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T03: 157|4M45y573µ5 - Coggle Diagram
T03: 157|4M45y573µ5
Systems
volume can change (a fixed mass of gas expanding)
mass not allowed to enter or leave
Input - Output = Accumulation
First Law of Thermodynamics
consider energy transferred by
heat
and
work
Work
To raise a weight
To stretch a spring
To rotate a shaft
Heat
energy transfer due to temperature difference
Conduction
collisions between molecules, momentum transferred from faster to slower
R values add in multilayered surfaces
Convection
Conduction and mass transfer
Radiation
every body emits radiation, can also be transmitted through vacuum
Systems
energy added into the system by heat increases its internal energy; work done by the system transfers energy out of the system, decreasing its internal energy
special processes
Isometric / Isovolumetric / Isochoric Process
(no work is done if the system boundaries are fixed)
for an ideal gas
e.g. a gas in a fixed container
Isobaric Process
for an ideal gas
1 more item...
include any non-equilibrium work
e.g. gas in a container with a movable piston
Isothermal Process
for an ideal gas
2 more items...
use tables to find u
include any non-equilibrium work
e.g.
Adiabatic Process
needs an insulated volume or a quick process in which there is
no time for a significant amount of heat transfer
(e.g. compression and expansion of gases in a cylinder of an engine)
for an ideal gas
1 more item...
1 more item...
non-equilibrium work are usually not allowed (they complicate things)
Polytropic Process
for an ideal gas
1 more item...
general process including adiabatic (n=k), isobaric (n=0), isothermal (n=1), and isovolumetric (n->inf)
simply the law of conservation of energy for systems
for the systems of interest, no changes in potential and kinetic energy occur
Control Volumes
Mass in - Mass out = Mass accumulated
Steady Flow
many devices of interest operate in steady-state mode
physical properties remain constant at each point (only need to be defined at boundaries)
Mass in = Mass out
Continuity Equation
velocity perpendicular to area (no dot product); steady flow (no accumulation); uniform flow at inlet and outlet(constant density and velocity across area simplify integral; constant enthalpy, pressure simplify energy eq.); only one inlet, one outlet (only two terms)
conservation of mass
Energy Equation / First Law
conservation of energy and mass
Unsteady Flow
Mass in - Mass out = Mass accumulated
devices
Pump
powered by a motor to increase the pressure of a liquid (neglect KE' Ug')
Compressor, blower
powered by a motor to increase the pressure of a gas (neglect KE' Ug')
Turbine
work is done by the fluid to a set of rotating blades (neglect KE' Ug')
Throttle
only provide a pressure drop (isoenthalpic process)
Mixing chamber
enthalpy in = enthalpy out ; Pressure in =Pressure out
Heat exchanger
Diffuser and Nozzle
