The Relation Between Work Transfer & Heat Transfer During a Manufacturing Process

P M V SubbaraoProfessor

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

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• 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.

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An Universal Characteristic : Independent of Path

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Any variable, which is independent of path (process) during a changeof state is called as a property.

Let this variable be E.

ab

b

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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:

• Ea = Eref +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.