Thermodynamics, Open System Entropy Problem

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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