Basic Thermodynamics


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Basic Thermodynamics

  1. 1. Introduction
  2. 2. Basic Thermodynamics Concepts <ul><li>Heat. </li></ul><ul><li>System. </li></ul><ul><li>State. </li></ul><ul><li>Path . </li></ul><ul><li>Process. </li></ul><ul><li>Cycle. </li></ul><ul><li>Property . </li></ul>
  3. 3. Contd.. <ul><li>Process - Any change that a system undergoes from one equilibrium state to another is called a process . </li></ul><ul><li>Path - The series of state through which a system passes during a process is called a path </li></ul><ul><li>Cycle - A process with identical end states is called a cycle . </li></ul>
  4. 4. A review of basic thermodynamics: A refresher The ball represents mass exchange The arrow represents energy exchange
  5. 5. Zeroth Law of thermodynamics <ul><li>The Zeroth Law deals with thermal equilibrium and provides a means for measuring temperatures. </li></ul><ul><li>Difference between thermal equilibrium and Thermodynamic equilibrium. </li></ul>
  6. 6. Zeroth Law of thermodynamics
  7. 7. First Law of thermodynamics <ul><li>The first law is the law of conservation of energy. </li></ul><ul><li>The algebric sum of the work transfers is proportional to the algebric sum of heat transfer. </li></ul>
  8. 8. Limitations of First Law <ul><li>It does not place any distinction on the direction of the process under consideration. </li></ul><ul><li>It will not help to predict, whether the system would undergo a change or no. It simply states that in a certain process heat and work are mutually convertible. </li></ul>
  9. 9. Second Law of thermodynamics <ul><li>The Second law of clausis states that </li></ul><ul><li>It is impossible to construct a device that operates in a cycle and produces no effect other than the removal of heat from a body at one temperature and the absorption of an equal quantity of heat by a body at a higher temperature. </li></ul>
  10. 10. Second Law of thermodynamics contd.. <ul><li>The Second law of Max Planck’s states that </li></ul><ul><li>It is impossible to construct an engine working on a cyclic process whose sole purpose is to convert all the heat supplied to it into equivalent amount of work. </li></ul>
  11. 11. Few Examples <ul><li>Some common examples. </li></ul><ul><li>All processes in nature occur unaided or spontaneously in one direction. But to make the same process go in the opposite direction one needs to spend energy. </li></ul>
  12. 12. Third Law of Thermodynamics <ul><li>It is impossible by any procedure no matter how idealized, to reduce any system to the absolute zero temperature in a finite number of operations . </li></ul>
  13. 13. Summation of three laws <ul><li>You can’t get something for nothing </li></ul><ul><ul><ul><ul><ul><li>To get work output you must give some thermal energy </li></ul></ul></ul></ul></ul><ul><li>You can’t get something for very little </li></ul><ul><ul><ul><ul><ul><li>To get some work output there is a minimum amount of thermal energy that needs to be given </li></ul></ul></ul></ul></ul><ul><li>You can’t get every thing </li></ul><ul><ul><ul><ul><ul><li>However much work you are willing to give 0 K can’t be reached. </li></ul></ul></ul></ul></ul>
  14. 14. Definitions of Reversible Process <ul><li>A process is reversible if after it, means can be found to restore the system and surroundings to their initial states. </li></ul><ul><li>Some reversible processes: </li></ul><ul><li>Constant volume and constant pressure heating and cooling -the heat given to change the state can be rejected back to regain the state </li></ul>
  15. 15. Reversible Process (contd…) <ul><li>Isothermal and adiabatic processes -the work derived can be used to compress it back to the original state. </li></ul><ul><li>Elastic expansion/compression (springs, rubber bands) </li></ul>
  16. 16. Some Irreversible Process
  17. 18. Thermodynamic Processes <ul><li>A process in which the volume remains constant </li></ul><ul><li>constant volume process. Also called isochoric process / isometric process </li></ul><ul><li>A process in which the pressure of the system remains constant. </li></ul><ul><li>constant pressure process. Also called isobaric process </li></ul><ul><li>A process in which the temperature of the system is constant. </li></ul><ul><li>constant temperature process. Also called isothermal process </li></ul><ul><li>A process in which the system is enclosed by adiabatic wall. </li></ul><ul><li>Adiabatic process </li></ul>
  18. 19. Rankine Vapor power cycle
  19. 20. T-s diagram Rankine power cycle
  20. 21. P-V diagram Rankine power cycle
  21. 22. Rankine Cycle contd… <ul><li>Process 1-2: Water from the condenser at low pressure is pumped into the boiler at </li></ul><ul><li>high pressure. This process is reversible adiabatic. </li></ul><ul><li>Process 2-3: Water is converted into steam at constant pressure by the addition of heat </li></ul><ul><li>in the boiler. </li></ul><ul><li>Process 3-4: Reversible adiabatic expansion of steam in the steam turbine. </li></ul><ul><li>Process 4-1: Constant pressure heat rejection in the condenser to convert condensate </li></ul><ul><li>into water. </li></ul><ul><li>The steam leaving the boiler may be dry and saturated, wet or superheated. The </li></ul><ul><li>corresponding T-s diagrams are 1-2-3-4-1; 1-2-3’-4’-1 or 1-2-3”-4”-1. </li></ul>
  22. 23. Thermal efficiency of rankine cycle <ul><li>Consider one kg of working fluid, and applying first law to flow system to various processes with the assumption of neglecting changes in potential and kinetic energy, we can write, </li></ul><ul><li>δ q - δ w = dh </li></ul><ul><li>For process 2-3, δw = 0 (heat addition Process), we can write, </li></ul><ul><li>( δ q )boiler= (dh )boiler =(h3-h2) </li></ul>