Lecture Notes: Thermodynamics Class

Announcements:

• Midterm Exam:
  • Scheduled for Monday.
  • Allowed to use a 3x5 inch note card for equations only.
  • Covers sections 4.3 through 7.1.
  • More information and questions session on Friday.
• Homework:
  • Due today.
  • Solutions posted outside the professor's office.
  • Homework will be part of the midterm material.

Example Problem Overview

• Problem Focus: Rate of entropy generation.
• Approach:
  • First law problem with second law considerations.
  • Solve for heat transfer rate first.
  • Entropy change calculated using inlet and exit states.
  • Mass flow rate and energy assumptions are essential.
• Calculations and Data:
  • Use tables for superheated vapor data.
  • Key values: Enthalpy and entropy for initial and final states.

Solving Thermodynamic Problems

• First Law Equation: Heat transfer minus work equals change in enthalpy.
• Assumptions: No changes in potential or kinetic energy.
• Sign Conventions: Important to maintain accuracy in equations.

Adiabatic and Isentropic Processes

• Adiabatic Process:
  • No heat transfer.
  • Entropy change of surroundings is zero.
• Internally Reversible Process:
  • Adiabatic reversible process is isentropic.
  • Indicated by constant entropy (S2 = S1).

Example Problems

1. Piston-Cylinder Device:
   • Isentropic process (internally reversible and adiabatic).
   • Use specific volume to find mass.
   • Calculate work using first law.
2. Compressor Problem:
   • Isentropic process using R134A.
   • Find exit temperature and enthalpy change.
   • Add-on: Calculate power required using volumetric flow rate.

Thermodynamic Diagrams

• TS Diagram:
  • Illustrates isentropic processes (vertical lines).
• HS (Mollier) Diagram:
  • Useful for superheated vapors and high-quality mixtures.
  • Previously used extensively in industry.

TDS Relationships

• Essential for analysis of solids, liquids, and ideal gases.
• Two key equations:
  1. Tds = du + pdv
  2. Tds = dh - vdp

Solids and Liquids Entropy Change

• Assumption: Incompressible with negligible specific volume change.
• Equation: ds = cdT/T
• Integration for Constant C: S2 - S1 = C ln(T2/T1)

Conclusion

• Midterm Preparation: Use the weekend to prepare and bring questions to Friday's class.
• Next Steps: Further exploration of solids, liquids, and gases using specific heat data. Solve more example problems to reinforce understanding.