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+---
+title: Thermodynamics
+created_date: 2024-12-05
+updated_date: 2024-12-05
+aliases:
+tags:
+---
+# Thermodynamics
+## Course Recap
+- Different primary energy forms (chemical, nuclear, solar, kinetic) need to be converted into useful energy (mechanical, electrical). 
+- Applications are engines, aircraft/rocket propulsions, wind turbines, fuel cells, steam and gas turbines, combustion, compressors, pumps
+- Thermodynamics provides us with tools for design, performance assessment, improvements and optimization.
+- Efficiencies: generally speaking is the desired output divided by the required input.
+	- $$ \eta_{thermal} = \frac{Useful work/energy}{energy provided}$$
+	- Total efficiency is usually the multiplication of each individual stage
+		- $\eta_{total}=\eta_{compressor} \eta_{turbine} \eta_{generator}$
+	- Examples
+		- Combustion: gasoline ~35%, diesel ~42%
+		- fossil power production: ~35-48%
+		- solar thermal power production: ~18-22%
+
+### Laws of Thermodynamics
+
+> [!important] 0th law: Equilibrium
+> If two systems are both in thermal equilibrium with a third system, then they are in equilibrium with each other.
+
+This law establishes the concept of temperature, which is a fundamental and measurable property. This allows to measure and compare systems and states.
+We have different kinds of equilibriums: mechanical (pressure), thermal (temperature), phase (mass of each phase doesn't change) and chemical (chemical composition does not change with time).
+
+> [!important] 1st law: Energy Conversation
+> The change in internal energy of a closed system is equal to the heat added to the system minus the work done by the system on its surroundings
+> $$ \Delta U = Q - W$$
+
+Energy is conserved: it cannot be created nor destroyed. The two forms of energy are heat and work.
+
+> [!important] 2nd law: Entropy
+> In any natural thermodynamic process, the total entropy of a system and its surroundings always increases.
+
+Every system evolves towards thermodynamic equilibrium, which has the greatest entropy amongst the states accessible to the system.
+Entropy measures disorder and randomness. It implies that some energy is always dispersed as heat, increasing the overall entropy
+
+
+> [!important] 3rd law: Absolute Zero
+> As the temperature of a system approaches absolute zero, the entropy of a perfect crystal approaches a constant minimum.
+
+This implies that we typically assume 0 entropy at 0° Kelvin.
+
+### Thermodynamic System, State and Properties
+A system consists of a boundary which separates the system from the surroundings. Energy transfer across the boundary can happen through work, heat or mass transfer.
+- *Adiabatic*: a system without heat transfer
+- *non-adiabatic*: a system with heat transfer
+- *closed*: a system without mass transfer
+- *open*: a system with mass transfer
+- *isolated*: a system without any energy transfer
+
+The thermodynamic state is defined as the set of thermodynamic properties the characterise the state, independently of the form of the system and the process through which it was achieved.
+
+#### Properties
+Properties can be *intensive* (also called *specific*, non-mass dependent, lower-case letter) or *extensive* (mass dependent, Upper-case letter). The molar state is a lower case with tilde ($\tilde u$)
+- V, volume, [m3]
+- p, pressure, [Pa]
+- U, internal energy, [J]  
+- T, temperature, [K]  
+- H, enthalpy, [J]
+- S, entropy, [J/K]
+- F, Helmholtz free energy, [J]  
+- G, Gibbs free energy, [J]
+
+#### Processes
+Processes are a change from one state to another. This is best visualized on a pV-graph as the line connecting two state points.
+- Isothermal (T=const)
+- Isobaric (b=const)
+- Isochoric (v=const)
+- Isentropic (s=const)
+- Adiabatic ($\dot Q=0$)
+
+#### Cylces
+A *cycle* is a series of processes that return the system to initial state. (On a pV-graph this returns to the original state and thus forms a loop.)
+There are two classes of cycles: power cycles and refrigeration/heat pump cycles.
+- *Power cycles* use temperature differences to create work and refrigeration cycles use work to create heat transfer ($Q_{in} > Q{out}$).
+	- Efficiency: $\eta_{th}=\frac{W_{cycle}}{Q_{in}} = 1-\frac{Q_{out}}{Q_{in}}$
+- *Refrigeration cycles*: With aid of work move heat from cold reservoir to a hot reservoir (against natural process) ($Q_{out} > Q_{in}$).
+	- Efficiency: $COP_{cooling}=\frac{Q_{in}}{W_{cycle}} = \frac{Q_{in}}{Q_{out}-Q_{in}}$
+	- Efficiency: $COP_{heating}=\frac{Q_{out}}{W_{cycle}} = \frac{Q_{out}}{Q_{out}-Q_{in}} = COP_{cooling} + 1$