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Miscellaneous Modes of Thermodynamic Work

Miscellaneous Modes of Thermodynamic Work. P M V Subbarao Professor Mechanical Engineering Department I I T Delhi. More forms of work driving the Industry & Nature!!!. Why cutting of a solid consumes power?. Why cutting occurs at A Particular value of stress?.

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Miscellaneous Modes of Thermodynamic Work

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  1. Miscellaneous Modes of Thermodynamic Work P M V Subbarao Professor Mechanical Engineering Department I I T Delhi More forms of work driving the Industry & Nature!!!

  2. Why cutting of a solid consumes power?

  3. Why cutting occurs at A Particular value of stress?

  4. Who controls the Growth Shape & Equilibrium Shape of A Crystal

  5. Who decides the beauty of Table Cloth ???

  6. The Role of Surface Tension in Engineering • When splitting a solid, the amount of energy required is 2sA, where 2A is the area created (one A on each side). • This energy is less than that needed just to break the bonds, since there is atomic and electronic relaxation. • The surface energy is always positive because the atoms are less bound at the surface. • The surface tension can be defined as the reversible work of formation of a unit area of surface at constant T, V, m. • The surface tension is the two-dimensional analog to the pressure.

  7. Surface Tension On the surface there are atoms on one side only, so there is a net inward cohesive force. This creates a force on the surface that tries to minimise its area. When considered as a force rather than an energy, the force is called "surface tension".

  8. Thermodynamic Definition of Surface Tension The relative change in internal energy of a control mass w.r.t. change in surface area at constant temperature, volume. Law of a Nature: The tendency to minimize surface energy is a defining factor in the morphology and composition of surfaces and interfaces. This Is important for Solids & Liquids.

  9. Values of Surface Tension for Selected Materials

  10. Work Associated with the Stretching of a Liquid Film

  11. Blood Vessels & Blood Pressure • For a cylinder of radius R and length  l such as a blood vessel, the wall supplies an inward force and the liquid supplies an outward pressure. • Infinitesimal work to be done by blood on vessel: This work is stopped by surface tension of the blood vessel material

  12. There is a greater pressure difference for a smaller radius than a larger one. This inverse relationship is called Laplace's law.

  13. The Faraday’s Work : An Amazing form of Work Transfer • Consider a conducting rod PQ moving at a steady speed V perpendicular to a field with a flux densityB. • An electron (negative charge e) in the rod will experience a force (= Bev) that will push it towards the end P.

  14. Description of Work done by A Conductor • The same is true for other electrons in the rod, so the end P will become negatively charged, leaving Q with a positive charge. • As a result, an electric field E builds up until the force on electrons in the rod (unit length) due to this electric field (= Ee) balances the force due to the magnetic field Force per unit charge on Rod of unit length:

  15. For a rod of length L, define the EMF as : What happens when the EMF drives a current in an external circuit? To do this, imagine that the rod moves along a pair of parallel conductors that are connected to an external circuit

  16. Electrical Loading of Conductor The EMF will now cause a current to flow in the external resistor R. This means that a similar current flows through the rod itself giving a magnetic force, BIL to the left.

  17. Quantification of the Faraday’s Work L is now the separation of the two conductors along which the rod PQ moves. An equal and opposite force (to the right) is needed to keep PQ moving at a steady speed. In a time dt, the rod moves a distance dx = Vdt Infinitesimal Work done on the rod

  18. The Pairs of Work Transfers Energy dissipated in R = power x time = EMF× I× t Giving : B × I × L ×V × t = EMF × I × t or, as before, EMF = B × V × L http://tap.iop.org/fields/electromagnetism/414/page_46948.html ?

  19. Generation of Shaft Work Energy transmission with a rotating shaft is very common in engineering practice. A force F acting through a moment arm r generates a torque T of

  20. Isothermal Process of Real Gases in a Control Mass • Van der Waals EOS

  21. Displacement Work done by Superheated Steam During An Isothermal Process

  22. Spring Work

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