Thermodynamics rigid tank, determine electrical energy supplied to air

[getfreshcrue]

An insulated 8-m^3 rigid tank contains air at 600 kPa and 400 K. 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 during the process is maintained constant by an electric resistance heater placed in the tank. Determine the electrical energy supplied to air during this process.

HELP!

 

[rock.freak667]

So if in the process the temperature is kept constant, what the volume after the air escapes?

 

[getfreshcrue]

Equations to help with this?

 

[laestat]

try change in entropy(at constant temp, the volume remains const as this is a rigid tank)= change in heat transfer/temperature(constant) & you get, the change in heat transfer as the rate of Electrical energy supplied by the electrical resistance placed..

 

[rock.freak667]

Equations to help with this?

You should know how pressure relates to temperature at constant volume and how to find heat transfer at a given temperature difference.


I think this should give you the same value as the entropy method.

 

[laestat]

yep..there is.. but try relating entropy changes.. there are change in entropy relations with volume, pressure & temp..no need to go for ΔT values as Temperature is made constant by electric resistance heater... i ll try to solve it when i find time & post them..