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Lecture 10

This lecture discusses the concept of work in Physics 211 and ME 322. It covers topics like the nature of work, integration of work, the significance of dW, various work modes, mechanical work, moving boundary work, the polytropic process, and work in ideal gases.

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Lecture 10

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  1. Lecture 10 Work as an Energy Transport Mode

  2. What is Work? From Physics 211 … Questions … Is work a vector or a scalar? When you integrate dW do you get W2 – W1? What is the significance of dW? In ME 322 …work can occur in several different ways. However, they are all analogous to a ‘force’ through a ‘distance’.

  3. Possible Work Modes Mechanical Work Other types of Work

  4. Moving Boundary Work P(dV) Work

  5. Moving Boundary Work Example: Expansion of a fluid in a piston-cylinder assembly The work done can be found by integration, In order to find the work done, the pressure-volume relationship needs to be known. Work is a path function!

  6. Boundary Work is a Path Function Process A Process B

  7. The Polytropic Process This process is common in many thermodynamic analyses. A polytropic process obeys the following relationship, The constant can be evaluated anywhere on the process curve. Therefore,

  8. The Polytropic Process Evaluation of the integral results in, For the case where n = 1, The polytropic process defines a relationship between end states,

  9. The Polytropic Process – Ideal Gas The previous relationship is valid, independent of the fluid, If the fluid is an ideal gas, This leads to two additional relationships for ideal gases,

  10. The Polytropic Process – Ideal Gas The work done during a polytropic process is, If the fluid is an ideal gas,

  11. Some New Terminology ... • An aergonic process • A process that occurs without any work modes • Example: A process in a closed, rigid container • An adiabatic process • A process that occurs without any heat transfer modes • Example: An process that occurs in an insulated container

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