Approximations • For instance, atmospheric pressure is 101 kPa

8. Problem-Solving Technique • Physical Laws • Write down relevant physical laws, equations, etc. • Properties • Find the unknown properties (use tables, etc.) • Calculations • Solve for the unknown(s) • Reasoning, Verification and Discussion • Does it make sense?

9. Chapter 2: Energy, Energy Transfer, Energy Analysis • Energy cannot be created or destroyed, only transformed • Forms of Energy • Total Energy: E, kJ or Btu • Total Energy per unit mass: e = E/m, kJ/kg, Btu/lbm • In thermodynamics, we are interested in changes in energy levels and not in absolute values of energy

10. Forms of Energy • Total Energy, E • Two main groups (Macroscopic and Microscopic) • Macroscopic • Forms of energy a system possesses with respect to an outside reference frame • Kinetic • Energy that a system possesses as a result of its motion relative to a reference frame • Potential • Energy that a system possesses as a result of its elevation in a gravitational field

11. Forms of Energy • Two main groups (cont.) • Microscopic • Forms of energy related to the molecular structure of a system and the degree of molecular activity, and independent of outside reference frames • Sum of microscopic forms of energy is called Internal Energy, U • If the absence of magnetic, electric, and surface tension effects, the total energy of a system is: • Per unit mass:

12. Internal Energy (U) • Internal Energy: reflects degree of molecular activity • Sum of kinetic and potential energies of molecules • Sensible energy: kinetic energies of molecules • Latent energy: internal energy associated with phase of system

13. Imaging the Dimers in Si (111) 7x7E. Bengu, R. Plass, L.D. Marks, T. Ishimiya, P. M. Ajayan, and S. IijimaPhysical Review Letters 77, 4226 (1996) http://www.numis.northwestern.edu/Research/Current/current.shtml

14. Imaging the Dimers in Si (111) 7x7E. Bengu, R. Plass, L.D. Marks, T. Ishimiya, P. M. Ajayan, and S. IijimaPhysical Review Letters 77, 4226 (1996) http://www.numis.northwestern.edu/Research/Current/current.shtml

15. Nuclear Energy http://news.bbc.co.uk/2/shared/spl/hi/sci_nat/05/nuclear_fuel/html/mining.stm

16. Mechanical Energy • Form of energy that can be converted to mechanical work completely and directly by an ideal mechanical device (i.e. pump, turbine, etc.) • Types of mechanical energy • Kinetic and Potential • Flow energy: Energy required to move fluid element a certain distance • Flow work: Pressure acting on a fluid element • Mechanical energy per unit mass:

17. Stationary Systems • Closed system whose Velocity and Elevation remain constant during a process →KE = PE = 0 • Referred to as Stationary Systems → → Chapter 4 deals with Closed Systems

18. Control Volumes • Open systems that involve fluid flow for long periods of time Chapter 5 deals with Control Volumes (Open Systems)

19. Rates • Mass flow rate, kg/sec • Energy flow rate, kJ/sec or kW

20. Static and Dynamic Energy • Static: contained or stored energy • Dynamic: Not stored, energy interactions • Recognized at the system boundary (gained or lost) • For Closed Systems: Energy interactions are • Heat Transfer: Energy transfer due to temperature difference • Work: the other energy interactions that are not heat transfer • For a control volume (open systems): Energy is transferred by heat, work and energy content of mass

21. Energy Transfer by Heat, Work and Mass • Energy can cross boundaries in two forms: Work and Heat

22. Definitions • Heat: Form of energy that is transferred between two systems or surroundings by virtue of temperature difference(DT) • Adiabatic process: No heat is gained or lost by the system (Adiabatic ≈ Insulated) • Adiabatic system: Does not exchange heat with its surroundings

23. Examples Heat is energy in transition

24. Examples No heat transfer (no energy transfer in the form of heat)

25. Heat Transfer • Conduction: Transfer of heat due to the flow of energy from energetic particles to less energetic particles (solid-solid, etc.) • Convection: Transfer of heat due to fluid motion • Radiation: Transfer of energy due to the emission or reception of electromagnetic waves or photons

26. Heat Transfer due to Conduction = heat flow per unit time (W) kt = thermal conductivity (W/mK) A = area normal to heat flow (m2) = temperature gradient in the direction of heat flow (C/m) http://en.wikipedia.org/wiki/Conduction_%28heat%29

27. Heat Transfer due to Convection = heat transfer rate (W) A = heat transfer area (m2) h = convective heat transfer coefficient (W/m2K) Ts= surface temperature (K) Tf = bulk fluid temperature away from the surface (K) http://en.wikipedia.org/wiki/Convective_heat_transfer

28. Heat Transfer due to Radiation Heat transfer by radiation can take place in vacuum, no-fluid, no-air environment http://en.wikipedia.org/wiki/Thermal_radiation = heat transfer per unit time (W) A = surface area for heat transfer (m2) σ = Stefan-Boltzmann constant, 5.67x10-8 W/m2K4 and 0.1713x10-8 BTU/h ft2 R4  = emissivity Ts= absolute temperature of surface (K) Tsurr = absolute temperature of surroundings (K)

29. Energy Transfer by Work • If the energy crossing the boundary of a closed system is notheat, then it must be work • Work: Energy transfer associated with a force through a distance Force distance Work = Force*Distance

30. Sign Convention • Heat, Q: • Into system: Positive (+) • Leaving the system: Negative (-) • Work: • Work done by a system: Positive (+) • Work on a system: Negative (-) Q (+) Work (+) Q (-) Work (-)

31. Heat and Work Similarities • Heat and Work are boundary phenomena • They cross or may not cross boundaries • Systems possess energy, but not work nor heat (work and heat are forms of energy transfer) • Heat and Work are processes, not states • Heat and Work are path functions • Magnitudes depend on the path followed

32. Processes State 1 P1 Process line, or path P3 P2 State 2 Properties are point functions and have exact differentials → Properties depend on the state only, and not how the system reaches a given state

33. Work are path functions and have inexact differentials → Exact differential → Inexact differential → DVA = 3 m3; WA = 8 kJ DVB = 3 m3; WB = 12 kJ Work is obtained by following the process path and adding differentials

34. Examples of Energy Transfer • Burning of a candle in an insulated room • System: Candle and air in room • Boundary: Room insulation and walls • *Determine if there is any heat transfer and change in internal energy Internal Energy: Chemical Energy (Combustion) → Sensible Energy (Molecular kinetic Energy)

35. Examples of Energy Transfer • Heating of a potato (25 °C) in an oven (200° C) • System: Potato • Boundary: Skin of potato • *Is there any heat transfer during the baking process? Depends on how the system boundary is defined

36. Heat or Work • Heat: Due to temperature difference, exchange between two system or the surroundings • Work: Associated with a force through a distance *Does the heating element represent heat or work? Work! Because the heating element is already part of system and the system does not exchange heat with the surroundings (W = VN) Insulation System Boundary + -