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First Law of Thermodynamics
- Conservation of energy principle - energy cannot be created or destroyed, it can only change forms
- E entering - E leaving = E change in system
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total energy of system
E = U + KE + PE
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internal energy
U, the sum of energy contained within the molecules of a system other than kinetic and potential energys of the system as a whole
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stationary system
- When a system does not move with a velocity and has no change in elevation
- E in - E out = change U
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Heat transfer
Q; heat is energy transfer caused by temp difference between the system and its surroundings
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adiabatic systems
heat transfer Q is zero
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Work
W; energy transfer at a system boundary, weight to be raised
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Mass flow
m; as mass flows into a system, the energy of the system increases by the amount of energy carried by the mass, or vis versa
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Differentials
Total heat transfer or weak is obtained by following the process path and adding the differential amounts of haet/work along the way
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classical sign convention
- Positive - heat transfer to or work done by a system
- Negative - heat transfer from or work done on a system
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conduction
- a progressive exchange of energy between the molecules of a substance
- Fourier's law, Q = kA(T/x)
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convection
- the energy transfer between a solid surface and the adjacent liquid/gas that is in motion, involves combined effects of conduction and fluid motion
- Q = hA(Ts-Tf)
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radiation
- energy in transition from the surface of one body to the surface of another due to electromagnetic radiation
- A = epsilon*sigma*A*(T^4 - T^4) surf. vs. surround.
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Electrical Power
the rate of electrical work done by electrons crossing a system boundary, P = VI
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mechanical vs. thermodynamic work
- force acting through a distance
- energy in transition across a system boundary, done by a system if the external could have been raising of a weight
- W = Fdscos(theta)
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