MODULE 3: FURTHER OVERVIEW OF BASIC CONCEPTS
DEFINITIONS Work, W, an energy interaction. Indeed, Wadiabatic is used to evaluate energy changes Monitor the W at the CS. W is process dependent (more later on this topic). W is equivalent to raising a weight It is organized and macroscopic
INCLUDING BASIC DEFINITIONS
Heat, Q is another energy interaction at the CS a no Q is process or system adiabatic Q is also process dependent Q cannot be fully equivalent to raising a weight it is random or disorganized and microscopic by inference: energy transfer due only to temperature difference
AND FEATURES OF PROCESSES AND SYSTEMS Module 3
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ENERGY, E a function or feature (a part?) of the system itself ΔE is evaluated in an adiabatic CM process, a consequence of the first law macroscopic forms: potential and kinetic microscopic form: internal, which is essentially microscopic PE and KE
OUTLINE OF THIS MODULE Definitions Properties and Process Dependency Reversibility
Are their other forms of energy?
Equilibrium
thermodynamics concerns itself with changes in energy not the absolute values
Uniform and Steady States
E = mc 2 is mostly irrelevant to thermo, Absolute E is unimportant in thermo. Module 3
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PROPERTY, function of state, snapshot categories intensive, point values, P, T, μ inherently size independent extensive, size dependent, m, V, E
SYSTEMS closed system or CM open system or CV isolated system phase environment or surroundings add sketch of CS
specific extensive per mass, v =
molar (n.b., Bejan writes “molal”) extensive per mole (n.b., kmole), V v = v = , N = mole number N bulk: overall average specific or molar property, V vˆ = v AVG = v = , X = m or N X phase: property of a particular phase, P, T, vf , vg
STATE instantaneous condition of a system defined by its properties only a few properties are needed to define the state of an equilibrium system
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CRITICAL ROLE OF THE SYSTEM IN THERMO The mass, energy, entropy, and exergy equations of thermodynamics are fundamentally integro-differential equations! (explain?) They are meaningless unless the extent and the interactions of the system are defined.
V m
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PROCESS, change of state CYCLE, a process that returns to original state, a closed path Q and W require the entire process to be monitored or completely specified, a cinema not a snapshot is required
In contrast, the mass-continuity, momentum, and continuum energy eqns of fluid mechanics are true differential eqns (however useless wo/IC and BC)
sketch process and cycle
Sometimes we can write true differential equations especially for so-called phases, but most thermodynamic energy analysis is linked to specific open, closed, or isolated systems. Module 3
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PROPERTIES CONTRASTED WITH PROCESS DEPENDENT QUANTITIES
EQUILIBRIUM Absence of change.
E, P, V, T, etc. compared with Q or W snapshot for property versus cinema for Q or W function of state, E, compared with path dependent quantity
Equilibrium state, no further change. Only a few properties are required to define an equilibrium state. Example, T, v and m to define the extensive state of a fluid system Example, T and v define the intensive state of a fluid system
point out intensive F and extensive X
sketch E as function of time
2
W12 = ∫ F dX
E
QUASIEQUILIBRIUM processes (QEP) have negligible departure from equilibrium during process: Properties stay well defined in a QEP. A QEP is not necessarily reversible.
1
t, time
2
ΔE = E2 − E1 = ∫ dE 1
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UNIFORM STATE AND STEADY STATE REVERSIBILITY Uniform state is uniform with respect to space at any given time. May change with time.
A globally reversible process can be reversed and the system and the surroundings returned to initial states. In an internally reversible process the irreversibilities are confined to the surroundings. In an externally reversible process the irreversibilities are confined to the system. An irreversible process is not completely reversible for whatever reason. Any local or partial irreversibility makes the entire system or process irreversible. Module 3
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Eb
Tb
Tf
Ef ≠Eb
Note b for beginning, f for finial. A steady state system does not change with time. It may not be and probably is not uniform with respect to space.
TH
Module 3
ESS
TL
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SUMMARY OF THIS MODULE Definitions Properties and Process Dependency Reversibility Equilibrium Uniform and Steady States
Module 3
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