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May 30, 2015

Homework Help: Thermodynamics again.

Posted by jody on Saturday, June 16, 2007 at 8:41am.

For the following problem... I found the second pressure by solving P1V1/T1 = P2V2/T2. The Volumes is const so those cancel and then i am able to find the P2. From there i looked at the 1st law and came up with delt U = Qin which = mCvdelta T but that is where I am stuck. Can anyone give me a push?
3.3 A closed rigid tank with a volume of 2 m3 contains hydrogen gas initially at 320 K and 180 kpa. Heat transfer from a reservoir at 500 K takes place until the gas temperature reaches 400 K.
a) Calculate the entropy change (kJ/K) and entropy generation (kJ/K) for the hydrogen gas during the process if the boundary temperature for the gas is the same as the as the gas temperature throughout the process. (0.6264, 0 kJ/K)
b) Determine the entropy generation (kJ/K) for an enlarged system which includes the tank and the reservoir (0.1772 kJ/K)
c) Explain why the entropy generation values differ for parts a) and b)
d) Find the entropy generation for the gas and the total value (kJ/kg) if the system boundary temperature is 450 K throughout the process. (0.1273, 0.1772 kJ/K)
e) The hydrogen gas process is repeated, but paddle-wheel work is used instead of heat transfer. Calculate the entropy generation is this case. (0.6264 kJ/K)
f) Compare the relative irreversibility of processes a), d.) or e)

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