Entropy Balances or The 2nd Law
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- Info Page links lead to definitions, expanded explanations, and related material—because sometimes you really do need to explain it.
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Introduction
The Second Law of Thermodynamics introduces directionality into thermodynamics. While the First Law tells us that energy is conserved, the Second Law tells us which processes are possible, which are impossible, and how far real systems fall short of ideal behavior.
The central concept of the Second Law is entropy. Entropy balances are used to quantify irreversibility, determine ideal limits on performance, and analyze the efficiency of turbines, compressors, pumps, power cycles, and refrigeration systems.
This section begins with the basic statements of the Second Law and then develops the tools needed to apply entropy balances to real engineering systems.
2nd Law of Thermodynamics
Intro
This video introduces the Second Law of Thermodynamics, heat engines, entropy, and the basic limitations imposed by irreversibility.
Resistance is Futile. Entropy Always Wins
Intro to 2nd Law
Video, Info Page, Visuals
Calculating Entropy Changes
Once entropy is introduced, the next step is learning how to calculate entropy changes for common substances and processes.
The ΔS-sentials of Calculating Entropy Changes
Calculating \(\Delta S\) for heat reservoirs, ideal gases, and Steam
Video, Info Page, Visuals
The Carnot Engine
The Carnot cycle provides the ideal benchmark for heat-engine performance and shows how the Second Law limits thermal efficiency.
Sadi Carnot and the Power of Fire, the 1824 Edition Part 1
The Air-Standard Carnot Cycle
Video, Info Page, Visuals
Sadi Carnot and the Power of Fire, the 1824 Edition Part 2
The Steam Carnot Cycle
Video, Info Page, Visuals
Entropy Balances
These videos develop the entropy balance equations for closed systems, open steady-state systems, and transient systems.
How Much Entropy Can You Balance on the Head of a Pin (or in an Open Steady-State System)?
The 2nd Law for Closed, Open Steady-State, and Open Transient Systems
Video, Info Page, Visuals
Turbomachinery, Pumps, Nozzles, and Valves
Entropy balances become especially useful when evaluating real devices and comparing their performance with ideal, isentropic behavior.
Entropy Made Me Do It: Turbines, Compressors, and Other Second-Law Shenanigans
Turbines and Expanders, Isentropic and Isothermal Compressors
Video, Info Page, Visuals
Entropy Made Me Do It: Pumps, Nozzles, and Other Second-Law Shenanigans
Pumps, Nozzles, and Valves or Throttles
Video, Info Page, Visuals
The Rankine Cycle
The Rankine cycle is the standard steam power cycle and one of the most important applications of the Second Law in thermal engineering.
Boil, Expand, Condense, Repeat: The Rankine Cycle in Action Part 1
The Ideal Rankine Cycle
Video, Info Page, Visuals
Boil, Expand, Condense, Repeat: The Rankine Cycle in Action Part 2
The Rankine Cycle with \(\eta_\mathrm{pump}\) and \(\eta_\mathrm{turbine}\)
Video, Info Page, Visuals
Modeling the Rankine Cycle in DWSIM
Modeling the Rankine Cycle in DWSIM
Video, Info Page
Air Standard Cycles
These videos examine simplified gas power cycles that model engines and turbines using air as the working fluid.
Cycle Wars: The Power Awakens
Listing the common Air-Standard cycles, and modeling the Air-Standard Carnot cycle
Video, Info Page, Visuals
Cycle Wars: The Rise of Otto Cycles
Modeling the Otto, Diesel, Brayton, Turbojet, Ericsson, & Stirling Cycles
Video, Info Page, Visuals
The Vapor Compression Cycle
The same thermodynamic ideas used to analyze power cycles also apply to refrigeration and heat-pump cycles.
Revenge of the Fridge: Vapor Compression Strikes Back
The Vapor Compression Cycle
Video, Info Page, Visuals
Modeling the Vapor Compression Cycle in DWSIM
Modeling the Vapor Compression Cycle in DWSIM
Video, Info Page