1. Thermodynamics Carlos Silva November 11 th 2009

2. The power of heat From the greek therme (heat) and dynamis (power,force) The capacity of hot bodies to produce work Sadi Carnot (1796-1832) Réflexions sur la puissance motrice du feu et sur les machines propres à développer cette puissance

3. Laws of thermodynamics 0 th Definition of temperature Systems at different temperatures exchange energy until reaching a thermal equilibrium 1 st Conservation of energy heat is a form of energy 2 nd Entropy of an isolated system never decreases perpetual motions of machines is impossible 3 rd Entropy at absolute zero temperature (0 K) it is impossible to cool a system until zero

4. BASIC DEFINITIONS

5. Closed Systems and Control Volume System a set of interacting or interdependent entities, real or abstract, forming an integrated whole Closed System System that is isolated from its surroundings In thermodynamics a closed system can exchange heat and work (energy), but not matter, with its surroundings Isolated system cannot exchange anything Control Volume Region of space through which mass flows

6. Work, Power, Energy Work (J) Measure of motion accomplishment of a system due to the action of a force over a distance and time (Dynamics) (…) work expresses the useful effect that a motor is capable of producing. This effect can always be linked to the elevation of a weight to a certain height(…) the product of the weight multiplied by the height to which it is raised” (Sadi Carnot) Power (W=J/s) The rate at which work is done Energy (J) Amount of work that can be accomplished by a force Is the capacity of a system to perform work

7. Tonne of oil equivalent Energy released by burning one tonne of crude oil (Toe) Approximately 42 GJ (oil properties can vary) International Energy Agency: 10 Gcal 41,868 GJ 11,630 MWh 7,4 barrels of oil

8. Energy: Primary and Final Primary Energy contained in raw fuels Final Energy available after conversion and transportation systems Útil Energy after utilization Sankey diagram for S.Miguel 2007

9. Property, State and Process Property – macroscopic characteristic of a system Extensive properties The value for the overall system is the sum of the values for its parts (mass, volume, energy) Intensive properties The values are not additive, may vary from one place to the other at any time (pressure, temperature, specific volume) State – a condition of a system, described by the properties usually a snapshot in time x(t)=(P,T) Process – change of properties and therefore state of the system brings the system from x(t) to x(t+1)

10. Specific volume, Density Specific volume volume occupied by a unit of mass (mass / volume) water 4º - 1dm 3 /kg Iron -128,2 cm 3 /kg Density mass by unit of volume (volume/mass) Water at 4º - 1000kg/m 3 / water at 20º - 998kg/m 3 Iron - 7800kg/m 3

11. Temperature and Pressure Pressure (Pa=N/m 2 ) Effect of a force in a surface Caused by the collision of molecules to the boundaries of a system Temperature (K) At the microscopic scale, is a measure of the energy of the particles solid state (vibration of molecules) liquid (translation movement) gas (vibration and rotation movements Thermal equilibrium – system does not change temperature

12. Heat, Specific Heat Heat (J) is the process of energy transfer from one body or system due to thermal contact can be defined as thermal energy energy of a body that increases with temperature Specific heat energy required to increase 1 degree of a 1unit (kg or mol) of a substance Can be measured at constant pressure (Cp) Water - 4,186 J/(g·K) (25 º C) / 2,080 J/(g·K) (100º C) Can be measured at constant volume (Cv)

13. Efficiency Thermal Efficiency Heat Engines Carnot Efficiency

14. Coefficient of Performance Some devices use work to move heat from one place to other inverse process of thermal machines Heat Pumps Air conditioners

15. ZERO TH LAW Laws of thermodynamics

16. Systems thermodynamic equilibrium When two systems are put in contact with each other, there will be a net exchange of energy between them unless or until they are in thermal equilibrium, that is, they are at the same temperature "If A and C are each in thermal equilibrium with B, A is also in thermal equilibrium with C.“ single temperature and pressure can be attributed to the whole system

17. FIRST LAW Laws of thermodynamics

18. Enthalpy (H) Measure of internal energy of a closed system sum of internal energy plus the product of pressure and volume For constant pressure, the enthalpy increases with heat Specific enthalpy (J/kg) Energy per unit of mass (PCI) Low (hidrocarbonets) Fuel 42MJ/kg Propane 46 MJ/kg High

19. Conservation of Energy The total amount of energy in a closed system remains constant over time (are said to be conserved over time) The increase in the internal energy of a system is equal to the amount of energy added by heating the system minus the amount lost as a result of the work done by the system on its surroundings. Energy cannot be created nor destroyed Energy can change form (for example chemical to thermal)

20. SECOND LAW Laws of thermodynamics

21. Entropy (S) Thermodynamics Measure of uniformity of the distribution (quality) of energy Information For a system whose exact description is unknown, its entropy is defined as the amount of information needed to exactly specify the state of the system

22. Entropy increases in nature Temperature differences between systems in contact with each other tend to even out and that work can be obtained from these non-equilibrium differences, but that loss of heat occurs, in the form of entropy, when work is done In a system, a process that occurs will tend to increase the total entropy of the universe Heat generally cannot flow spontaneously from a material at lower temperature to a material at higher temperature (Clausius) It is impossible to convert heat completely into work in a cyclic process (Kelvin)

23. Reversible and Irreversible Processes Reversible (ideal) system and surroundings can be restored to the initial state from the final state without producing any changes in the thermodynamics properties it should occur infinitely slowly due to infinitesimal gradient all the changes in state occurred in the system are in thermodynamic equilibrium with each other Irreversible (natural) All processes in nature are irreversible Finite gradient between the two states of the system heat flow between two bodies occurs due to temperature gradient between the two bodies;

24. THIRD LAW Laws of thermodynamics

25. Entropy at absolute zero (0 K) As a system approaches absolute zero, all processes cease and the entropy of the system approaches a minimum value decreasing entropy of a system requires increasing the entropy of surroundings

26. THERMODYNAMIC PROCESSES

27. Boyle’s Law The absolute pressure and volume of a gas (ideal) are inversely proportional, if the temperature is kept constant within a closed system Ideal Gas law k - Boltzman constant (8.314 J·K −1 mol -1 )JK mol n – number of moles

28. Different Processes IsobaricIsometric Adiabatic ΔT ≠ 0 but Q = 0 Isothermal ΔT = 0 but Q ≠ 0 Cyclic If clockwise – heat engine If counterclockwise – heat pump

29. Ideal (Carnot) Cycle Carnot Theorem No engine operating between two heat reservoirs can be more efficient than a Carnot engine operating between those same reservoirs Pressure-Volume Temperature-Entropy

30. Real Cycles There are no ideal cycles Irreversible systems, losses of heat