Lp03

• Thermodynamics


  A branch of physics which deals with the energy and work of a system
• Thermodynamics deals only with the large-scale response of a system which we can observe and measure in experiments
• In aerodynamics, the thermodynamics of a gas plays an important role in the analysis of propulsion systems and in the understanding of high-speed flows
• First law of thermodynamics

  Defines the relationship between the various forms of energy present in a system (kinetic and potential), the work which the system performs and the transfer of heat. Energy is conserved in all thermodynamic processes.
• Bringing a hot object into contact with a cold object

  The hot object cools down and the cold object heats up until an equilibrium is reached. Heat transfers from the hot object to the cold object.
• A system where heat transfers from the cold object to the hot object does not violate the first law of thermodynamics
• Second law of thermodynamics

  1. Heat flows spontaneously from a hotter to a colder object, but not vice versa. 2. No heat engine that cycles continuously can change all its heat-in to useful work-out. 3. If a system undergoes spontaneous change, it will change in such a way that its entropy will increase or, at best, remain constant.
• The Second Law tells the manner in which a spontaneous change will occur, while the First Law tells whether or not the change is possible
• Sadi Carnot

  • Considered the "father of thermodynamics", responsible for the origins of the Second Law of Thermodynamics and various other concepts
• Rudolf Clausius


  • Developed the Clausius statement: "Heat generally cannot flow spontaneously from a material at a lower temperature to a material at a higher temperature"
• William Thomson (Lord Kelvin)


  • Formulated the Kelvin statement: "It is impossible to convert heat completely in a cyclic process"
• Constantin Caratheodory


  • Created his own statement of the second law: "In the neighborhood of any initial state, there are states which cannot be approached arbitrarily close through adiabatic changes of state"
• The second law occurs all around us all of the time, existing as the biggest, most powerful, general idea in all of science
• Lord Kelvin's hypothesis about the Earth's surface being extremely hot and cooling at a slow pace

  Used thermodynamics to conclude the Earth was at least 20 million years old, which was incorrect due to lack of knowledge about radioactivity
• Evolution does not violate the Second Law of Thermodynamics because the Earth is not an isolated system, with constant energy increases from the sun
• Thermodynamics

  A branch of physics which deals with the energy and work of a system
• A natural process that starts in one equilibrium state and ends in another

  Will go in the direction that causes the entropy of the system plus the environment to increase for an irreversible process and to remain constant for a reversible process
• Reversible process


  The combined entropy of the system and the environment remains constant. An example is an idealized flow through a constricted pipe.
• Thermodynamics deals only with the large-scale response of a system which we can observe and measure in experiments
• In aerodynamics, the thermodynamics of a gas plays an important role in the analysis of propulsion systems and in the understanding of high-speed flows
• First law of thermodynamics

  Defines the relationship between the various forms of energy present in a system (kinetic and potential), the work which the system performs and the transfer of heat. Energy is conserved in all thermodynamic processes.
• Irreversible process


  The combined entropy of the system and the environment must increase. An example is a hot object put in contact with a cold object until they reach equilibrium.
• Bringing a hot object into contact with a cold object

  The hot object cools down and the cold object heats up until an equilibrium is reached. Heat transfers from the hot object to the cold object.
• A system where heat transfers from the cold object to the hot object does not violate the first law of thermodynamics
• Entropy (S)

  A state variable for a system in equilibrium. When heat AQ enters a system at an absolute temperature T, the resulting change in entropy of the system is AS = AQ/T for a reversible process.
• Two changes in entropy have to be considered at all times: the entropy change of the surroundings and the entropy change of the system itself
• Nicolas Léonard Sadi Carnot

  • Considered the "father of thermodynamics", responsible for the origins of the Second Law of Thermodynamics and various other concepts
• Ideal gas


  Gas confined to a cylinder by a piston
• William Thomson (Lord Kelvin)

  • Formulated the Kelvin statement: "It is impossible to convert heat completely in a cyclic process"
• Compression of gas

  1. Piston pushed down slowly

  2. Temperature remains at 20.0°C

  3. 730 J of work done on the gas
• The second law occurs all around us all of the time, existing as the biggest, most powerful, general idea in all of science
• Lord Kelvin's hypothesis about the Earth's surface being extremely hot and cooling at a slow pace

  Used thermodynamics to conclude the Earth was at least 20 million years old, which was incorrect due to lack of knowledge about radioactivity
• Evolution does not violate the Second Law of Thermodynamics because the Earth is not an isolated system, with constant energy increases from the sun
• During the isothermal compression, the internal energy of the ideal gas did not change
• Entropy

  The measurement of disorder within a system. The change of entropy suggests that time itself is asymmetric with respect to order of an isolated system, meaning a system will become more disordered as time increases.
• The Second Law of Thermodynamics states that the state of entropy of the entire universe, as an isolated system, will always increase over time
• The entropy change is negative, the disorder of the gas decreased as it was pushed into a smaller volume
• Reversible process

  The combined entropy of the system and the environment remains constant if the process can be reversed
• Irreversible process

  The combined entropy of the system and the environment must increase. The final entropy must be greater than the initial entropy.
• Entropy change of the universe

  Equivalent to the sum of the changes in entropy of the system and surroundings