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Thermodynamic systems and properties


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notes on thermodynamics system and properties ,which is the on of the basics of thermodynamics useful for mechanical ,chemical engineering,physics students also can read this. for practice objective questions on thermodynamic visit free online web portal

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Thermodynamic systems and properties

  1. 1. Whatis Thermodynamics?  The science of energy that concerned with the ways in which energy is stored within a body.  Energy transformations –mostly involve heat and work movements.  The Fundamental law is the conservation of energy principle: energy cannot be created or destroyed, but can only be transformed from one form to another. MACROSCOPIC AND MICROSOPIC APPROACH OF THERMODYNAMICS: Macroscopic Thermodynamics: when matter are considered as continuous function of space variables. It is classical approach of thermodynamics, which requires simple mathematical for mule for analyzing the system. Microscopic Thermodynamics: All the atoms and molecules of the system are considered and the summation of all the atoms and molecules are used. it is statistical approach of thermodynamics. CONCEPT OF CONTINUM: The concept of continuum is kind of idealization of a continuous description of matter where the properties of the matter are considered as continuous function of space variables.
  2. 2. One of the factors considered important in determining the validity of a continuum model is molecular density. It is the distance between the molecules which is charactersitised by mean free path, a dimensionless parameter knows as Knudsen number. THERMODYNAMIC SYSTEM, SURROUNDING & BOUNDARY A region in space in which investigation is going on or small part of the universe to which we can apply the laws of thermodynamics called as Thermodynamic system. Or The system is a macroscopically identifiable collection of matter on which we focus our attention. Thermodynamic system is analogous to free body diagram to which apply the laws of mechanics (i.e. Newton’s laws of motion) System ,Surroundingand Boundary Surrounding The combination of matter and space, external to the system that may be influenced by changes in the system is called surrounding or environment. Boundary: The Thermodynamics system and surroundings are separated by an envelope called Boundary of the system. The Boundary can be real or imaginary and may change shape, volume, position and orientation relative to the observer. It can be of two types
  3. 3. (a) Adiabatic: Boundary which does not allow heat transfer named as adiabatic. (b) Diathermic: Boundary which allows heat transfer named as Diathermic. TYPES OF THERMODYNAMIC SYSTEM: Thermodynamic system can be classified as: (1) Closed system or Control Mass system (2) Open system or Control volume system (3) Isolated system (1) Closed system or Control Mass system: Closed system (a) It is a system of fixed mass with fixed identity. (b) There is no mass transfer across system boundary. (c) Energy transfer can takes place into or out of the system. (d) Examples: Cylinder fitted with a movable piston, Bomb Calorimeter, Motor Car battery, Pressure Cooker, Kitchen Refrigerator, Ice cream freezer. (2) Open System or Control Volume system:
  4. 4. (a) It is a system of fixed volume. (b) Mass transfer can takes place across a control volume (c) Energy transfer may also occur into- out of the system. (d) A control can be seen as a fixed region across which mass and energy transfer are studied. (e) Any arbitrary region in space can be selected as a control volume. There are no concrete rules for the selection of control volume, but the proper choice certainly makes the analysis much easier. (f) The boundaries of control volume are called control surface and they can be real or imaginary. (g) Examples: Motor car engine, Water wheel, Steam generator, steam turbine, (3) Isolated system: (a) It is a system of fixed mass with same identity and fixed energy. (b) No interaction of mass or energy takes place between system and surrounding. (c) An isolated system is like a closed shop in a busy market. (d) Example: Thermos flask
  5. 5. HOMOGENEOUS AND HETROGENEOUS SYSTEM: Based on phase change a system may be classified as a homogeneous system and a heterogeneous system. A phase represents a quantity of matter that is uniform throughout in physical structure and in chemical Composition. Physical uniformity implies that the matter is all gas, or all liquid or all solid. Uniformity of chemical composition means that the chemical composition does not vary from one part of the system to another. An iron piece, a liquid contained in a vessel a gas enclosed within a container and a mixture of gases represent one phase systems. A system consisting of liquid and gas is a two phase system of a liquid phase and a gaseous phase. Likewise a mixture of solid, liquid and gas constitutes a three phase system. A system consisting of a single phase is called homogenous system. Examples are: (a) Ice,water,dry saturated steam (b) Mixture of ammonia in water (c) Mixture of air and water vapour (d) Water plus nitric acid. A system whose mass content is non-uniform throughout, i.e., it consists of more than one phase is called heterogeneous system. The examples are: (a) Mixture of ice and water (b) Mixture of non-miscible liquids (water + mercury) (c) Water plus gasoline (d) Wet steam (vapours in contact with liquid being evaporated)
  6. 6. PROPERTIES OF THE THERMODYNAMIC SYSTEM Any measureable quantity that is used to describe the condition or state of thermodynamic system, e.g., temperature, pressure, chemical composition, color, volume, energy etc. Salient Aspects of Thermodynamic Properties: (1) Its differential is exact. (2) It depends only on the state of the system (3) It has a definite unique value when system is in particular state. (4) Since thermodynamic property is a function of the state of a system, it is referred to as a Point Function or a State Function TYPES OF THERMODYNAMIC PROPERTY: There are four types of thermodynamic properties: (1) Intensive Property (2) Extensive Property (3) Specific Property (4) Molar Property (1) Intensive Property: Thermodynamic property whose value is independent of size or extent i.e., mass of the system means they are not dependent on mass. Example: Pressure, Temperature,Density,Surface tension,Composition,viscosity, Thermal conductivity, electrical potential etc. (2) Extensive Property: Thermodynamic property whose value depends on mass or extent of the system. Example: energy, enthalpy, entropy, volume, etc.
  7. 7. (3) Specific Property: An extensive property expressed per unit mass of the system. Example: specific energy, specific entropy etc. (4) Molar Property: The ratio of extensive property to mole number is known as molar property. STATE, PATH, PROCESS AND CYCLE State: A set of properties that describes the condition of a Thermodynamic system. Example: Temperature, Volume Path: The locus of the series of states through which a system passes in going from initial state to its final state constitutes the path. Process: change from one equilibrium state to another equilibrium state is called process Cycle: When a system in a given state undergoes through a series of processes such that the final and initial state is identical is called cyclic process. The change in the value of any property of the system for a cyclic process is zero.
  8. 8. THERMODYNAMIC EQUILIBRIUM: A system which is simultaneously in a state of mechanical equilibrium, thermal equilibrium and chemical equilibrium is said to be in a state of thermodynamic equilibrium. (a) Mechanical Equilibrium: Condition or state in which there is no unbalanced force within the system and nor at its boundaries. it implies uniformity of pressure i.e there is only one value of pressure for the entire system. (b) Chemical Equilibrium: system in Mechanical equilibrium may undergo a spontaneous change of internal structure due to chemical reaction or diffusion. (c) Thermal Equilibrium: Condition or state in which the temperature of the system is uniform. QUASI-STATIC OR QUASI-EQUILIBRIUM PROCESS: (a) The deviation from thermodynamic equilibrium is infinitely small. (b) All states of the system pass through the equilibrium states. (c) It takes infinite time to reach one position to another position because each equilibrium needs some time. Quasi and non quasi equilibrium compression process
  9. 9. REVERSIBLE AND IRREVERSIBLE PROCESS Reversible Process: A thermodynamic process is reversible if the system passes through a continuous series of equilibrium states. Following conditions need to the satisfied for a process to be reversible: (a) There should be no friction; solid or fluid (b) The heat exchange to or from the system, if any, should be only through infinitely small temperature difference (c) The process should be quasi-static; it should proceed at infinitely slow speed. (d) All the states in thermodynamic equilibrium state (e) Process can be run in any direction. Examples of reversible process: (1) Motion without friction (2) Restricted and controlled expansion and compression (3) Isothermal and frictionless adiabatic process. (4) Elastic stretching of a solid (5) Restrained discharge of a battery (6) Electric circuit with Zero resistance (7) Polarization and magnetization effects and electrolysis Reversible and Irreversible Process
  10. 10. Irreversible Process: If the Thermodynamic system passes through a sequence of non-equilibrium states, it is called irreversible process. An irreversible process is identified by the following characteristics: (a) It can be carried out in one direction only. (b) It occurs at a finite rate (c) It cannot be reversed without causing permanent changes in the surroundings (d) The system is never in equilibrium state at any instant during an irreversible process Examples of irreversible process: (1) Spontaneous chemical reaction (2) Viscous flow, (3) Inelastic deformation and hysteresis effects (4) Electric circuit with resistance (5) Diffusion of gases mixing of dissimilar gases (6) Energy transfer as heat with finite temperature differences (7) Free expansion and throttling process. `