Thermodynamics, Open System Entropy Problem

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SUMMARY

The discussion centers on calculating the entropy generation in a thermally insulated piston-cylinder device containing air, with an initial volume of 0.2 m³ and mass of 0.8 kg at 20 degrees Celsius. The problem involves introducing air at 600 kPa and 80 degrees Celsius, increasing the volume by 50%. The relevant equation for entropy change is provided: dS/dt = Q/T + dm/dt(si-so) - Sgen. Participants emphasize the challenge of applying this equation without a defined outlet for the system.

PREREQUISITES
  • Understanding of thermodynamics principles, specifically open system analysis.
  • Familiarity with the ideal gas law and properties of air as an ideal gas.
  • Knowledge of entropy concepts and calculations in thermodynamic systems.
  • Proficiency in using specific heat capacities for air at varying temperatures.
NEXT STEPS
  • Study the application of the first law of thermodynamics in open systems.
  • Learn about calculating entropy changes for ideal gases under varying conditions.
  • Investigate the concept of entropy generation in closed versus open systems.
  • Explore practical examples of piston-cylinder devices in thermodynamic cycles.
USEFUL FOR

Students and professionals in mechanical engineering, particularly those focusing on thermodynamics, as well as anyone involved in energy systems analysis and design.

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Homework Statement



A thermally insulated piston cylinder device initially contains 0.2m^3, 0.8kg of air at 20 degrees celsius, and the piston is free to move. Now air at 600kPa and 80 degrees celsius is slowly applied to the device through a supply line until the volume increases by 50 percent. Using constant specific heats and assume air as ideal gas, determine the entropy generation.

Homework Equations



dS/dt = Q/T + dm/dt(si-so)-Sgen


The Attempt at a Solution



I have no clue how to solve this problem, the equation above is the only one that we learned for open system problems and it requires an outlet, without it I don't know where to reference the inlet entropy.
 
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Can anyone help me out? Thanks
 

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