ENGINEER

• Thermodynamics

  • Comes from the Greek word Therme – meaning “heat” and dynamics – meaning “power”.

  • It is branch of science which deals with energy.

  • It deals with the conversion of energy from one to another, the direction of the flow of heat, and availability of

  the energy to do work.
• Dimensions and Units

  • It refers to several basic physical ideas that are involved in the natural process and are more or less directly

  visible to our senses. (e.g. mass, length, energy)

  • Primary Dimensions - basic dimensions such as mass (M), length (L), and temperature (T).

  • Secondary Dimensions – quantities that described using the primary dimensions, energy, velocity, force,

  volume, etc.
• Units are the magnitudes assigned to dimensions.

  • Basic Units – are assigned to primary dimensions.

  • Derived units - are units assigned to secondary dimensions.
• There are different systems units used:

  • Foot-Pound-Second (FPS)

  • Centimeter-Gram-Second (CGS)

  • Meter-Kilogram-Second (MKS)

  • System Internal (SI) – this is the system of unit used as of today.
• BASIC UNITS

  • Length
  • Mass
  • Temperature
  • Time
• DERIVED UNITS

  • FORCE
  • ENERGY
  • POWER
  • PRESSURE
• Scientific Notation

  • It is a technique of expressing numbers that are either too big or too little to be represented in decimal form.
• Prefix

  • Word that attached to the beginning of the unit that resembles a factor.
• Thermodynamic System

  • refers to a definite quantity of matter most often contained with some closed surface chosen

  for study.
• System – also known as thermodynamics system or control system.

  o Surroundings – mass or region outside the system.

  o Boundary - the real or imaginary surface that separates the system from its

  surroundings.
• Control Boundary – boundary defined for separating the system to its

  surroundings.

  ➢ Control Volume – volume enclosed within a boundary.

  ➢ Control Space – space enclosed within a boundary.

  o Universe – when the system and its surroundings are combined.
• Types of Thermodynamic System

  1. Open System

  o Also known as steady-flow system; systems are able to exchange energy and mass

  across the system boundary

  o e.g., automobile engine, human body
• Types of Thermodynamic system

  Closed System

  o Also known as non-flow system; able to exchange energy across the system

  boundary but not mass.

  o e.g., earth, covered beaker of water.
• Isolated System

  o Very isolated from the environment; no exchange of heat, work, or mass across the

  system boundaries.

  o e.g., closed thermos bottle
• Properties and State

  Thermodynamic Property

  o Observable characteristics of the thermodynamic system (e.g., pressure, temperature,

  volume).

  o Sometimes observable directly and sometime indirectly.
• Intensive Property – are those properties which have same value for any part

  of the system or the properties that are independent of the mass system (e.g.

  pressure, temperature)
• Extensive Property – are those which depend upon the mass of system and

  do not maintain the same value of any path of the system. (e.g., mass, volume,

  energy, enthalpy)
• Path, Process and Cycle

  Thermodynamic Process

  o It refers to the manner in which a system’s state changes (e.g., constant pressure

  process, constant volume process, etc.)
• T. Process 

  • ISOBARIC PROCESS- pressure remain constant.
  • ISOCHORIC PROCESS- volume remains constant.
  • ADIABATIC PROCESS- No heat transfer.
  • ISOTHERMAL PROCESS- temperature remains constant
• Thermodynamic Path

  o It refers to the series of state changes through which the system passes during a process.
• Thermodynamic Cycle

  o A typical sequence of processes in which the initial and final states are identical is referred

  to as a cycle.
• Reversible Process

  o It is a thermodynamic system capable of reverting to its previous condition by

  reversing the factors that caused the process to occur, return to its original state.

  (e.g., extension of springs)

  Irreversible Process

  o It is a property of a system that prevents it from retracting the same route when the

  circumstances that cause the state change are reversed; do not maintain

  equilibrium during the occurrences of a process. (e.g., mixing two different

  substances that cannot be separated)
• Thermodynamic Equilibrium

  o The term “equilibrium” refers to a scenario in which a system’s “state” does not change

  over time without the intervention of any external actor.
• Mechanical Equilibrium – the net force and moment shall zero.

  ▪ Thermal Equilibrium- if the temperature states of the system do not

  change.

  ▪ Chemical Equilibrium – if the chemical potential of the systems interacting

  are same.

  ▪ Electrical Equilibrium- electrical potential of the systems interacting are

  same.
• Thermodynamic Properties

  Density

  o The density  of any substance is its mass per unit volume (SI unit: kg/m3

  )
• Specific Volume

  o Specific volume is an intensive property of matter that is unaffected by how much of a

  substance exists or where it was sampled.
• Specific Gravity

  o Also called relative density (no unit)
• Specific Weight

  oAlso called weight density (SI unit: N/m3

  )

  oDefined as weight per unit volume or force of gravity on unit volume.
• Pressure

  o It is a measure of the force exerted per unit area on the boundaries of a system (SI unit:

  Pa or N/m2 or kg/m  s

  2

  )
• Types of Pressure

  o Atmospheric Pressure

  ▪ It is the pressure caused by the weight of the atmosphere.
• Gauge Pressure

  ▪ It is the pressure difference between the system and the atmospheric

  pressure. It is either above/below atmospheric. But is commonly used above

  atmospheric.
• Vacuum Pressure

  ▪ Is a temperature significantly lower than atmospheric pressure. It is also called

  as gauge pressure below atmospheric.
• Critical Pressure

  ▪ Minimum pressure needed to liquefy gas its critical temperature.
• Temperature

  o It is used to measure the degree of hotness or coldness of a thermodynamic substance

  with reference to a standard value
• Melting Point


  The temperature at which the substance changes its state from solid to liquid. Usually called as "Freezing Point"
• Boiling Point


  The temperature at which the substance changes its state from liquid to gas. Usually called as "Condensation Point"
• Triple Point


  A point (combination of temperature and pressure) at which all three phases of the substance coexist simultaneously. It is also the point where liquid is stable.
• Critical Point


  A point on a three-dimensional graph of temperature, pressure and molar volume beyond which that substance can only exist as gas.
• Energy

  It is the ability to do work

  Summation of different forms of energy

  • Transferred to or from a system by three forms: heat, work and mass flow.
• Energy in Transition

  refers to energy that is moving or changing between

  substances or regions due to various driving potentials such as differences in force,

  temperature, or electrical potential.