Thermodynamic Work

P M V SubbaraoProfessor

Mechanical Engineering Department

I I T Delhi

Civilized methods for manufacturing works!!!

Definition of Thermodynamic Work

• Positive work is done by a system, during a given process, when the sole effect external to the system could be reduced to the rise of a weight.

• This definition may appear arbitrary.

• This is enforced on the readers/users to identify all possible work actions in engineering.

Discussion of the Definition

• Positive work is done by a system, during a given process, when the sole effect external to the system could be reduced to the rise of a weight.

• Rise of weight is obviously work.

• Sole Effect: Entire effect (100 %)

• External: Only at the boundary or magnitude depends on the boundary

• Could be reduced to: It need not be just rise of weight. Any thing that can be translated into to rise of weight.

• Will it consider Mechanical work?

Mechanical Work Generating System

Mechanical work

Before triggering

After triggeringF

System

Surroundings

S

Positive work is done by a system, during a given process, when the sole effect external to the system could be reduced to the rise of a weight.

Thermodynamic Work

h

W

W

Mechanical Work is Thermodynamic work and vice versa.

hWsF

Broader Applications of the Thermodynamic Work

What Action is present at this boundary?

Convector

Battery

Equivalence of Raising of A Weight

Rise

W

Turbine Generator

Convector

Hot copper

An Unknown Action

Negative Work

• When a system does positive work, its surroundings do an equal quantity of negative work.

• Conversely, when surroundings do positive work, the system does and equal quantity of negative work.

Types of Work Transfers

• Moving Boundary work (displacement work)– Extrusion

– Metal cutting

– Forging

• Electrical work• Shaft work• Flowing fluid work

Displacement work : Extrusion

• Extrusion is the process by which a block/billet of metal is reduced in cross section by forcing it to flow through a die orifice under high pressure.

• Most metals are hot extruded due to large amount of forces required in extrusion.

Thermodynamic Process for Extrusion

Simple Processes for Displacement Work

pdVW21

Study of Pressure-Volume Diagrams.

• The rapid rise in pressure during initial ram travel is due to the initial compression of the billet to fill the extrusion container.

• For direct extrusion, the metal begins to flow through the die at the maximum pressure.

• This pressure is called as the breakthrough pressure.• As the billet extrudes through the die the pressure required to maintain flow progressively decreases with decreasing lengthof the billet in the container.• At the end of the stroke, the pressure rises up rapidly and it is usual to stop the ram travel so as to leave a small discard in the container.

Innovative Design to modify Pressure volume Diagram