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Introduction of Thermodynamics & Basic Concepts

Types of System’s in Thermodynamics

  • System is defined as a set of partials in the substanceair-balloon
  • Example for system is air balloon, in balloon contains set of air partials is known as system
  • Systems in Thermodynamics are different types they are Closed System, Open System, Isolated System, Adiabatic System, Homogeneous System, Heterogeneous System

Thermodynamic Equilibrium

  • Thermodynamic Equilibrium is states that when the system is constant and there is no changes in thermal, mechanical and chemical state.
  • Thermal equilibrium is in the system there is no change in temperature with respect to time
  • Mechanical equilibrium is in the system there is no unstable forces with respect to time
  • Chemical equilibrium is in the system there is no chemical reaction with respect to time


  • Thermal state of body is known as Temperature
  • Normal temperature measuring instrument is Thermometer
  • High temperature measuring instrument is Pyrometer
  • Temperature Measuring Instruments are divide into two categories, those are Non-electrical methods and Electrical method
  • Non-electrical methods are Volume of a liquid, Pressure of a gas and Vapor pressure when the temperature is changed
  • Electrical methods are by using Thermocouples, Resistance of material etc. with change in temperature
  • Temperature in SI units is Degree centigrade (ºC)

Type of Thermometers

  • Thermometers majorly six type. Those are Expansion thermometer, Pressure thermometer, Thermocouple thermometers, Resistance thermometers, Radiation pyrometers, Optical pyrometers
  • Expansion thermometers are again divide as bellow
  1. Liquid in glass thermometers
  2. Bimetallic thermometers
  • Pressure thermometers are again divide as bellow
  1. Vapor pressure thermometers
  2. Liquid filled thermometers
  3. Gas filled thermometers


  • Pressure is defined as a force per unit area
  • Pressures are created by liquids, vapors and gases
  • Instrument which is used to calculate pressure is based on atmospheric pressure
  • The value indicates in the instrument above the atmospheric pressure is positive value, is known as Gauge pressure
  • The value indicates in the instrument bellow the atmospheric pressure is negative value, is known as Vacuum
  • When a pressure becomes zero and only vacuum takes place is called Zero absolute pressure
  • The reading of pressure measured from zero absolute pressure is called Absolute pressure. This reading of pressure independent of the atmospheric pressure
  • Units of pressure is N/m2
  • The relation between gauge, vacuum and absolute pressure as shown in the bellow
  • the-relation-between-gauge-vacuum-and-absolute-pressure

Type of Pressure Measurement Devices

  • Pressure can able to measure by indicating gauges or recorders
  • Type of pressure measuring instruments are Mechanical instruments, Electro mechanical instruments and Electronic instrument
  • Mechanical type instruments are again classified are Manometer gauges (U tube manometer, Cistern manometer, Micro manometer), Pressure gauges (Bourdon tube pressure gauge, Diaphragm gauge, Vacuum gauge)

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