The Relation Between Work Transfer & Heat Transfer During a Manufacturing Process P M V Subbarao Professor Mechanical Engineering Department Search for a Simple arithmetic Relation… A Law of Thermal sizing for Manufacturing Equipment…..

Possible Actions During a Manufacturing Process(change of state)? Work transfer Heat transfer Mass transfer What is the relation among (qualitative & qunatitative) these actions?

Combined Heat Work Transfer : Sign Conventions

Conservation of Energy Energy can neither be created nor be destroyed !!!! During a process, total work Transfer may not be equal to total Heat Transfer. Even for an infinitesimal process, the work transfer necessarily equal to the heat transfer. According to conservation of energy: the difference between infinitesimal heat transfer and work transfer during a quasi-static process must be equal to increase in energy of the system. This is noted as the First Law of Thermodynamics. Though the heat transfer and work transfer are path functions, change in energy is a points function!!!

First law for a Control Mass during a Process The change in energy of a system during a change of state is numerically equal to the algebraic sum of heat transfer during the process and the work transfer during the process. Remarks: 1.Only change of energy has been defined. 2.Zero Energy has to be expressed with respect to some arbitrary reference! 3.Q and W must be measured in same units.

An Universal Characteristic : Independent of Path Any variable, which is independent of path (process) during a change of state is called as a property. Let this variable be E. E is having units of heat or work and is called as total energy of the system.

Further Remarks on Definition of Energy The Energy of a system at any state A is: E a = E ref +  E. How to Define zero energy state? One popular definition: Stagnant Liquid at triple point at sea level will have zero energy. Energy is an extensive property. The energy of a system of unit mass is called as specific energy. Specific energy is an intensive property.

Members of the Family of Energy FORMS OF ENERGY All forms of energy fall under two categories Microscopic or Macroscopic and/or Potential Energy or Kinetic Energy. Potential energy is stored energy and the energy by the virtue of state or position. Macro Potential Energy : Gravitational Energy or Strain energy. Micro Potential Energy : Chemical energy and Nuclear energy. Kinetic energy is due to motion (Motive Energy) - the motion of waves, electrons, atoms, molecules and system.

Potential Energy CHEMICAL ENERGY : Chemical energy is the energy stored in the bonds of atoms and molecules. Biomass, petroleum, natural gas, propane and coal are examples of stored chemical energy. NUCLEAR ENERGY : Nuclear energy is the energy stored in the nucleus of an atom - the energy that holds the nucleus together. The energy of nucleus of a uranium and Thorium atoms is an example of nuclear energy. STORED MECHANICAL ENERGY : Stored mechanical energy is energy stored in objects by the application of a force. Compressed springs and stretched rubber bands are examples of stored mechanical energy. GRAVITATIONAL ENERGY : Gravitational energy is the energy of place or position. Water in a reservoir behind a hydropower dam is an example of gravitational potential energy.

Kinetic Energy RADIANT ENERGY : Radiant energy is electromagnetic energy that travels in transverse waves. Radiant energy includes visible light, x-rays, gamma rays and radio waves. Solar energy is an example of radiant energy. THERMAL ENERGY : Thermal energy is the internal energy in substances - the vibration and movement of atoms and molecules within substances. Geothermal energy is an example of thermal energy. MOTION :The movement of objects or substances from one place to another is motion. Wind and hydropower are examples of motion. SOUND : Sound is the movement of energy through substances in longitudinal (compression/rarefaction) waves. ELECTRICAL ENERGY: Electrical energy is the movement of electrons. Lightning and electricity are examples of electrical energy.