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Basics of Thermodynamics with problems

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Basics of Thermodynamics with problems

  1. 1. THERMODYNAMICS Mr. I. SATISH ASSISTANT PROFESSOR MECHANICAL DEPARTEMENT
  2. 2. Introduction: • Thermodynamics is the science of energy transfer and its effect on the physical properties of substances. • Thermo means Heat, dynamics means Motion. • Applications: Steam and nuclear power plants, Internal combustion engines, gas turbines etc.
  3. 3. Thermodynamic System: • System is defined as a quantity of matter or a region in space upon which attention is concentrated in the analysis of a problem. • Everything external to the system is called surroundings by the system boundary. • The boundary may be either fixed or moving.
  4. 4. Systems can be: • Open: Mass and Energy can transfer between the System and the Surroundings • Closed: Energy can transfer between the System and the Surroundings, but NOT mass • Isolated: Neither Mass nor Energy can transfer between the System and the Surroundings
  5. 5. System : • All engineering devices/Components are referred as Systems. • A system is a finite quantity of matter or region upon which our attention is focused. Surrounding: • Things that are external to the system are referred as Surrounding. Boundary: • It is an interface between system and surrounding. • System and surrounding interact through boundary. • Boundary can be real (or) imaginary. Boundary can be fixed (or) moving.
  6. 6. Interaction Between System and Surrounding Interaction between system and surrounding Mass Transfer Energy Transfer Heat Work Based on the type of interaction, the systems are classified as • CLOSED SYSTEM • OPEN SYSTEM • ISOLATED SYSTEM
  7. 7. • CLOSED SYSTEM No mass transfer occurs but only energy transfer occurs Eg: A certain amount of gas enclosed in a cylinder piston arrangement.
  8. 8. • OPEN SYSTEM Both mass transfer and energy transfer occurs eg: A certain amount of gas entering and leaving a cylinder pistonarrangement.
  9. 9. • ISOLATED SYSTEM Neither mass transfer nor energy transfer occurs. eg:If our entire universe is considered as a single system then it is an isolated system.
  10. 10. Mass Transfer Energy Transfer Type of System No Yes Closed System Yes Yes Open System No No Isolated System
  11. 11. Macroscopic and Microscopic Viewpoint: • In the macroscopic approach, a certain quantity of matter is considered, without the events occurring at molecule level being taken into account. • From the microscopic point of view, matter is composed of myriads of molecules.
  12. 12. Thermodynamic Properties, Process and Cycle • Every system has certain characteristics by which its physical condition may be described, e.g., volume, temperature, pressure, etc. • Such characteristics are called properties of the system. • These all are macroscopic in nature. • When all properties of a system have definite values, the system is said to exist at a definite state. • Any operation in which in which one or more of the properties of a system changes is called a change of system.
  13. 13. PATH • It is the succession of intermediate states passed during a change of state. (OR) • It is the loci of intermediate states passed during a change of state.
  14. 14. PROCESS If the path followed by the system during change of state is specified or defined completely, then it is called a process. eg: Constant pressure process Constant temperature process Constant volume process Adiabatic process Polytropic process
  15. 15. CYCLE Series of processes executed by the system in such a way that the initial and final states of the system are same.
  16. 16. Homogeneous and Heterogeneous: • A quantity of matter homogeneous throughout in chemical composition and physical structure is called a phase. • Every substance can exist in any one of the three phases, viz. solid, liquid and gas. • A system consisting of a single phase is called a homogeneous system. • While the system consisting of more then one phase is known as a heterogeneous system.
  17. 17. A system is said to be in thermodynamic equilibrium if it is in the following equilibriums Thermal Equilibrium Mechanical Equilibrium Chemical Equilibrium
  18. 18. Thermal Equilibrium: The temperature at all points of the system remains the same anddoesnot changewithtime. Mechanical Equilibrium: No unbalanced forces acts within the system or between system andsurrounding. Chemical Equilibrium: Nochemicalreaction takes place within thesystem.
  19. 19. Zeroth law of Thermodynamics • Base for all temperature measurement. • Thermal equilibrium is the key word for zeroth law Definition: When a body A is in thermal equilibrium with a body B, and also separately with a body C, then B and C will be in thermal equilibrium with each other.
  20. 20. Zeroth law of Thermodynamics
  21. 21. Zeroth law of Thermodynamics
  22. 22. Electrical resistance thermometer:
  23. 23. Thermocouple:
  24. 24. Work: The action of force on a moving body or through a distance. In Mechanics the work is defined as: the work is done by a force as it acts upon a body moving in the direction of force In Thermodynamics, Work transfer is considered as occurring between the system and surrounding. Work is said to be done by a system if the sole effect on the things external to the system can be reduced to the rising of a weight.
  25. 25. WORK:
  26. 26. PdV-Work or Displacement Work:
  27. 27. Path function and Point function:
  28. 28. Mechanical Forms of Work Expressing Boundary Work on a P-V Diagram Since a gas can follow different paths as it expands from state 1 to state 2, each path will have a different area underneath it. The work associated with each path will be different because the area under each curve will be different. 62
  29. 29. Mechanical Forms of Work Some typical process 1. Boundary work at constant volume process. If the volume is held constant, dv=0 and the boundary work equation becomes 63
  30. 30. Mechanical Forms of Work Some typical process 2. Boundary work at constant pressure If the pressure is held constant the boundary work equation becomes. 64
  31. 31. Mechanical Forms of Work Some typical process 3. Boundary work at constant temperature If the temperature of an ideal gas system is held constant, then the equation of state provides the pressure volume relation. 65
  32. 32. Problem 1. Consider as a system, the gas in the cylinder. The cylinder is fitted with a piston on which number of small weights is placed. The initial pressure is 200kPa, and the initial volume of the gas is 0.04 m3. 1.Let the gas in the cylinder be heated, and let the volume of the gas increase to 0.1 m3 while the pressure remains constant. Calculate the work done by the system during this process.
  33. 33. 2. Consider the same system and initial condition, but at the same time the cylinder is being heated and the piston is rising, let the weights be removed from the piston at such a rate that, during the process the temperature of the gas remains constant.
  34. 34. 3. For the same system, let the weights be removed at such a rate that the expression PV1.3 = const. Again the final volume is 0.1 m3. Calculate the work.
  35. 35. 4. Consider the system and initial state as before, but let the piston be held by a pin so that the volume remains constant. In addition, let heat transfer take place from the cylinder so that the pressure drops to 100kPa. Calculate the work.
  36. 36. Problem:- Consider a gas closed in a piston cylinder arrangement. The gas is initially at 150KPa and occupies a volume of 0.03 m3 The gas is now heated until the volume of gas increases to 0.2m3 .Calculate the work done by the gas if volume of the gas is inversely proportional to the pressure.
  37. 37. Problem:-A gas under goes a reversible non flow process according to the relation P=(- 3V+15) bar where V is the volume in m3 where P is the pressure in Bar. Determine the work done when the volume changes from 3 to 6 m3 .
  38. 38. Other types of Work Transfer: 1. Electrical Work: 2. Shaft Work:
  39. 39. 3. Paddle-wheel Work or Stirring Work:
  40. 40. 4. Flow Work:
  41. 41. Free expansion with zero work transfer:
  42. 42. Heat is the form of energy that is transferred between two systems (or a system and its surroundings) by virtue of temperature difference. It is recognized only as it crosses the boundary of a system. Heat transfer is not a property. Heat transfer between two states is denoted by Q A process during which there is no heat transfer is called an adiabatic process. Heat Transfer
  43. 43. Surrounding System at higher temperature looses energy as heat System and surrounding at same temperature, no energy is transferred as heat System at lower temperature gains energy as heat QAbsorbed = Positive (+) Qreleased = Negative (-) System System System Surroundings Surroundings Heat Transfer
  44. 44. Rate of Heat Transfer: The rate of heat transfer is the amount of heat transfer per unit time It is denoted by and it can be given by: The unit of is kJ/s, which is equivalent to kW
  45. 45. An insulated rigid vessel is divided into two parts by a membrane. One part of the vessel contains air at 10 Mpa and other part is fully evacuated. The membrane ruptures and the air fills the entire vessel. Is there any heat and / or work transfer during this process? Justify your answer.
  46. 46. A certain fluid expands from 10 bar, 0.05m3 to 2 bar, and 0.2m3 according to linear law. Find the work done in the process.
  47. 47. A spherical balloon of 0.5 m diameter contains air at a pressure of 500 kPa. The diameter increases to 0.55m in a reversible process during which pressure is proportional to diameter. Determine the work done by the air in the balloon during this process. Also calculate the final pressure.

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