Thermodynamics - Entropy generation Q

[DrVirz]

Hi all,

Just doing some thermo study and am stuck on a question. I am not sure where to start this Q as normally I am given a property at the exit..?

Any help is appreciated.

 

[Chestermiller]

This is a co-current heat exchanger, and both fluids are flowing in the same direction. So, you need to set the enthalpy increase for the oxygen stream equal to the enthalpy decrease for the nitrogen stream. This will give you the exit temperature of both gases. So you know the starting temperature of each gas and the exit temperature of each gas. Do you know how to calculate the entropy change per kg of a gas if you know its initial temperature and its final temperature? (You don't have to take into consideration the effect of pressure on the entropy of each gas, because you are told that the pressure drops of the two gases are negligible). If so, what is the entropy change per kg of the oxygen and of the nitrogen in passing through the heat exchanger?

Chet