Thermodynamic Work P M V Subbarao Professor Mechanical

Thermodynamic Work P M V Subbarao Professor 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 System 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. Before triggering Surroundings S F After triggering

Thermodynamic Work h W W Mechanical Work is Thermodynamic work and vice versa.

Broader Applications of the Thermodynamic Work Convector What Action is present at this boundary? Battery

Equivalence of Raising of A Weight Rise W

An Unknown Action Turbine Generator Hot copper Convector

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

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 length of 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