# Thermo Lecture 4

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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
energy in transition from the surface of one body to the surface of another due to electromagnetic radiation.
• • 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
 Author: Anonymous ID: 5774 Card Set: Thermo Lecture 4 Updated: 2010-02-01 00:12:19 Tags: Engineering Thermodynamics Folders: Description: Thermo Show Answers: