An insulated 5 m3 rigid tank contains air at 500 kPa and 57 degree C. as shown i

Question

An insulated 5 m3 rigid tank contains air at 500 kPa and 57 degree C. as shown in the figure. A valve connected to the tank is now opened, and air is allowed to escape until the pressure inside drops to 200 kPa. The air temperature dining this process is maintained constant by an electric resistance heater placed in the tank. Determine: the electrical entity supplied during the rocess. in kJ. and the total entropy change, in kJ/K. Assume air is an ideal gas with variable specific heats and use the ideal gas tables. For the exit air stream, assume average pressure of air in the tank.

Explanation / Answer

since temp is constant
heat required is work done =v(P2-P1)
work done= 1500 K joule
a) energy supplied Q= 1500 kj
b) entropy change =Q/T= 1500kj/330=4.54 K joule/kelvin

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