Thermo Lecture 4

Card Set Information

Thermo Lecture 4
2010-01-31 19:12:19
Engineering Thermodynamics

Show Answers:

  1. Energy boundary crossing
    • closed system - form of heat or work
    • open system - (control surface) heat, work, and mass transfer
  2. 1st Law of Thermo / conservation of energy principle
    • (total energy entinering the system) - (total energy leaving the system) = (change in total energy of the system)
    • or delta (E = U + KE + PE)
  3. Esystem
    • E = U + KE + PE
    • internal + kinetic + potential
  4. Internal Energy
    U - dependent on the state and mass of the system
  5. stationary system
    • System not moving with velocity/changing elevation
    • delta E = delta U
  6. Heat Transfer
    Q - caused by temperature difference between system and surroundings. Heat transfer into system is energy increase, out of system is decrease. Adiabatic system, Q = 0.
  7. Work
    W - energy transfer at a system boundary, the force acting through a distance or energy to lift a weight. Transfered into system energy increases, out of system energy decreases.
  8. Mass flow
    m - mass flowing into system, energy increases by the amount of energy carried with the mass. m = 0 for closed systems.
  9. Heat and Work similarities
    • 1. Boundary phenomena
    • 2. systems posses energy, not heat/work
    • 3. Associated with process, not state
    • 4. path function
  10. Total heat transfer/work
    • Calculated by following the process path and adding differential amounts along the way
    • δQ = Q12 or δW = W12
  11. classical sign convention
    • positive - heat transfer to a system/work done by a system
    • negative - heat transfer from a system/done done on a system
  12. conduction
    heat transfer in progressive exchange of energy btwn the molecules of a substance
  13. Fourier's law of heat conduction
    • k - thermal conductivity [W/mK]
    • dT/dx - temp gradient, direction of heat flow
  14. Convection
    heat transfer of the energy transfer btwn a solid surface and adj liquid or gas in motion, and involves combined effects of conduction and fluid motion.
  15. Newton's law of cooling
    • h - convection heat transfer coe [W/m2K]
    • Ts - surface temp, Tf - bulk fluid temp
  16. Radiative Heat Transfer
    energy in transition from the surface of one body to the surface of another due to electromagnetic radiation.
  17. Radiative Heat Transfer Eq.
    • sigma - Stefan-Boltzmann constant, 5.57x10-8 W/m2K4
    • epsilon - emissivity
  18. Electrical Power
    • rate of electrical work done by electrons crossing a system boundary
    • P = VI
  19. Mechanical vs. thermo work
    • force of a distance vs. energy to lift weight
    • angle bten force and displacement vector
    • delta means it is path dependent
  20. Types of Mechanical Work
    shaft, spring, elastic solid bars, stretching liquid film, raise/accelerate a body